status report of the new darmstadt polarized electron injector*
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 3
S-DALINAC
Design values: Max. energy: Energy spread: Max. beam current: Duty cycle:
130 MeV±10-4
60 µA3 GHz cw
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 4
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 5
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 6
Chopper
Test stand
1 m
Electrongun
Preparationsystem
Lasersystem
Alphamagnet
Wien filterMott
Polarimeter Prebuncher
Differentialpumping
stage25 cm
• Cathode material: GaAs• Laser wavelength: 830 nm
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 7
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).
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 8
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 9
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 10
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 11
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 12
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 13
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 14
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 15
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 16
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)%
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 17
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 18
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 19
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 20
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
April 20, 2023 | PESP2008 | Yuliya Poltoratska | 21
100 keV Mott and Wien filter