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

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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

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SLIDE 1

Wire Scanners for the 100 keV Polarized Electron Beam Line at the S-DALINAC*

*Supported by DFG through SFB 634

SFB 634

Christian Eckardt DITANET 2011 Sevilla 09.11.2011

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SLIDE 2

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 2

Outline

  • S-DALINAC
  • Polarized Electrons
  • Polarized Injector SPIN
  • Wire Scanners
  • Outlook
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SLIDE 3

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 3

S-DALINAC

Design values:

  • Max. energy:

Energy spread:

  • Max. beam current:

Duty cycle: 130 MeV ±10-4 20 (60) µA 3 GHz cw

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SLIDE 4

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 4

S-DALINAC

1 3 1 2 3

Experiment sites:

Injector: Photon scattering NEPTUN: Tagged Photon scattering QClam spectrometer 2 4 4 High-resolution spectrometer

Photon Scattering: e- T arget  Radiator Ge- Detector 

SFB 634

2 1 3 Thermionic Gun: 200 keV Injector Linac: 10 MeV Main Linac: 130 MeV (after 3 passes) 1 2 3

(e,e‘x)-Coincidence experiments e p, n,  T arget e‘ Spectrometer Ge-Detector Scintillators Neptun Tagger e-  Radiator e- Strip Detector Detector/ Exp.

4

Polarized Source

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SLIDE 5

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 5

  • 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

Planned Experiments

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SLIDE 6

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 6

Strained GaAs

substrate active layer

+1/2

  • 1/2
  • 1/2
  • 1/2

+1/2 +1/2 +3/2

  • 3/2

s1/2 p1/2 p3/2 valence band conduction band 

+-absorption

Surface preparation: Negative electron affinity (Thin CsO layer)

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SLIDE 7

1 m Electron Gun Preparation System Laser System Alpha Magnet Wien Filter Mott Polarimeter Differential Pumping Stage

  • Cathodes: Bulk GaAs, Strained Layer GaAsP
  • Laser wavelength: 830 nm and 780 nm

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 7

Test Stand

Wire scanner

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SLIDE 8

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 8

Polarimetry: Mott Polarimeter

  • Elimination of the instrumental asymmetry by helicity switching

Bulk GaAs: P = (35 ± 2)% Strained superlattice: P = (86 ± 3)% (830 nm)

  • Foil thickness extrapolation – self supporting gold foils 40 - 500 nm
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SLIDE 9

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 9

Wirescanner Unit

  • 50 mm tungsten wire
  • Insulated mounting
  • Pneumatic and electric actuator
  • Position readout with

10 MW potentiometer

  • 24-bit 2-channel data readout
  • Position - beam current link

30 mm

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SLIDE 10

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 10

Quadrupol Field Gradient

  • Non-uniform field gradient complicates determination of emittance
  • Double-Solenoid used for emittance measurement
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SLIDE 11

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 11

Emittance measurements

σ11 𝑙 = 𝑏 𝑙 − 𝑐 2 + 𝑑

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

Laser diode @ 830 nm

 =

𝑏𝑑 𝑀2

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SLIDE 12

SPIN at the S-DALINAC

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 12

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SLIDE 13

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 13

A B D ii A B 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 E E E E Experiments with polarized electrons/photons D

SPIN at the S-DALINAC

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SLIDE 14

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 14

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 238U with polarized bremsstrahlung
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SLIDE 15

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt | 15

Collaboration

Institut für Kernphysik, TU Darmstadt

  • U. Bonnes,
  • R. Eichhorn,
  • J. Enders,
  • Y. Fritzsche,
  • M. Wagner
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SLIDE 16

22.03.2011 | DPG 11 Münster | Christian Eckardt | 2

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SLIDE 17

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

17

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

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SLIDE 18

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

550 600 650 700 750 800 850 900 950 10

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 10

1

QE (%)  (nm)

10 20 30 40 50 60 70 80 90

P (%)

Messung St. Petersburg Messung Mainz Messung Mainz (optimiert) Messung St. Petersburg Messung Mainz

Quantum Efficiency and Polarisation

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SLIDE 19

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Emittance  : A definition

  • 2-dim phase space
  • Beam matrix
  • Emittance
  • Normalized emittance

ε = σ11σ22 − σ12

2

ε𝑜 = βγε σ = σ11 σ12 σ21 σ22

( P.Forck, Lecture Notes, JUAS, 2007 )

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SLIDE 20

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Profile Measurement

( P.Forck, Lecture Notes, JUAS, 2007 )

  • Several beam profile measurements at different refraction strength
  • Fit Gaussian model distribution to acquired data points

𝑁σ 𝑡0 𝑁𝑈 = σ 𝑡1

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SLIDE 21

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Bunch Length

2 stage harmonic buncher

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SLIDE 22

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

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

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SLIDE 23

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

80 mm

Position of photocathode

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).

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SLIDE 24

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

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SLIDE 25

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Spin Manipulation and Polarimetry

1 m 100 keV Mott polarimeter Wien filter Chopper Electron gun Preparation system Laser system Alpha magnet Prebuncher Differential pumping stage Beam B E

5 cm

1 2 3 4

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SLIDE 26

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Progress of Implementation

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SLIDE 27

Progress of Implementation

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

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SLIDE 28

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

  • Intensity stabilization

 Electro optical modulator

  • Polarization

 Pockels cell (PC)

  • T

elescope  small focus  Small emittance

Laser Beam Line: 40 m

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SLIDE 29

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Photofission Experiments

  • θ

E N

P ≥ 75%

e-

238U Target

 Bremstarget θ

Unpolarized test experiment Sensitivity A ≈ 10-3 Expected A ≈ 10-4 → Active T arget Role of weak interaction in nuclei Bremsstrahlungspectrum

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SLIDE 30

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

Polarized Bremsstrahlung

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

Photon emission angle [degrees] J.W. Motz and R.C. Placius, Nuovo Cimento 15 (1960) 571

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SLIDE 31

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

(e,e´x) Experiments

 

T T T L T L TT TT LT LT T T L L Mott

W v W v W v W v W v W v d d d d

   

     W  W  

  • Inclusive electron scattering
  • two structure functions: longitudinal/transversal
  • Exclusive electron scattering
  • interference terms: L, T

, LT , TT

  • Polarized electron scattering
  • parity violation, final state interaction
  • Polarized electrons and polarized targets
  • polarization transfer

e e ’  A A* x A

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SLIDE 32

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

„Fifth Structure Function“

  • Only two data sets:

2D(e,e’p) 12C(e,e’p)

  • S-DALINAC

Low momentum transfer

  • S. Dolfini et al., PRC 60 (1999) 064622

D(e,e‘p )

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SLIDE 33

09.11.2011 | DITANET Conference 11 Sevilla | Christian Eckardt

3He Break-Up Reaction

Estimated statistical uncertainty after two weeks of beam time

Three-Body-Force investigation No data at low momentum transfer

Calculations by

  • J. Golak, Crakow