2010/03/16
RIKEN Harima InstituteResearch Promotion Division

Report on Advanced Electron Beam Physics Laboratory Periodical Review
Laboratory Leader: Chief Scientist, SHINTAKE, Tsumoru (Ph. D)
Date: Tuesday, January 19th, 2010
Venue: RIKEN Harima Institute (SPring-8)
Reviewers: Prof. Kwang-Je Kim (Advanced Photon Source, Argonne National Laboratory)
Prof. Marie Emmanuelle Couprie (Synchrotron SOLEIL)
Prof. Katsunobu Oide (KEK)Prof. Hiroyuki Hama (Tohoku University)
Prof. Akira Noda (Kyoto University)

Abstract of the reports:
1. General comments
The Chief Scientist of the AEBPL, Dr. Shintake, is a first rate accelerator scientist with high level oftechnical skill with unique visions in broad areas, able to find original solutions for challenging problems
in accelerator physics and technology. He has built up a research group consisting of highly talented
members with diverse expertises covering all AEBPL activities. He has also worked closely withJapanese industry to realize his novel conception to actual accelerator construction. The culmination ofthis effort is the success of the SCSS Test Accelerator, which serves as the model for the SPring-8 XFEL
currently under construction.

This Committee congratulates Dr. Shintake and his staff for theremarkable success, and suggests that RIKEN ensure that the creative activity of this unique group becontinued.

1.1 Research objectives (novelty, scientific significance, etc.)
Entering relatively late in the international scene of x-ray free electron laser R&D, the AEBPL set anambitious goal of constructing an novel accelerator-XFEL system which is “compact” with a schedule not
too far behind the LCLS at SLAC.

It takes a great depth in basic and practical knowledge in accelerator

science and technology as well as creative mind to succeed in such endeavor.

The success in 2007 of

the low energy test-system SCSS Test Accelerator demonstrates the soundness of the AEBPL approachand is the basis of the SPring-8 XFEL construction.

1.2 Research results (originality, scientific significance, social impact, etc.)
The AEBPL R&D accomplishments are many, including:•2-D synchrotron radiation simulator: an easy-to-use program showing radiation emanating from anarbitrarily moving charge by 2-D graphics. The program is freely available from Shintake’s website
1and is highly instructive.
•An injector starting with a thermionic cathode (CeB6 crystal), pulsed 500 kV DC voltage: This is a highly
original approach in view of the fact that all high-brightness electron injectors are based on aphotocathode. The performance is remarkable; it has shown an emittance as small as the best rf gunsin the world with better stability in the beam, the cathode reaching a lifetime of 20,000 hours.
•C-band high-gradient accelerator:

The conception of this iconoclastic approach for high-gradient,choke-mode damped accelerating structures dates back to Shintake’s KEK days.

With the SCSSTest Accelerator, the practical advantage of the C-band for a high-energy acceleration has beenclearly demonstrated, achieving an accelerating gradient of 40 MV/m.

The testing of the choke mode

operation will need to wait until multi-bunch operation.
•LLRF for C-band accelerator:

The C-band LLRF is not simply a rescaled S-band devices but novel

approaches have been made. Such as the single-package klystron with modulator, and the multi-cell
pulse-compression cavity with high rf stability.
•Cavity BPM: This is another conception dating back to the KEK days and proved to be high resolution
and practical. It is copied widely by other accelerator projects such as LCLS and ILC.
•In-vacuum undulator:

Although this is a critical part of the SCSS Test Accelerator, it is beyond thescope of this review since it is a contribution of Kitamura’s laboratory.
•Pioneering experiment on seeding with higher laser harmonics in gas in collaboration with a Frenchgroup:The technique is expected to become an important part of the future short wave generation

with seeded FELs.

The SCSS Test Accelerator test facility has been delivering UVU light to the users since 2007 incollaboration with laser research group in RIKEN, which would have positive impact for VUV sciences aswell as preparing the future x-ray users of the SPring-8 XFEL. The success of the innovative accelerator
ideas employed for the SCSS Test Accelerator system has been noticed worldwide by the accelerator
community and would influence plans for future light source facilities.

The Committee wishes to make the following observations/suggestions•The coherent synchrotron radiation (CSR) is identified as one of the major causes of beam degradationin other XFEL projects such as LCLS. The effect was predicted by simulation and confirmed by adetailed experiment at LCLS. However, the effect was not found at SCSS Test Accelerator, neither bysimulation nor in experiment.
XFEL project.

No provisions are planned against the CSR effects for the SPring-8

The Committee finds this unsettling and suggests that the issue to be revisited. Thiscan begin by exchanging the simulation codes used by the RIKEN and SLAC teams; performing theLCLS simulation with the AEBPL code and the SCSS Test Accelerator/SPring-8 XFEL simulation withthe ELEGANT code used by the LCLS team.
•In the same spirit, the Committee suggests that the beam dynamics through the 8 GeV linac for theSPring-8 XFEL project be reviewed, taking into account the beam loading, misalignments, wake field,
orbit correction strategy, BPM accuracy, etc. Although this may not be the role of AEBPL, the2Committee feels that it is important for the SPring-8 project.

1.3 Management of the laboratory (laboratory member composition, researchers’ interaction, facilities
and equipment, etc.)•The success of SCSS Test Accelerator, a large accelerator system with several innovative but untestedcomponents, was accomplished by the leadership of the CS, the dedicated effort by AEBPL staff, theefforts by industrial partners, and with collaboration from KEK. The Committee also acknowledges therole of the RIKEN management in the oversight of this complex enterprise.
•The CS has established a strong contact with industrial partners in developing innovative ideas topractical devices.

A good working relationship with industry should continue in the future and will berequired, for example, for developing a solid state based Klystron modulator.

The Committee is pleased to find that all members of AEBPL are accomplished scientists in their own
right, with a desirable spread in expertises as follows:•Dr. H. Maesaka: Beam diagnostics, especially the cavity BPM•Dr. T. Inagaki: C-band cavity and the associated rf technology•Dr. K. Togawa: CeB6 Thermionic cathode development with DC voltage•Dr. Y. Otake: Femtosecond synchronization technology, also acts as the deputy manager of the AEBPLInterview meetings with AEBPL staff members showed that they are in general pleased with the workenvironment and proud of their achievement. However, it appears that the duty related to the XFEL
project does not leave much time for further R&D and dissemination of the research results.

TheCommittee recommends that this creative and productive group be given at least a minimum ofopportunities for research and for publishing the research results in international high-standard journals.
This is particularly important for the younger members of the group.

The Committee suggests also thatthe AEBPL takes up the task of training PhD students and postdocs from and outside Japan.

An activity

that can start immediately is regularly scheduled seminars and/or journal clubs devoted to research
topics or scientific news items.

1.4 Future research plan (possibility of cooperation with related fields, etc.)
Several future directions were presented:•Upgrade of thermionic-cathode injector for a higher repetition rate: The upgrade will widen theapplicability of the injector for high average brightness FELs such ARC-EN-CIEL, NLS, XFEL
Oscillator, and possibly ERLs. Two international collaborations were mentioned; Cockcroft Institute inUK, and Argonne National Laboratory in USA.
•Solid state klystron R&D:This area is pursued vigorously by other laboratories. For instance, SOLEIL,

which employs solid state amplifiers for the 352 MHz superconducting cavities, has done a technology
transfer to ELTA.
•Femtosecond timing system capable of resolving a few fs: This is critical for XFEL application in the3pump probe experiment. The Committee recognizes the capability and promise of the AEBPL team inthis important area and strongly recommend this effort to be continued, or even further strengthened,in view of the large impact for the future XFEL application.
•6-D beam profile measurement: This is essential for the proper full characterization of the electron
beam for commissioning as well as for daily monitoring of the electron beam during the user operation.
•Two approaches for seeding to produce harder x-rays, one with the combination of High order
Harmonics generated in Gas (HHG) and High Gain Harmonic Generation (HGHG) in cascade, andone with wavelength compression associated with cascade HGHG: This is important as offering
another route to temporally coherent hard x-rays other than the self-seeding, the X-ray FEL Oscillator,or possibly the Echo-assisted high harmonic generation.
•Topics beyond accelerator physics, such as the phase retrieval issues: This is one of the major issues
on XFEL applications, on which Shintake proposed a new approach recently.

1.5 Overall assessment
The AEBPL is endowed with the highest calibre of accelerator scientists, in originality and capability. The
success of SCSS Test Accelerator is remarkable in view of two major innovations, a thermionic-cathodebased injector for stability and C band accelerating system for compactness.

The SPring-8 XFEL,

when it begins to operate in 2011, will be one of the highest brightness x-ray sources in the world,
together with the LCLS at SLAC and the Euro-XFEL at DESY. Thus the AEBPL completely matches toone of the RIKEN’s missions; “Establish a research infrastructure of the highest standard for theresearch community and provide opportunities for its use.”4