11/8/2010
SLAC X-band RF Development and Commercialization Proposal
Executive Summary:
The SLAC National Accelerator Laboratory (SLAC) proposes a five year program of expanded normal
conducting X-Band (11~12 GHz) RF development and commercialization that is well matched to its core
competencies, its long term programmatic goals, the broader accelerator community’s needs and the
Department of Energy Office of Science (OS) mission to develop accelerator technologies for
institutional and national needs. The program would fill a needed role and implement the most promising
results from the ongoing US High Gradient research program, making them available to the broader
accelerator community. The five year program would culminate with a full technical design for a 500
MeV demonstration X-Band linac that would be constructed using mainly industry-built components
(modulators, klystrons, waveguides and accelerator structures) developed with this program. The linac
would be designed to be compact (high gradient), reliable and capable of delivering low emittance beams
comparable to those used in linacs for X-ray FEL’s and TeV-scale e+/e- linear colliders.
The High Energy Physics, Basic Energy Sciences and other programs within the Office of Science stand
to benefit significantly from this research. SLAC pioneered X-Band technology and is currently providing
it for a number of projects world-wide, including the CERN CLIC R&D program, the LLNL MEGa-ray
gamma-ray source, and RF systems to control the longitudinal phase space at BNL, Trieste, PSI and the
LCLS at SLAC. Many decades ago SLAC very successfully developed the S-band technology which
resulted in its widespread adoption for linear accelerators; this proposal aims to start the same process
with the X-band RF technology. Commercialization of X-Band technology will help maintain US
competitiveness and will drive down costs, opening up new industrial and medical applications for this
technology. Without such a program in the next few years, the center of X-band technology development
will move off-shore.
Normal-conducting RF (NCRF) technology is highly relevant to SLAC and the broader accelerator
community and is complementary to the superconducting RF (SCRF) efforts. Specifically X-Band NCRF,
with its smaller dimensions, higher acceleration gradients and lower cost is important in that:

X-Band technology offers the possibility of higher energy reach for e+e– colliders. X-Band has
been chosen by the CLIC team for the main linac accelerator structures, which in the baseline
configuration are powered from RF generated by a high current drive beam as a two beam
accelerator (TBA). Klystron powered structures are being considered for a staged approach to
achieve the multi-TeV CLIC energy goals in case the TBA technology is delayed or as a low cost
initial stage. CERN has expressed interest in collaborating with SLAC in this staged approach.

X-Band is ideal for a variety of applications. LCLS has shown that an X-ray FEL can operate
with low bunch charge, making X-Band linacs a natural choice for FELs. For example, a linac
that operates at 70 MV/m, at least twice the gradient in any existing or proposed light source,
could be built with existing components and run at power and gradient levels already
demonstrated. Such a compact linac design is critical if the site size is limited, which is generally
true at existing laboratories. Also, X-Band RF technology is generally more energy efficient than
NC S-Band (3 GHz) or C-Band (6 GHz) RF and the cost is expected to be significantly less than
S-band RF and SCRF designs. X-band linacs are also a good choice for a number of other
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SLAC X-band RF Development and Commercialization Proposal
applications: medical (e.g., compact X-ray and hadron sources for cancer therapy) , industrial
(e.g., weld inspection and food sterilization) and national security (e.g., cargo X-ray inspection
and gamma ray generation for detection of fissionable materials).

High power microwave technology is a core competency of SLAC, which has extensive NCRF
experience from the 50 years of operation and improvements to its 3 km long S-Band linac. More
recently, SLAC has become the world leader in the design of X-Band RF power sources, pulse
compression systems, low loss RF transport lines and accelerator structures. It also has an active
X-Band high gradient program that explores the fundamental limits of high gradient accelerator
operation in collaboration with labs worldwide.
SLAC started developing X-Band RF technology twenty years ago for the proposed Next Linear Collider
(NLC). This effort, in which over $100M was spent, culminated in 2004 with the demonstration of a 300
MeV accelerator at SLAC that met the basic NLC linac requirements. While the International Technology
Recommendation Committee acknowledged that an X-band based linear collider was viable, SCRF was
chosen instead in 2004 as the preferred linear collider technology, in part because of its perceived broader
application at that time. Then in 2007, with the adoption of X-Band technology by the CLIC group at
CERN and the establishment of the US High Gradient Program, the overall X-band effort has ramped up
and new collaborations have been formed. CERN is collaborating with SLAC on X-band RF technology
and SLAC is working with most of the S-band linac-based X-ray FEL sources to install X-band RF
systems to achieve optimal bunch compression. More recently, the success at LCLS in using low charge
bunches to generate intense X-ray FEL pulses has generated a broad interest in using X-band linacs as
main drivers for X-ray FEL’s as was evidenced by the recent adoption of X-band RF technology for the
MARIE project, a 50 keV hard X-ray FEL proposed at Los Alamos National Laboratory.
The present state of X-band technology and development needs is summarized as follows:

X-Band RF structure design is well advanced. The US High Gradient collaboration has shown
accelerating gradients well over 100 MV/m and a wide range of X-band accelerator structures
have been developed for single and multi-bunch operation with gradient limits that are generally
above those needed for a cost-optimal design which presently is around 70 MV/m. These
structures can be readily designed to match specific needs, and they can be easily built in
industry. Likewise, waveguide and RF compression systems are well developed, can be
customized (e.g. tradeoff efficiency for compactness), and can be readily built by industry.

RF sources and associated HV supplies (modulators) are less advanced. X-Band klystrons need
improved power handling capability. At present there are no commercial sources for a high power
klystron and it is imperative that tube companies, of which there are only a few, learn to build
such klystrons using the technology already developed at SLAC. In parallel, modulator
companies need to provide units to drive high power tubes. X-Band RF sources are also needed
for applications where lower power, higher pulse rate or higher efficiency is a premium. Some of
these needs are beginning to be addressed in Europe.

It is critical to complete the next stage of X-band component optimization (especially for the
klystrons), commercialize these items and use them to build a demonstration linac capable of low
emittance beam transport. The biggest impediments to a wider adoption of X-Band technology
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SLAC X-band RF Development and Commercialization Proposal
are the lack of an operating X-Band accelerator demonstrating excellent beam parameters and the
lack of commercial X-Band klystrons. Potential users of X-Band technology typically see the
advantages but are unwilling to take the risk of using technology that has not been
commercialized or thoroughly demonstrated. Once the technology becomes more readily
available and its reliability has been demonstrated, it should become much more widely adopted.
At present, the total funding for all high power RF activities at SLAC is approximately $12.5M per year.
This consists of approximately $3M of Accelerator Science funding per year for the SLAC portion of the
US High Gradient collaboration, $2M of Accelerator Development funding for X-Band research, $6M of
ILC money for L-band (1 GHz) RF source development and $1.5M for experimental facility support. At
present, this $12.5M funding supports the core competency in high power RF at SLAC.
The US High Gradient Collaboration is focused on fundamental research on high gradient accelerator
structures and power sources. This ongoing research program has successfully demonstrated accelerator
structures with well over 100 MV/m gradients and will start focusing on novel rf power sources.
However, no program exists to apply the results of this research and reduce them to practice. The SLAC
Accelerator Development program has been examining the limits the current high power X-band tubes
and is considering ways of making them more robust but the program is presently too small to fully
develop and commercialize the technology. Both a development and a commercialization effort are
needed to fully benefit from the ongoing NCRF research.
This proposal is focused on developing and commercializing the most promising results from the research
programs. The proposal requires an increase in the annual funding for the SLAC X-band RF program
(including the research, development and commercialization) from about $6M to approximately $10M
over the next three years and then continuing it at this level for an additional two years. In addition, if the
X-Band development and commercialization is successful, an additional two years of funding at the
$10M per year level will be requested to build and commission a 500 MeV demonstration linac. Thus,
this funding profile allows for five years to design, develop and commercialize X-Band devices and to
build collaborations with possible users of this technology. It also positions us to build a small
demonstration linac that would provide an experience base for those wanting to build higher energy Xband linacs. It is expected that the funding for ILC RF power sources would ramp down considerably
during this period and thus the $10M annual funding would also maintain the US core competency in
high power RF technology while developing viable X-band systems.
The deliverables for the proposed 5-Year X-Band plan are:






Optimized X-band klystron for linear collider and light source applications
Suite of X-band components designed to be cost optimized for linacs up to a few GeV aiming at a
cost per GeV that is less than 25% the present cost
Several high power X-band klystrons and modulators built in industry with technology
transferred from SLAC
Design and cost estimate for a 500 MeV X-band demonstration linac
Comprehensive list of other uses for compact X-band accelerators and associated designs
A realistic cost model for large scale X-Band accelerators
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SLAC X-band RF Development and Commercialization Proposal
Document Outline:
Preface (summarizes document layout)
Table of Contents
Executive summary
1.
Overview (present status and the X-band plan)
a.
Introduction (includes chapter abstract, chapter layout)
b.
Motivation and Commercialization (refer down to Chapter 2, 3)
b.
History of X-band
c.
Present Status of X-band (what exists, who is doing what and where, what
is still needed for successful linac demonstration)
d.
High Gradient Research Status (add how it feeds into X-band R&D and
our plan)
e.
Plan Summary (refer down to Chapters 3, 4, 5)
d.
Goals & Milestones & Risks (include risk if plan is not adopted)
2.
Motivation and Applications
a.
Introduction (includes chapter abstract, chapter layout)
b.
HEP (CLIC, LC)
c.
Light Sources (compact FELs, ERLs, specialty uses)
d.
Industrial/Medical (Compact accelerators for cancer; get a list for
industrial)
3.
R&D and Commercialization
a.
Introduction (includes chapter abstract, chapter layout)
b.
RF Power Supplies and Distribution
c.
Klystrons
d.
Structures
e.
Specialty Devices (X-band guns, linearizers )
f.
Advanced RF Power R&D (evolution of High Gradient program to
advance plan)
g.
Demonstration Linac Design
4.
Expected Results and Benefits
a.
Expected Results (over the 5 year lifetime of the plan)
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SLAC X-band RF Development and Commercialization Proposal
b.
Expected Effect on Applications (applications that may be able to move
forward, e.g. demonstration linac construction)
c.
Risks (involved in carrying out Plan and in not doing the Plan)
5.
Cost & Schedule & Implementation
6.
Conclusions
Bibliography
Appendix A. Expression of Interest, Letters of Support
(brief descriptions of projects expressing interest in X-band, copies of letters of support)
Possible letters and collaborations from potential users
1. CERN – linear collider
2. PSI – BC linearizer & FEL upgrade
3. Trieste – BC linearizer & FEL upgrade
4. LLNL – ICS source
5. ELI-NP Romania – ICS source
6. LANL - XFEL
7. Idaho Accelerator Center – ICS source
8. KVI Netherlands - XFEL
9. UCLA – High brightness injector
10. Shanghai – XFEL ??
11. PAL – XFEL ??
12. Cockcroft – technology and ZFEL
13. Australian Collaboration for Accelerator Science - technology
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