1. 10 October 2006 MICE CM-16 at RAL 1 Distributed versus Lumped Coupling Magnets Michael A. Green and Soren Prestemon Lawrence Berkeley Laboratory, Berkeley CA 94720, USA Marco Apollonio and Holger Witte Oxford University Physics, Oxford OX1-3RH, UK

2. 10 October 2006 MICE CM-16 at RAL 2 Why would on want to change the design of the RFCC magnet? One would like to reduce the magnetic field at the coil so that the coupling magnet temperature margin is increased. One would like to reduce the stored energy of the magnet, in order to improve quench protection. One would like to reduce the field at the HTS leads and at the cooler. The high temperature end of the HTS lead is most affected by field. This affects the position of the cooler and leads.

3. 10 October 2006 MICE CM-16 at RAL 3 Lumped Coupling Magnet (the baseline design with new tracker) Lumped Coupling Magnet

4. 10 October 2006 MICE CM-16 at RAL 4 Field on Axis of MICE from Lumped Coupling Magnet in the Flip Mode Muon average momentum = 240 MeV/c

5. 10 October 2006 MICE CM-16 at RAL 5 Magnetic Field from MICE with a Lumped Coupling Magnet in the Flip Mode p = 240 MeV/c

6. 10 October 2006 MICE CM-16 at RAL 6 Distributed Coupling Magnet

7. 10 October 2006 MICE CM-16 at RAL 7 Field on the Axis of MICE from Distributed Coupling Magnet in the Flip Mode Muon average momentum = 240 MeV/c

8. 10 October 2006 MICE CM-16 at RAL 8 Magnetic Field from MICE with a Distributed Coupling Magnet in the Flip Mode p = 240 MeV/c

9. 10 October 2006 MICE CM-16 at RAL 9 The green is the field for the lumped case. The red is the first optimized extended case. The blue below is the on axis field change from the lumped case. On Axis Magnetic Field for MICE with the Lumped and Optimized Extended Coupling Magnet

10. 10 October 2006 MICE CM-16 at RAL 10 The black is the TRD case beta. The green is the beta for the lumped case. The red is the beta for the optimized extended coupling coil case. MICE Channel Beta Function with Lumped and Optimized Extended Coupling Magnet

11. 10 October 2006 MICE CM-16 at RAL 11 p = 240 MeV/c RF Iris Lumped and Extended Coil Fields

12. 10 October 2006 MICE CM-16 at RAL 12 Magnet Parameters for both types of Coupling Magnets Muon average momentum = 240 MeV/c  = 420 mm  = 320 mm

13. 10 October 2006 MICE CM-16 at RAL 13 Magnet Module Forces both Types of Coupling Magnets Muon average momentum = 240 MeV/c  = 420 mm  = 320 mm

14. 10 October 2006 MICE CM-16 at RAL 14 Lumped and Extended Coupling Magnet Load Lines and Temperature Margin Lumped Temperature Margin = 0.6 K @ 240 MeV/c Extended Temperature Margin = 2.4 K @ 240 MeV/c Both cases are in the flip mode.

15. 10 October 2006 MICE CM-16 at RAL 15 Magnetic Field at z = 1.375 m versus Radius Muon average momentum = 240 MeV/c Lumped coil outer R = 841 mm Distributed coil outer R = 762 mm

16. 10 October 2006 MICE CM-16 at RAL 16 The current in the coupling coil must increase about 15 percent to about 242 A. The magnet temperature margin is about 2 K at 240 MeV/c. The current in the focusing magnet will decrease about 21 percent to 199 A. The temperature margin for the magnet is 1.6 K at 240 MeV/c. The forces on the magnet cold mass will change and become closer to the nominal case with the lumped coupling magnet. The force changes are dictated by the tracker tuning coils. The peak  in the cavities and tracker will go down to the value for the TRD case. What happens when the beam  in the AFC is increased to the nominal 420 mm?

17. 10 October 2006 MICE CM-16 at RAL 17 Benefits from a Change of the Design of the RFCC magnet The peak magnetic field at the coil is reduced by a factor of two. The magnet temperature margin is increased by nearly 1.4 K. The magnet stored energy is reduced by 45 percent. The field on the outside of the coils is reduced. This is important for coolers, leads and vacuum pumps. The cryostat outside diameter is reduced. Less current is needed for the AFC coils, thus their temperature margin is increased about 1 K.

18. 10 October 2006 MICE CM-16 at RAL 18 Problems caused by a change the design of the RFCC magnet Two of the RF couplers, two cavity tuners (8 to 12) 25 to 50 mm  ports) must pass through the magnet, which complicates the cryostat design. The RFCC vacuum pumping ports may be a little too long, which will reduce the conductance. The magnet and the RF vacuum vessel will have to be fabricated as a single unit. The cost of fabricating the magnet and its cryostat is increased, but the cost of the RF cavity vacuum vessel is eliminated. We must get vendor budgetary quotes to see how much the cost is increased.

19. 10 October 2006 MICE CM-16 at RAL 19 Potential Issues brought on by a change the design of the RFCC magnet The magnetic field within the the cavities is more uniform than in the lumped coil case. The field on the outside of the center cavities is lower. The field on the outside of the end cavities may be higher. The effect of the distribution is unknown. In all cavities the field is more parallel to the cavity axis. The magnetic field in the RF couplers is different in both magnitude and direction than in the lumped case. For the two center cavities the field is lower and perpendicular to the coupler axis. For the two end cavities the field is parallel to the coupler axis.

20. 10 October 2006 MICE CM-16 at RAL 20 A Cross-section through RF coupler Port of a Distributed Coupling Magnet that can be Built

21. 10 October 2006 MICE CM-16 at RAL 21 Where do we go from here? It is clear that lengthening the coupling coil has benefits, but there are also problems caused by the extended coupling coil presented here. We should stay with the baseline magnet design which uses a single coupling coil. It is worth the extra effort to lengthen this coil to increase the temperature margins for both the coupling and AFC magnets. Lengthening the coil will reduce the field on the outside of the magnet. The magnet must fit through the MICE hall door.