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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

ton

s/e

V

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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-5 -4 -3 -2 -1 0 1 2 3 4 5 (mrad)

Inte

ns

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/mra

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Intensity Profile of 12 keV X-rays With 0.4% Full Width Energy Filter

dx/dz (mrad)

dy/

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d)

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x 104

9 mrad diameter

9 mrad

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

oto

ns

/mra

d^

2/e

V

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