Transcript ICS S2E

MIT Compact X-ray Source
William S. Graves
MIT
March 27, 2006
1
ICS Operating Modes
High average flux optimized for protein crystallography and
medical x-rays.
•10 MHz repetition rate
Today’s
focus
•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
2
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
3
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 [mm]
7
Opening angle RMS [mrad]
7
Results from 3D-code of W. Brown, MIT Lincoln Lab
4
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
600
Photons/eV
500
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
400
300
200
100
0
10
Total X-ray dose per pulse = 6.2x106
10.5
11
11.5
12
X-ray Energy (keV)
X-ray dose in 4 mrad full angle cone = 8.9x104
Photons/pulse = 8.9 x 104
Spectral Width (FWHM) in cone = 0.15 keV
On-axis spectral width (FWHM) = 0.08 keV
FWHM = 0.15 keV (1.3%)
Rms source size = 3.7 microns
5
12.5
ICS Modeling Results
Results of 3D code assuming design electron and laser parameters
Intensity Profile of 12 keV X-rays With 0.4% Full Width Energy Filter
4
x 10
35000
4
2.5
2
2
0
1.5
-2
1
-4
-6
-6
Intensity (keV/mrad^2)
dy/dz (mrad)
6
0.5
9 mrad
30000
25000
20000
15000
10000
5000
0
-5
-4
-2
0
2
dx/dz (mrad)
4
-4
-3
6
9 mrad diameter
6
-2
-1 0 1
 (mrad)
2
3
4
5
MIT Inverse Compton Source Prototype
Yb:YAG
Power
Supply
SRF
gun
Photoinjector
laser
SESA
M
pum
p
diod
e
Diodes
Focusing
quadupoles
SRF linac
Collimating
chicane
LHe
Dewar
LHe Refrigerator
7
1.5 m
3m
Linac
Power
Supply
Solenoid
Pre ampl.
Multi-passYb:YAG Amplifier
7m
Injector
Power
Supply
Yb:YAG Oscillator
Yb:YAG
Diode-pumped Photocathode Laser
To achieve a homogeneous e-beam bunch
Spatially parabolic beam
Yb:YLF,
200 fs,
10 MHz, 20W,
1030 nm
4th-Harmonic
Generation
with
BBO crystals
Beam
shaper
(parabolic
beam)
<0.5ps, 50nJ, 10MHz
@257 nm
8
Bi-Cavity Cryomodule
Stainless steel vacuum vessel
LN2 port
Helium port
He gas collector
Titanium He vessel
RF cavity
RF couplers
RF waveguides
9
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
Beam voltage
Grid bias voltage
Output power
Collector dissipation
Efficiency
Drive power
Gain
Bandwidth
1300MHz
24kV
- 50V
16.4kW
5.1kW
68.3%
63W
24dB
5MHz
Specification from CPI. Similar tubes
available from Thales and EEV.
10
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
11
Linde L280 LHe
liquifier
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.
12
RF Field Model of SRF Photoinjector
Two dimensional model of
cylindrically symmetric cavities
Accelerating electric field lines
Niobium cavities
Beampipe exit
Photocathode
FZR SRF 3.5 cell photoinjector modeled with
standard RF design program SUPERFISH
13
RF Field Model of Linac Cavity
Two dimensional model of cylindrically symmetric cavities
Beampipe
entrance
Accelerating electric field lines
Niobium cavities
TESLA 9-cell cavity modeled by SUPERFISH
14
Beampipe
exit
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
15
Initial Conditions at Photocathode
Surface electric field
33 MV/m
Initial RF phase
80 degrees
Parabolic laser intensity profile in each dimension.
Modest peak current of
25 Amp.
Thermal emittance reaches
peak of 0.6 mm for edge
radius of 1.5 mm
Plot of x-y laser intensity
on cathode
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)
16
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
Energy
rms DE = 3 keV
growth due to
space charge
X vs RF phase
Xrms = 7 mm at IP
17
Thermal emittance
is preserved from
cathode to IP
Emittance
Start-to-End Modeling Results
Output of 3D ICS code using electron distribution from start-to-end
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
18
16
Photons/mrad^2/eV
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
14
12
10
8
6
4
2
0
11
Total photons per pulse = 2.8x106
11.5
12
X-ray Energy (keV)
Photons in 0.4% b.w. = 1.7x104
FWHM = 0.20 keV (1.7%)
On-axis spectral width (FWHM) = 0.2 keV
Rms source size = 5.1 microns
18
12.5
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
6
7000
9000
6000
8000
2
Intensity (keV/mrad^2)
dy/dz (mrad)
4
5000
4000
0
3000
-2
2000
6000
5000
4000
3000
2000
1000
-4
1000
-6
-6
7000
0
-5
-4
-2
0
2
dx/dz (mrad)
4
-4
-3
6
Photons/pulse = 1.67 x 104
19
-2
-1 0 1
 (mrad)
2
3
4
5