MIT Presented at High Brightness Electron Beams Workshop San Juan PR March 2013 High Brilliance Xrays from Compact Sources 1 WS Graves MIT March 2013 2 People MIT K Berggren J ID: 178515
Download Presentation The PPT/PDF document "W.S. Graves" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
W.S. Graves MITPresented at High Brightness Electron Beams WorkshopSan Juan, PRMarch, 2013
High Brilliance X-rays from Compact Sources
1
W.S. Graves, MIT, March 2013Slide2
2PeopleMITK. Berggren, J. Bessuille, P. Brown, W. Graves, R. Hobbs, K.-H. Hong, W. Huang, E. Ihloff, F. Kaertner, D. Keathley, D. Moncton, E. Nanni
, M. Swanwick, L. Vasquez-Garcia, L. Wong, Y. Yang, L. Zapata
DESYJ. Derksen, A. Fallahi, F. Kaertner
NIU
D.
Mihalcea
, P.
Piot
, I. Viti
SLACV. Dolgashev, S. Tantawi
Jefferson LabF. Hannon, J. Mammosser, ...
W.S. Graves, MIT, March 2013
With funding from DARPA
AXis
, DOE-BES, and NSF-DMRSlide3
3
Gun
Linac
ICS
IR laser or THz
X-rays
3 m
ebeam
dump
Cathode laser
Basic Layout for ICS
Quads
W.S. Graves, MIT, March 2013Slide4
RF GUNLINACEMITTANCE EXCHANGE LINE
ICS X-RAY GENERATOR
ELECTRON SPECTROMETER
Not shown
- klystron and modulator housed in one 19” X 6’ rack
- instrumentation & power supplies housed in one 19
” X 6’
rack
- 10W (10
mJ at 1 kHz) mode locked Ti:Sapp amplifier for photocathode and ICS collision
- x-ray opticsX-band ICS source with 1 kHz rep rate
Equipment cost $3M
X-rays 0.1 – 12 keV
W.S. Graves, MIT, March 2013Slide5
RF GUNLINACEMITTANCE EXCHANGE LINE
ICS X-RAY GEN.
ELECTRONSPECTROMETER
X-band ICS source with 1 kHz rep rate
W.S. Graves, MIT, March 2013Slide6
6Simulated p-mode with couplingStanding wave accelerator structure with distributed coupling
Feed power
Coupler to two adjacent cells
Just 3 MW RF power to accelerate 20 MeV in 1 m
1 kHz rep rate with 9.3 GHz klystron developed for medical
linacs
1 kHz solid-state modulator with <.01% stability
RF gun is 2.5 cell 9.3 GHz structure needing just 2 MW to produce 200 MV/m on cathode
Optimized X-band SW Structure
S
tructures by S.
Tantawi
and V.
Dolgashev
of SLAC
W.S. Graves, MIT, March 2013Slide7
7
RF amp
RF amp
RF amp
Superconducting RF
photoinjector
operating at
400
MHz and 4K
RF amplifiers
4 MeV
30 kW beam dump
30 MeV
Bunch compression chicane
Coherent enhancement cavity with Q=1000 giving multi MW cavity power
multi kW cryo-cooled Yb:YAG drive laser
Inverse Compton scattering
X-ray beamline
Electron beam of ~1 mA average current at 10-30 MeV
8 m
High Repetition Rate ICS with SRF Linac
W.S. Graves, MIT, March 2013Slide8
Niowave Inc SRF gunJefferson Lab SRF linac
Emittance exchange beamline
ICS x-ray generator
High Repetition Rate ICS with SRF Linac
E
quipment cost $15M
X-rays 0.1 – 12 keV
W.S. Graves, MIT, March 2013Slide9
Superconducting Accelerator R&D for Coherent Light Sources PI: J. Mammosser, JLab
Goal: develop a low cost, high efficiency SRF solutionsuitable for compact light sources and other uses
Compare spoke and elliptical b=1 cavities
Evaluate cavity materials, including Nb
3
SN
Evaluate beam dynamics for highest brightness.
Develop digital LLRF system for cavity / module testing
Evaluate options for a low cost versatile cryostat
RF system
Spoke cavity
Elliptical cavity
Nb
3
Sn
CLS concept
Single cell
Beam dynamicsSlide10
Superradiant
X-rays via ICS
Steps
Emit array of electron
beamlets
from cathode 2D array of
nanotips
.
Accelerate
and manipulate correlations of beamlet array.
Perform emittance exchange (EEX) to swap
transverse
beamlet
spacing into
longitudinal
dimension. Arrange dynamics to give desired period.
Modulated electron beam backscatters laser to emit ICS x-rays in phase
. FEL gain appears possible.
ICS (or undulator) emission is not a coherent process, scales as N
Super-radiant emission is in-phase spontaneous emission, scales as N
2
N electrons
W.S. Graves, MIT, March 2013Slide11
Beamlets from tips
x
y
x
x’
t
Current
t
Current
x
x’
t
Energy
Acceleration
EEX
t
Energy
x
y
Bunched beam emits coherent ICS
Emittance Exchange (EEX)
W.S. Graves, MIT, March 2013Slide12
12Layout for Super-radiant ICS
RF gun
Linac
Emittance Exchange (EEX)
RF deflector
Quads
Dipoles
Nanocathode
X-rays
IR laser or THz
ebeam
dump
ICS
W.S. Graves, MIT, March 2013Slide13
13Nanostructured CathodesW.S. Graves, MIT, March 2013Slide14
14
Au
Nanopillar
Array
Geometry
10 nm
30 nm
80°
W.S. Graves, MIT, March 2013Slide15
110 nm wide Au lines at 500 nm pitch 18 nm wide Au lines at 100 nm pitch
Nano Stripes
Note similarity of stripes to wavefronts.
Emittance exchange
demagnifies
pattern and transforms periodicity from ‘x’ to time.
15
SEMs of tips fabricated by R. Hobbs, MIT Nano Structures Lab
W.S. Graves, MIT, March 2013Slide16
16Currenttime
Cathode stripes
Laser spot
Current
time
x
y
Laser spot
Cathode spot size maps to pulse length
EEX
EEX
Number cathode stripes illuminated sets number of
micropulses
after EEX
Small laser spot makes short pulse
Large laser spot makes long pulse
W.S. Graves, MIT, March 2013Slide17
17t
x
y
y
x
t
Tune resonant wavelength with quadrupole
Longer wavelength
EEX
EEX
Weak quad images cathode at low demagnification
Strong quad images cathode at large demagnification
Current
Current
Shorter wavelength
W.S. Graves, MIT, March 2013Slide18
5M particles tracked, similar to full bunch chargeBunching at 13.5 nm
z-
d slope due to imperfect matching (correctable)
10
fs
bunch length
Simulation of 300x40
Tip Array through EEX
W.S. Graves, MIT, March 2013Slide19
19Tests of coherent ICS code
Simulations by NIU grad student Ivan Viti using
Lienard-Wiechert solver written by Alex Sell of MIT. Work in progress.Examine radiation from many nanobunchesSimulations are designed to study coherent radiation opening angle, bandwidth, and electron beam size effects.
Emittance is set unrealistically small to remove its effect. Purpose is to explore radiation properties.
W.S. Graves, MIT, March 2013Slide20
20Radiation from many nanobunches
Bandwidth tends to 1/(number bunches) for large numbers of bunchesOpening angle tends to
W.S. Graves, MIT, March 2013Slide21
2113.5 nm photons/shotRMS electron beam size (microns)
Bunching factor = 0.2
13.5 nm flux
vs
transverse
ebeam
size
W.S. Graves, MIT, March 2013Slide22
2213.5 nm GENESIS Simulations*Undulator period = ½ laser wavelength
Laser parameters
Units
Pulse energy
100
mJ
Pulse length
1
ps
Waist
size w0
7
micron
Pulse shape
flattop
A0 at waist
0.3
Wavelength
1.0
micron
Undulator period*
0.5
micron
Electron parameters
Units
Peak current
100
A
Pulse length
45
fs
Norm. emittance
0.01
micron
Energy
1.7
MeV
RMS energy spread
0.1
%
Bunching factor
0.2
Beta function at IP
1
mm
.01 micron emittance is consistent with 150 MV/m cathode field and 5
pC
45
fs
bunch length contains 1000 periods at 13.5 nm
Assume uniform bunching factor of 0.2 (not yet a start to end simulation)
FEL rho parameter = .0012
FEL gain length = 20 microns
W.S. Graves, MIT, March 2013Slide23
2313.5 nm FEL Simulations
Power
growth over 300 periodsBunching factor
280 kW peak
14
nJ
or 10
9
photons/pulse
in 0.15% bandwidth
Emittance requirement during exponential gain
=50
Very different ratio than cm period undulator
W.S. Graves, MIT, March 2013Slide24
24
280 kW peak
5
0
fs
0.15% BW
Spectrum
Power
vs
time
Radiation RMS size during interaction
13.5 nm Power and Spectrum Simulations
Optical guiding allows larger
ebeam
size
W.S. Graves, MIT, March 2013Slide25
25GENESIS Simulated 13.5 nm Performance13.5 nm Output
1 kHz rep rate
Units
Photons
per pulse
10
9
Pulse energy
14
nJ
Average
flux*
10
12
photons/s
Bandwidth
(FWHM)
0.1
%
Average
brilliance*
5
x
10
14
photons
/(s
.1
% mm
2
mrad
2
)
Peak brilliance
3
x
10
25
photons/(s .1% mm
2
mrad
2
)
Opening angle
0.8
mrad
Source size
1.5
m
m
Pulse length
50
fs
Repetition rate
1
kHz
Avg
current
5
nA
*
Avg
values rise
5 orders of magnitude
for SRF linac
Simulations use aggressive but achievable parameters
Complete start-to-end simulations in development
W.S. Graves, MIT, March 2013Slide26
26SummaryNanobunched beam and ICS heading toward tabletop x-ray laserDevelop accelerator technology specifically for this application
SRF at 4K with low heat load and modular constructionkHz rep rate x-band gun & linac using only 6 MW total RF power
Inexpensive to test and developCompact highly stable RF power supplies are commercially available
Nanoengineered cathodes likely to have big impact on high brightness beams
$3M
~$15M
W.S. Graves, MIT, March 2013