Wire Scanners for the 100 keV Polarized Electron Beam Line at the - PowerPoint PPT Presentation

Wire Scanners for the 100 keV Polarized Electron Beam Line at the S-DALINAC * Christian Eckardt DITANET 2011 Sevilla 09.11.2011 SFB 634 *Supported by DFG through SFB 634

Outline  S-DALINAC  Polarized Electrons  Polarized Injector SPIN  Wire Scanners  Outlook 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 2

S-DALINAC Design values: Max. energy: 130 MeV ± 10 -4 Energy spread: Max. beam current: 20 (60) µA Duty cycle: 3 GHz cw 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 3

S-DALINAC (e,e‘x) -Coincidence experiments Neptun Tagger 1 2 Photon Scattering: 2 1 Spectrometer Ge-  e‘ e - 3 Detector/ Detector Exp. e  p, n,  3 Radiator  e - Ge-Detector 4 T arget Strip Scintillators e - Detector Radiator T arget Experiment sites: Thermionic Gun: 200 keV 1 Injector: Photon scattering 1 Injector Linac: 10 MeV 2 2 NEPTUN: Tagged Photon scattering Main Linac: 130 MeV 3 3 QClam spectrometer (after 3 passes) 4 4 High-resolution spectrometer SFB 634 Polarized Source 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 4

Planned Experiments  Low-q (< 1 fm -1 ) experiments with polarized beams → Completely unexplored field Polarized electron and photon scattering  Parity-violation effects → Polarized bremsstrahlung  Additional nuclear structure functions → Polarized electron scattering 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 5

Strained GaAs conduction s 1/2 -1/2 +1/2 band active layer  + -absorption valence p 3/2 +3/2 -3/2 band p 1/2 -1/2 +1/2 -1/2 +1/2 substrate Surface preparation: Negative electron affinity (Thin CsO layer) 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 6

Test Stand • Cathodes: Bulk GaAs, Strained Layer GaAsP • Laser wavelength: 830 nm and 780 nm Preparation Electron System Gun Wire scanner Alpha Magnet Wien Filter Differential Laser Mott Pumping System 1 m Polarimeter Stage 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 7

Polarimetry: Mott Polarimeter  Elimination of the instrumental asymmetry by helicity switching  Foil thickness extrapolation – self supporting gold foils 40 - 500 nm Bulk GaAs: P = (35 ± 2)% Strained superlattice: P = (86 ± 3)% (830 nm) 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 8

Wirescanner Unit  50 m m tungsten wire  Insulated mounting  Pneumatic and electric actuator  Position readout with 10 M W potentiometer 30 mm  24-bit 2-channel data readout  Position - beam current link 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 9

Quadrupol Field Gradient  Non-uniform field gradient complicates determination of emittance  Double-Solenoid used for emittance measurement 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 10

Emittance measurements Laser diode @ 830 nm Bulk GaAs  n,x = (0.14 ± 0.03) mm mrad  n,y = (0.19 ± 0.09) mm mrad Strained GaAs  n,x = (0 . 13 ± 0 . 03) mm mrad  n,y = (0 . 18 ± 0 . 07) mm mrad σ 11 𝑙 = 𝑏 𝑙 − 𝑐 2 + 𝑑 𝑏𝑑  = 𝑀 2 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 11

SPIN at the S-DALINAC 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 12

SPIN at the S-DALINAC A i D B C E D E E D Source ii i Source of Polarized Electrons ii Laser Systems Polarimeters 100 keV Mott Polarimeter C Møller Polarimeter A B D Compton Transmission Polarimeter 10 MeV Mott Polarimeter E Experiments with polarized electrons/photons 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 13

Outlook  Measurements with pneumatic and electric manipulators  Slit measurement for determination of beam pulse length  Characterization of polarized injector SPIN  Automatization of emittance measurements  Preparation for first experiment:  Photofission on 238 U with polarized bremsstrahlung 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 14

Collaboration Institut für Kernphysik, TU Darmstadt U. Bonnes, R. Eichhorn, J. Enders, Y. Fritzsche, M. Wagner 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 15

22.03.2011 | DPG 11 Münster | Christian Eckardt | 2

Laser System Titanium-Sapphire-Laser: • possible wavelength 680…1000 nm • currently 780 nm • cw-operating at 3 W • Soft aperture mode locked with repetition rate of 75 MHz, and pulse length of approximately 200 fs and power at 2 W • Temperature stabilization, 4m m transfer line, acitve stabilization Diode-laser (ECDL): • wavelength variable between 780 and 788 nm • cw-operating at 80 mW (without amplifier) • pulse operating at 3 GHz with pulse length of 50 ps and average power 10 mW 17 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Quantum Efficiency and Polarisation 90 1 10 80 0 10 70 60 -1 10 QE (%) P (%) 50 -2 10 40 30 -3 10 Messung St. Petersburg 20 Messung Mainz -4 10 Messung Mainz (optimiert) 10 Messung St. Petersburg Messung Mainz -5 0 10 550 600 650 700 750 800 850 900 950  (nm) 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Emittance  : A definition  2-dim phase space σ 11 σ 12 σ = σ 21 σ 22  Beam matrix 2 ε = σ 11 σ 22 − σ 12  Emittance  Normalized emittance ε 𝑜 = βγε ( P.Forck, Lecture Notes, JUAS, 2007 ) 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Profile Measurement  Several beam profile measurements at different refraction strength  Fit Gaussian model distribution to acquired data points 𝑁σ 𝑡 0 𝑁 𝑈 = σ 𝑡 1 ( P.Forck, Lecture Notes, JUAS, 2007 ) 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Bunch Length 2 stage harmonic buncher 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

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) 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Electrode  EM – Simulations* • Cathode surface: E = 0.85 MV/m • Edges: E = 4 MV/m 80 mm  Fabrication: • Material 1.4429-ESU (316 LN) Position of • High polished surface photocathode *(CST EM Studio TM ). 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

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 lifetime ~ 250 h, further bake out cycle planned 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Spin Manipulation and Polarimetry B Preparation 1 Electron 4 system E gun 2 3 Beam Alpha 5 cm magnet Chopper Wien filter Differential Laser pumping system 100 keV stage 1 m Mott polarimeter Prebuncher 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Progress of Implementation 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Progress of Implementation 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Laser Beam Line: 40 m • Intensity stabilization  Electro optical modulator • Polarization  Pockels cell (PC) • T elescope  small focus  Small emittance 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Photofission Experiments Role of weak interaction in nuclei Unpolarized test experiment Bremstarget  e - θ - θ 238 U Target Bremsstrahlungspectrum P  ≥ 75% Sensitivity A ≈ 10 -3 Expected A ≈ 10 -4 N  E  → Active T arget 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Polarized Bremsstrahlung Photon emission angle [degrees] J.W. Motz and R.C. Placius, Nuovo Cimento 15 (1960) 571 Theory: H.K. T seng and R.H. Pratt, Phys. Rev. 7 (1973) 1502 Exp.: No exp. results for long. pol. Electrons Collaboration: KTH Stockholm, GSI, Universität Heidelberg 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

(e,e ´ x) Experiments   d d         v W v W v W v W v W v W     W W L L T T LT LT TT TT L T L T T T d d Mott  Inclusive electron scattering - two structure functions: longitudinal/transversal x A e  Exclusive electron scattering ’  - interference terms: L, T , LT , TT A*  Polarized electron scattering - parity violation, final state interaction A e  Polarized electrons and polarized targets - polarization transfer 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

„Fifth Structure Function“ • Only two data sets: 2 D( e,e’p ) 12 C( e,e’p ) • S-DALINAC Low momentum transfer D(e,e‘p ) S. Dolfini et al., PRC 60 (1999) 064622 09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt