Collaboration. Patricia Aguar Bartolomé

Transcrição

1 2 Collaboration CB Collaboration Meeting Mainz, September 23, 2008

2 OVERVIEW Magnetic Holding Field - Solenoid design - Numerical calculations - Solenoid test Target Cell Preparation Measurement of Polarization - Mechanical rail system - External holding field

3 MAGNETIC HOLDING FIELD Polarized targets require a magnetic holding field, B 0, to provide a quantization axis. SOLENOID The strength and uniformity of the field play an important role in obtaining long polarization relaxation times. Depolarization effects due to field gradients should be smaller than the relaxation due to surface effects. Main constraints Produce magnetic holding field of 7G with a relative field gradient of 10-3 cm -1 for 6 bars in the target cell area. Appropriate outer radius to fit inside the Crystal Ball detector. The outgoing particles have to pass the coil minimization of the wire thickness.

4 MAGNETIC FIELD CALCULATION Numerical calculation of the field and gradients with a finite element code (FEMM) Geometric parameters for the solenoid Parameter Value Solenoid length 80 cm N 0 windings 1457 Current Inner coil diameter Outer coil diameter Copper wire diameter 0.3 A 0.82 cm 0.83 cm cm Coil wound on a CFK-tube with cross section of 82 x 1 mm 2 and 120 cm length. B magnitude determined using the three axis magnetometer MAG-03 MS (Bartington Instruments Ltd.)

5 SOLENOID TEST Magnetic field for a solenoid L=80cm 7 B(r=0cm) B(r=1cm) B(r=2cm) 6 B(G) x x x10-4 Homogeneity for a solenoid L=80cm db(r=0cm) db(r=1cm) db(r=2cm) 2 4.0x z(cm) ( Β/ z)/β ο (cm -1 ) 2.0x x x x10-4 Target Region -8.0x x z(cm)

6 TARGET CELL DESIGN 20 cm length and 6 cm diameter Non-magnetic materials in order to avoid depolarization of the gas - Quartz glass cell coated with Cesium - Aluminium caps - 50 µm Mylar windows metalized with Aluminium 3 He gas target (P = 6 bar) nucleons / 20 cm First tests with prototype are in process

7 FIRST T 1 MEASUREMENT WITH UNCOATED CELL

8 MEASUREMENT OF POLARIZATION Mechanical rail system to carry the target cell from the center of the solenoid to the center of the external holding field 1) 2) 3) 4)

9 EXTERNAL HOLDING FIELD Helmholtz coils needed to measure the polarization. Parameter Value Coils diameter 160 cm Current 4 A N 0 windings 150 Copper wire diameter 0.2 cm

10 TRANSPORT SOLENOID Solenoid to carry the target cell from the center of the CB to the center of the Helmholtz coils. Parameter Value Solenoid length 40 cm N 0 Windings 800 Current 0.3 A Inner coil diameter 0.82 cm Outer coil diameter 0.83 cm Copper wire diameter cm

11 SUMMARY AND OUTLOOK Conclusions A solenoid produced to provide the holding field for the 3 He target was designed and tested First homogeneity measurements of the solenoid with the polarized gas cell inside id give values of B Z = 1 10 B 0 First measurement of T 1 with uncoated cell gives 4h Future plans Fix the leak on the target cell prototype Measurement of T 1 with coated cell Production of mechanical rail system 3 cm 1