Talk outline 1 st talk: –Magnetic forces –Quench in the absorber cryostat 2 nd talk: –Shielding of magnetic fringe fields

MICE Magnetic forces and quench issues Elwyn Baynham James Rochford MICE Meeting Berkley December 2003

Magnet and quench issues Look at two topics –Magnetic forces Containment of normal operational forces Imbalance in normal forces following a quench –Quench in the absorber cryostat Forces in absorber windows Power dissipation in hydrogen

261 T310 T Internal force restraint Suspension (transferring nett internal force) Force restraint Between cryostats Nett 49T Detector cryostat Coupling coil LH Containment of forces in normal Operation For Flip mode 240MeV/c,b=43cm (Forces shown for outer most pair of flip coils)

208 T157 T Internal force restraint Suspension (transferring nett internal force) Force restraint Between cryostats Nett 51 T Coupling coil module LH Detector cryostat Containment of forces in normal Operation For Non Flip mode 240MeV/c,b=7cm (Forces shown for outer most pair of flip coils)

Normal operation - summary –Internal forces Tonnes Contained within the magnet former Any nett force transferred to warm cryostat Hydrogen system independent sees no force –Inter cryostat forces Tonnes Transferred between cryostats No nett force over complete channel Containment of forces in normal Operation

Changes in forces Quench in all focusing pairs Magnet Quench - force imbalance For Flip mode 240MeV/c,b=43c m (all forces in KN) Inter cryostat force

Magnet Quench - force imbalance Quench in coupling pair Changes in forces Inter cryostat force For Flip mode 240MeV/c,b=43c m (all forces in KN)

Magnet Quench - force imbalance Loss of detector coils Changes in forces Inter cryostat force For Flip mode 240MeV/c,b=43c m (all forces in KN)

Quench imbalance summary –During a quench imbalanced forces Experience big change in forces Change of direction Magnitudes comparable to normal operation –Conclusion Imbalance forces do not need any special considerations and are readily contained in normal design Magnet Quench - force imbalance QuenchMax inter cryostat force Focus coil modules13 tonnes Coupling coil79 tonnes Detector coil module31 tonnes

–Effects of a Quench in the focus coil module 2d and 3d finite element models –Eddy currents –Forces on thin windows –Power dissipated in the hydrogen Focus coil quench internal effects

2d Quench model T eff 1mm T eff 0.2mm 128 A/mm 2 S.steel Al6061 Effective window thickness

Focus coil quench internal effects Current rundown during a quench for 51H with no protection resistance

Focus coil quench internal effects Eddy current distribution in holders and windows 2s into a quench whilst operating in 240MeV/C,Beta=43cm mode Eddy current distribution in absorber windows in flip mode Peak currents

Focus coil quench internal effects Power dissipated in the inner vessel windows during a quench in 240MeV/C,Beta=43cmm mode ~10J dissipated in the Hydrogen Not a problem

Focus coil quench internal effects Power dissipated in the inner vessel bodies during a quench in 240MeV/C,Beta=43cmm mode ~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

Focus coil quench internal effects Force on the inner vessel windows during a quench in 240MeV/C,Beta=43cm mode Atmospheric pressure 1x10 5 Nm 2 Force on window ~8KN

Focus coil quench internal effects Using expression We can estimate the peak stress in the window Note the max yield strength for AL6061 is 273MPa. This is 10 times less than the peak stress seen in the windows

Focus coil quench internal effects Model changed to look at the effect of offsetting the absorber axially Absorber vessel moved by 5mm axially What is the effect of an offset absorber ?

Focus coil quench internal effects Force on the Absorber vessel body during a quench in 240MeV/C,Beta=43cm mode with the vessels offset axially by 5mm

Focus coil quench internal effects Eddy current distribution in holders and windows 2s into a quench whilst operating in solenoid mode -240MeV/C,Beta=7cm Eddy current distribution in windows for Solenoid mode

Focus coil quench internal effects Power dissipated in the inner vessel windows during a quench for solenoid mode -240MeV/C,Beta=7cm ~40J dissipated in the Hydrogen Not a problem

Focus coil quench internal effects Power dissipated in the inner vessel bodies during a quench for solenoid mode -240MeV/C,Beta=7cm ~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 Pessimistic Solid absorber body Heat capacity for 18k 240MeV/c Still just acceptable

Focus coil quench internal effects Force on the inner vessel windows during a quench for solenoid mode -240MeV/C,Beta=7cm Atmospheric pressure 1x10 5 Nm 2 Force on window ~8KN

Focus coil quench summary –Forces during a quench Looked at worst possible cases Small, 100’sN - 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 240MeV/c-36kJ Enough to raise the vapour pressure to 1.6Bar This easily contained in hydrogen system Focus coil quench internal effects

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MICE Coils magnetic shielding James Rochford Iouri Ivaniouchenkov MICE Meeting Berkley December 2003

Shielding Requirements Areas with public access The stray field must be below 5 gauss in these regions Areas occupied by detectors The stray field at the ends of the magnetic channel must be low enough for the TOF Cerenkov and calorimetric detectors to operate.

Areas with public access Shielding Requirements

Main shield Open ended rectangular box model 20mm thick iron plate length +/-8.5m Coils offset Detector shield 50mm thick iron plate ID 40mm OD 1.8m 2m 3.8m 6.5m 17m 6m 3d models

Fringe field on outer walls 5gauss contour Model results For flip mode 200Mev/c, beta 43cm

for Solenoid mode 200MeV/c, beta=7cm The proposed simple 20mm box shield is inadequate to shield the ISIS\MICE control rooms Field on wall surface peaks at 72 gauss Field on wall surface peaks at 32 gauss Model results

Shielding summary Have shown the simple box shield is adequate for normal operation at 200mev/c. This will also be ok for the 240Mev/c case. The simple shield is not sufficient to shield solenoid mode. As it stands the proposed shield will need some modifications to accommodate solenoid mode –Increase thickness –Multiple layers –Close ends

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Changes in forces Quench in all focusing pairs Magnet Quench - force imbalance For Flip mode 240MeV/c,b=43c m (all forces in KN) Inter cryostat force

Magnet Quench - force imbalance Quench in coupling pair Changes in forces Inter cryostat force For Flip mode 240MeV/c,b=43c m (all forces in KN)

Magnet Quench - force imbalance Loss of detector coils Changes in forces Inter cryostat force For Flip mode 240MeV/c,b=43c m (all forces in KN)