1. Development of a superconducting shield for a transversely polarized target for the PANDA-Experiment Bertold Fröhlich (PhD), Frank Maas, Luigi Capozza, Cristina Morales HIM/JGU HPH2020 brainstorming meeting: „Dedicated Magnet Systems for polarized Targets“. U. Bonn, 2014, January 21

2. Timelike Electromagnetic Form Factors Sapcelike and timelike region intimately connected PANDA unprecedented luminosity Antiproton annihilation opens a new window to Precision electromagnetic (EM) probe hadron structure observables Spacelike: real Timelike: complex Polarisation q 2 < 0 (GeV/c) 2 q 2 > 0 (GeV/c) 2 time q2q2 q 2 = 0 /GeV/c) 2

3. WP3: transversely polarised Target in PANDA

5. transversely polarised Target in PANDA PANDA Solenoid: 2T longitudinal field

6. transversely polarised Target in PANDA PANDA transversely polarized target: shield 2T longitudinal field

7. Requirements Possible solutions: Superconducting shielding solenoid (active) Superconducting shielding tube (passive) Material requirements: High critical current density Highest Temperature Low material budget (for charged particles: 0.1 X 0 ) Manufacturer Adaptable to geometry

8. Principle: Superconducting Shield (passive) Induced current in superconducting tube Surface current Expellation of magnetic flux Thickness Of Supcerconductor Superconductor with no current Superconductor with current at critical current density

9. Advantage: Superconducting Shield (passive) Compensation of the longitudinal flux 10 000 Gauß (1 Tesla) Small material budget Passive shield No power supply:  No wire from power supply  No contact (no heat) Self adjusting no torque due to misalignment maximal shielding Quench behaviour ? Material choice critical: high critical current density Operating point (temperature) Induction in an external magnetic field High critical current throughout the whole material

10. Material choice: Bulk Properties

11. Material choice: Our limit for 1T

12. Advantage: Superconducting Shield YBCO Characteristics (melt-textured) Sintered ca. 1 order of magn. lower (no data at 4.2 K) Sintered 85 -90 % Radiation Length: X 0 = 1.9 cm at 6.38 g/cm 3 Radiation Length: X 0 = 2.2 cm at 6.38 g/cm 3 : 10% X 0 = 2.2mm

13. Advantage: Superconducting Shield Fagnard, Shielding efficiency and E(J) characteristics measured on large melt cast Bi-2212 hollow Cylinders in axial magnetic fields BSCCO ParameterValue Critical Temperature92 K Density6 g/cm 3 Young's Modulus (E-Modul) Longitudinal (approx. transv.) 55 GPa Critical Current Density J c (10 K, 1T)16 kA/cm 2 BSCCO Characteristics (melt-textured) Radiation Length: X 0 = 1.5 cm at 6 g/cm 3 10% X 0 = 1.5 mm

14. Induced field calculation: Solenoid, Biot-Savard

15. 4 mm Gap

16. Induced field calculation: Solenoid, Biot-Savard 50 mm Gap, (One Segment left out)

17. Transversely polarised Target in PANDA Finite Element Analysis with OPERA Current Distribution in SC-tube Model in OPERA: solid tube Model in OPERA: solid tube with bore

18. Transversely polarised Target in PANDA Test in cryostat in Bonn YBCO-123 Critical temperature T C 92 K Operational temperature T 1.4 K Wall thickness5 mm Length150 mm Radius50 mm Compensated fluxat least 40 000 Gauß With (very) friendly support from H. Dutz and S. Runkel from U. Bonn, Phys. Inst.

19. Shielding tests at 1.4 K and 77 K II. with bores (Nov. 2013) I. without bore (Jan. 2013) Transversely polarised Target in PANDA Test in cryostat in Bonn

20. Measurements at 1.4 K Test results: Shield outer field down to below 0.4% January 2013 Thickness Of Supcerconductor Superconductor with no current Superconductor with current at critical current density 5 mm thickness for 4 T 2.5 mm thickness for 2T

21. Measurement in Liquid Nitrogen (77K) Test results: Shield about 20% of the outer field January 2013 Measurement in Liquid Nitrogen

22. November 2013 Measurements at 1.4 K Test results: (Almost) no shielding observed

23. Conclusion: January 2013: Almost complete Shielding of outer field observed. November 2013: No shielding observed. Tube damaged due to hole drilling? Hall-probe damaged? 10% minimum shielding expected (with values from 92K) New measurements with a simple setup in Mainz (A. Thomas): YBCO (sintered) is under Test Tube with hole Tube (thinner) no hole SC-Solenoid for external field Next Step: BSCCO. Horizon 2020: 1 PhD-Student (Travel money)