Undulator Spectra as a Diagnostic for Electron Beam Energy Spread
and Emittance
M. Bakeman, J. van Tilborg, T. Sokollik, C. Toth, W. Fawley, C. Schroeder, K. E. Robinson, E. Esarey, and W. Leemans
Lawrence Berkeley National Laboratory
Introduction
Loasis 1GeV Laser Wakefield Accelerator
Undulator Radiation as a beam diagnostic
THUNDER Undulator Characterization
Quadrupole Electron Beam Transport
XUV Spectrometer Design and Calibration
Conclusions and Future Work
3
First GeV Electron Beam from LWFA
Laser: a0 ~ 1.46 (40 TW, 37 fs) Capillary: D = 312 mm; L = 33 mm
W.P. Leemans et. al, Nature Physics 2 (2006) 696; *Simulation using VORPAL
1 GeV beam
0
250
500
0.9 1.1[GeV]
[pC/GeV]
expt.
sim.*
Sim ExptQ (pC) 25-60 35E (GeV) 1.0 1.1dE/E RMS (%) 4 2.5div. (mrad) 2.4 1.6
Undulator Radiation Diagnostic to Measure Emittance and Energy Spread
Single shot electron beam measurements: charge, energy, energy spread, transverse emittance
Undulator undulator radiationLaser
beam
0.5 GeV,Electron
beam
~ cm
LBNL-LWFA
plasma
2.18 cm period 66 periods
K=1.25
Compact high-gradient quadrupoles
magnetic spectrometer
(1.2 T)
phosphor imaged onto CCD
grating
CCD~1 m
ICT
BPMBPM BPM
e-beam
Schematic layout:
Supporting systems: Quads for refocusing BPMs for positioning OTR, phosphor screens
Emittance and energy spread affect the undulator spectra
6
Undulator radiation based diagnostic will allow for single shot DE/E and e measurement
Phot
ons/
shot
/(0.1
%B
W)
Photon energy (eV)
/ = 2.5%
1 mm-mrad
Phot
ons/
shot
/(0
.1%
BW
)
/ = 0.25%
1 mm-mrad
Changing energy spread
Flux Ratio vs. Emittance
00.050.1
0.150.2
0.250.3
0.350.4
0.45
0 2 4 6 8 10 12
Emittance (nm-rad unormalized)
Harmonic Flux Ratio
2nd/1st 2nd/3rd
Line Width vs. Energy Spread
0
5
10
15
20
25
30
0 0.5 1 1.5 2 2.5 3
Energy Spread (%)
FWHM (eV)
1st Harmonic3rd Harmonic5th Harmonic
Experimental Setup in the Loasis lab
MagneticSpectrometer
Undulator
XUV Spectrometer
THUNDER Undulator Magnetic Properties
Length = 1.5m Magnetic period = 2.18cm Number of periods = 66 Peak Field = 0.61T Wiggler Parameter K = 1.25 Betatron period = 3.7m
Magnetic Characteristics
THUNDER tuned and characterized with the Spring-8 SPECTRA code
Phot
ons/
shot
/(0.1
%B
W)
Real B Field
/ = 0.25%
1 mm-mrad
Phot
ons/
shot
/(0.1
%B
W)
Perfect B Field
/ = 0.25%
1 mm-mrad
E-beam trajectory before tuning E-beam trajectory after tuning
Quadrupoles transport E-beam to undulator
New capillary chamber designed to fit quads and stages
Micro-Channel Plate Based Spectrometer from 8 - 62nm
Optical Characteristics XUV Spectrometer properties
First harmonic = 20nm Natural divergence = 1 mrad Pulse length = < 25 fs First harmonic flux = 1x105
8-62nm spectral range Four jaw Aperture System MCP detector with CsI photocathode Aberration corrected concave grating
Characterization completed at the Advanced Light Source
Characterized on beamline 6.3.2 8-62nm Spectral Range 0.07nm resolution at 20nm Hitachi Aberration Corrected
Concave Grating
XUV Spectrometer Calibration
Wavelength vs. Detector Position
Spectral Resolution vs. Wavelength
Conclusions and Future Work
Undulator radiation can be used as a singe shot emittance and energy spread beam diagnostic
Experiments will be conducted using the Loasis LWFA at 500MeV
Undulator characterized and installed on beamline XUV spectrometer built and characterized Quadrupoles and magnetic spectrometer will be
installed this spring
First experiments to begin this spring at Loasis
This work is supported by the Defense Threat Reduction Agency and the Director, Office of Science, High Energy Physics, U.S. Dept. of Energy under Contract no. DE-AC02-05CH11231
