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Spectrometer SolenoidDesign and Cost Update

Michael A. Green

Lawrence Berkeley Laboratory

10 February 2005

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Spectrometer Solenoid Options

• INFN solenoid as per the baseline document

• General Electric 3 T large bore MRI magnet with the appropriate matching coils

• A MICE detector solenoid built by LBNL as proposed in the MRI proposal to NSF

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INFN Detector Solenoid

Iron Shield

End Coil 2

End Coil 1

Center Coil

Match Coil 1

4.2 K Cooler

Cold Mass Support

Match Coil 2

He Cooling Pipe

Radiation Shield

Al Coil Spacer

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Using the General Electric 3 T MRI Solenoid as a Detector Magnet

• It has been proposed that the spectrometer magnet could be a 3 T MRI magnet. This magnet produces only 3 T, but it may be attractive if the price is right.

• U. Bravar has shown that one can match into the GE magnet using a set of match coils or a large coupling coil. The cost of the match coils is not much different from the cost of the Lab G solenoid. If the GE solenoid is free, then this option may make economic sense.

• The GE solenoid is actively shielded, so its field does not reach like most magnets this size (Coil D = 1.05 m, and Coil L = 1.5 to 2.0 m depending on the magnet).

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GE 3-T MRI Solenoid continued

• The coupling coil or match coils will overwhelm the MRI magnet shim coils, but this may not be an issue.

• The forces on the GE coils may be an issue. The GE magnet can only take a few tons of force in the longitudinal direction. The new magnets are better than the old magnets in this regard.

• Because the GE magnet is large (even though it is actively shielded) a quench in an adjacent magnet could trigger a quench in the GE solenoid

• The GE magnet field could have a negative impact on the PMTs needed for the detectors. It depends on where the PMTs are located.

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The LBNL Solenoid for the MRI Proposal

• The NSF proposal call for LBNL to build a single detector solenoid with match coils. This magnet must be compatible with the INFN detector magnet.

• The LBNL solenoid is less expensive to build because there is less superconductor in the coil. The margin is nearly the same as the INFN magnet even though the conductor current density is much higher. This is allowed because there is an 1100 aluminum bore tube to cause quench back in the magnet coils.

• The currents and current centers in the LBNL coils are nearly the same as the INFN coils. As a result, magnetically the magnets are nearly identical.

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The LBNL Solenoid will look more like this, except the coils will be thinner.

250 mm230 mm

~2550 mm

End Coil #1, L = 120 mm t = 116 mm

~300 mm Φ

Lead and Cryogen Neck

#2, = 149 , = 64.8 End Coil L mm t mm

#1, = 202 , = 50 Matching Coil L mm t mm

#2, = 202 = 73 Matching Coil L mm t mm

40 K Shield

4 T Good Field Region

0.3 m Φ , 1.0 m L

, = 1260 , = 50 Center Coil L mm t mm

2 00 mm

~460 mm 255 mm

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LBNL Solenoid Possible Parameters

Parameter Match 1 Match 2 End 1 Center End 2

Z distance from MICE Center* (mm) 3512 3958 4393 4552 5890Coil Length (mm) 198 188.1 120.5 1298.5 120.5Coil Inner Radius (mm) 281.8 273.6 293.2 269 295Coil Thickness (mm) 46.2 19.8 61.6 22.0 68.2Number of Layers 42 18 58 20 60Number of Turns per Layer 120 114 71 787 75Coil Overall Current Density (A mm-2) 147.8 161.8 136.4 141.8 146.0Coil Current (A) 267.8 293.8 248.8 257.8 266.7Coil Self Inductance (H) 15.9 5.0 12.6 47.0 15.1Peak Induction in the Coil (T) 4.8 3.8 4.9 4.0 5.2Coil Stored Energy at Current above (MJ) 0.57 0.22 0.39 1.56 0.54

The number of turns in the 2nd match coil is off by -0.196 percent.The number of turns in the 1st end coil is off by +0.297 percent.The number of turns in the center coil is off by -0.065 percent.The other coils have exactly the correct number of turns.All of the errors are within an acceptable range according to U. Bravar.

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LBNL Solenoid continued

• The potential for cost reduction is based on not only the superconductor mass, but it is also based on the vendor LBNL will use as well as the low cost of the US dollar.

• The LBNL design is based on using the conductor at high current densities. The quench protection system depends on quench back from the mandrel to the coils. This is key e for safe quenching of the long center solenoid. The detector magnet mandrel can be made from 1100 aluminum because the longitudinal stresses in the magnet are compressive.

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Powering the LBNL Detector magnet and Magnet Quench Protection

PSPower Supply10 V, 300 A

PSPSPSPSPower Supply10 V, 50 A

Shorted Secondary circuits

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LBNL Solenoid continued

• The LBNL coils can be put in series with like coils in the INFN magnet in the event the detector magnets are built by both laboratories.

• The LBNL design allows for a liquid helium to be on the outside of the coils. The T from the coil hot spot to the cooler cold head can be minimized.

• Further optimization may allow the number of 4.2 K coolers to be reduced from three to two, which results in a further reduction of the magnet cost.

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Concluding Comments

• The GE 3-T MRI magnet is attractive only if the capital cost for the magnet is low. Matching coils are required to match the GE magnets to the rest of MICE. There are a number of other technical issues associated with using the GE magnets.

• The LBNL detector magnet will behave the same way the INFN detector magnet behaves. The two magnets are nearly identical in their performance, except during a magnet quench. The LBNL solenoid is attractive in cost, but it is not clear that two can be built in the US.

• A change in the scope of work may be needed for a number of the partners in MICE, because of a lack of money. Creativity is key to getting MICE built.