MIT Compact X-ray Source
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Transcript of MIT Compact X-ray Source
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MIT Compact X-ray Source
William S. GravesMIT
March 27, 2006
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ICS Operating Modes
High average flux optimized for protein crystallography and medical x-rays.
•10 MHz repetition rate
•5 x 1012 x-rays per second (2 x 1011 in 0.1% bandwidth)
•0.1 nC charge per bunch
•1 kW average laser power
High peak flux optimized for single-shot, time-dependent studies
•10 Hz repetition rate
•4 x 109 x-rays per shot (goal is > 1 x 1010 per shot)
•1.0 nC charge per bunch
•0.2 kW average laser power
Today’s focus
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Large Time-Average-Flux Performance
Photon energy [keV] 12
Total x-ray flux per pulse (5% BW) 5e5
Peak spectral density per pulse [photons/eV] 800
Repetition rate [MHz] 10
Average x-ray flux @ 10 MHz (5% BW) 5e12
Average x-ray flux @ 10 MHz (0.1% BW) 2e11
On-axis spectral width FWHM [keV] 0.1
Spectral width FWHM [keV] 0.6 (5%)
Avg on-axis brilliance [photons / (mm2 mrad2 sec 0.1%)] 6e14
Peak on-axis brilliance [photons / (mm2 mrad2 sec 0.1%)] 2e19
Pulse length FWHM [ps] 0.1 - 3
RMS size of source [mm] 4
RMS opening angle [mrad] 3.5
Results from 3D-code of W. Brown, MIT Lincoln Lab
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High Flux-Per-Pulse Performance
Photon energy [keV] 12
Total x-ray flux per pulse (17% BW) 4e9
Peak spectral density per pulse [photons/eV] 2e6
Repetition rate [Hz] 10
Average x-ray flux @ 10 Hz [photons/sec] (17% BW) 4e10
On-axis spectral width FWHM [keV] 0.2
Spectral width FWHM [keV] 2 (17%)
Average brilliance [photons / (mm2 mrad2 sec 0.1%)] 1.4e10
Peak brilliance [photons / (mm2 mrad2 sec 0.1%)] 1.4e20
Pulse length FWHM [ps] 9
Size of source RMS [m] 7
Opening angle RMS [mrad] 7
Results from 3D-code of W. Brown, MIT Lincoln Lab
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X-ray Energy (keV)P
ho
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s/e
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Photons/pulse = 8.9 x 104
FWHM = 0.15 keV (1.3%)
Electron Beam Parameters:E = 25 MeVnx = 0.3 m
= 4 mm (rms spot size = 5 m)Rms bunch length = 1 psCharge = 0.1 nC
Laser Parameters:W = 10 mJzR= 0.3 mm (rms spot size = 5 m)
Rms Laser Duration = 0.5 ps = 1.03 m
a0 = 0.063
Total X-ray dose per pulse = 6.2x106
X-ray dose in 4 mrad full angle cone = 8.9x104
Spectral Width (FWHM) in cone = 0.15 keV
On-axis spectral width (FWHM) = 0.08 keV
Rms source size = 3.7 microns
Results of 3D ICS code assuming design electron and laser parameters
ICS Modeling Results
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Inte
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Intensity Profile of 12 keV X-rays With 0.4% Full Width Energy Filter
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9 mrad diameter
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ICS Modeling ResultsResults of 3D code assuming design electron and laser parameters
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MIT Inverse Compton Source Prototype
SRF gun
7 m
Yb:YAG Power Supply
Injector Power Supply
Linac Power Supply
3 m
SESAM
Yb:YAG Oscillatorpump diode
Yb:YAG
Pre ampl.
Multi-passYb:YAG Amplifier
Diodes
1.5 mSRF linacSolenoid Collimating
chicanePhotoinjector laser
Focusing quadupoles
LHe RefrigeratorLHe
Dewar
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Diode-pumped Photocathode Laser
To achieve a homogeneous e-beam bunch
4th-HarmonicGeneration
with BBO crystals
<0.5ps, 50nJ, 10MHz@257 nm
Yb:YLF, 200 fs,
10 MHz, 20W,1030 nm
Beamshaper
(parabolicbeam)
Spatially parabolic beam
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RF waveguides
RF couplers
RF cavity
He gas collector
Titanium He vessel
LN2 portHelium port
Stainless steel vacuum vessel
Bi-Cavity Cryomodule
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16 kW 1.3 GHz
Inductive Output Tube (IOT)
Operational frequency 1300MHzBeam voltage 24kVGrid bias voltage - 50VOutput power 16.4kWCollector dissipation 5.1kWEfficiency 68.3%Drive power 63WGain 24dBBandwidth 5MHz
RF Power
At full gradient of 15 MV/m, 1 mA of current requires 15 kW of RF power per cavity. Need additional power for RF wall losses.
Specification from CPI. Similar tubes available from Thales and EEV.
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Preliminary Cryogenic Specification
Photoinjector•Static heat load 10 - 15 W.
•Dynamic heat load <50 W for a gradient of 23 MV/m in CW operation.
Linac Bi-cavity module•Static heat load 10 - 15 W .
•Dynamic heat load (RF dissipation) <105 W for a gradient of 15 MV/m CW.
Total•180 W at full power in CW mode
•Heat load scales as (beam energy)2
•Use standard Linde L140 or L280 LHe refrigerator
Linde L280 LHe liquifier
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Start-to-End Simulation
Goal is to generate a self-consistent simulation from the photocathode drive laser all the way through production and manipulation of x-rays
•Include all photon and electron beam physics
•Include optical and electron transport aberrations
•Multi-dimensional, time-dependent codes
Report first results today – more optimization to be done.
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RF Field Model of SRF Photoinjector
FZR SRF 3.5 cell photoinjector modeled with standard RF design program SUPERFISH
Niobium cavities
Photocathode
Accelerating electric field lines
Beampipe exit
Two dimensional model of cylindrically symmetric cavities
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RF Field Model of Linac Cavity
TESLA 9-cell cavity modeled by SUPERFISH
Niobium cavities
Accelerating electric field linesBeampipe
exit
Two dimensional model of cylindrically symmetric cavities
Beampipe entrance
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Accelerator Lattice Model
Quad triplet #1
Quad triplet #2
Dipole chicane
Dispersion reaches 38 mm in collimator
Minimum beta function ~4mm at interaction point (IP)
RMS size at IP = 7 m
Total demagnification = 1/45
Lattice designed with MAD
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Initial Conditions at Photocathode
Thermal emittance reaches peak of 0.6 mm for edge radius of 1.5 mm
Modest peak current of 25 Amp.
FWHM = 4 ps
Plot of x-y laser intensity on cathode
Surface electric field 33 MV/m
Initial RF phase 80 degrees
Parabolic laser intensity profile in each dimension.
Transverse parabolic profile is required, but can use arbitrary (short) longitudinal profile for charge < 300 pC
See O.J. Luiten et al, Phys Rev Lett 93 (2004)
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Upper row shows beam properties at photoinjector exit.
Lower row shows beam properties at interaction point.
PARMELA Modeling Results
rms E = 0.3 keV
rms E = 3 keV growth due to space charge
Thermal emittance is preserved from
cathode to IP
Xrms = 7 m at IP
Energy
Energy
X vs RF phaseEmittance
Emittance
X vs RF phase
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Start-to-End Modeling Results
Electron Beam Parameters:E = 25 MeVnx = 0.68 m
= 5 mm (rms spot size = 8.6 m)Rms bunch length = 2.1 psCharge = 0.1 nC
Laser Parameters:W = 10 mJzR= 0.3 mm (rms spot size = 5 m)
Rms Laser Duration = 0.5 ps = 1.03 m
a0 = 0.063
Total photons per pulse = 2.8x106
Photons in 0.4% b.w. = 1.7x104
On-axis spectral width (FWHM) = 0.2 keV
Rms source size = 5.1 microns
FWHM = 0.20 keV (1.7%)
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X-ray Energy (keV)
Ph
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Output of 3D ICS code using electron distribution from start-to-end
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Intensity Profile of 12 keV X-rays With 0.4% Full Width Energy Filter
Photons/pulse = 1.67 x 104
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Start-to-End Modeling ResultsOutput of 3D ICS code using electron distribution from start-to-end