motivation polarized 3 he gas target solenoid design and test 3 he feasibility test summary and...

• Motivation

• Polarized 3He gas target

• Solenoid design and test

• 3He feasibility test

• Summary and outlook

Johannes Gutenberg-Universität Mainz Institut für Kernphysik

Study for the use of the polarized Study for the use of the polarized 33He He target at the photon beam of MAMItarget at the photon beam of MAMI

Patricia Aguar Bartolomé

MotivationMotivation Test of the GDH sum rule on the Test of the GDH sum rule on the

neutronneutron Double polarization experimentsDouble polarization experiments 33He gas as neutron target for real He gas as neutron target for real

photon beamsphoton beams

• Number of neutrons 2 cm D-butanol target 20 cm 3He gas target (p = 6 bar)

cmnucleons 2/104.8 23cmnucleons 20/103.1 22


Polarized Polarized 33He gas targetHe gas target 33He is made of two protons and one neutronHe is made of two protons and one neutron

In the ground state the two protons couple together cancel In the ground state the two protons couple together cancel their spin contribution to the nuclear magnetic momenttheir spin contribution to the nuclear magnetic moment

33He spin is carried by the unpaired neutron He spin is carried by the unpaired neutron neH

3


33He Polarization He Polarization Metastability Exchange Optical PumpingMetastability Exchange Optical Pumping

(Colegrove et al., Phys. Rev. 132 (1963) 2561)(Colegrove et al., Phys. Rev. 132 (1963) 2561)

Electronic optical pumping in the 2 3S1 State + transfer of polarization to the Nucleus by hyperfine coupling

Metastability collisions transfer of Nuclear polarization to the 1 1S0 state

ResultNuclear polarization of the 1 1S0 ground state


33He polarization relaxationHe polarization relaxation

p

hT dipol817

1

totTtP

1

1exp

totT1The polarization decays with a time constant,

The overall relaxation time, is given by

The relaxation is caused by

Magnetic dipole-dipole interactions between 3He atoms ( )

Wall relaxation on the inner surface of the cell ( ) Gas stored in special ironfree glass vessels.

beamimpgradwalldipoltot TTTTTT 111111

111111

totT1

dipolT1

wallT1


33He polarization relaxation (cont.)He polarization relaxation (cont.)

1217500 hbarcm

gradT1

p

rBB

hT grad2

01

Magnetic field gradients ( )

Interactions with gas impurities ( ) The cell and gasses must be very clean.

The required relative field gradient is

Ionization due to the experimental photon beam ( ).

13

0

10

cm

Bz

B hhT grad 3001 GBbarp 7;6 0

impT1

beamT1

Transport in homogenousmagnetic field


Solenoid designSolenoid design

• Main constraints

Appropriate outer radius to fit inside the Crystal Ball detector.

Target cell dimensions determine the inner radius.

The outgoing particles have to pass the coil minimization of the wire thickness.

Produce magnetic holding field of 7G with a relative field gradient of 10-3 cm-1 for 6 bars in the target cell area.

Polarized targets require a magnetic holding field, B0,

to provide a quantization axis.

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.

SOLENOID


Magnetic field calculationMagnetic field calculation• Numerical calculation of the field and gradients with a finite element code (FEMM)

• Geometric parameters for the solenoid

Longitud solenoide No vueltasCorrienteDiámetro interiorDiámetro exteriorDiámetro conductor

80 cm14570.3 A82.0 mm83.06 mm0.53 mm

Parameter

Value

• Coil wound on a CFK-tube with cross section of 82 x 1 mm2 and 120 cm length.

• B magnitude determined using the three axis magnetometer MAG-03 MS (Bartington Instruments Ltd.)


Solenoid testSolenoid test

-20 0 20 40 60 80 100

0

1

2

3

4

5

6

7

Magnetic field for a solenoid L=80cm

B(r=0cm) B(r=1cm) B(r=2cm)

B(G

)

z(cm)

-20 0 20 40 60 80 100-1.0x10-3

-8.0x10-4

-6.0x10-4

-4.0x10-4

-2.0x10-4

0.0

2.0x10-4

4.0x10-4

6.0x10-4

8.0x10-4

1.0x10-3

Target Region

Homogeneity for a solenoid L=80cm

dB(r=0cm) dB(r=1cm) dB(r=2cm)

z

(cm

-1)

z(cm)


33He feasibility testHe feasibility test• Goal: Study the ratio of nuclear scattering events produced on the windows of the target cell compared to that produced on the gas.

• Detectors

Scattering experiment performed with the 855 MeV polarized photon beam at MAMI.

Main detector was CB.

Vertex detector consisting of two coaxial MWPCs with cathode readout.

PID coaxial with the MWPCs used to identify charged particles.


Experimental setupExperimental setup

• Quartz• 100 cm3

• 0.4 cm wall• Pressure up 10 bar• kapton windows

• Entrance cell window placed 2 cm downstream from CB center• Leak test performed in the whole system

20 cm

m50 m50

m50


Data analysis and resultsData analysis and results

Z-Ve rte x fro m 2 Tra je c to rie s

Z (c m )

No

rma

lize

d C

oun

ts (a

.U.)

e m p ty ta rg e t

4He (7 b a r)(sa m e a ng ula r a c c e p ta nc e )

N / N 0.936554Wind o ws 4He

Analysis focused on identifying hadronic events from the particles scattered in the target cell.

Nw / Ng = 0.93

Experiment is possible!!!


Summary and outlookSummary and outlook Conclusions

A solenoid produced to provide the holding field for the 3He target was designed and tested

First measurements of the homogeneity give values of

3He feasibility test was successfully performed giving a 0.93 ratio which is in good agreement with the 0.89 theoretical prediction EXPERIMENT IS POSSIBLE!!!

Future Production of a new cylindrical target cell aluminosilicate materials present better relaxation times

New measurements for the relaxation time in a polarized cell placed inside the solenoid

13

0

101

cm

BZ

B


33He PolarizationHe PolarizationSpin-exchange optical pumpingSpin-exchange optical pumping(Bouchiat et al., Phys. Rev. Lett. 5 (1960) 373)(Bouchiat et al., Phys. Rev. Lett. 5 (1960) 373)

Circularly polarized light at 795 nm optically pumps an alkali-metal vapor optical electron spins aligned along the quantization axis.

Spin-exchange collisions between Rb and the 3He transfer of angular momentum from Rb to 3He nuclei


motivation polarized 3 he gas target solenoid design and test 3 he feasibility test summary and...

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