Background
The Mercury Intense Target (MERIT) is an experimental initiative aimed at developing a high-power production target for Neutrino Factories and Muon Colliders Engineers at Oak Ridge National Laboratory (ORNL) have designed a free-jet mercury target that will interact with a 24-GeV proton beam within a 15 Tesla solenoid Initially, the experiment will be set up at the Massachusetts Institute of Technology (MIT) for integrated systems testing, followed by a one-month testing phase in 2007 at CERN's TT2A tunnel.
Design Overview
The design of the target system includes primary and secondary containment boundaries, an Hg delivery system with associated piping, proton beam windows, and a laser-optics diagnostic from Brookhaven National Laboratory (BNL) Additionally, it features a support structure that interfaces with the solenoid This system aims to generate a 1-cm diameter free jet at a nozzle velocity of 20 m/sec, achieving a flow rate of up to 95 liters per minute.
The target system is designed to continuously deliver a mercury jet into a high field solenoid while intersecting a 24-GeV proton beam, ensuring the jet's duration overlaps with the solenoid's peak field of one second It features a syringe pump system for discharging, collecting, and recycling elemental mercury, all housed within a secondary containment boundary A CAD model of the MERIT system is illustrated in Figure 1.
Figure 1 Hg target system within the secondary containment enclosure
Material Compatibility
Two criteria were adopted for selecting materials for the design of the target system:
1) compatibility with elemental mercury (e.g., resistance to mercury-induced corrosion), and
To ensure safety and effectiveness in applications involving elemental mercury, it is crucial to use non-ferromagnetic materials that provide transparency to magnetic fields Additionally, since elemental mercury can dissolve metals like copper, which are typically used for flange gaskets, all components and surfaces that may come into contact with elemental mercury or its vapor must be made from materials that exhibit relative inertness to mercury.
Non-magnetic materials are specifically chosen to prevent the forces exerted on ferromagnetic substances near magnets Additionally, the gamma dose from neutron-activated materials in the target structure is projected to be under 10^4 rads, ensuring that all selected organic materials can effectively endure this level of radiation.
The following list summarizes the materials of construction for the MERIT system:
• austenitic stainless steel, type 316 or 304 – pump cylinders, piping, fittings and connectors, the storage tank,
• Nitronic 50 – tie rods for the cylinder assembly,
• buna-N elastomer – gasket material for removable cover seals,
• Ti6Al4V alloy, grade 5 for the proton beam windows, grade 2 for the piping and nozzle,
• Lexan ® – secondary enclosure cover and the sump tank cover, and
• 6061 aluminum alloy – base support structure.
Fasteners and miscellaneous items are non-magnetic wherever practical Gaskets are non- reactive with mercury and capable of withstanding radiation doses of at least 10 5 rads.
For enhanced fire safety, non-metallic materials are preferred in the Hg delivery system, with a detailed list of these materials and their respective quantities available in Table 1.
Table 1 Non-metallic materials used in Hg delivery system
Component Description Location Materials Quantity Comments
Hydraulic Power Unit power cable provided by CERN TT2 tunnel CERN-approved TBD CERN-approved electrical power cable hydraulic line - steel reinforced hose
Parker Tough Cover®, 451 TC-12 (3/4"), MSHA IC- 40/26, SAE 100R17-12
TT2 tunnel synthetic rubber tube, steel wire reinforced, synthetic rubber cover
75 ft magnetic hose hydraulic line - suction
TT2 tunnel synthetic rubber tube, steel wire reinforced, synthetic rubber cover
6 ft none hydraulic line - supply TC 782-16 TT2 tunnel synthetic rubber tube, steel wire reinforced, synthetic rubber cover
15 in none hydraulic line - fiber reinforced hose
Parflex®, 575X-12 TT2A tunnel polymeric core, fiber reinforced, urethane cover
25 ft non-magnetic hose hydraulic fluid Quintolubric® 888
46 TT2 tunnel fire resistant, synthetic fluid that contains no hazardous ingredients
40 gallons contained in the steel reservoir tank on the hydraulic unit and the lines; a 55-gal drum will contain the remaining 15 gallons of fluid expansion tank
Pentair® #0835, cylindrical bladder tank mounted on the hydraulic unit, 5-gal.
TT2 tunnel fiberglass wrapped, polyethylene shell 1 unit Parker Hannifin reservoir isolation tank
Component Description Location Materials Quantity Comments
Hg Delivery System Primary Containment
Lexan® cover transparent top cover of the sump tank, 22" diameter x 1/2" thick
TT2A tunnel polycarbonate 1 piece allows viewing of the mercury stream returning to the tank
TT2A tunnel sapphire 8 pieces allows viewing of the mercury stream returning to the tank
Hg Delivery System Secondary Containment
Lexan cover transparent top cover of the secondary containment, 70" x 40" x 1/2"
The TT2A tunnel features a one-piece polycarbonate design that facilitates visual inspection of key components within the primary containment gaskets Additionally, the multiple Buna-N options provide effective mechanical sealing for the 45 mil thick elastomer sheeting The tunnel also includes 84 sq ft of EPDM rubber, which can serve as a protective barrier beneath the target equipment platform; however, if utilized, berm material will be necessary to create a dike.
Support Baseplate low friction surface
- target cart assembly low friction sheet to allow for the
"sliding" adjustment of the secondary containment box
32" x 46" x 1/4" thick, ultra high molecular weight polyethylene (UHMW PE)
1 sheet does not contain halogens; this material is sandwiched between two aluminum (6061-T651) plates and only its edges are exposed; see dwg 203-HJT-0300 low friction surface
- common base assembly low friction sheet to allow for the
"sliding" adjustment of the solenoid
38" x 48" x 1/4" thick, ultra high molecular weight polyethylene (UHMW PE)
1 sheet does not contain halogens; this material is sandwiched between two aluminum (6061-T651) plates and only its edges are exposed; see dwg 203-HJT-0100
Component Description Location Materials Quantity Comments
P136-29, MSHA, 14 AWG; U.L. approved 2-wire, single ground
The TT2 tunnel features a 250 ft PVC insulation that is utilized exclusively during the equipment setup phase for 24-volt instruments within the control cabinet This insulation, along with a nylon jacket, ensures optimal protection for the wiring Additionally, the TT2 tunnel incorporates standard fiberglass circuit boards, all securely housed within a steel control cabinet, as illustrated in the accompanying photos.
Note: MSHA – Mine Safety and Health Administration
Design Specifications and Requirements
The target system is composed of four key subsystems: the primary containment structure, the secondary containment structure, a syringe pump system, and the support base structure Each subsystem is meticulously designed to address the challenges posed by elemental mercury, a hazardous heavy metal that will become mildly activated during beam tests, as well as to manage the mildly radioactive materials that will be present after testing concludes.
The system is designed to function effectively in 1-atmosphere air environments within both primary and secondary containments Since the air is not purged between pulses, air-activation issues involving isotopes like 13 N, 15 O, and 41 Ar are minimized, ensuring containment boundaries remain secure throughout testing Should there be a need to breach either barrier after testing begins, a one-hour waiting period will allow for the decay of these isotopes This method is more straightforward than using equipment for helium evacuation and backfilling, avoiding the complexities associated with a mercury ventilation and filtration system.
The target system consists of the equipment to produce a mercury jet for a duration of up to
A 12-second mercury jet requires 23 liters of mercury, with testing at ORNL and MIT aimed at establishing the minimum time to achieve a steady-state Hg jet This research will also identify the least amount of mercury necessary for beam tests at CERN, highlighting the importance of minimizing activated liquid mercury for operational efficiency.
The equipment features a double-contained design for elemental mercury, securely mounted on a support structure that integrates both the target equipment and solenoid system This support structure is equipped with Hilman® rollers, allowing for manual movement along the proton beam line Additionally, it offers adjustable elevation and pitch for optimal positioning of the integrated system.
The target system will initially allow unlimited hands-on access, but after beam operations begin, it must be maintained with minimal personal contact Consequently, the design of the target system has been developed to facilitate eventual disassembly and safe shipment back to ORNL Key features have been integrated to ensure the safe handling of mildly activated components that are contaminated with mercury, as well as activated mercury, thereby minimizing personnel exposure.
Design Specification - ISO 2919
The design of the target system for MERIT was based on the criteria outlined in ISO 2919, specifically Class 2 from Table 2, “Classification of Sealed Source Performance.” This standard, recommended by the CERN Safety Commission at the project's inception, was deemed the minimum requirement for the design process Additionally, it was determined that compliance with these standards could be achieved through analysis or engineering judgment rather than relying solely on performance tests.
The materials outlined in Section 1.3 are appropriate for operation within the specified temperature range, featuring the buna-N elastomer with a range of -40º C to +100º C, and the Lexan® cover, which operates effectively between -135º C and +115º C.
External Pressure 25 kPa absolute (60 psi) to atmospheric
This is not applicable to the secondary enclosure because it does not appear possible for the pressure in the tunnel to exceed one atmosphere.
Impact 50 grams (1-3/4 oz.) from 1 meter, or equivalent imparted energy
Sapphire windows are the most vulnerable components in the target system A successful impact test demonstrated that a 6-mm thick sapphire window could withstand a 1.75-cm diameter "paintball" traveling at 95 m/s This impact had a momentum equivalent to that of a 7-mm diameter mercury droplet moving at the same speed.
Vibration 3 times 10 minutes, 25-500 Hz at 49 m/s 2 (5 gn, acceleration maximum amplitude)
To ensure the stability of equipment in the TT2A tunnel during seismic events, it may be necessary to anchor the base support structure to the tunnel floor This precautionary measure will prevent any movement of the equipment, enhancing safety and reliability.
Puncture 1 gram (0.03 oz.) from 1 meter, or equivalent imparted energy
A sharp object with minimal momentum is unlikely to penetrate the 12.7-mm thick Lexan® cover or the 6-mm thick stainless steel sides of the secondary enclosure.
Geometry
The geometric configuration of the target system is based on the following criteria that optimizes muon production and results in a full-beam interaction length of 30-cm:
- Proton beam, solenoid axis, and Hg jet all reside in a common vertical plane,
- Solenoid axis tilted 67 milliradians (3.84°) with respect to proton beam,
- Hg jet flows from the "up-beam" to the "down-beam" direction, the same direction as the proton beam,
- Hg jet begins above the proton beam and crosses the beam at an angle of 33 milliradians (1.89º),
- The jet crosses the beam at Z = 0, the center of the solenoid and location of the highest intensity magnetic field,
- Nominal height of the proton beam is 120-cm (47.64-in.) above the tunnel floor,
- Service end of the solenoid is positioned in the "up-beam" direction, and
- The mercury pumping loop is located "down-beam" of the solenoid.
Relative to the magnetic axis, Z = 0 at the center of the solenoid bore, -Z refers to the "up- beam" end of the solenoid, and +Z refers to the "down-beam" end.
The technical limitations of the PS accelerator machine allow the extraction of beam pulses at
The experiment involves extracting a particle beam at 24 GeV/c for durations of up to two microseconds, corresponding to a single turn extraction For longer pulse lengths exceeding two microseconds, the kicker must be activated multiple times, which requires a reduced beam momentum of 14 GeV/c due to the limited capacity of the kicker's power supply The primary objective of this study is to investigate pulse lengths extending up to 100 microseconds.
The target system's overall geometry is illustrated in Figure 2, highlighting a horizontal "kick" of 7 milliradians (0.4°) in the proton beam at Z = 0, corresponding to a beam energy of 24 GeV This kick intensifies to 12 milliradians (0.7°) when the beam energy is reduced to 14 GeV.
Figure 2 MERIT baseline geometry configuration
Figure 3 shows a detailed view of the geometric relationships between the magnetic axis, the beam axis, and the Hg jet.
Figure 3 Nozzle and solenoid relative to beam.
Operating Temperature
The mercury's operating temperature is projected to range from 15°C to 35°C Testing at Oak Ridge National Laboratory (ORNL) will measure the actual temperature increase after each jet pulse, using a temperature sensor in the sump tank The objective is to maintain the mercury temperature significantly below its boiling point, which should be achievable given the nominal 30-minute dwell time between pulses.
Mercury Containment Boundaries
The primary containment boundary consists of mercury-wetted hardware, including the Hg cylinder, nozzle, supply piping, jet chamber with proton beam windows, optical diagnostic viewports, and sump tank with associated piping To minimize leakage and flow losses in the mercury, the primary containment is designed with a limited number of valves and fittings.
Figure 4 Target system primary containment
Secondary containment systems are essential for detecting mercury vapor leaks from the primary containment boundary, ensuring safety and compliance A schematic representation of both the primary and secondary containment boundaries is illustrated in Figure 5.
Hg Target System Containment Boundaries
Figure 5 Target system containment boundary schematic.
Windows
The primary containment boundary features two types of windows: proton beam windows and diagnostic optical windows The proton beam windows, constructed from 1-mm thick Ti6Al4V material, are single-layered, while the deflector window, also made from Ti6Al4V, is thicker at 2 mm to withstand potential impacts from the downstream jet In contrast, the diagnostic windows are 6-mm thick, single-layered, and made from optically transparent sapphire material, allowing for optical observation of the interaction region at four locations along the proton beam line Both the diagnostic windows and laser components will be supplied by BNL, designed to meet the primary containment's interface requirements, with the diagnostic equipment installed as a module.
The double proton beam windows, constructed from 1-mm thick Ti6Al4V, are designed for secondary containment and feature interstitial monitoring to detect any failures caused by beam interaction As illustrated in Figure 6, these windows effectively protect the containment area while allowing the proton beam, depicted in red, to pass through.
In the MERIT Hg system, the beam passes through three windows prior to interaction with the Hg jet and three windows after jet interaction.
Figure 6 Downstream beam window mounted to the secondary containment enclosure
The diagnostic windows, installed at four strategic viewing locations on the primary containment, are constructed from 6-mm thick sapphire and secured in a retaining ring Additionally, the backside viewports feature a reflector assembly A section cut at Z = 0, depicted in Figure 7, illustrates the components of the laser diagnostic system, along with the containment boundaries, mercury supply line, and jet.
Figure 7 Laser diagnostic components, windows, and reflector; section cut taken at Z = 0
Brookhaven National Laboratory (BNL) is tasked with the design and fabrication of optical diagnostic components, as illustrated in Figure 8, which showcases a diagnostic support bracket along with three of the four fiber bundles, prisms, retaining rings, and windows Additionally, Figure 9 features a window assembly that incorporates elastomer gaskets on both sides of each window, ensuring optimal performance and reliability.
10 shows the reflector assemblies mounted opposite to each of the windows for the incoming laser light The viewports are located at Z=-15, 0, +15, and +30cm.
Figure 8 Passive optical diagnostic components and support bracket
Figure 9 Sapphire window mounted between elastomer gaskets
Before conducting water tests and mercury tests, all gasketed joints in the diagnostic assemblies will undergo leak checks using the soap bubble technique to identify any potential leak paths.
Alignment
The target system's base support structure includes features to align the assembled target for insertion into the solenoid bore and to position the solenoid/target system within 1 mm of the proton beam line The positioning will rely on measurements from fiducials attached to the solenoid and target module, as well as beam diagnostics from the CERN PS group To address concerns about the movement of the target module within the magnet bore, a wedge system may be implemented to secure the module firmly in place This challenge will be addressed during the testing conducted by ORNL and MIT.
Assembly and Shipping
The design of the target system and its base support structure prioritized easy assembly, disassembly, and transport, ensuring efficient handling for installation Initially, the equipment will be transported by truck to MIT and then to ORNL before being shipped in a sealand container to CERN The target system accommodates the spatial needs for moving components from above ground into the TT2A tunnel at CERN, while meeting the handling requirements set by the CERN Rigging Group Key components are equipped for overhead lifting and pallet handling, and the base support structure features rotatable casters for seamless movement of the assembled target system in and out of the beam line Further details on the packing and transportation of the target equipment and solenoid can be found in Section 6.
Component Size and Weight
Table 2 is a listing of the weight of each component that may be separately handled during installation at MIT or CERN.
Table 2 Estimated Component Sizes and Weights.
MERIT (fully assembled on baseplate)
Hydraulic Fluid Drum 61dia x 97tall (24dia x 38tall) 230 (500)
Mercury Flask 15dia x 30 tall(6dia x 12tall) 34 (76)
Instrumentation
The target system design integrates multiple instruments linked to the MERIT remote control station, including a mercury vapor sensor specifically designed to monitor the atmosphere within the secondary containment area.
The current strategy involves positioning a vapor sensor in the TT2 tunnel, away from radiation exposure, with a long sampling tube linked to the secondary containment Testing at ORNL will assess the reliability of monitoring from distances of up to 10 meters and evaluate any potential time delays in measurement If this setup proves ineffective, the sensor will be relocated to the top of the secondary enclosure to minimize radiation exposure Additionally, a temperature sensor will be installed to monitor the mercury levels in the sump tank.
This sensor will be used to monitor the Hg temperature rise after each pulse o Position sensor mounted to each drive cylinder to monitor flow in the supply line.
The system will utilize two position sensors for redundancy, with each sensor mounted on a drive cylinder to accurately calculate the mercury flow rate A Labview controller will then convert the linear displacement data into nozzle velocity Additionally, pressure sensors will be installed in the hydraulic system, specifically at the hydraulic pump discharge (supply line) and the return line, to monitor system performance effectively.
The arithmetic difference between the two sensors will reveal the pressure drop within the hydraulic loop, enabling effective monitoring of the drive cylinders' performance This includes the pressure sensor positioned at the discharge end of the pump cylinder.
The sensor will monitor the mercury (Hg) pressure near the Hg cylinder discharge, enabling the assessment of total pressure drop in the Hg supply line This data will support the findings from the pipe flow analysis and quantify the extra pressure drop induced by the magnetic field Additionally, a hydraulic reservoir low-level sensor with a cutoff switch will be implemented for enhanced safety and efficiency.
The sensor is designed to monitor the hydraulic fluid level in a 150-liter (40-gallon) reservoir tank, automatically shutting down the syringe pump system in the event of fluid loss Additionally, a conductivity probe is positioned at the lower end of the secondary enclosure to detect any significant leaks.
In the event of a major leak from the primary containment, the conductivity probe will send a signal to the Hg system controller.
Table 3 is a listing of the various Hg system instruments arranged by type of sensor signal.
Table 3 List of sensors for the target system.
Proportional control valve Hydraulic pump
Proportional control valve Hydraulic pump
Sensors play a crucial role in delivering vital information to operators who are situated in a separate building, as they cannot directly observe the hazardous testing environment.
The top covers of the secondary enclosure and sump tank are made of clear Lexan®, enabling visual inspection of the syringe pump equipment and allowing observation of the return flow of water or mercury into the sump tank during system testing.
Stray Magnetic Fields
The target system is designed to function within magnetic fields reaching up to 15 Tesla at the center of the solenoid, specifically at coordinates (Z = 0, R = 0) As the distance from the beam interaction point increases, the magnetic field strength diminishes to mere hundredths of a Tesla A graphical representation, shown in Figure 11, illustrates the stray magnetic fields based on the Rxyz coordinates in relation to the pump system's position, highlighting that the peak 15 Tesla field is located at the solenoid's center.
Figure 11 Stray magnetic field plot around the solenoid and the target equipment
Figure 12 shows the magnitude of the field contours The nozzle is located in a field that is
The syringe pump cylinders operate within a magnetic field of 0.26 to 0.1 T, while the structural beam linking the drive cylinders to the pump cylinder experiences a field greater than 0.03 T Utilizing non-magnetic materials in the target system eliminates the necessity for calculating and designing for Lorentz forces.
221in (563cm) Figure 12 Magnitude of the field contours.
Radioactivation of Components
Simulation analysis with the MARS 15 Code revealed that radioactivity levels in the target system are sufficiently low to allow hands-on access to most target equipment and the mercury inventory after brief cooling periods Table 4 provides a summary of key components of the target equipment, detailing absorbed doses, dose rates at shutdown, and dose rates following extended cooling periods, with data primarily sourced from Reference 3.
Table 4 Radioactivity of Target System Components.
Residual Dose Rate – at Shut Down
Residual Dose Rate – at Shut Down
Residual Dose Rate – 100 Hrs Cool Down
(mrem/h) Equipment in solenoid bore 10 4 – 10 6 1 100 - -
Ventilation filter in secondary encl (1)
(1) Pure carbon material used for calculation; impregnated sulfur not included.
(2) 1 day of decay at 1 meter distance; M Magistris and M Silari, EDMS No 601754,
CERN Technical Note CERN-SC-2005-049-RP-TN, June 16, 2005.
(3) After 1 month, dose rate at 1 meter distance is 0.1 mrem/h.
Flow Analysis
An analysis of the Hg flow was conducted using Applied Flow Technologies (AFT) Fathom software, which models incompressible flow systems and networked piping systems, including pumps and valves Although Fathom is not a computational flow dynamics (CFD) program, it effectively provides essential flow characteristics such as pressure, velocity, and frictional losses throughout the piping system Notably, the software simulates conditions without magnetohydrodynamic effects, focusing solely on scenarios without a magnetic field.
The flow of Hg from the cylinder to the nozzle was simulated using Fathom, utilizing geometric dimensions, lengths, and elevation data sourced from the CAD model of the piping system In Fathom's terminology, the system comprises junctions, which are "nodes" like tees and elbows, and pipes that link these junctions A schematic representation of the model is illustrated in the accompanying figure.
13 The Hg cylinder was modeled as a constant flow source, and the nozzle exit was modeled as a specified pressure of 1-atmosphere The analyses referenced in this section are included in i.
Calculating the flow-induced pressure drops in the nozzle supply piping allows for an estimation of the maximum pressure in the Hg cylinder, which was found to be approximately 45 bar (650 psi) under nominal conditions of a 1-cm diameter, 20 m/s Hg jet requiring 1.6 liters per second (25 gpm) To ensure safety and account for potential underestimations of system pressure drop and MHD-induced losses, both the cylinder and primary containment are designed to withstand pressures up to 100 bar (1500 psi).
Figure 14 Fathom stagnation pressure output.
Syringe Pump System
For the MERIT experiment, a syringe pump was selected to move the mercury (Hg) fluid due to the challenges posed by pressure and temperature in centrifugal pumps The Hg cylinder is designed to deliver a jet for up to 12 seconds under nominal flow conditions To accommodate the geometric constraints of the experimental setup in the TT2A tunnel, the Hg cylinder has a diameter of 25.4 cm (10 inches) and a stroke length of 38.1 cm (15 inches), complemented by two side-mounted hydraulic cylinders that facilitate syringe motion The complete pump system, illustrated in Figure 15, features a large tie-beam connecting the drive cylinder rods to the Hg cylinder rod, with the drive cylinders operating in unison via hydraulic system piping Importantly, the cylinder volumes remain isolated, preventing any interaction between the Hg and hydraulic fluids, and all materials used for the cylinders and tie-beam are non-magnetic to ensure compatibility with the solenoid's high magnetic field.
The hydraulic power unit (HPU) that operates the drive cylinders is depicted in Figure 16 This pump system will be installed in the TT2 tunnel, with hoses linking the drive cylinders to the pump passing through the wall that separates the TT2 and TT2A tunnels The system utilizes a low-flammability, vegetable-oil-based hydraulic fluid for enhanced safety.
The HPU features basic manual controls for syringe pump operation, including Power On/Off, system enable, local emergency stop, and diagnostic indicators, but these controls lack the precise velocity control required for the MERIT experiment Additionally, a pendant-controlled emergency stop is integrated into the HPU system For remote operation, a laptop running Labview software will serve as the control system, with further details available in the specified section.
Figure 17 Syringe HPU on-board controls
The syringe pump system was designed and fabricated by Airline Hydraulics Corporation based in Bensalem, PA, USA Detailed design calculations and documentation for the system are provided in ii, while Table 5 presents a summary of the design and performance characteristics of the syringe system.
Table 5 Syringe Pump Performance Parameters.
Design Standard ANSI/B93.10-1996, Static Pressure Rating Methods of
Square Head Fluid Power Cylinders
Dimensions Hg cylinder: 25.4cm (10in) dia, 38.1cm (15in) stroke,
Drive cylinders: 15.2cm (6in) dia, 38.1cm (15in) stroke Piston Velocity 3cm/sec (1.2in/sec) at nominal condition
Design Pressure Hg cylinder: 103 bar (1500psi)
Operational Safety Features Hydraulic fluid high temperature switch
Primary Containment
The primary containment system encompasses all components that come into contact with mercury (Hg), including the Hg cylinder, nozzle, supply piping, jet chamber, optical view ports, primary beam windows, and sump tank with its piping As illustrated in Figure 18, this system is primarily constructed from stainless steel, titanium, Teflon, or sapphire, with seals being the only exception.
The target module of the primary and secondary containments is specifically designed to fit within the solenoid's bore, which experiences vertical and axial shifts of a few millimeters during thermal cycles To accommodate these positional changes, the target module incorporates flexibility in the mercury (Hg) flow paths by utilizing short sections of hose, while maintaining rigidity in all other Hg flow path components.
Primary containment is engineered as a sealed system maintaining a 1-atm air environment, which includes the sump tank, both sides of the mercury (Hg) cylinder, and all associated Hg piping As the Hg cylinder moves, the air volume at the rod-end connects to the sump tank via tubing, ensuring that any significant Hg leakage past the piston seals is redirected back into the sump tank To mitigate exposure to Hg vapor within the cylinder, the rod is protected by a bellows that prevents vapor escape into the secondary containment, with the bellows vented directly to the primary charcoal filter for added safety.
During normal operations, components such as the Hg jet chamber, return hose, sump tank, and sump tank drain line should not be subjected to pressures exceeding atmospheric levels However, leak checking procedures may necessitate temporarily pressurizing these parts to 1 atm gauge or applying vacuum conditions.
While no operating scenario is anticipated to cause over-pressure in the sump tank, it is equipped with a check-valve for system protection In the event of over-pressure, the check-valve exhaust is directed to a charcoal filter This safety mechanism may activate during the mercury (Hg) filling process, as Hg displaces air within the sump tank.
The flow system, illustrated in Figure 19, features an Hg cylinder equipped with two flanged ports: the lower port serves as the inlet while the upper port functions as the discharge Hg is gravity-fed from the sump tank into the cylinder inlet as it extends, passing through a manual shut-off valve and a check-valve The manual valve, primarily used during ORNL testing, will remain open during shipment and installation at MIT and CERN, as it is not accessible through secondary containment Additionally, the cylinder inlet doubles as the system drain, connected via a manual valve and quick-disconnect to the secondary containment wall; this valve safeguards the quick-disconnect and is subjected to cylinder pressure with each stroke The check-valve ensures that Hg does not flow back to the sump tank during operation.
Figure 19 Sump tank and piping
During a pressure stroke, mercury (Hg) is expelled from the cylinder via the discharge port, navigating through the nozzle supply piping where it undergoes a 180° direction change and a reduction in flow area before being released as a 1-cm diameter jet into the jet chamber The Hg supply piping primarily consists of 1-inch Schedule 40 and 3/4-inch Schedule 10 welded piping, all fabricated to ASME IX standards, with commercially available components utilized wherever feasible The components listed in Table 6 are designed to withstand the pressure of the Hg cylinder; however, as long as the cylinder pressure remains within its rated limits, downstream component pressure will not exceed that of the cylinder Hg pressure will be closely monitored near the cylinder discharge, and comprehensive pressure characterization will be conducted through testing at ORNL and MIT before the equipment is installed at CERN.
Table 6 Hg Supply Component Pressure Ratings.
Component Dwg Ref Material Description
Item 1 SS 10-inch bore, 15-inch stroke NFPA cylinder 103 (1500)
Cylinder drain tubing 203-HJT-0680 SS 3/8-inch, 0.065" wall rigid tubing 350 (6500)
Cylinder drain valve 203-HJT-0760 SS Swagelok SS-8UW-TP3 170 (2500)
Cylinder drain quick- disconnect 203-HJT-0760 SS Swagelok SS-QC6-S1-
Cylinder discharge 203-HJT-0670 SS 1-inch, SCH40 piping 130 (1900)
Hg cylinder inlet piping 203-HJT-0680 SS304L 3/4" SCH40 piping 225 (3300) per ASME IX
Hg cylinder inlet piping 203-HJT-0680 SS304L 1" SCH40 piping
Pipe weld connector 203-HJT-0670 SS Swagelok 1" SS-1610-1-
Component Dwg Ref Material Description Pressure
Flexible hose 203-HJT-0670 SS/Teflon Swagelok 8R series 137 (2000)
Hg supply line 203-HJT-0620 Ti 3/4-inch SCH10 piping 165 (2400)
Hg supply reducer 203-HJT-0624 Ti6Al4V Custom design 180 (2600)
Nozzle 203-HJT-0620 Ti 12-mm, 1-mm wall rigid tubing 200 (2900)
The jet, upon exiting the nozzle, is contained within the jet chamber and may impact the titanium deflector plate, which also functions as the primary exit beam window To enhance the design's durability, the thickness of the window was increased from 1mm to 2mm to better withstand the impact loading of the mercury (Hg) jet After exiting the rectangular chamber, the Hg is directed back to the sump tank via a 4-inch flexible stainless steel hose.
An analysis was conducted on the flow forces within the Hg supply line bend, focusing on the worst-case flow scenario This examination, along with additional calculations related to the primary containment system, is detailed in section iii Figure 19 illustrates a schematic diagram depicting the flow forces at the pipe bend.
Figure 20 Hg axial flow force analysis
The analysis revealed a resultant force of 2kN (450 lbf) in the +X direction, which could potentially separate the nozzle flange from the jet chamber flange if the Hg flow path were rigidly constructed However, since the flexible hoses for both supply and return flows are more compliant than the flange interface, the risk of leakage from this separating force is minimal The primary concern lies in the movement of the entire target module due to the flow force, and testing at ORNL will assess the necessity for physical restraints.
Secondary Containment
The secondary containment system of the Hg delivery apparatus encases the primary containment, effectively preventing any leakage of liquid mercury or mercury vapors from entering the TT2A tunnel during operations As illustrated in Figure 21, this system consists of several key components.
• SS box housing the syringe cylinders and sump tank,
• SS circular sleeve covering the jet chamber and optical diagnostics,
• Flexible SS duct connecting the sleeve to the box,
• Target module support structure used during shipping and handling,
• Two double beam windows with provisions for leakage monitoring,
• Multiple ports to allow access to the interior volume for hydraulic fluid, Hg fill & drain, and sensors,
• Filtration systems to trap Hg vapors.
Figure 21 Secondary containment left side
The secondary containment box features multiple ports, each equipped with a flange that utilizes a gasket to ensure a secure seal against the box's exterior The functionality of these flanges is illustrated in Figures 21 and 22.
• Hydraulic: two quick-disconnects for the hydraulic fluid supply and return hoses.
• Electrical: two Amphenol ® connectors for multi-conductor cables used for syringe and environment sensors.
• Optics: multiple optical fibers (light sources and receivers) for up to four view ports.
The Hg drain system features a manual valve and quick-disconnect designed to safely extract mercury (Hg) from the delivery system without compromising secondary containment An external pump facilitates the Hg extraction, while the Hg drain port is subjected to full cylinder pressure during jet formation, as outlined in section 3.3 The manual valve acts as a protective device, isolating the quick-disconnect from pressure pulses; during installation, this valve is secured in the closed position with a wire tie Additionally, when equipped with a special connecting plug, the quick-disconnect can handle full cylinder pressure.
• Hg fill: quick-disconnect used to load Hg into the sump tank without opening the secondary containment.
• Emergency Hg extraction: quick-disconnect with rigid tubing into small sump within the secondary containment Should a major breach of the primary containment occur,
Hg will collect in this sump and can be removed using an external pump.
Hg vapor filters consist of two filter assemblies that include sulfur-impregnated charcoal and HEPA filters, equipped with a port for connecting an external ventilation system Typically, these ports remain capped, but in the event of elevated Hg vapor levels, they can effectively remove harmful vapors from the containment area The dual-port design allows one port to function as a fresh air inlet while the other extracts vapors, ensuring efficient air quality management and facilitating filter replacement.
Figure 22 Secondary containment right side
During the fill and drain operations of Hg, it is essential to implement precautions to prevent leakage when connecting or disconnecting quick-disconnect fittings Utilizing wipes or containers during these processes can effectively contain any potential spills.
The secondary containment box features two robust stainless steel rectangular tubes that provide support while on the transport cart and facilitate rigging Nylon straps can be threaded through these tubes for safe lifting, and protective spreaders will be included at the top of the box to safeguard both the straps and the enclosure's sides from damage.
Analyses and documentation for the secondary containment are included in iv.
Baseplate Support Structures
The MERIT experiment's baseline geometry necessitates a tilt of the magnetic axis relative to the horizontal proton beam, with the solenoid center aligned in the beam path To achieve this configuration, a dedicated support structure is essential Additionally, the integration of the solenoid with the mercury delivery system indicates the advantage of utilizing a common support structure, enabling the assembled equipment to be managed as a cohesive unit The integrated setup is illustrated in Figure 23, highlighting its relation to the proton beam.
Figure 23 Solenoid and Hg system on common baseplate
The installation and assembly of the solenoid and mercury (Hg) delivery system rely on various support structures, as illustrated in Figure 24 These structures were designed based on weight estimates of 53 kN (12 tons) for the solenoid and 17.8 kN (2 tons) for the mercury-loaded delivery system.
During the design of the support structures, multiple analyses were conducted, with key findings highlighted in this section For a comprehensive overview of all analyses, please refer to section v.
Figure 24 Baseplate support structures design drawing
The common baseplate, illustrated in Figure 25, serves as the essential support structure for the Hg system and solenoid, ensuring correct tilt and elevation throughout the experiment Additionally, it functions as a mobility platform for the solenoid within the CERN tunnels It is crucial to emphasize that the built-in lift points on the baseplate are intended solely for its own weight and should never be used to hoist the baseplate while it is supporting the solenoid or Hg system To prevent accidental misuse, the lift points are removable and should be appropriately labeled.
Figure 25 Common baseplate and support beam
The common baseplate incorporates several design features and functions:
Jack brackets are four detachable components designed for use with hydraulic jacks to elevate a loaded baseplate equipped with an onboard Hg system and solenoid These brackets are distinct from the integrated lift points, which feature side-mounted swivel hoist rings.
- Anchor brackets: four adjustable brackets that can be used with concrete anchor bolts to fasten the baseplate to the floor.
- Levelers: six threaded leveling jacks that provide fine elevation/tilt adjustment of a loaded baseplate These levelers support the weight of the baseplate during the experiment.
- Rails: two stainless steel roller guides attached to the baseplate that allow the target cart to be transferred from the transporter to the common baseplate during target module insertion.
- Solenoid restraint brackets: two adjustable brackets which affix the magnet to the support plate upon which it sits.
- Cart positioning brackets: two brackets with jack bolts that hold the target cart in a fixed axial position during operations Can also be used to provide fine axial positioning adjustment.
- Solenoid lateral positioning: two jack bolts on each side provide lateral position adjustment of the solenoid by sliding the magnet support plate over a low-friction surface.
- Tow hooks: one on each end used to maneuver the baseplate.
- Roller pads: three pads provide a means to set the baseplate onto high-capacity rollers during baseplate transport and gross positioning operations.
Extensive stress analyses were conducted to evaluate the performance of the common baseplate under various loading scenarios, given the significant weights it must support Additionally, critical welds were analyzed to ensure structural integrity The findings from these analyses are presented below.
A fundamental analysis was conducted to model the loading conditions of a baseplate supported by three rollers, which is typical during initial beam alignment procedures The findings are illustrated in Figure 26, while Figure 27 presents the safety factor distribution observed on one of the outer channels.
Figure 26 Induced stresses of baseplate on three rollers
Figure 27 Safety factor distribution for outer baseplate channel on three rollers
The analysis revealed a minimum safety factor of 1.9, falling short of the target safety factor of 3 Despite this, high stress was confined to small areas around bolt holes, not reflecting overall stress levels In fact, just beyond these localized stress points, the safety factor rose to 10 or higher, indicating that the structure is adequate for the given loading conditions.
The simulation of the baseplate supported by four out of six levelers revealed localized high-stress areas near the bolt holes; however, the overall stress levels remained significantly lower These localized stresses are expected to self-relieve through local deformation and are not viewed as structural concerns Additionally, load testing will be conducted on the baseplate to verify its load-carrying capacity.
In the analysis of the loading case where a loaded baseplate is supported by four hydraulic jacks, the jacking bracket weldment was evaluated separately due to its role in load distribution The most critical scenario involves the two brackets located beneath the magnet, each estimated to bear a load of 26.6 kN (6000 lbf) distributed evenly across two bolt holes As illustrated in Figure 28, the minimum calculated safety factor in localized areas around the bolt holes is 1.4, with the safety factor rapidly increasing to levels above this threshold.
10 just outside the holes Welds on this bracket were analyzed separately, and the analysis gave a safety factor > 9.
Figure 28 Safety factor distribution for the jacking bracket weldment
The target transporter is designed to facilitate the movement of the Hg delivery system and target cart within the TT2 and TT2A tunnels, featuring a design similar to the common baseplate It is equipped with temporary rollers for mobility and levelers for height adjustment and support Swivel hoist rings enable the lifting of the unloaded transporter, while tow hooks are positioned at both ends for towing convenience.
The transporter frame is structurally similar to the common baseplate, differing only in length, and since the total load on the transporter is significantly lower than that of the common baseplate, a separate analysis of the transporter frame was deemed unnecessary.
Figure 29 Target cart and supporting transporter
The Hg delivery system component supports the transfer from the transporter frame to the common baseplate while facilitating the insertion of the target module into the solenoid bore Constructed primarily from aluminum, the cart features a lateral position adjustment system that aligns the Hg system horizontally with the solenoid for accurate beam alignment Although there is no vertical positioning adjustment, the flexible components of the target module are designed to handle slight vertical misalignments, with leveling screws on the magnet available for final adjustments.
A finite element analysis was made of the primary cart structure Results are shown in Figure
30 and indicate the cart is capable of supporting the full weight of the Hg system with a minimum FOS of four.
Figure 30 Safety factor distribution for the cart structure
The common baseplate utilizes threaded levelers for weight support, but positioning the magnet center in the beamline often requires one pair of levelers to extend near their upper limit, raising stability concerns To address this issue, a separate structural support beam was designed to occupy approximately 15 cm of space, enabling the levelers to remain closer to their lower limit This aluminum beam structure will be placed beneath the baseplate while supported by lifting jacks, enhancing overall stability.
A structural analysis was made of the beam, and the results are shown in Figure 31 The minimum FOS was calculated to be 13.
Figure 31 Safety factor distribution for solenoid support beam
The baseplate support structures underwent successful load testing at ORNL to confirm the design and analysis accuracy The weights used during testing exceeded the estimated loading conditions expected at CERN by 113% The load test setup is illustrated in Figure 32.
Control System
The syringe pump hydraulic power unit includes basic on-board controls, which are insufficient for the MERIT experiment The experimental equipment is situated in TT2A, while the hydraulic power unit is located in TT2 Although the ISR tunnel was initially proposed for the remote control room, it has now been relocated to Building 272.
The development of the control system for the MERIT experiment emphasized the need for flexibility to accommodate various sensor types Labview® was selected as the control software, operating on a laptop in a remote control room far from the experimental area To avoid the impracticality of running long sensor wires for a short-term experiment, the solution involved integrating Labview®-compatible sensor modules within the HPU control cabinet and utilizing an Ethernet network for communication Consequently, all MERIT sensors are consolidated in the TT2 tunnel, regardless of their origin in TT2 or TT2A.
From a system safety perspective, an independent remote emergency stop is essential, separate from the MERIT control system The syringe system was initially equipped with a 76m (250ft) emergency stop pendant wired directly into the HPU power cabinet, aligned with the original ISR control room location However, due to the significant increase in distance to the final control room, an alternative method for controlling power to the HPU is necessary.
Figure 33 MERIT layout in the CERN tunnels
The Labview-based control system is still under development, but the basic screen layout can be seen in Figure 34 The system provides the following capabilities/functions:
- Jet configuration: the velocity profile of the jet can be configured within the constraints of loaded Hg volume & available piston stroke.
- Operation: provides control of the syringe HPU Supports manual and triggered operating modes.
- Performance: graphical representation of syringe movement & sensor feedback during operating cycle.
- Data logging: provides capability to record history file.
Figure 34 Labview control system operator interface
Filling and Draining Mercury
A fundamental requirement for designing the Hg delivery system was that filling and draining
To safely remove Hg from the system, it is essential to do so without opening the secondary containment This containment features a fill-port on its sidewall, which connects directly to the sump tank, as illustrated in Figure 35 Additionally, the drain port is situated at the front of the enclosure, as depicted in Figure 22.
A peristaltic pump will facilitate the transfer of mercury from standard 2-liter flasks through a stainless steel tube connected to flexible Tygon® tubing, utilizing U.S Department of Transportation-approved containers The pump, as shown in Figure 36, was successfully demonstrated for mercury transfer operations at ORNL, with detailed results from 1999 tests for the Spallation Neutron Source - Target Test Facility available in ix Notably, during the transfer process, only the inner wall of the tubing contacts the mercury, ensuring that the pump mechanism remains uncontaminated, with contamination limited to the tubing itself.
Figure 36 Peristaltic pump for transferring mercury
The procedure for transferring mercury into the sump tank is as follows:
1 Position the pump and the flask at an elevation higher than the fill port.
2 Place the pump and flask in a plastic tray lined with gauze, or provide other suitable containment for spill control.
Ensure that all auxiliary support equipment, including the digital scale, portable vapor monitor, and portable snorkel, is correctly positioned and functioning properly Additionally, connect the Tygon® tube fitting to the fill port connector.
4 Weigh and record the flask weight; (the tare for each numbered flask will have been determined from the tests at ORNL).
To begin the process, remove the flask plug and insert the stainless steel suction tube connected to the other end of the Tygon® tube, then activate the pump, which has already been calibrated based on prior testing at ORNL.
6 Siphon the mercury from the flask until the suction in the tube is lost; record the weight of the empty flask.
During the fill operation, up to 23 liters of displaced air will be vented from the sump tank to the primary filter unit atop the enclosure This air will be filtered and monitored for mercury vapor while also being collected into a portable snorkel.
The precise volume of mercury required for testing at CERN has been established based on previous tests conducted at ORNL and MIT To ensure accuracy, a meticulous accounting of the weight will confirm the amount of mercury utilized in the target.
The mercury transfer process will utilize a peristaltic pump, which connects to a quick-disconnect fitting on the secondary enclosure, directing flow to the sump tank drain tube During this operation, the secondary enclosure will remain securely closed.
The ORNL testing will explore an alternative method for transferring mercury from the target, which aims to prevent the risk of overfilling a flask.
1 Place a 3-liter clear plastic bottle, marked with a 2-liter “fill line” under the drain port Connect a flexible tube with a quick-disconnect to the Hg drain port on the secondary enclosure.
To effectively control the flow, utilize the drain valve to gravity-drain two liters of mercury into a 3-liter bottle To prevent vapor lock during the draining process, attach a manual or check valve with a quick-disconnect fitting to the mercury fill port, allowing air to enter the sump tank.
3 Using the peristaltic pump, transfer 2-liters of mercury from the plastic bottle to a steel flask; install the flask plug and record the weight.
4 Repeat steps 2 and 3 until all mercury that can be gravity-drained from the system has been removed.
5 Remove mercury remaining in the sump tank or the drain line using the peristaltic pump.
To ensure precise tracking of mercury levels, it is essential to measure the weight of mercury extracted from the target, allowing for an accurate estimation of the remaining mercury volume in the system This remaining amount must be documented in the transportation paperwork for the return shipment of the target equipment to ORNL.
All waste materials, including mercury-contaminated gloves and gauze, will be securely double-wrapped in plastic bags, taped, and disposed of in the designated Satellite Accumulation Area, specifically the 55-gallon drum outlined in Table 5 Additionally, tools that may become contaminated and other reusable items for future mercury handling will also be double-wrapped and stored in a sealable plastic bin to ensure safety and compliance.
Mercury Vapor Filtration
The secondary enclosure features two sulfur-impregnated charcoal filter assemblies, with the larger filter mounted on the top cover and the smaller one on the down beam wall These filters are adaptations of those used in portable snorkels The primary filter measures 432 x 255 x 51 mm (17 x 10 x 2 inches), while the secondary filter on the back wall measures 267 x 267 x 38 mm (10-1/2 x 10-1/2 x 1-1/2 inches) Each filter is designed to connect to a 127-mm (5-inch) diameter hose of the portable snorkel, as illustrated in Figure 1.
During routine operations, each filter port remains closed to prevent air exchange between the secondary enclosure and the TT2A Tunnel, maintaining pressure equilibrium as long as the enclosure temperature aligns with that of the tunnel Temperature changes in the mercury and air within the enclosure will be documented between pulses during ORNL tests, ensuring that the continuously monitored air for mercury vapor in the secondary enclosure remains isolated from the tunnel air.
Before mercury is introduced into the sump tank, the primary filter cover is removed to allow displaced air from the sump tank to be pushed through the filter Mercury vapor levels are then monitored with a portable vapor monitor If any vapor is detected, a snorkel can be attached to enhance filtration and prevent mercury vapor from entering the tunnel environment This process ensures effective containment of hazardous vapors.
“single” and “double” filtration will be demonstrated as part of the testing at ORNL.
The estimated lifetime of the filter was determined using calculations from ORNL’s Target Test Facility, alongside data from the filter material's manufacturer The sample calculation indicates that the filter can endure 185 hours of vapor exposure before reaching 12% saturation.
- Flow Rate 110 cfm (through the snorkel filter)
- Filter Weight 6 lbs (80% charcoal, 20% sulfur)
- Allowable Filter Saturation 12% (vendor information)
(Note: The calculation does not include the reduction for adsorption of humidity.)
The following equations were used for the calculation [5]
When replacing the primary or secondary filter, utilize the portable snorkel to ensure negative pressure in the secondary enclosure while effectively filtering the extracted air The procedure for replacing the primary filter is as follows.
2 0 Hg 3 P sat mbar sat K sat P T
The procedure for routine operations, where the secondary enclosure vapor monitor indicates no vapor presence, is outlined by the equation 5.3105 logP sat = −T 0 K This process will be demonstrated during testing at ORNL.
1 The operator will be dressed with proper personal protection equipment (PPE); the assistant operator will handle the portable vapor monitor.
2 Connect the snorkel hose to the secondary filter port; turn on the snorkel to achieve a low flow rate, i.e., 280 liters/min (5-10 cfm).
3 Remove the 5-inch diameter cover from the primary filter to permit an inflow of air into the secondary enclosure.
To enhance the snorkel flow rate during ORNL testing, first remove the filter pack assembly and monitor for vapor around the filter After testing, securely place the filter in a sealed plastic bag.
5 Install a new filter; decrease the flow to the snorkel to zero and cover the primary port.
The same procedure will be used for replacing the secondary filter except in step 2, the snorkel hose will be connected to the primary filter port.
Off-Normal Conditions
The article outlines several off-normal conditions that could affect the target system's operations, specifically highlighting two critical scenarios: the presence of measurable vapor in the secondary enclosure and a spill from the primary enclosure that remains contained within the secondary enclosure Other conditions considered during system design are not deemed relevant to operational contexts.
Vapor Leak Into Secondary Containment
The secondary containment system is equipped with a Jerome 431-X monitor that continuously checks for mercury vapor every five minutes via a flexible tube in the adjacent tunnel (TT2) This monitor interfaces with the Labview® control system, providing visual and audible alerts when vapor levels reach the threshold limit value (TLV) of 0.0125 mg/m3, as established for the Target Test Facility The system can be easily adjusted to accommodate different TLV settings, adhering to current U.S and ORNL standards.
-OSHA TLV: 0.050 mg/m 3 for up to a 10 hour work day, 40 hours per week
-TTF action level (when respirators are required): 0.0125 mg/m 3
Upon receiving an alarm signal, the operator will first examine the conductivity probe sensor for signs of a significant leak from the primary containment and the secondary vapor monitor in the tunnel If the conductivity probe shows a zero reading and other sensors, including the secondary vapor monitor, report normal signals, it can be concluded that there may either be a minor leak from the primary containment or that the vapor monitor has generated a false-positive signal.
To ensure the monitor's proper functionality, a portable sensor will be swapped with the monitor in tunnel TT2, allowing for immediate personnel access Operations can proceed uninterrupted until the end of the shift, at which point a visual inspection of the system will be conducted As indicated in Table 3, the dose rate at the top of the secondary enclosure will be less than 1 mrem/h at shutdown or shortly thereafter, making it safe for visual inspection.
During the inspection in TT2, the vapor monitor in the adjacent tunnel (TT2A) will be assessed for vapor presence If vapor is detected solely within the secondary enclosure, it will remain contained unless there is a breach or leakage from the enclosure filters A portable monitor will be utilized to investigate these potential issues if vapor is found in the tunnel Should the tunnel show no vapor but indicate leakage into the secondary enclosure—evidenced by the absence of elemental mercury in the enclosure sump—operations are expected to continue as planned.
Mercury Leak Into Secondary Containment
If elemental mercury is found in the secondary enclosure, it confirms a breach in the primary containment As per CERN's operational guidelines, the primary containment must remain closed throughout the experiment's duration, leading to an immediate halt in test operations and a subsequent cool down period of up to one month After this period, the mercury's contact dose will be reduced to less than 10 -2 mSv/h (or