3.5

Department of Advanced
Accelerator Technologies
The Department of Advanced Accelerator Technologies (AAT)
has been promoting R&D activities in selected topics according to the KEK’s research strategy. There was reorganization
within AAT in FY2016. In FY2015, three project offices, theLinear Collider project office, the ERL project office, and theDetector Technology project office used to be in operation.
In FY2016, however, technological developments of the accelerator and detector of the linear collider were carried out inthe framework of the IPNS, ACCL, and ARL, instead of AAT, toenable this R&D work to be more effectively coordinated overthe institute and laboratories. The Advanced Laser Science
Project, which was supported by AAT up to FY2015, is nowa project in ACCL. In FY2016, there also was a revision in the30

2016 a t K E K A n n u a l R e p o r t

strategy of photon science in KEK to follow the “KEK Project
Implementation Plan (KEK-PIP)” [1], which was intended todrive projects described in the “KEK Roadmap 2013” [2]. The
research activity in the ERL (Energy Recovery Linac) project
office in FY2016 was focused on making the ERL technology
industrially applicable.

Reformation of ILC promotion activity
KEK reformed the organization of the International Linear Collider (ILC) project in April 2016. ILC is a next generation highenergy physics collider where electrons and positrons will be
accelerated in a linear tunnel from opposite directions and will
collide with unprecedented energy to explore laws of physics

at the highest energy. The technical developments and design works have been carried out within a worldwide framework. The International Committee for Future Accelerators(ICFA) set up the Linear Collider Board (LCB) and the LinearCollider Collaboration (LCC) to promote linear collider projects
worldwide. The Japanese high energy physics community
released a statement in October 2012 to express its intention
to host ILC in Japan as a global project. This proposal was
welcomed by the worldwide high energy physics community
as shown, for example, in the statements by ICFA on ILC [3].
In Japan, the Ministry of Education, Culture, Sports, Science,and Technology (MEXT) set up the ILC Advisory Panel in May
2014, and various issues related to hosting ILC in Japan havebeen investigated by the panel.
At KEK, R&D for the ILC project had been carried out under the linear collider project office at AAT for a long time. The
planning office for the ILC was established in February 2014.
Since the roles of the two offices somewhat overlapped, andthe ILC project was entering an important phase toward its
realization, KEK decided to restructure the framework for thepromotion and R&D activities of the ILC project. On the one
hand, all project promotion efforts would be set by the ILC
planning office headed by the KEK director general. On theother hand, R&D of accelerator and detector technologies
and ILC design works would be carried out within the framework of the institutes and laboratories of KEK, namely, IPNS,ACCL, and ARL. Since coordination is needed for these technical works, an ILC R&D project leader was assigned to leadthe joint teams working on the ILC technical developments. In
this annual report, accelerator and detector developments for
ILC are included separately in each institute/laboratory report.

ERL Project Office
The ERL project office was established in 2006 to progress
R&D of the ERL accelerator technology from the viewpointof a future light source. With this future light source, twooutstanding features such as coherent light and femtosecond
short pulse are important for material science studies. To
realize these features, low emittance of less than 1 mm∙mrad,and a short electron bunch width of ~100 fs of the electron
beam should be milestones of the R&D activities.
In FY2015, a beam current of 1 mA was successfullyachieved at Compact ERL (cERL), and the beam normalized emittance at 7.7 pC/bunch was demonstrated as
1.5 mm∙mrad (horizontal) and 1.1 mm∙mrad (vertical). Furthermore, the bunch compression was achieved as ~150 fs
using a combination of off-crest acceleration in the main linac
and non-zero longitudinal dispersion (R56), and also by correction of the second order energy dependent path length

by means of sextuple magnets.
In FY2016, however, the synchrotron radiation community
decided to choose the 3 GeV storage ring as the light source
instead of the 3 GeV ERL, because there was still much R&D
to be done to realize the 3 GeV ERL light source. The KEK
roadmap was revised accordingly. Subsequently, R&D ofcERL as a future synchrotron radiation facility was stopped.
On the other hand, the technologies developed with the cERL
will have industrial applications such as an Extreme Ultraviolet-Free Electron Laser (EUV-FEL) light source, a security
system for nuclear material based on gamma ray production
by means of laser Compton scattering, and a high resolution
medical X-ray imaging system. In KEK-PIP, the “Industrial
application of ERL technology” is listed as one of the projects
conducted using the general funds of KEK with efforts being
made to obtain external funding. In an industrial setting, it ismuch more important to establish low emittance operation(~1 mm∙mrad) at a high bunch charge (60 pC/bunch).
At the end of FY2016 (March 2017), KEK operated cERL
to demonstrate this low emittance operation. Subsequently,
the normalized emittance was demonstrated as 2.4 mm∙mrad(horizontal) and 1.4 mm∙mrad (vertical) with 40 pC/bunch.
Figure 1 shows the experimental emittance data using theslit scanning method. The obtained value does not completely coincide with the expected value; nevertheless, theseefforts are important to realize the industrial applicability ofERL technology.

Detector Technology Project Office
The KEK Detector Technology Project (KEKDTP) office isnow focusing on six R&D projects to enhance the level ofadvanced detector technologies at KEK, to establish it as aworld leading accelerator laboratory.
In FY2016, the Silicon-On-Insulator (SOI) pixel project
moved to the stage of practical use. The SOI photon imaging array sensor (SOPHIAS) detector developed for X-ray
imaging by the RIKEN group was used in several beam lines
at SPring-8 facility. The X-ray SOI pixel (XRPIX) detector
developed for X-ray astronomy by a Kyoto University group
achieved the highest ever energy resolution of 400 eV for an
X-ray with an energy of 13.95 keV by lowering the noise levelto around 10 electrons at a temperature of −60 °C.
To use the SOI detector in high energy particle accelerator experiments, radiation hardness is an important factor.
The SOI project group has succeeded in enhancing radiation hardness by introducing double SOI wafer technology,
with the remaining issue of drain current decrease of PMOS
(P-type metal-oxide semiconductor) transistor, as indicatedin the left plot of Fig. 2. Further analysis identified that the3 L a b o r a to r y A c t i v i t i e s31

Fig. 1. Emittance measurement experimental data at the condition of 40 pC/bunch by using slit scanning method on (a) horizontal direction and (b) vertical direction, respectively.

Fig. 2. Drain current decrease by irradiation. (Left) normal LDD dose case. (Right) six times higher LDD dosecase. The effect of the irradiation is very much reduced.

dose of LDD (Lightly Doped Drain) region of the transistor isa key parameter for the radiation effect, and it was successfully demonstrated that the six times higher LDD dose could
recover the drain current, as shown in the right plot of Fig. 2.
The R&D project in fundamental technologies to realizea large Liquid Argon Time Projection Chamber (LArTPC) detector has made good progress with the development of an
ionized charge signal readout system including a high voltage system and argon purification system. In FY2016, theproject group successfully developed charge signal readout
electronics (analog amplifier application-specific integrated322016 a t K E K A n n u a l R e p o r t

circuit, ASIC), which can be operated at a cold temperature.
The group plans to verify the functionality of the signal readout
electronics at a large scale engineering prototyping detector(CERN WA105). It will be commissioned shortly in the context
of the worldwide cooperative R&D effort. A high voltage system is also being intensively developed for extremely long drift
distance using a small setup at KEK as well as by simulation
to understand the electric field formation in the Time Projection Chamber (TPC).
The goal of the CO2 Cooling project is to develop coolingsystems for advanced detectors using two phase CO2 as theFig. 3. The signal from Nb/Al-STJ to the SOI amplifier (upper) and the amplified output (lower).

coolant. This will realize more efficient and stable cooling withless material inside the detectors. At KEK, a unique systemusing a gas compressor for circulation of the CO2 coolant isbeing developed. After completion of a proof-of-principle
system, the group developed an automatic pressure control
system, which precisely stabilized the temperature of twophase CO2 for detector cooling. A CO2 dryer system using amolecular sieve was also added to the cooling system.
In FY2016, the Superconducting Detector (SCD) project
developed a cryogenic detector system composed of a Nb/
Al Superconducting Tunneling Junction (STJ) sensor with
an amplifier circuit formed using fully depleted SOI technology. The system was cooled down to 0.3 K, and visible lightpulses with a wavelength of 465 nm were irradiated onto STJ.
Figure 3 shows the pulse signals obtained. The group successfully detected the amplified STJ signals at the cryogenictemperature. Furthermore, it succeeded in reducing the leakage current in the STJ made of Hf down to 8% of the previous
sensor by depositing a thin Al layer on the HfO insulator, anddetecting the pulse signals of visible light.
One of the tasks for the detector technology project isto promote its achievements toward users outside the fieldsof particle and nuclear physics of which development of theuser-friendly Micro Pattern Gas Detector (MPGD) system is animportant goal. In FY2016, the group developed the systemwith new DAQ software in which all service connections wereintegrated conveniently at one side. Gas tightness and circulation inside the chamber were also improved significantlyfor easier operation. Simpler and easier DAQ software wasdeveloped with several user-friendly options. The MPGD systems using Gas Electron Multiplier (GEM) foil for a neutron de-tector are used in several beam lines in the Materials and Life
Science Experimental Facility (MLF) of J-PARC, at Hokkaido
University and Kyoto University, as well as at the Rutherford
Appleton Laboratory in the UK because of its reliability andhigh performance in spatial and timing resolution.

References[1] KEK Project Implementation Plan (KEK-PIP), http://www.kek.jp/en/About/Roadmap/.
[2] KEK’s Roadmap (5-Year Plan) 2013, http://www.kek.jp/en/About/Roadmap/.
[3] ICFA statements, http://icfa.fnal.gov/wp-content/uploads/ICFA_Statement.pdf (February 2014); http://icfa.fnal.gov/wp-content/uploads/ICFA_Statement_20140706.pdf (July 2014).

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