2001/9/20 Laser Driven Target http://ldt.mit.edu

1

Laser Driven Target at MIT

Chris Crawford, Ben Clasie, Jason Seely,Dipangkar Dutta, Haiyan Gao

•Introduction

•Optical pumping

•Spincell optimization

•Components of the LDT

•Atomic Fraction Results

•Preliminary Polarization

•Future Work

2001/9/20 Laser Driven Target http://ldt.mit.edu

2

Atomic Beam Source

• Well established technology

• Can create pure spin states

• 8 x 1016 atoms/s

• 84% atomic fraction

• 80% polarization

Laser Driven Target

• Compact design

• Active pumping—higher flux

• 2 x 1018 atoms/s

• 60% atomic fraction

• 50% polarization

Overview

2001/9/20 Laser Driven Target http://ldt.mit.edu

3

Optical Pumping

At spin temperature equilibrium, the population of each spin state n(mF) is controlled by the Boltzmann equation.

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Spincell Optimization

•Developed a code to simulate recombination and depolarization

•One must minimize the Surface Area / Volume ratio, and the length of the transport tube Dimensions: 2” diameter spherical spincell with 5 cm neck

spincell neck target# wall collisions 640 96 768dwell time (ms) 6.8 0.3 3.1

spin temp time (ms) 0.075

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Target Chamber

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Polarimeter

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Sextupole Magnet

2001/9/20 Laser Driven Target http://ldt.mit.edu

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QMA Detector

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Studies of atomic fraction vs dissociator aperture diameter

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

H2 flow (sccm)

Be

st

ato

mic

fra

cti

on

(%

)

1mm,~100MHz

1mm,~160MHz

1.5mm,~100MHz

1.5mm,~160MHz

2.1mm,~100MHz

2.1mm,~160MHz

new diss,~160 MHz

Diameter and RF Can Frequency

Dissociator Trials

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Atomic Fraction

Atomic fraction at the target cell using the new dissociator.

55

60

65

70

75

80

85

90

95

20 40 60 80 100 120 140 160 180

Temp (C)

Ato

mic

Fra

ctio

n (%

)

Spincell heating up

Potassium heating up, spincell at 180C

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Negative Helicity

0

1

2

3

4

5

6

7

8

9

10

0.2

0.22

0.24

0.26

0.28

0.3

0.32

0.34

Positive Helicity

0

1

2

3

4

5

6

7

8

9

10

0.2

0.22

0.24

0.26

0.28

0.3

0.32

0.34

0.36

0.38

Preliminary Polarization

Laser transmission

Laser transmission

QMA mass 1 signal

QMA mass 1 signal

•polarization: 20% (+ helicity) and 23% (- helicity)

•polarization preserving mirrors only 87% efficient

2001/9/20 Laser Driven Target http://ldt.mit.edu

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Future Work

•Redo polarization tests with correct mirrors.

•Fine-tune operational parameters.

•Investigate the quality of the spincell coating.

•Investigate performance of sextupole filter.

•Run tests with deuterium.

•Redesign target for operation at BLAST.