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

Timelike Electromagnetic Form Factors

Sapcelike and timelike region intimately connectedPANDA unprecedented luminosityAntiproton annihilation opens a new window to Precision electromagnetic (EM) probe hadron structure observables

Spacelike: real Timelike: complex Polarisation

q2 < 0 (GeV/c)2 q2 > 0 (GeV/c)2

time time

q2

q2 = 0 /GeV/c)2

WP3: transversely polarised Target in PANDA

WP3: transversely polarised Target in PANDA

transversely polarised Target in PANDA

•PANDA Solenoid: 2T longitudinal field

transversely polarised Target in PANDA

•PANDA transversely polarized target: shield 2T longitudinal field

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 X0) •Manufacturer•Adaptable to geometry

Principle: Superconducting Shield (passive)

• Induced current in superconducting tube• Surface current• Expellation of magnetic flux

ThicknessOf Supcerconductor

Superconductor with no current

Superconductor with current at criticalcurrent density

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 supplyNo 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

Material choice:

Bulk Properties

Material choice:

Our limitfor 1T

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: X0 = 1.9 cm at 6.38 g/cm3Radiation Length: X0 = 1.9 cm at 6.38 g/cm3

Radiation Length: X0 = 2.2 cm at 6.38 g/cm3: 10% X0 = 2.2mm

Advantage: Superconducting Shield

Fagnard, Shielding efficiency and E(J) characteristics measured on large melt cast Bi-2212 hollow Cylinders in axial magnetic fields

BSCCO Parameter Value

Critical Temperature 92 K

Density 6 g/cm3

Young's Modulus (E-Modul) Longitudinal (approx. transv.)

55 GPa

Critical Current Density Jc (10 K, 1T) 16 kA/cm2

BSCCO Characteristics (melt-textured)

Radiation Length: X0 = 1.5 cm at 6 g/cm3 10% X0 = 1.5 mm

Induced field calculation: Solenoid, Biot-Savard

Induced field calculation: Solenoid, Biot-Savard

4 mm Gap

Induced field calculation: Solenoid, Biot-Savard

50 mm Gap, (One Segment left out)

Transversely polarised Target in PANDAFinite Element Analysis with OPERA

Current Distribution in SC-tube

Model in OPERA: solid tube

Model in OPERA: solid tube with bore

Transversely polarised Target in PANDATest in cryostat in Bonn

YBCO-123 Critical temperature TC

92 K

Operational temperature T

1.4 K

Wall thickness 5 mm

Length 150 mm

Radius 50 mm

Compensated flux at least 40 000 Gauß

With (very) friendly support from H. Dutz and S. Runkel from U. Bonn, Phys. Inst.

Shielding tests at 1.4 K and 77 K

II. with bores(Nov. 2013)

I. without bore(Jan. 2013)

Transversely polarised Target in PANDATest in cryostat in Bonn

Measurements at 1.4 KTest results: Shield outer field down to below 0.4%

January 2013

ThicknessOf Supcerconductor

Superconductor with no current

Superconductor with current at criticalcurrent density

5 mm thickness for 4 T2.5 mm thickness for 2T

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

January 2013 Measurement in Liquid Nitrogen

November 2013

Measurements at 1.4 KTest results: (Almost) no shielding observed

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)