24 June 2013 GSI, Darmstadt Helmholtz Institut Mainz Bertalan Feher, PANDA EMP First Measurements for a Superconducting Shield for the PANDA Polarized Target

Outline 1.Motivation, installation into PANDA 2.Measurements 3.Modeling a superconductor 4.Numerical simulation 5.Further Steps 2

3 Transverse Polarization of the Target We are interested in the reaction Form Factors in the time like region are complex The single spin polarization observable Allows the access to the relative phase with the scattering angle Θ Transverse target polarization as high as possible More nucleon-structure observables requiring transverse polarization

4 PANDA Solenoid Compensation Target

5 B PANDA Solenoid Compensation

6 Transverse Field B PANDA Solenoid Compensation

7 Advantage of a Superconducting Shield Meißner-Ochsenfeld effect Surface current Expellation of magnetic flux Type I superconductor

8 Advantage of a Superconducting Shield Compensation of the longitudinal flux Gauß (1 Tesla) Small material budget Passive shield No power supply:  No wire from power supply  No contact (no heat) Self adjusting (no torque) No "quench" Induction in an extern magnetic field High critical current throughout the whole material Type II superconductor

Test of Tube in 1 K Cryostat Operational temperature 1.4 K Wall thickness5 mm Length150 mm Radius25 mm Aspect ratio L/R6 Compensated flux Induced current YBCO-123 Radiation Length 1.9 cm YBCO-123 Critical Temperature 92 K Like PANDA solenoid Superconducting shield

Ramping Rate of the Extern Magnet Different ramping rates 0.4% residual flux II. I. III. + IV. VI.

Residual 40 Gauß y-intercept [Gauß] Slope Slope Measurement I. Applied Gauß

Residual 40 Gauß y-intercept [Gauß] Slope y-intercept [Gauß] Slope

Range [Gauß][0;20000][20000;30000][30000;40000] y-Achsenabschnitt [Gauß] -- Slope [Gauß/s]10±

Residual 80 Gauß Residual 40 Gauß Applied Gauß Range [Gauß][0;20000][20000;30000][30000;40000] y-Error [Gauß]±0.5 x-Error [Gauß]±90±950±200 y-Absolute Value [Gauß] -- Slope Residual 40 Gauß Residual 80 Gauß Residual 160 Gauß

Range [Gauß][0;40000] y-Error [Gauß]±9 x-Error [Gauß]±2500 y-Absolute Value [Gauß] Slope Current density Residual 160 Gauß

Relaxation of Induced Current I GaußII GaußIII GaußIV Gauß y-Error [Gauß]±0.5 x-Error [Gauß]±0.04 y-Absolute value (residual field) [Gauß] Slope [Gauß/s]

Measurement in Liquid Nitrogen Range [Gauß][0;40000] x-Error [Gauß]±0.5 y-Absolute Value [Gauß] 16 Slope 1056 Current density

18 Geometry Used for Simulation a) Cylinder without the holes in the wall b) Cylinder with gap for the target pipe Simulation with Biot-Savart using Bean-Model Current density for BSCCO at 10 K Homogeneous current density Gauß applied magnetic flux density Variables L, R, gap Shielding at 1.4 K is expected to be much better x z x z * Fagnard, Shielding efficiency and E(J) characteristics measured on large melt cast Bi-2212 hollow Cylinders in axial magnetic fields

19 Variation of Length and Radius No Gap Residual Flux at Target (x =0, z = 0) 1.B < 0 is not physical 2.Absolut offset 3.3% Overcompensation due to deficiency of model 4.Numerical calculation is correct 5.Best compensation L/R = 10

20 Variation of Length and Radius, 4 mm Gap Residual Flux at Target (x =0, z = 0)

21 Variation of Length and Radius, 8 and 12 mm Gap Residual Flux at Target (x =0, z = 0)

Ongoing study: Simulation with Finite Element Method 3 Dimensional modeling Time dependent extern magnetic field Current density distribution Magnetic flux density distribution Real hole in the cylinder wall

ECEC JCJC k40 Time Step0,1 s Output of Resultnach 100 s Ramp Rate1 Gauß/s Length150 mm Radius60 mm Thickness5 mm

Measurement at 4.2 K Compensate residual 40 G Adjustment of compensating solenoid Optimization Geometry of Shield and Coil (Length, Diameter, Thickness) Remaining Studies:

Flux penetration due to holes Holding dipole specification Effect of inner coils on superconductor Simulation of effect on particle momentum resolution Cryogenic system for cooling the superconductor

28 Conclusion and Outlook First idea is a shielding of the PANDA solenoid with a superconducting tube Feasibility depends on: residual magnetic field, inhomogeneity, material budget Simulation with Bean-Model Compensated flux depends on wall thickness, radius, length and the gap Experimental verification with YBCO at 1.4 K, residual flux 40 Gauß (0.4%) Measurement at 4.2 K Direct calculation of induced current in the superconductor Include field map into PANDA simulations to verify momentum resolution