Magnetic shielding for MICE

James Rochford Yury Ivanvushenkov MICE “video" conference meeting January 28 2004

Introduction • To comply with health and safety requirements MICE needs magnetic shielding.

• Early Finite Element Models models have shown that a simple open ended box structure can achieve this for 240MeV/c,b=43cm flip mode.

• Basic geometry used in models – 2 sides and a top – All made from 20mm thick iron plate • Now have a baseline detector shield to be incorporated in all the models

This study addresses • Consequence of removing top of shield – It is desirable to see if it is possible to remove the top of the shield leaving two free standing walls.

• Modifications needed to shield solenoid mode – Simple geometry looked at thus far cannot shield for high field case of solenoid mode 200MeV/c,b=7cm nonflip mode

Critical areas • ISIS control room wall • MICE control room wall • ISIS injector wall – Because of its increased distance the field here is lower than on the control room wall.

Is shield top required ?

• Flip model-240MeV/C, beta43cm

Is shield top required ?

• Flip model-240MeV/C, beta43cm

Is shield top required ? • Non flip model-200MeV/C, beta7cm

Is shield top required ?

• Non flip model-200MeV/C, beta7cm

Is shield top required ?

• Not for flip model-240MeV/C, beta = 43cm • But it is still needed for 200MeV/C, beta = 7cm non flip model • • Unless we modify shield

Modifications required for solenoid mode • Potential solutions to shielding solenoid mode – Use a thicker shield – Use multiple shields

Modifications to shield for solenoid mode • Increasing thickness to 40mm

Modifications to shield for solenoid mode • Increasing thickness to 60mm

Modifications to shield for solenoid mode • Results of increasing shield thickness of a

single shield

Shield thickness (mm) 20 Peak field on wall (gauss) 13.8

40 60 7.3

5.4

• 60mm is almost acceptable

Modifications to shield for solenoid mode • Using multiple shields – With layered shields get a multiplicative effect – Provided we get the correct spacing between the layers. – A gap of 10’s of mm will not be effective on these scales. - We need 100’s of mm gap – This is a problem we have limited space inside the radiation shielding -Fortunately there is a practical solution

Modifications to shield for solenoid mode • Using multiple shields – The concrete shielding blocks are ~600mm wide . – If we place 20mm thick plates on both surfaces we have a natural 600mm gap, with the blocks providing a support structure for fixing the plates.

- Is this gap enough to provide effective shielding ?

600mm gap 20mm thick iron plates

Modifications to shield for solenoid mode • Using a multiple shields over the full +\-8.5 meters

Modifications to shield for solenoid mode • Using multiple shields over central high field section +\- 5.5meters

Modifications to shield for solenoid mode • Results of using multiple shields Number of shields Shield thickness (mm) Outer shield length Separation (mm) Peak field on wall 1 2 20 20 +/-(mm) 8500 8500 600 (gauss) 13.8

6.7

2 20 6500 600 • A 600mm separation is close is almost acceptable 8.1

Modifications required for solenoid mode

Both potential solutions are promising for shielding solenoid mode Thicker shield

• Single 60mm thick shield gets to 5.4 gauss

Multiple shields

• A double shield with 20mm thick plates separated by 600mm over concrete blocks gets to 8.1 gauss

Modifications required for solenoid mode

Guess at what a practical working shield May look like

• 30mm thick inner shield • With a double outer 20mm thick plate placed on the outer surface of the radiation shielding blocks

This work points the way to the solution

But we still need to begin to incorporate a more realistic geometry compatible

End of main shielding talk

Appendices: New detector shield • All models shown have included new detector shield • The geometry for new baseline detector shield proposed by Gishlain has been used in all the models. – However the BH curve used is iron.

All models have included new detector shield • Field in the detector region for high field Flip case 240mev/c,beta=43cm

All models have included new detector shield • Field at the detector positions for high field Flip case 240mev/c,beta=43cm

All models have included new detector shield • Field in the detector region for high field Non flip case 200mev/c,beta=7cm

All models have included new detector shield • Field at the detector positions for high field Non flip case 200mev/c,beta=7cm