MICE collaboration meeting

Osaka –

AFC Module update & Plan

Presented by

Wing Lau -- Oxford University

Items for discussion

• Response to the Safety Review report;

• Situation with the burst window test & window survey;

• Progress on welded window R & D;

• Progress on the Absorber development and the MTA test

• Use of CryoCoolers for the absorber & magnets;

• Alternative designs for the radiation Shielding valve;

• Hydrogen Gas Handling & Venting system

• Remove buffer tank and vent the hydrogen out directly - implemented

• Remove relief valves in the hydrogen vent lines and have burst disks only – retained

• Completely separate vent system for the absorber and vacuum spaces -implemented

•  Detail specification of the Relief valve – work in progress

• Is hydrogen detector appropriate in the vacuum line – still under consideration

• Hydrogen detectors are needed in the ventilation system and in the personnel space around the experiment – will be implemented

Response to the Safety Review

A report was prepared and is ready to be sent to the Review Panel. The following is a summary of actions taken against the comments / recommendations made by the penal:-

• R & D on the Metal Hydride system • The use of hydride system requires active control.

• The panel suggested an scaled model test.

• It also asked the group to examine the safety issues associated with this system

--- R&D proposal defined and submitted

Response to the safety review

• Hydrogen Gas Handling & Venting system (cont.)• Examine the level to which piping should be Argon jacketed – will be addressed

• Replacing the flame arrestor with a vent pipe with an inert atmosphere – implemented

• Adopt Fermilab requirement vacuum system volume 52 x LH2 volume – not implemented

• Practicality of using intrinsically safe electrical equipment – response already drafted

• Pipe joints – will be as requested

• Detection of Hydrogen in Personnel areas – agreed

• Attention to Interlocks, alarms and control system - ongoing.

• Continuation of HAZOP assessment – agreed

• Response to Absorber system leak scenario – ongoing

• Potential of liquid hydrogen sloshing in warmer part of the feed pipe – to be addressed in level control.

• Leak between the helium and hydrogen compartment in Absorber unit - ongoing

Safety Review panel – Additional Points

Situation with the burst window test & window survey

Burst Window test & window thickness measurement

The burst test conducted on a 21cm window in April this year had mixed success.

• The recorded burst pressure was 144 psi which is 44% above the required burst pressure for safety;

• No shrapnel was found and the window burst out from the centre;

However….

• No definitive record of how thick the window centre was;

• No Photogrammetry was taken on the window deformation during the pressure test to enable a direct comparison with FEA results;

• The window did not leak before it broke which was predicted in the latest FEA analysis;

What worries us is………..

Prior to the current window test, it was accepted that the Photogrammetry technique would be a reliable way of taking the window thickness measurement. This view is now somewhat in doubt. The reason:

The resource constraint

The technique depends heavily on the availability of a single source – John Greenwood. The resource situation at NIU & Fermilab was such that John is assigned to a number of projects which require equal or higher priority. Dona Kubik who was deeply involved with the last Photogrammetry test has moved on within NIU to pursue other interest.

In a multi-task environment, people’s dedication would inevitably be affected. This may affect the individual’s level of attention and commitment to the project and may have an impact on the quality of their work.

What worries us is………..

The quality issue:

1) The required minimum thickness is 105 microns;

2) The CMM measurement at the manufacture’s place put the window thickness at 117 micron (reference from Ed Black’s email);

3) The Photogrammetry measurement gave a figure of 192 microns;

4) Thickness measurement of the fragmented piece after burst was 105mm;

Based on (4), it is reasonable to say that the minimum thickness would be around 117 mm. This would imply that the CMM measurement made at Mississippi was not an unreasonable yardstick.

So, why was there such a large discrepancy in the Photogrammetry results?

What worries is………..

The quality issue:

1) The required minimum thickness is 105 microns;

2) The CMM measurement at the manufacture’s place put the window thickness at 117 micron (reference from Ed Black’s email);

3) The Photogrammetry measurement gave a figure of 192 microns;

4) Thickness measurement of the fragmented piece after burst was 105mm;

Based on (4), it is reasonable to say that the minimum thickness would be around 117 mm. This would imply that the CMM measurement made at Mississippi was not an unreasonable yardstick.

So, why was there such a large discrepancy in the Photogrammetry results?

What worries is………..

The quality issue:

1) The required minimum thickness is 105 microns;

2) The CMM measurement at the manufacture’s place put the window thickness at 117 micron (reference from Ed Black’s email);

3) The Photogrammetry measurement gave a figure of 192 microns;

4) Thickness measurement of the fragmented piece after burst was 105mm;

Based on (4), it is reasonable to say that the minimum thickness would be around 117 mm. This would imply that the CMM measurement made at Mississippi was not an unreasonable yardstick.

So, why was there such a large discrepancy in the Photogrammetry results?

John Greenwood’s message showing thickness at the window centre (x=0) being 0.192mm

What worries is………..

The quality issue:

1) The required minimum thickness is 105 microns;

2) The CMM measurement at the manufacture’s place put the window thickness at 117 micron (reference from Ed Black’s email);

3) The Photogrammetry measurement gave a figure of 192 microns;

4) Thickness measurement of the fragmented piece after burst was 105mm;

Based on (4), it is reasonable to say that the minimum thickness would be around 117 mm. This would imply that the CMM measurement made at Mississippi was not an unreasonable yardstick.

So, why was there such a large discrepancy in the Photogrammetry results?

……It is difficult to draw a conclusion to this. It could well be a one-off event due to the lack of attention because the key person was over-loaded with other project commitment. From the project’s point of view, we do need to review our strategy in future window thickness measurements

Is Photogrammetry still our preferred technique? If so, how do we make sure that its quality is not operator dependent?

The current window is substantially stiffer than the previous design (torispherical shape). This would allow the conventional CMM survey back into the race again.

Other thoughts?

The FEA comparison

The earlier version of the window design predicted a bursting pressure of around 100psi at the centre, and the actual burst pressure was recorded at 144 psi. So, why such a large discrepancy?

The accuracy of the FEA depends on a number of criteria such as:

• The accurate representation of the as-built geometry;

• The material properties;

• The loading;

The as-built situation:

• The required minimum thickness was 105 micron. The as-built thickness was between 117 microns to 192 microns, a variance of 11% to 83%;

• The standard material property shows a yield stress of 273 MPa and a UTS of 310 MPa. The material certificate shows a value of between 272 to 293 MPa on yield, and between 298 to 315 on UTS.

• Similarly, the max. elongation was found to be only 11 - 12% while the standard material shows a figure of 17%.

The bursting mode

Why didn’t it leak at a distance away from the centre (as predicted) before it broke?

• In the light of the Safety review the primary window requires to withstand an external pressure of 1 bar without buckling. This has lead to some 20% increase in window thickness. This would delay the burst of the window and shifts the highest stress point away from the centre.

• This thickness increase was however not reflected in the window used in the burst test.

Against this background and in the absence of a true record of how the window deformed during pressure test, it would be difficult to have a direct comparison between the test and the FEA results.

High bending stress area

Status of the welded window R & D test

WELDED WINDOW

• Objectives– to investigate a practical weld seal solution for the vessel

windows

– incorporating a bayonet lock feature to react the internal pressure force

– to have the capability of refurbishment and re-use of both vessel and window

– compliant with construction codes and operational requirements

Vessel Manufacture.

Body Bayonet thread Window Bayonet thread

Assembly weld prep Welded assembly

Design/Test overview

• Material: AL 6061 for body and dummy window

• Incorporate axial lock against internal pressure force

• Minimise weld for vacuum/pressure sealing only

• Thermal shock cycle on weld 3 cycles of RT>80k>RT

• Vacuum leak check

• Pressure test 6.8 barG (100psi)

• Vacuum leak check

• Refurbishment procedure

Welding parameters

Welding parameters Initial weld

Pre Heat: ~ 80 CCurrent: AC 240 ampsAC Balance: penetration 7 ACHF: continuousShield gas: Argon 6 l/minBack shield Argon nonePre flow: 3 secPost flow: 9 secFiller wire: AW 5356 5% mag (BS 2901 pt4)Wire dia: 1.6 mmTungsten dia 3.2 mm LathinatedManual TIG (no rotary manipulator)

Welding parameters Re-weld after refurbishment

Pre Heat: 85 CCurrent: AC 240 ampsAC Balance: penetration 4 ACHF: continuousShield gas: Argon 6 l/minBack shield Argon nonePre flow: 3 secPost flow: 7 secFiller wire: AW 5356 5% mag (BS 2901 pt4)Wire dia: 1.6 mmTungsten dia 3.2 mm LathinatedManual TIG (no rotary manipulator)

We should compare notes with KEK who supplies the Absorber body which requires similar welding

Initial results• Weld test #1 (no thermo-couple used)

– Leak test after thermo-cycle no detectable leak at 1x10-10 mbar Ls-1

– Pressure test (6.8barG hold30 min) no detectable leak

– Pressure cycling (no hold) 2x 0>6.8barG>0

– Leak test after pressure cycle no detectable leak at 1x10-10 mbar Ls-1

• Weld test #2 (after refurbishment)

With thermo-coupletemp Weld run

C completeAmbient 17 0%Pre heat 85 StartInitial running 75 20%Advancing to TC 95 33%Peak passing TC 160 60% < 30 secReceeding from TC 140 70%Post weld 95 100%Window 54 100% + 1min

Current Status

In system for vacuum and pressure test

Comment on the progress made

• With the current budget and resource constraint, the progress made by RAL is satisfactory

• Welding parameters that guarantee consistent welding quality have been established

• Initial test result shows no detectable leakage

• Further work is continuing to establish if this quality would be impaired by the refurbishment and the re-use of both the vessel and the window

The results so far meet with our expectation

Progress on the Absorber and the MTA test results

This talk is being covered by Shigeru in a separate presentation shortly after this session.

Use of CryoCooler for the absorber and magnet

The technical justification for using CryoCoolers for the LH2 Absorber & Coil cooling is outlined in a separate document presented by Mike Green.

The following summarises Mike’s concluding comments and looks at the engineering arrangement of fitting the coolers within the AFC module

The Sumitomo SDRK 415-D GM Cooler – as one of the possible choices

300 K Attachment Ring

Cryocooler First StageT = 25 K to T = 80 K

Cryocooler Second StageT = 2.5 K to T = 20 K

• 1.5 W is delivered at 4.2 K at the second stage.

• 18 W is delivered at 15 K at the second stage.

• With 50 Hz power, the cooler delivers 38 W at 50 K at the first stage.

• Cooling delivered at both stages concurrently.

Characteristics of the 415D GM Cooler

Date source provided by Mike Green

Cooler Requirements for MICE Magnets – concluding comments from Mike Green’s talk

• The coupling coils have a single pair of 300 A leads. Use a single 1.5 W cooler: 1 cooler T = 3.9 K

• The focusing coils have two pairs of 300 A leads. Use two coolers: 1 cooler T = 4.7 K; 2 coolers T = 3.6 K

• The detector magnet has five coils. Each magnet coil has a pair of 300 A leads. Three coolers are needed: 2 coolers T = 5.1 K; 3 coolers T = 4.2 K

• In total as many as fourteen coolers may be needed to cool the MICE magnets.

Connection of the Cooler

• If one wants to cool a magnet down with a cooler, the cooler second stage must be connected directly to the magnet with a flexible OFHC copper strap. The first stage can be connected to the shields using a copper strap.

• The temperature drop between the magnet high field point and the cooler cold head has a negative effect on magnet operation. Even a 0.4 K temperature drop will affect the performance of the MICE coupling and focusing coils.

• A gravity separated heat pipe can connect the cooler 2nd stage cold head to the load with a very low temperature drop (0.1 to 0.2 K) between the magnet hot spot and the cold head.

Cooler Connection through a Flexible Strap

The temperature drop from the load to the cold head is proportional to the strap length and inversely proportional to the strap area and the strap thermalconductivity.

T L

kATc

Tc = contact resistance

Tc is usually small.

P

Q

T3T2

T1

T0

Cryocooler Cold Head

Cryostat Boundary

Cooling Cryogen

Cooled Load

Liquid Fill Valve (if needed)

Relief Valve

Flexible Cu Strap

T = T3 - T0

Details of the Copper Strap Arrangement

Note: For T = 0.1 K, L = 0.15 m, andk = 600 W m-1 K-1, then A = 0.0025 m-2

and Tc = 0.

Note: For T = 5 K, L = 0.3 m, andk = 1000 W m-1 K-1, then A = 0.00006 m-2

and Tc = 0.

In addition heat flow through 6061 Alis quite poor at 4 K (k = 6 W m-1 K-1).

Cooler Connection through a Heat Pipe

The temperature drop from the load to the cold head is independent of the distance between the load and the cooler cold head.

Liquid He distributes the cold around the coil.

T Tb Tf TcP

Q

T3T2

T1

T0H

h = head for circulating the liquid cryogen

Cryocooler Cold Head

Condensation Plate

Cryostat Boundary

Liquid Tube (any length)

Gas Tube (any length)

Cooling Cryogen

Cooled Load

Gas Charge Valve (if needed)

Relief ValveTb = Boiling T DropTf = Condensing T DropTc = Contact ResistanceThese can be made small.

T = T3 - T0

Cooler Requirements for the Absorbers

• The absorber total heat leak should be 10 W or less. Beam heating and dark current are not a factor in MICE.

• A single cooler should be capable of holding the intrinsic heat load into a MICE liquid hydrogen absorber. Direct cool down of a MICE liquid hydrogen absorber using a cooler may be difficult. The cooler first stage plays almost no role in cooling the absorber.

• A liquid helium absorber can not be cooled.

Cool Down Circuit

304 St. St, Can ~ 4 liters

304 St. St, Neck Tube, 30 mm ID

Cu Pipe 15 mm ID

St. St. to Cu Braize Joint

St. St. to Al Transition

St. St. to Al Transition

St. St. to Cu Braize Joint

Cu Pipe 6.4 mm ID

H2 Condensing Surface

Neck Part of Absorber Vacuum Vessel

Absorber Vacuum Vessel below Neck

LH2 Absorber Vessel ~20 liters

LH2 Level Gauge

< 20 K Cooler Cold Head

Optional Cu Cool Down Strap

Heat Exchanger

Absorber Cooling with a Small Cooler

General arrangement of the CryoCoolers for the LH2 Absorber and the helium bath for the

magnet in the Focus Coil Module

Concluding Comments

• It appears that a coupling magnet can be cooled with a single cooler. The use of a heat pipe is advised to keep the T between the far side of the magnet and the cold head down to 0.1 K.

• The focusing magnets may require two coolers to cool the magnet and its leads. The leads are the dominant reason for needing a second cooler. The coolers may be connected to the magnet directly and through a heat pipe so that T < 0.1 K.

• The detector magnet requires three coolers to cool the magnet. The dominant heat load is the leads on both stages of the coolers. Direct conduction cooling is precluded by the INFN magnet design.

Concluding Comments (cont.)

• It is unlikely that small coolers will be used to cool down the magnets to 80 K. Using coolers to cool down some of the magnets from 80 K to 4 K is possible, but it is probable that liquid cryogens will be used to cool down the magnets over the entire range of temperature. Recent results from the MTA absorber cool down will be studied to see what we can learn from there

• It appears that the liquid hydrogen absorber can be cooled using a small cooler. The total heat leak into the absorber must be less than 10 W. A heat pipe connection between the 2nd stage cold head and the absorber is probably mandatory

• Direct cool down of the absorbers may be possible, but the cooling strap length is long and the cross-section area must be kept small. Liquid cryogen cooling using the absorber heat exchanger will be the most likely absorber cool down scenario.

Alternative designs to the radiation shielding

Background

• The equivalent of 50mm thick lead is needed to protect the fibre trackers during the tuning of the RF cavities to full gradient.

• Ed Black suggested using commercial gate valve , which requires a minimum space of 370mm when all the flanges and connecting plates are included. As a result, the space between the final focus coil and the first match coil was set at about 600mm.

• The physics and engineering benefits of reducing the gap spacing from 600mm to 450mm have already been discussed extensively in several talks (Green & Bravar) in this meeting

Radiation Shielding Design Options

As a result, a design study was carried out to reduce the thickness of the current ”Gate Valve”, proposed by Ed Black, to 220mm, or less, to fit in a space of 450 between the final focus coil and the first matching coil. The new design will be presented by Stephanie Yang at a separate session this afternoon.

• Rotating shutter with hydraulic motor design

• Double shutter with linear actuator design

• Double shutter with ‘bicycle chain’ design

• The ‘sash window’ shutter type design

In this talk, we shall address some of the issues surrounding the interface between this module and the modules that are connected to it.

Connection between the radiation shield module, AFC module and the Detector modules

Note that the stud bolt is not connected to the Radiation Shield module flange to isolate any transmission of forces from AFC

Bellow flange is threaded and fitted with vacuum seal

Magnet forces

Stud bolts are used in compressing the bellow to create a gap during the insertion of the AFC module.

Remarks• Reducing the gap between the coils from 600 mm to 450

mm is acceptable. A gap less than 450 mm may increase detector magnet heat load.

• More than one shield design will fit into a 450 mm gap between the coils.

• Rigid & leak tightness connection between the Radiation shield module & the detector module

• Flexible connection to the AFC module using bellows isolates any magnet forces transmission from the AFC / Coupling module to the Detector module. This protects the Radiation Shield module casing from any excess bending load