MICE Collaboration Meeting

RAL 31 May – 3 June 2009

AFC status

By

Wing Lau, Oxford University

Everything you want to know about the AFC, but didn’t know how to ask.

Let me unfold this to you in the following sequence.

• Issues, Hiccups & points of interest

• Progress since last reported

• Current schedule

• Contract variance

Quench Issue on the AFC Module

There has been some discussion in the context of the AFC module as the best method to control quench. There are basically two approaches were considered:

Active system

The use of an active system where there are heaters embedded in the coils. Upon detection of a quench electronics provide power to these heaters which dissipate the stored energy.

ProsDoesn’t rely on thermal contact between the coils and the former – a slip plane can be used.

ConsExpensive More complex as heaters have to be installed in the coils

The price tag – over £100K!!!

Issues:-

Quench Issue on the AFC Module (cont.)

Passive (Quenchback)

This relies on there being good thermal contact between the coils and the former. A quench induces currents in the former which heat the inner surface of the coils and dissipates the energy.

ProsSimple constructionNo complicated electronicsPassive

ConsNeed good and reliable thermal contact between the coils and the formerFor MICE we will need a separate power supply for each module

Baseline solution

The systems above were reviewed in the context of MICE and as a baseline, the passive system was chosen. Tesla have been charged with coming up with a design that ensures there is adequate thermal contact between the coils and the former

The Hiccups

Hiccups so far:-

Space envelope clashes:-

This came about when we agreed to Tesla increasing the bobbin end plate thickness from 25mm to 35mm.

As a result, the following happened:

13.5

7.0

25.0

2.05.0

309.5

47.5

39.0

12.5

422.0

bobbin

Thermal radiation shield

Magnet cryostat

Large End Flange

386.0

362.0

24.0

The leading dimensions shown on the interface drawing to both KEK and Tesla

9.4

14.5

35.0

4.05.0

309.5

32.1

39.0

12.5

422.0

bobbinThermal radiation shield

Magnet cryostat

Large End Flange

386.0

377.4

8.6

Hydrogen Absorber and the feed pipes are already made and tested.

The constraint from KEK:

Constraint from Tesla:-

Tesla needs 10mm for the extra thickness for the bobbin end plate. They also increased the gap at and thicken up the thermal radiation shield sheet metal. This extends their space envelope by as much as 15.4mm.

Fo

ul!!

Clash between LH2 pipe and magnet cryostat !!!

The design as it stands

If nothing done, the following will happen:

9.4

14.5

35.0

4.0

5.0

310

47.5

39.0

447.9

bobbinThermal radiation shield

Magnet cryostat

Large End Flange

386.0

377.9

24

10.0

The absorber has to be shifted by 15.9 mm upstream

15.9mm

12.5

The Large End Plate will stick out of the AFC cryostat flange face by 15.9mm

The solution:

Agreed change with Tesla:-

1) Reduce space between Magnet cryostat & radiation shield;

2) Local thinning of Large End flange to give H2 pipe a clearance gap of 47.5mm

9.4

9.0

35.0

4.0

5.0

310

47.5

2.5

422.4

bobbinThermal radiation shield

Magnet cryostat

Large End Flange

396.0

372.4

24

Agreed change with KEK:-The LH2 feed pipe to be extended by 10mm

0.4mm

Large End Flange locally thinned down to 2.5mm 39.0

Absorber stays at coil centre

Negligible stick out

Details of the local thinning of the large flange end plate at the LH2 pipe area

Arrangement for the local hatch of the Large Flange end plate

Justification for the local thinning on the large end plate – by FEA

Applied pressure:- 1 bar

Local peak stress:- 90.5 MPa

Max. bending stress:- 62 MPa

Pro-rata to the design pressure of 1.5 bar (Table 1.8 of tech,spec), the max. bending stress = 93 MPa.

Allowable bending stress for Al T6061 at room temp = 1.5 x 78 = 117 MPa.

Stress in the thinned down area does not seem to be affected – mainly because of the reinforcement effect from the rest of the plate which is 12.5mm thick.

This area has a thickness of only 2.5mm

End load effect (from Safety window) is accounted for and is applied onto this area

The issue has been addressed by the Technical Board who has accepted the technical proposal for the change.

Issues of interests

Points worth highlighting here:-

Cryocooler:-

Power supply - we opted for 280 / 420VAC; 3 phase at 50 Hz.

Beam height

Now fixed at +1544mm from mounting platform. AFC support to be made with a tolerance of +0,-30mm. This allows the module to be shimmed at site.

HTS Leads

SS shunts are incorporated. Each is 225mm long and has an area of between 38.2mm2 and 59.6mm2. We still need to establish how long will it take for the power supply to react in the case of a lead quench

Coil Cooling

Indirect cooling is now incorporated. SS banding wire on the outside any space outside the coil is filled up with epoxy to ensure good thermal contact between coil and bobbin – a requirement for the passive

Progress on PRR

1 Current lead thermal analysisThe current design uses a lead with a high RRR (around 50). The use of copper with a lower RRR of 10 or less is safer and will prevent thermal runaway. Tesla will re-model the lead with a lower RRR material

Completed

2 Thermal modelThe coil has been modelled as an isotropic block of copper. Tesla will re-model the copper block assuming different and more realistic conductivities in the three directions (note that this data is already in the quench modelling)

Tesla modelled with the thermal boundary conditions as noted above – the maximum temperature of the coil is 4.56 which leaves only 0.25K margin.Issues:Need to ensure that there is good thermal contact between the coil and the bobbin/former, this ensuring reliable quenchback. If MICE power all the coils individually then the requirement for active quench protection is removed. Thermal contact can be ensured by overwinding/increased tension to 170 MPa and filling the outside volume with epoxy, as well as using banding wire. Tesla has agreed.This will be confirmed once the re-run of the thermal model takes place

2 Thermal modelThe coil has been modelled as an isotropic block of copper. Tesla will re-model the copper block assuming different and more realistic conductivities in the three directions (note that this data is already in the quench modelling)

Tesla modelled with the thermal boundary conditions as noted above – the maximum temperature of the coil is 4.56 which leaves only 0.25K margin.Issues:Need to ensure that there is good thermal contact between the coil and the bobbin/former, this ensuring reliable quenchback. If MICE power all the coils individually then the requirement for active quench protection is removed. Thermal contact can be ensured by overwinding/increased tension to 170 MPa and filling the outside volume with epoxy, as well as using banding wire. Tesla has agreed.This will be confirmed once the re-run of the thermal model takes place

3 Thermal modelThe contact resistance on the cryocooler first stage looks optimistic. How is the load applied and what load can be applied ? - Tesla to confirm that the values used are realistic including the contact area.

Reply from Tesla: “ .... We have a customer with over 200 turrets in the field using this method, therefore we do not believe it will be an issue” This item was closed but will be revisited in view of the issue raised due to the extended length of the bobbin

4 ConductorTesla to demonstrate satisfactory splice technique.

Tesla has proposed superconductor splice overlap of around 350 mm. This would have been done be in April but the superconductor delivery was late. This is not a hold point for the PRR, but we will monitor its progress.

5 ConfigurationTesla to evaluate the direct and indirect cooling option and propose the preferred solution. Note that the MICE team will allow an increase in the coil inner radius to reduce the stresses. This could be increased to 268mm. MICE will provide a simple sketch showing the relevant dimensions.

Revised dimensions have been agreed. This item is closed.

6 ConfigurationThe aim will be to reach a decision on the bobbin dimensions within two weeks from the meeting (20th November).

Bobbin dimensions agreed.Bobbin forging has been ordered since. This item is closed

7 Mechanical Issues on Indirect Cooled Bobbin DesignLoads to be consideredWinding loadCool-down static loadsMagnetic loadCool down transientQuenchTransportSelf weightPre-load on suspension strapsTesla will estimate the level of these loads and apply to a set of scenarios including normal operation, quench, cool-down and transport.

This was discussed as part of action #2. Tesla will be reviewing the winding tension as part of the investigation into improving the thermal contact. The cool down transient load needs to be estimated and is still outstanding. This item remains open.

8 Quench protectionTesla will consider the issues of redundancy in the active quench protection system

Active quench back design was proposed and a price tag of well over £100K was submitted by Tesla. As a result of discussion on #2 and #7, it is now agreed that Tesla will adapt the quench back design. Tesla will model the former assuming there is sufficient contact between coil and bobbin, We have not heard from Tesla opposing the use of Quench back design.A formal clarification is needed to close this item.

9 Worst Case One of the cases considered in the thermal model gave a force of 90t. How was this arrived at and what were the MICE conditions ?

Item resolved and is now Closed

10 Vent lineThe configuration of the vent line was discussed at the meeting. Issues raised were the size of the line and a possible heat load at a critical area.

The layout has changed and this has been incorporated in MN’s thermal model. There are no problems with the new design.This item is closed

11 Critical Items ListThe beam height will be checked, confirmed and documented by RAL

RAL replied and this item is now closed

12 Critical Items ListThe meeting highlighted the importance of the tolerances on the vessel flanges that connect to neighbouring modules and the magnet alignment. Tesla to confirm the adequacy of the approach.

This was done and a few items were spotted, e.g. the clocking of the flange bolt holes.All the critical items have now been looked at. The remaining issue is the boundary space envelop which resulted in a commercial variance raised – to extend KEK’s LH2 feed pipes and the local machining of the large end plate to give back KEK its 47.5 mm space.

13 CryocoolerFor indirect cooling there are issues associated with the size and configuration of the condensing lines and the sensitivity to impurities at the bottom of the cryostat. Tesla to consider these issues in the design.

As a result, a sump has been added and an expansion tank included on the top.

14 HTS LeadsTesla will confirm that there is flexibility in the installation to accommodate thermal contractions

Tesla confirmed that a shunt has been incorporated. Shunt is 225mm long and has an area of between 38.2mm2 and 59.6mm2. In the case of a lead quench, it is important to know how long will it take for the power supply to react.Tesla to confirm.15 HTS Leads

Tesla will confirm that there is adequate thermal clamping in the region of the G10 block near to the coil

Issue resolved and is now closed.

16 HTS Leads and CryocoolerTesla will check orientation and position of the HTS leads (and the magnetic shielding thickness) and the cryocooler motor with respect to the magnetic field.

Action completed

17 Radiation shieldAt the moment 6063 is being used - it has been suggested that a better grade may be 1100 - Tesla to consider its use

TBD at the right time

18 Support strapsTesla to confirm the actual UTS values achieved with the S-glass straps

Action completed

19 Support for current leadsThe weight of the current leads needs supporting to avoid damage to the feedthroughs. RAL will advise on the routing and where to place supports

Still open, awaiting reply from RAL.

20 Instrumentation and servicesTesla will provide an inventory of the pipes, services and instrumentation to the AFC module for external routing.

MC (RAL) to advise.

21 Hydrogen systemTesla will move interconnects higher up into the turret

In new design may be moved even further up where there is more room– This is now done.

22 Hydrogen systemRAL will advise on the heat exchanger required on the cryocooler first stage

Pipework pre-assembled on to copper bobbin – approximately 2.5m incorporated. Condensing line enters condensing pot through main condensing line.Action complete

23 Hydrogen systemTesla will confirm that the two vacuum systems are able to withstand atmospheric/vacuum combinations

Action completed

24 Hydrogen systemThe instrumentation wires on the hydrogen system are routed through a vacuum port. Tesla to check that the pumping is not compromised by this.

Inventory from KEK was passed onto Tesla. Action completed.

25 Fault casesFault cases need consideration e.g. over-current, wrong polarity both in the AFC and external components.

MICE to provide feedback. TB to coordinate

26 Mechanical Some of the weld qualifications need adding (this does depend on final mechanical solution)

On Tesla QIPP plans, and has been address through there.Item closed

27 Hydrogen systemCheck if a dummy outer (safety) window flange is available to check fit. Also, MICE to provide a go-nogo gauge for the warm bore.

No dummy is available but OU will provide a go-nogo gauge (wooden).

28 DisassemblyTesla to check that critical items can be removed and replaced in case of failure. Items could be HTS leads, feedthroughs, cryocoolers, etc…

Item closed

The schedule

Money issues

Contract variance:-

Two contract variance were raised by Tesla so far;

On the Bobbin design and indirect cooling etc.

This has resulted in a cost variance of £16K and a schedule delay of 2 months.

This has been resolved and MICE has accepted the request.

On the space envelope

Tesla has submitted a cost variance in the region of £11K and a schedule delay of a further 2 months. It is not clear what the £11K include. Clarification is being sought.

Approval is needed from the MICE PM board to accept the variance request.