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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.

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Status report of the new Darmstadt polarized electron injector*

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  1. 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

  2. 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

  3. 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

  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 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 4

  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 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 5

  6. 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

  7. 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

  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 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 8

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. „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

  15. 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

  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)% 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 16

  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 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 17

  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 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 18

  19. 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 19

  20. 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

  21. 100 keV Mott and Wien filter 23. Oktober 2014 | PESP2008 | Yuliya Poltoratska | 21

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