Internal sc Coils for Dilution Refrigerators

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Damon Mitchell
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1 Internal sc Coils for Dilution Refrigerators Hartmut Dutz, Stefan Goertz, Ralf Heinz, Thomas Ludwig -1-

2 Frozen-Spin-Target (Saclay/Bonn-type) P y P y P Z -2- limited angular acceptance ( low energy scattering experiments)

3 Replace external holding magnet Small internal sc coil Follow the refrigerator symmetry P y P y -3- increased angular acceptance complex handling (moving) system

4 Internal sc holding-coil for a Frozen-Spin-Target field strength : ~ T as thin as possible (minimized absorption) low current reduced heat load mechanical feasibility simplest solution: solenoid geometry: mm, length: mm B = μ 0 N NC: ampere-turn : N*I ~ 50 ka superconducting wire necessary Solve Biot-Savart-law on the symmetry-axis I l -4-

5 Solve Biot-Savart-law on the symmetry-axis -5- β = α = b a 1 a a 2 1

6 Solve Biot-Savart-law off axis (elliptical integral method) K(k), E(k) Legendre elliptical integrals, with Numerically solved FELD.C-code: R. Gehring ( 93) -6-

7 Field distribution in the target volume First coil: R. Gehring (1993) length: 160 mm, 66 mm, thickness : 0.5 mm, Cu-carrier: 0.3 mm wire: 100 µm, J ~ 1550 A/mm² B max ~ A, L ~ H, T 2.2K -7-

8 Internal sc holding-coil for a Frozen-Spin-Target Splitted solenoid for target Asymmetry measurement Radiation shield first solenoid -8-

9 Longitudinal holding-coil for longitudinal Frozen-Spin-Target -9- large angular acceptance frozen-spin-taget (0.98*4π LS)

Longitudinal holding-coil for CB-Frozen-Spin-Target B H = 0.

10 Longitudinal holding-coil for CB-Frozen-Spin-Target B H = 33A holding coil : sc-solenoid Sc-wire: 210µm 45 mm, wall: 1.3 mm -10- Reliable technique for frozen-spin-targets

11 Longitudinal holding-coil for CB-Frozen-Spin-Target copper carrier superconducting coil heat exchanger tube -11- NbTi-wire : 100µm 44 mm, l = 120 mm, N = 4000 d = 0.7mm reliable operation at B h = A, T < 1.2 K

12 Longitudinal holding-coil for CB-Frozen-Spin-Target -12-

13 Longitudinal holding-coil for CB-Frozen-Spin-Target -13-

14 Transverse holding-coil for a horizontal dilution refrigerator P z P y -14-

15 Transverse holding-coil for a horizontal dilution refrigerator transverse holding coil: Saddle coil-type magnet: 7 layers, 30 A P y -15-

Transverse holding-coil for a horizontal dilution refrigerator B H = 0.52 T @ 30A sc.

16 Transverse holding-coil for a horizontal dilution refrigerator B H = A sc. race track coil 2 dipoles transverse field Wall: 2 mm -16- Design: PT-Bonn manufacturer (winding of the coil): ACCEL

17 Transverse holding-coil for a horizontal dilution refrigerator -17-

18 Transverse holding-coil for a horizontal dilution refrigerator -18- Expected delivery: end of 2008 test under real conditions: 2009/02 Th. Ludwig

19 Transverse holding-coil for a horizontal dilution refrigerator -19-

20 Transverse holding-coil for a horizontal dilution refrigerator -20-

21 Limitations of the frozen spin technique -21-

22 Toward an internal polarizing magnet Requirements: High field (~2.5 T) High homogeneity (ΔB/B ~10-4 ) in the target region Constraints on: Magnet thickness (particle absorption) Number of Bias Leads (heat load) Mechanical feasibility SC winding Target region -22- Well, that s challenging! A. Raccanelli, R. Mayer (FZ-Jülich), R. Krause (INS Bonn)

23 Toward an internal polarizing magnet Design of a 150 mm long solenoid Homogeneity contour lines for a 150 mm long solenoid (units of 10-4 ) Uncorrected solenoid -23- C. Rohlof, PhD thesis, Bonn 2003

24 Toward an internal polarizing magnet Design of a 150 mm long solenoid With 38 correction windings -24- C. Rohlof, PhD thesis, Bonn 2003

25 Toward an internal polarizing magnet Analytical and numerical shape optimization For a given homogeneity optimize current distribution (Habrecht-model [Habrecht/Krause/Zarife 08]) -25- F. Zarife, Dipl. thesis, Bonn 2008

26 Toward an internal polarizing magnet Analytical and numerical shape optimization Field homogeneity of the optimized coil Design parameters: length: 125 mm, 44.6 mm, Cu-carrier: 0.3 mm d max ~ 1.3 mm wire: 220 µm, 4 layers, N = 4000, B max ~ A, T 1.2K -26- F. Zarife, Dipl. thesis, Bonn 2008

27 Toward an internal polarizing magnet 4π horizontal dilution refrigerator Horizontal dilution refrigerator incl. internal polarizing magnet for CB opt. run as frozen spin target Tmin ~ 50 mk good angular acceptance (~ 4π) high luminosity L ~ /cm²s (N /s) high mean polarization target materials: alcohols, ammonia, LiH/D -27- design completed components under construction

28 Conclusion Internal sc Coils for Dilution Refrigerators Internal holding coil : Internal holding coil extend the use of frozen spin targets large acceptance frozen spin target Field strength no limit thickness/current/head load Field orientation depending on the symmetry no restriction Realiable operation (JLab, Mainz, Bonn, PSI) Internal polarizing magnet : Design studies completed homogeneity reachable Field strength up to 2.5 T thickness/current/head load Test coil under construction 4π continuous mode polarized target -28-

The Bonn Frozen Spin Target

The Bonn Frozen Spin Target Status and perspectives Hartmut Dutz, Stefan Goertz, Scott Reeve, Stefan Runkel, Thomas Voge (T. Ludwig, R. Heinz) -1- Status and perspectives -2- Polarization Double polarization experiments @ 2008 2011