w.s. graves mit presented at high brightness electron beams workshop san juan, pr march, 2013
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High Brilliance X-rays from Compact Sources. W.S. Graves MIT Presented at High Brightness Electron Beams Workshop San Juan, PR March, 2013. W.S. Graves, MIT, March 2013. People. MIT - PowerPoint PPT PresentationTRANSCRIPT
W.S. Graves MIT
Presented at High Brightness Electron Beams Workshop
San Juan, PR
March, 2013
High Brilliance X-rays from Compact Sources
1W.S. Graves, MIT, March 2013
2
People
MITK. 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
NIUD. 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-DMR
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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 2013
RF GUN
LINAC
EMITTANCE 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 optics
X-band ICS source with 1 kHz rep rate
Equipment cost $3MX-rays 0.1 – 12 keV
W.S. Graves, MIT, March 2013
RF GUN LINAC
EMITTANCE EXCHANGE LINE
ICS X-RAY GEN.
ELECTRONSPECTROMETER
X-band ICS source with 1 kHz rep rate
W.S. Graves, MIT, March 2013
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Simulated 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
Structures by S. Tantawi and V. Dolgashev of SLAC
W.S. Graves, MIT, March 2013
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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 2013
Niowave Inc SRF gun
Jefferson Lab SRF linac
Emittance exchange beamline
ICS x-ray generator
High Repetition Rate ICS with SRF Linac
Equipment cost $15MX-rays 0.1 – 12 keV
W.S. Graves, MIT, March 2013
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 Nb3SN• Evaluate beam dynamics for highest brightness.• Develop digital LLRF system for cavity / module testing • Evaluate options for a low cost versatile cryostat
RF systemSpoke cavity Elliptical cavity
Nb3Sn
CLS concept Single cell
Beam dynamics
Superradiant X-rays via ICS
Steps
1. Emit array of electron beamlets from cathode 2D array of nanotips.
2. Accelerate and manipulate correlations of beamlet array.
3. Perform emittance exchange (EEX) to swap transverse beamlet spacing into
longitudinal dimension. Arrange dynamics to give desired period.
4. 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 N2
N electrons
W.S. Graves, MIT, March 2013
Beamlets from tips
x
y
x
x’
t
Current
t
Current
x
x’
t
Energy
Acceleration
EEX
t
Energy
x
yBunched beam emits coherent ICS
Emittance Exchange (EEX)
W.S. Graves, MIT, March 2013
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Layout for Super-radiant ICS
RF gun Linac
Emittance Exchange (EEX)
RF deflectorQuads
Dipoles
Nanocathode
X-rays
IR laser or THz
ebeam dump
ICS
W.S. Graves, MIT, March 2013
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Nanostructured Cathodes
W.S. Graves, MIT, March 2013
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Au Nanopillar Array Geometry10 nm
30 nm
80°
W.S. Graves, MIT, March 2013
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.
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SEMs of tips fabricated by R. Hobbs, MIT Nano Structures Lab
W.S. Graves, MIT, March 2013
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Current
time
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 2013
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t
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 2013
5M particles tracked, similar to full bunch charge
Bunching 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 2013
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Tests of coherent ICS codeSimulations by NIU grad student Ivan Viti using Lienard-Wiechert solver written by Alex Sell of MIT. Work in progress.
Examine radiation from many nanobunches
Simulations 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 2013
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Radiation from many nanobunchesBandwidth tends to 1/(number bunches) for large numbers of bunches
Opening angle tends to 1wN
W.S. Graves, MIT, March 2013
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13.5
nm
pho
tons
/sho
t
RMS electron beam size (microns)
Bunching factor = 0.2
13.5 nm flux vs transverse ebeam size
W.S. Graves, MIT, March 2013
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13.5 nm GENESIS Simulations
*Undulator period = ½ laser wavelength
Laser parameters UnitsPulse energy 100 mJPulse length 1 psWaist size w0 7 micronPulse shape flattopA0 at waist 0.3Wavelength 1.0 micronUndulator period* 0.5 micron
Electron parameters UnitsPeak current 100 APulse length 45 fsNorm. emittance 0.01 micronEnergy 1.7 MeVRMS energy spread 0.1 %Bunching factor 0.2Beta 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 2013
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13.5 nm FEL Simulations
Power growth over 300 periods
Bunching factor
280 kW peak
• 14 nJ or 109 photons/pulse in 0.15% bandwidth
• Emittance requirement during exponential gain 4N x
gL b p
=50 Very different ratio than cm period undulator
W.S. Graves, MIT, March 2013
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280 kW peak
50 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 2013
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GENESIS Simulated 13.5 nm Performance13.5 nm Output 1 kHz
rep rateUnits
Photons per pulse 109 Pulse energy 14 nJAverage flux* 1012 photons/sBandwidth (FWHM) 0.1 %Average brilliance* 5x1014 photons/(s .1% mm2mrad2)Peak brilliance 3x1025 photons/(s .1% mm2mrad2)Opening angle 0.8 mradSource size 1.5 mmPulse length 50 fsRepetition rate 1 kHzAvg 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 2013
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Summary• Nanobunched beam and ICS heading toward tabletop x-ray laser
• Develop accelerator technology specifically for this application
• SRF at 4K with low heat load and modular construction
• kHz rep rate x-band gun & linac using only 6 MW total RF power
• Inexpensive to test and develop
• Compact 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