X-band Test
Accelerator &
New Initiatives
GARD Review @ SLAC
Cecile Limborg, Chris Adolphsen, Tor Raubenheimer
March 11, 2013
X-Band Test Accelerator (XTA)
Generation of high brightness beams is a key accelerator
technology
Goals for the XTA:
• High brightness injector (beams accelerated to 100 MeV)
- Study an approach to very high brightness beams
• Compact X-band linac
- Study operational issues (timing, alignment, …)
• Use facility to support new initiatives
Construct XTA leveraging existing infrastructure
• Installed in NLCTA enclosure, uses control room and rf sources
• Based on LCLS design; uses LCLS high-level controls & applications
Based on 20 years of X-band rf development
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NLCTA Facility
50 meter shielded enclosure containing NLCTA and XTA.
Facility has 4 X-band rf sources, 1 S-band rf gun, 1 X-band rf
gun, 3 laser systems and supports a variety of acceleration and
beam physics R&D activities
~50 meters
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X-band Test Accelerator
Compact (~6 meters) Injector Beamline
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High Brightness Electron Sources
State-of-the-art
Groups around the world are pushing on e- source brightness
• Peak and average brightness
• Focus on peak brightness largely driven by next generation
radiation sources: SwissFEL, PALFEL, MARIE, MEGA-ray, …
Two separate issues:
transverse and
longitudinal phase space
• LCLS S-band gun
From Aug, 2008
ICFA BD Newsletter
pushes both
• Cathodes will likely
yield further
improvements but gun is still limitation
Recently, strong focus on lower charge bunches Q << 1 nC
• Naturally matched to higher frequency rf guns
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High Brightness Electron Guns
What are the next Steps?
LCLS S-band rf injector performs extremely well
How to improve peak brightness?
• Many incremental improvements (better field comp, load lock, …)
• No concrete ideas for factor of 2 much less a factor of 10
What about different approaches?
• DC photo-injector (reduced space charge and emittance from gun)
• Low rf frequency gun (reduced field tolerances and peak current)
• High gradient rf gun (reduced space charge and bunch length)
X-band rf gun offers factor of ~8 improvement in brightness (in
simulation) but will be challenging to implement
• Broad synergies with other programs across SLAC
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RF Gun Emittance and Brightness Scaling
Benefits of shorter Wavelength
Simple scalings of emittance and brightness suggest: B ~ 1/l2
and ge ~ l where
Q ~ l and sz ~ l
From J. Rosenzweig modified by Feng Zhou for LCLS
Many applications
are optimizing toward
lower charge beams
Emittance vs. Charge
• LCLS was designed
for 1 nC and typically
operates at 150 pC
• Natural for high
rf frequency gun
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Mark-1 X-band RF Gun
Joint SLAC-LLNL Collaboration
First X-band gun design was built and tested at SLAC in mid-2000’s
Mark-1 incorporates
lessons from LCLS
• Racetrack coupler;
increased mode
separation; elliptical
iris shape
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RF Gun Simulation Studies
X-band gun 8x higher Brightness
ASTRA simulations results (after multi-parameter optimization)
Q [pC]
250
250
20
10
10
1
1
X-Band Test Acc. (Simulations)
LCLS (Simulations and measurements)
ex,95%
[mm-mrad]
0.25
0.28
0.075
0.076
0.118
0.016
0.036
ex,95%
[mm-mrad]
sl [mm]
Bpeak=
Q/sl/e2/1e3
0.40
0.15
0.620
0.220
2.52
4.04
sl [mm] Bpeak=
Q/sl/e2/1e3
0.228
17.5
0.184
17.3
0.109
32.6
0.055
31.5
0.042
17.1
0.080
48.8
0.025
30.9
High ERF,cathode to beat surface self-field
and reach smaller rlaser and thus smaller e┴
High dEz / dt for short bunches
rlaser 
Qe o
 ERF ,cathode
Cecile Limborg
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XTA Beamline Diagnostics
The XTA was built with extensive diagnostics similar to LCLS
• Beam will be accelerated to over 70 MeV to reduce space charge
• Includes 3 YAG and 3 OTR screens, large angle spectrometer,
transverse deflecting cavity, rf BPMs to align structure
Goal is to fully characterize the brightness of the X-band injector
8 MeV
Gun
200 MV/m
Solenoid
YAG/
FC
70 ~ 100 MeV
T105
~100 MV/m
TD11 (TCAV)
3MV
FC
YAG/OTR
FC
Cavity BPMs
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OTR
YAG/OTR
Spectrometer
4 Quadrupoles
with BPMs
Cecile Limborg
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XTA Hardware
Project started in 2011
TCAV
Starting with Mark-0
rf gun and old T105
accelerator structure
Mark-1
rf gun
View from dump
• Mark-1 is fabricated
• New T105 is almost
ready
YAG,
Laser Injection chamber
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Linac
Cecile Limborg
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XTA Commissioning Results
As of end of February, 2013
XTA routinely operated with charges up to 30-40 pC
Energy at ~8 MeV from gun and ~70 MeV out of linac
Transverse deflector installed and commissioned
Bunch lengths measured to be 250 fs rms for ~20pC, in agreement with
simulations
Tuning to small emittances is sensitive to strong jitter and low OTR light level
• Laser noise reduced from 350-500 fs rms down to 70 fs rms
• Contribution modulator HVPS measured ~175ppm rms (ie dF~ 0.6 deg rms,
•
dV/V ~3e-4); Contribution from LLRF still under investigation
OTR replaced by combined dual YAG/OTR
Low charge studies
• QE relatively low; increased by lengthening laser pulse
• Plans to measure thermal emittance and maybe laser cleaning
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Cecile Limborg
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Future XTA Commissioning Timeline
Complete commissioning in FY2013
Goal: demonstrate injector performance by end of 2013
Continue with Mark-0 rf gun through August, 2013
• Measure cathode properties: QE and thermal emittance; try
•
•
laser cleaning
Work on improving jitter sources: LLRF and modulators
Optimize slice emittance and bunch length
Install Mark-1 rf gun and new T105 in August down
• Measure cathode properties: QE and thermal emittance
• Optimize slice emittance and bunch length
Program is interlaced with other NLCTA efforts
• Operate a shift per day roughly 50% of time
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New Initiatives with X-band RF Gun
Inverse Compton Source and Ultra-fast Electron Diffraction
The high brightness source will enable many future programs
•
•
•
•
Improved beams for E-163 or Echo-75 at the NLCTA or LCLS or FACET
MEGA-ray experiments at LLNL (or SLAC)
An Inverse Compton Source at XTA
An Ultra-fast Electron Diffraction source at XTA
Ultra-fast Electron Diffraction
• Large dEz / dt in gun will allow large velocity compression of bunch
• X-Band technology (gun + compressor) promises
REGAE @ DESY
- 1pC,
few fs rms
with divergence < 0.5 mrad
- 8pC, 20 fs rms
Siwick @ McGill
• 2-3 orders of magnitude
better than present
technology
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Why Inverse Compton Scattering (ICS)?
Narrow bandwidth and high spectral brilliance
Bremstrahlung
Channeling
Compton
Undulator
Eg ~ 0 – Eb
Eg ~ 100g3/2
Eg ~ 4g2
Eg ~ 2x10-4g2
100% BW
10% BW
1~0.1% BW
0.1% BW
High flux
Moderate flux
Low flux
Moderate flux
Narrow spectral bandwidth key to improving S/N
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Inverse Compton Source Characteristics
 Two features of ICS source make it very powerful
» Easy variation of photon energy (pulse-by-pulse, if desired)
» Scan resonances, contrast enhahncement, etc.
» Narrow bandwidth with highly correlated Eg and q
» Core spectral width is ~0.1%  improved S/N and reduced dose
 Wide set of possible applications ranging from medical (oncology &
imaging), industrial (spectroscopy & imaging), science and security
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Inverse Compton Scattering Sources
 Two primary approaches to beam generation:
» Ring-based with high rep rate but larger emittance
» Linac-based with brighter beams
• SCRF linac has benefits of both
ThomX ICS design
» Very different technical challenges
 Brightness of source depends on
electron source brightness
 For high energy g’s a linac is
likely to provide a compact
cost-effective path
 Many applications are dose limited
and don’t require huge fluxes
MIT ICS design
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Some Existing or Planned ICS Facilities
Facility
PLEIADES
(LLNL)
AIST LCS
(Japan)
LUCX
(Quantum Beam)
*NERL
(UTNL, Tokyo)
*MIT
*MXI Systems
(Tennessee)
*PLASMONX
(SPARC, Italy)
Lyncean Tech
(California)
*NESTOR
(Kharkov IPT)
*ThomX
(France)
Type
X-ray E
(keV)
Rep. Rate
(Hz)
Bunches/
pulse
Source size†
(mm rms)
Linac
10-100
10
1
10
108
Linac
10-40
10
1-100
40
107-109
SC linac
~5-50
12.5 Hz
Linac
10-80
10
SC linac
3-30
108
1
Linac
8-100
10
1
Linac
20-380
10
1
100
(future 8x103)
104
10% BW
4-10% BW
8
??
75 x 60
109-2x1010 few % BW
2.4
1014
25% BW
(>1015 future ERL, FEL?)
5-10
ring
7-35
65 x 106
1
30-50
ring
~6-900
20-700 x 106
1
35
ring
50-90
21 x 106
1
40-70
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Spectral flux (approx.)
(ph/s/% BW)
1010
10% BW
109
~10% BW
(future FEL?)
109
3-4% BW
(future 5 x 1011)
??
1013
25% BW
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Scientific Opportunities with ICS
Examples of Applications
Developing a compact source with modest flux at high
photon energy will complement DOE SR light sources
• It would provide a relatively compact (room sized) system at a
moderate cost but with high performance needed for research
http://www.emsl.pnnl.gov/root/publications/docs/compact_xray.pdf
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Anne Sakdinawat, Yijin Liu, Mike Toney
Impact (Beyond Office of Science)
Example: Understanding lifecycle of rare earth elements
New Critical Materials Hub
recently created at DOE EERE
• “… challenges in critical materials,
including mineral processing,
manufacture, substitution, efficient use, and end-of-life recycling; …”
Rare earth K-shell binding energies range from 4 to 65 keV
• A moderate energy ICS would penetrate typical core samples
An ICS-based microscopy system could be instrumental as an
experimental tool in the analysis of the morphology and
composition of rare earth materials throughout their life cycle.
2013 General Accelerator R&D Review
Anne Sakdinawat, Yijin Liu, Mike Toney
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Impact (Beyond Office of Science)
Example: Understanding Carbon Sequestration and Storage
Goal: understand the flow and storage of hydrocarbons
• Determine generative potential
and pay type (i.e., gas vs. oil) to
catalog the organic resources
This type of investigation needs to be
carried out at different length scales
(resolution from ~mm to micron-level
to 30 nanometers)
Desired features of the source:
1. High beam energy (for penetrating large specimens)
2. Brightness (for desired resolution)
3. Energy tunability (in order to retrieve elemental distribution)
Anne Sakdinawat, Yijin Liu, Mike Toney
2013 General Accelerator R&D Review
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Impact (Beyond Office of Science)
Example: Microbeam Radiation Therapy (MRT)
Goal: Radiosurgery with reduced impact to surrounding tissue
• Microbeam Radiation Therapy (MRT) Serduc, et al., PLoS One. 2010 Feb 3;5(2): e9028
has been studied at BNL and ESRF:
Dilmanian, et al., Natl Acad Sci 2006
Jun 20;103(25):9709-14; Serduc, et al.,
PLoS One. 2010 Feb 3;5(2): e9028.
• “Growing experimental evidence is
showing remarkable tolerance of brain
and spinal cord to irradiation with
microbeam arrays delivering doses
up to 400 Gy with a beam width up
to 0.7 mm” (Neurol Res. 2011 Oct;33(8):825-31)
• Rat studies performed with 100 ~ 350 keV
photons; need ~MeV x-rays for people.
• ICS would be a possible, compact source
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Inverse Compton Experiment at X-band (ICE-X)
Goal: high brightness gamma beam for precision experiments
• Optimizing the system with photon science/medical school experts
Flux of >107 g/s of 0.1 ~ 2 MeV photons with B >109 (g/s/mm2/mrad2/0.1%)
• Narrow bandwidth achieved with high brightness beam and long-pulse
laser interaction  reasonable beam and laser parameters
- Commercially available 10 Hz, 3J, 3ns, YAG pump laser with 30 um laser waist
-
(I0 ~ 1x1014 W/cm2)
5 cm e- beta, 250 pC, ge < 0.4 mm-mrad
• Stable beam and laser  simpler operating conditions
Upgrades to increase flux & brightness by >1000
• Upgrade laser to 120 Hz
• Operate with multibunch train (30 bunches / rf pulse)
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Inverse Compton Experiment at X-band (ICE-X)
Build on the XTA
Build on the X-band Test Area (100 MeV X-band photo-injector)
• Build experimental hutch and borrow interaction laser
• Lengthen accelerator to generate 235 MeV e-  2 MeV g’s
Support for hutch and experiments from external programs
• Start with staged approach to illustrate feasibility
NLCTA Enclosure
Echo-75 beamline
XTA/ICS beamline
2013 General Accelerator R&D Review
NLCTA
Dump
Experimental hutch
(upgrade for Echo
beamline as well)
Staged Construction of ICE-X
ICE-Lite (FY2014 – FY2015)
Start from 100 MeV XTA configuration
•
•
•
•
•
•
Complete XTA injector demonstration – October, 2013
Borrow YAG pump laser system (3J, 3ns, 10 Hz at 1 um)
Add IR and laser to generate g’s – March, 2014
Start construction of g-hutch – July, 2014
Operate ICS at 50 to 200 keV – Sept, 2014
Upgrade with multibunch and laser rep. rate for 1000x flux
and brightness – FY2015
Upgrade linac to 235 MeV  ICE-X
• Install old T105 and two additional T55 structures
• Double klystrons in Station 2
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Summary
Quality and impact of research over the last four years:
• Working on new e- source with order-of-magnitude improvement in brightness
• XTA has gone from concept to beamline in <2 years and commissioning has begun
Expected deliverables over the next 5-10 years:
• Demonstration of a new high brightness electron source
- Key accelerator technology
• Utilization of electron source to demonstrate an optimized high energy, high brightness ICS
- Broad potential impact in medicine, industry, security as well as science
Benefits of additional investments:
• Need 1.5 M$/yr in FY14 and FY15 to complete modification to ICS
Impacts of reduced investment:
• Loss of opportunity to demonstrate HEP contribution to accelerator technology
Why at SLAC?
• Unique environment with required accelerator, laser and photon science expertise
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