Status report of the new darmstadt polarized electron injector
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Status report of the new Darmstadt polarized electron injector*. Yuliya Poltoratska PESP2008, 1.10.2008. S-DALINAC Polarized electron source Requirements Electron gun Characterization of the electron beam Implementation at the S-DALINAC. *Supported by DFG through SFB 634 and GRK 410.

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Status report of the new Darmstadt polarized electron injector*

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Status report of the new darmstadt polarized electron injector

Status report of the new Darmstadt polarized electron injector*

Yuliya Poltoratska

PESP2008, 1.10.2008

  • S-DALINAC

  • Polarized electron source

    • Requirements

    • Electron gun

    • Characterization of the electron beam

  • Implementation at the S-DALINAC

*Supported by DFG through SFB 634 and GRK 410


S dalinac

Photon Scattering:

Nucleon Polarizability

Ge-

Detector

p

g

e-

g

g

g

e-

Radiator

H2

NaI

(e,e‘x)-Coincidence experiments

Radiator

Target

1

1

2

2

4

3

3

4

Spectrometer

e‘

e

p, n, a

Thermionic Gun: 250 keV

Semiconductor

Scintillators

Target

2

2

Injector Linac: 10 MeV

1

1

Main Linac: 130 MeV (after 3 passes)

3

3

SFB 634

S-DALINAC

Experiment sites:

Injector: Photon scattering

Tagger: Photon scattering

Experiment to determine

nucleon polarizability

QClam spectrometer

High-resolution spectrometer

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 2


S dalinac1

Design values: Max. energy:

Energy spread:

Max. beam current:

Duty cycle:

130 MeV

±10-4

60 µA

3 GHz cw

S-DALINAC

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 3


Planned experiments

Planned experiments

  • Polarized electron and photon scattering

    • Parity-violation effects

    • → Polarized bremsstrahlung

    • Measurement of the additional structure functions

    • (polarized electron scattering)

    • Low-q (< 1 fm-1) experiments with polarized beams → Completely unexplored field

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 4


Polarized source requirements

Polarized source: requirements

  • Polarization: ≈ 80%

  • Average current: > 60 µA

  • Repetition frequency: 3 GHz cw

  • Long lifetime

  • Short maintenance period

  • Compact form:

    →max. height including safety distance 2.3 m

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 5


Test stand

25 cm

1 m

Test stand

  • Cathode material: GaAs

  • Laser wavelength: 830 nm

Preparation

system

Electron

gun

Alpha

magnet

Chopper

Wien filter

Differential

pumping

stage

Laser

system

Mott

Polarimeter

Prebuncher

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 6


Electrode

80 mm

Position of

photocathode

Electrode

  • EM – Simulations*

    • Cathode surface: E = 0.85 MV/m

    • Edges:

      • E = 4 MV/m

  • Fabrication:

    • Material 1.4429-ESU (316 LN)

    • High polished surface

*(CST EM StudioTM).

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 7


Vacuum system

Vacuum system

  • Achieved vacuum pressure (after 12 days bake out @ 220° C ):

  • Cathode and preparation chambers :

  • < 1.8·10-11 mbar (detection limit)

  • HV beam line after DPS: 6.0·10-9 mbar

  • Cathode vacuum life-time: (456 ± 30)h

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 8


Laser system

Laser system

Single mode Laser diode Sanyo DL-8032-001 (Wavelength 830 nm)

Semiconductor amplifier Toptica TA 100 (optional)

Laser

Lab

Optics assembly

below the source

  • 79 ps pulse length measured, limited by bandwidth of osciloscope

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 9


Spin manipulation and polarimetry

B

1

E

4

2

3

Beam

5 cm

Wien filter

100 keV

Mott polarimeter

1 m

Spin manipulation and polarimetry

Preparation

system

Electron

gun

Alpha

magnet

Chopper

Differential

pumping

stage

Laser

system

Prebuncher

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 10


Degree of polarization

Degree of Polarization

  • Elimination of the instrumental asymmetry by helicity switching

  • Foil thickness extrapolation – self supported gold foils 40 - 500 nm

Bulk GaAs

Bulk GaAs: P = (35.5 ± 1.4)%

Strained superlattice: P = (86 ± 3)% (830 nm)

P = (76 ± 2)% (808 nm)

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 11


Beam characteristics

coaxial Faraday cup

1 m

Beam characteristics

Bulk GaAs (λ=830 nm)

en,x = (0.146 ± 0.037) mm mrad

en,y = (0.197 ± 0.089) mm mrad

Electron

gun

Preparation

system

Alpha

magnet

Alpha

magnet

Alpha

magnet

Alpha

magnet

Chopper

Wien fliter

Differential

pumping

stage

Laser

system

Mott

polarimeter

Prebuncher

Fluorescent screen

Wire scanner

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 12


S dalinac polarized injector spin

S-DALINAC Polarized Injector („SPIN“)

100 keV Polarized Electron Gun

200 keV Thermionic Electron Gun

250 keV Thermionic Electron Gun

Experimental Area

10 MeV Injector

To Experimental Hall

40 MeV Linac

1st Recirculation

2nd Recirculation

Optical Fiber

From Optics Lab

5 m

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 13


Spin at s dalinac

„SPIN“ at S-DALINAC

Transport for:

100 keV polarized and 200 keV unpolarized beams

Preparation system

Polarized electron gun

Injector cryostat

Prebuncher system

Wien filter

Chopper

Mott polarimeter

Differential pumping stages

1 m

Optical fiber from laser lab

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 14


Polarimeters

i

ii

E

E

E

E

A

B

B

C

C

D

D

D

Polarimeters

A

i

Source

ii

Source of Polarized Electrons

Laser Systems

Polarimeters*

Møller Polarimeter

100 keV Mott Polarimeter

Compton Transmission Polarimeter

10 MeV Mott Polarimeter

Experiments with polarized electrons/photons

* (Christian Eckardt, Poster Session)

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 15


Summary

Summary

  • Test stand set up and put into operation successfully

  • Required vacuum pressure in the electron source achieved

  • Beam parameters:

    • Energy: 100 keV

    • Duty cycle: 3 GHz cw

    • Normalized Transverse Emittance (x): (0.146 ± 0.037) mm mrad

      (y): (0.197 ± 0.089) mm mrad

  • Degree of polarization:

    Bulk : (35.4 ± 1.4)%

    Strained-Superlattice: (86 ± 3)%

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 16


Outlook

Outlook

  • Intensity stabilization

  • Further improvement of cathode lifetime

  • Chopper-Prebuncher system

  • Titanium-Sapphire laser for pulsed operation of „SPIN“

  • Installation at the S-DALINAC – starting 2009

  • Installation & comissioning of polarimeters for experiments

  • Experiments – middle´09

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 17


Status report of the new darmstadt polarized electron injector

Collaboration

Institut für Kernphysik, TU Darmstadt

R. Barday, U. Bonnes, M. Brunken, C. Eckardt, R. Eichhorn,

J. Enders, C. Heßler, C. Ingenhaag, M. Platz, M. Roth, M. Wagner

Institut für Theorie Elektromagnetischer Felder,

TU Darmstadt

W. Ackermann, W. F. O. Müller, B. Steiner, T. Weiland

Institut für Kernphysik, Universität Mainz

K. Aulenbacher

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 18


Status report of the new darmstadt polarized electron injector

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 19


Electron energy

Electron energy

  • 100 keV injection energy to the superconducting Linac

  • 2-cell capture structure necessary

V-Code simulations

Injection energy:

Thermionic gun:

200 keV

Polarized gun:

100 keV

V-Code:

M. Krassilnikov, A. Novokhatski, T. Weiland,

W. Koch, P. Castro, ICAP2000, Darmstadt (2000)

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 20


100 kev mott and wien filter

100 keV Mott and Wien filter

23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 21


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