berkley talk

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MICE Magnetic forces and quench effects in the
absorber cryostat
James Rochford
MICE UK Meeting RAL March 2004
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Talk objective

• Summarise magnetic analysis work undertaken
• Quantify Magnetic forces on Absorber module
• Containment of normal operational forces
• Imbalance in normal forces following a quench
• Effects of a quench in the focus coils
• Forces in absorber windows
• Power dissipation in hydrogen

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Forces in normal operation

• Forces in normal operation
• 3d finite element model of all coils
• Magnetic forces between powered coils
• For Flip mode 240MeV/c,b43cm
• For Non Flip mode 200MeV/c,b7cm
• Imbalance in normal forces following a quench
• Quenches in surrounding modules
• Give rise to different force configurations

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Forces in normal operation
Force restraint Between cryostats
Coupling coil 13T
Detector cryostat 72T
For Flip mode 240MeV/c,b43cm
Suspension (transferring nett internal force)
261 T
310 T
Internal force restraint
Nett 49T
(Forces shown for outer most pair of flip coils)
LH
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Forces in normal operation
Force restraint Between cryostats
Coupling coil module 1.2 T
Detector cryostat 75 T
For Non Flip mode 200MeV/c,b7cm
Suspension (transferring nett internal force)
146T
99T
Internal force restraint
Nett 47 T
(Forces shown for outer most pair of flip coils)
LH
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Forces in normal operation

• Normal operation - summary
• Internal forces 250-300Tonnes
• All contained within the magnet former
• Any nett force transferred to warm cryostat
• Hydrogen system independent sees no force
• Inter cryostat forces 50-100 Tonnes
• Transferred between cryostats
• No nett force over complete channel

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Module Quench - force imbalance
1417
64
131
2653
334
3099
131
1417
64
334
3099
392
392
2609
2609
2653
91
91
Inter cryostat force
Quench in all focusing pairs
Changes in forces
For Flip mode 240MeV/c,b43cm (all forces in KN)
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Magnet Quench - force imbalance
Quench in coupling pair
Inter cryostat force
Changes in forces
76
76
302
30
For Flip mode 240MeV/c,b43cm (all forces in KN)
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Magnet Quench - force imbalance
Loss of detector coils
Inter cryostat force
Changes in forces
For Flip mode 240MeV/c,b43cm (all forces in KN)
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Magnet Quench - force imbalance

• Quench imbalance summary
• During a loss of a complete module
• Experience big change in forces
• Change of direction
• Magnitudes comparable to normal operation
• Result
• Imbalance forces do not need any special
  considerations and are readily contained in
  normal design

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Focus coil quench internal effects

• Quench in the absorber cryostat
• Dissipates stored energy into cryostat
• Energy dissipated in now normal coils
• Heats coils
• Ultimately taken out in Helium system
• Field coupled to local conducting structures
• eddy currents generated
• Gives rise to forces
• Of concern thin windows
• Power dissipation in hydrogen system
• Is this a problem

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Focus coil quench internal effects

• Quench modelling
• Modelled current rundown during a quench
• dI/dt
• Separate 2d and 3d finite element models
• Eddy currents
• Forces on thin windows
• Power dissipated in the hydrogen
• Here will concentrate on the 2d results

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Focus coil quench internal effects
S.steel
128 A/mm2
Al6061
Al6061
Teff 1mm
2d Quench model
Teff 0.2mm
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Focus coil quench internal effects
Current rundown assumed during a quench
Generated for single focus coil 51H with no
protection resistance
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Focus coil quench internal effects
Eddy current distribution in absorber windows in
flip mode
Eddy current distribution in holders and windows
2s into a quench whilst operating in
240MeV/C,Beta43cm mode
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Focus coil quench internal effects
30J dissipated in the Hydrogen Not a problem
Power dissipated in the inner vessel windows
during a quench in 240MeV/C,Beta43cmm mode
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Focus coil quench internal effects
15KJ dissipated in the Hydrogen For hydrogen
18k S.heat 8305 J/kgK Its effect is to raise the
temperature of the liquid from 18K to 19.8k
Power dissipated in the inner vessel bodies
during a quench in 240MeV/C,Beta43cmm mode
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Focus coil quench internal effects
Atmospheric pressure 1x105Nm2 Force on window
8KN
Force on the inner vessel windows during a quench
in 240MeV/C,Beta43cm mode
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Focus coil quench internal effects
Using expression
We can estimate the peak stress in the window
Note the yield strength for AL6061 is 267MPa in
tension and 238MPa in shear
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Focus coil quench internal effects
Absorber vessel moved by 5mm axially
Model changed to look at the effect of
offsetting the absorber axially
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Focus coil quench internal effects
Force on the Absorber vessel body during a quench
in 240MeV/C,Beta43cm mode with the vessels
offset axially by 5mm
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Focus coil quench internal effects
Eddy current distribution in windows for
Solenoid mode
Eddy current distribution in holders and windows
2s into a quench whilst operating in solenoid
mode 200MeV/C,Beta7cm
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Focus coil quench internal effects
90J dissipated in the Hydrogen Not a problem
Power dissipated in the inner vessel windows
during a quench for solenoid mode
-200MeV/C,Beta7cm
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Focus coil quench internal effects
36KJ dissipated in the Hydrogen For hydrogen
18k S.heat 8305 J/kgK Its effect is to raise the
temperature of the liquid from 18K to
22.3k Vapour pressure 1.6bar
Power dissipated in the inner vessel bodies
during a quench for solenoid mode
-200MeV/C,Beta7cm
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Focus coil quench internal effects
36KJ dissipated in the Hydrogen pretty
pessimistic 2d model is a solid block in reality
this structure has large non conducting volumes
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Focus coil quench internal effects
Atmospheric pressure 1x105Nm2 Force on window
8KN
Force on the inner vessel windows during a quench
for solenoid mode -200MeV/C,Beta7cm
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Focus coil quench internal effects

• Focus coil quench summary
• Forces during a quench
• Looked at worst possible cases
• Small, 100sN - much less than normal vacuum
  force
• Eddy current distribution concentrated in outer
  window
• Peak stress here of order 22MPa much less than
  yield stress 250MPa
• Power dissipation
• Worst solenoid mode 200MeV/c dissipate 36kJ
• Enough to raise the vapour pressure to 1.6bar
• This easily contained in hydrogen system

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END