1. MIT Compact X-ray Source
William S. Graves
MIT
March 27, 2006

2. 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

3. 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 10 MHz (5% BW)
5e12
Average x-ray 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]
RMS size of source [mm] 4
RMS opening angle [mrad]
3.5
Results from 3D-code of W. Brown, MIT Lincoln Lab

4. 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 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 [mm] 7
Opening angle RMS [mrad]
Results from 3D-code of W. Brown, MIT Lincoln Lab

5. Results of 3D ICS code assuming design electron and laser parameters
ICS Modeling Results
Results of 3D ICS code assuming design electron and laser parameters
Electron Beam Parameters:
E = 25 MeV
enx = 0.3 mm
b = 4 mm (rms spot size = 5 mm)
Rms bunch length = 1 ps
Charge = 0.1 nC
Laser Parameters:
W = 10 mJ
zR = 0.3 mm (rms spot size = 5 mm)
Rms Laser Duration = 0.5 ps
l = 1.03 mm
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
Photons/pulse = 8.9 x 104
FWHM = 0.15 keV (1.3%)

6. ICS Modeling Results 9 mrad 9 mrad diameter
Results of 3D code assuming design electron and laser parameters
Intensity Profile of 12 keV X-rays With 0.4% Full Width Energy Filter
9 mrad
9 mrad diameter

7. MIT Inverse Compton Source Prototype
Yb:YAG Power Supply
3 m
SESAM
Yb:YAG Oscillator
pump diode
Yb:YAG
Pre ampl.
Multi-passYb:YAG Amplifier
Diodes
1.5 m
7 m
Injector Power Supply
Linac Power Supply
Focusing quadupoles
SRF gun
Solenoid
SRF linac
Collimating chicane
Photoinjector laser
LHe Refrigerator
LHe
Dewar

8. Diode-pumped Photocathode Laser
To achieve a homogeneous e-beam bunch
Spatially parabolic beam
4th-Harmonic
Generation
with
BBO crystals
<0.5ps, 50nJ, 10MHz
@257 nm
Yb:YLF,
200 fs,
10 MHz, 20W,
1030 nm
Beam
shaper
(parabolic
beam)

9. Bi-Cavity Cryomodule Stainless steel vacuum vessel LN2 port
Helium port
He gas collector
Titanium He vessel
RF cavity
RF couplers
RF waveguides

10. Inductive Output Tube (IOT)
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.
16 kW 1.3 GHz
Inductive Output Tube (IOT)
Operational frequency 1300MHz
Beam voltage 24kV
Grid bias voltage V
Output power 16.4kW
Collector dissipation 5.1kW
Efficiency %
Drive power 63W
Gain 24dB
Bandwidth 5MHz
Specification from CPI. Similar tubes available from Thales and EEV.

11. Preliminary Cryogenic Specification
Photoinjector
Static heat load W.
Dynamic heat load <50 W for a gradient of 23 MV/m in CW operation.
Linac Bi-cavity module
Static heat load 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

12. 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.

13. RF Field Model of SRF Photoinjector
Two dimensional model of cylindrically symmetric cavities
Accelerating electric field lines
Niobium cavities
Beampipe exit
FZR SRF 3.5 cell photoinjector modeled with standard RF design program SUPERFISH
Photocathode

14. RF Field Model of Linac Cavity
Two dimensional model of cylindrically symmetric cavities
Beampipe entrance
Accelerating electric field lines
Beampipe exit
Niobium cavities
TESLA 9-cell cavity modeled by SUPERFISH

15. Accelerator Lattice Model
Quad triplet #1
Dipole chicane
Quad triplet #2
Lattice designed with MAD
Dispersion reaches 38 mm in collimator
Minimum beta function ~4mm at interaction point (IP)
RMS size at IP = 7 mm
Total demagnification = 1/45

16. Initial Conditions at Photocathode
Surface electric field 33 MV/m
Initial RF phase 80 degrees
Parabolic laser intensity profile in each dimension.
Thermal emittance reaches peak of 0.6 mm for edge radius of 1.5 mm
Plot of x-y laser intensity on cathode
Modest peak current of 25 Amp.
FWHM = 4 ps
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)

17. PARMELA Modeling Results
Upper row shows beam properties at photoinjector exit.
Lower row shows beam properties at interaction point.
X vs RF phase
Energy
Emittance
rms DE = 0.3 keV
Thermal emittance is preserved from cathode to IP
Energy
X vs RF phase
rms DE = 3 keV growth due to space charge
Xrms = 7 mm at IP
Emittance

18. Start-to-End Modeling Results
Output of 3D ICS code using electron distribution from start-to-end
Electron Beam Parameters:
E = 25 MeV
enx = 0.68 mm
b = 5 mm (rms spot size = 8.6 mm)
Rms bunch length = 2.1 ps
Charge = 0.1 nC
Laser Parameters:
W = 10 mJ
zR = 0.3 mm (rms spot size = 5 mm)
Rms Laser Duration = 0.5 ps
l = 1.03 mm
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%)

19. Start-to-End Modeling Results
Output of 3D ICS code using electron distribution from start-to-end
Intensity Profile of 12 keV X-rays With 0.4% Full Width Energy Filter
Photons/pulse = 1.67 x 104