status report of the new darmstadt polarized electron injector*

Status report of the new

Darmstadt polarized electron injector*

Yuliya PoltoratskaPESP2008, 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

April 20, 2023 | PESP2008 | Yuliya Poltoratska | 2

S-DALINAC

1

3

1

2

3

Experiment sites:

Injector: Photon scattering

Tagger: Photon scattering

QClam spectrometer

2

4

4 High-resolution spectrometer

Experiment to determinenucleon polarizability

Photon Scattering:

e-

Target

Radiator

Ge-Detector

SFB 634

2

1

3

Thermionic Gun: 250 keV

Injector Linac: 10 MeV

Main Linac: 130 MeV (after 3 passes)

12

3

Nucleon Polarizability

e-

H2

Radiator

p

NaI

(e,e‘x)-Coincidence experiments

ep, n,

Target

e‘Spectrometer

SemiconductorScintillators


S-DALINAC

Design values: Max. energy: Energy spread: Max. beam current: Duty cycle:

130 MeV±10-4

60 µA3 GHz cw


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


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


Chopper

Test stand

1 m

Electrongun

Preparationsystem

Lasersystem

Alphamagnet

Wien filterMott

Polarimeter Prebuncher

Differentialpumping

stage25 cm

• Cathode material: GaAs• Laser wavelength: 830 nm


80 mm

Position ofphotocathode

Electrode

Fabrication:

• Material 1.4429-ESU (316 LN)

• High polished surface

EM – Simulations*

• Cathode surface: E = 0.85 MV/m

• Edges: E = 4 MV/m

*(CST EM StudioTM).


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


Laser system

Pockelscell

beam expander

electro-opticmodulator

alignmentlaser

fibercoupler

amplifierdiode laser

system

retractablemirror

polarizer

opticalfiber

to cathode

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

Semiconductor amplifier Toptica TA 100 (optional)

Laser Lab

Optics assemblybelow the source

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


Spin manipulation and polarimetry

1 m100 keV

Mott polarimeter

Wien filter

Chopper

Electrongun

Preparationsystem

Lasersystem

Alphamagnet

Prebuncher

Differentialpumping

stage

Beam

B

E

5 cm

1

2 3

4


Degree of Polarization

• Elimination of the instrumental asymmetry by helicity switching• Foil thickness extrapolation – self supported gold foils 40 - 500 nm

Bulk GaAs: P = (35.5 ± 1.4)%Strained superlattice: P = (86 ± 3)% (830 nm)

P = (76 ± 2)% (808 nm)

Bulk GaAs


1 m

Chopper

Electrongun

Lasersystem

Alphamagnet

Prebuncher

Differentialpumping

stage

Wien fliterMott

polarimeter

Beam characteristics

Fluorescent screenWire scanner

coaxial Faraday cup

Bulk GaAs (λ=830 nm)

n,x = (0.146 ± 0.037) mm mrad

n,y = (0.197 ± 0.089) mm mrad

Preparationsystem

AlphamagnetAlpha

magnetAlpha

magnet


100 keV Polarized Electron Gun

5 m

10 MeV Injector

200 keV Thermionic

Electron Gun

To Experimental Hall40 MeV Linac

1st Recirculation

2nd Recirculation

Experimental Area

Optical Fiber

From Optics Lab

S-DALINAC Polarized Injector („SPIN“)

250 keV Thermionic

Electron Gun


Preparation system

Polarized electron gun

Differential pumping stages

Injector cryostat

Prebuncher system

ChopperMott polarimeter

Wien filter

1 m

Optical fiber from laser lab

„SPIN“ at S-DALINACTransport for:

100 keV polarized and 200 keV unpolarized beams


Polarimeters

A

B D

ii

AB

C

C

D

Polarimeters*

100 keV Mott Polarimeter

10 MeV Mott Polarimeter

Møller Polarimeter

Compton Transmission Polarimeter

D

Source

i

i

ii

Source of Polarized Electrons

Laser Systems

* (Christian Eckardt, Poster Session)

E

E

E

E

Experiments with polarized electrons/photons


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)%


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


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


Electron energy

V-Code:M. Krassilnikov, A. Novokhatski, T. Weiland,W. Koch, P. Castro, ICAP2000, Darmstadt (2000)

• 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


100 keV Mott and Wien filter

status report of the new darmstadt polarized electron injector*

Documents

yuliya poltoratskapesp2008

electron beam implementation

cathode surface

gaas laser wavelength

photon scatteringtagger

laser labtransport

mbar cathode vacuum

mvm edges