DTP International Review Committee
BONDAR, Alexander (BINP)
ENDO, Akira (Delft University of Technology)
GIBONI, Karl-Ludwig (SJTU)
IKEDA, Hirokazu (ISAS)
KAWAHITO, Shoji (Shizuoka Univ.)
KOHJIRO, Satoshi (AIST)KUBO, Hidetoshi (Kyoto Univ.)
MURAKAMI, Youichi, (KEK, IMSS)OKAMURA, Tetsuji (Tokyo Institute of Technology)
SEKIMOTO, Yutaro (NAOJ)SHIBAMURA, Eido (Waseda Univ.)
TAJIMA, Hiroyasu (Nagoya Univ.)
TAKETANI, Atsushi, (RIKEN)TURCHETTA, Renato (RAL)
2013/12/23

REVIEW REPORT OF KEK DETECTOR TECHNOLOGYPROJECTKEK Detector Technology Project (DTP) was started in 2005 to support horizontal efforts todevelop common key technologies for the advanced sciences in KEK. The DTP is also expected
to diversify its R&D efforts for the benefit of related communities.
The charges of the review committee is• to comment on the motivation and the aim,
• to evaluate the efforts and the achievements so far,• to suggest possible/necessary improvements• to guide proper direction for future
for each project, and• to comment on the selection of the projects• to suggest better organization and operation
for the DTP office.
The committee’s findings and recommendations for DTP office and common issues are
summarized first followed by reports for individual projects.

General	  Findings	
  The committee is impressed by the great progress made by the R&D efforts promoted by the
KEK DTP. The committee applauds that Silicon-On-Insulator (SOI), superconducting detectors(SCD), FPIX, application specific integrated circuit (ASIC), and CO2 cooling are developed withspecific applications in mind. In particular, the SOI project made extensive efforts to broadeninterest in SOI technologies and attract participants outside of the particle physics community,

including members of the astrophysics and photon science communities as well as international
participants from the US, Poland, Italy, Germany, France, Russia and China.
We are pleased that the local and external recognition of the importance of detector
technology has improved by the formation and performance of the DTP division. We areimpressed by the many collaborations in DTP among ASIC, SOI, and SCD, which is certainly
stimulated by being located in the same DTP unit. Especially, the DTP division has createdsynergy by having the SOI and SCD groups share the clean room and measurement facilities.
There are also many collaborations with universities, which demonstrates that the DTP plays animportant role in KEK to function as an inter-university institute.

Concerns	
  and	
  Shortcomings	
  The committee is impressed by the significant progress made by the DTP projects since the
DTP division is formed in 2008. However, we were concerned with general lack of clear goals,
resource management and associated development plans for each project. We understand that the
DTP office supports generic R&D efforts that are not aimed at specific applications, whichmakes it difficult to set clear goals. Unfortunately, the lack of clear goals may be responsible forthe lack of clear development plan in some projects. On the other hand, some projects are mixing
up DTP efforts and efforts for specific applications.
The committee is also concerned with selection and resource allocation procedures of DTP
projects. It appears there is no clear policy for these procedures. The steering committee includes
many project leaders, which creates an appearance of conflict of interests. In addition, thesteering committee may not have sufficient expertise to execute such functions effectively andreliably.
It appears there is no specific plan for technology transfer (and outreach). Usefuldevelopment might not be properly utilized without proper outreach and technology transfers.

Recommendations	  As expressed above, the review committee is concerned both with lack of clear goals for eachproject and with insufficient project management. With a view to improving these aspects, we
make following recommendations:• The DTP office should set up a project selection committee that includes external experts
with clear selection policies. The selection should be based on a critical evaluation of the
expected output, timescale, and resources. The possibility to attract external funding isshould also be considered. One possible form of implementation would be that the DTP
office invites proposals from the community every year, and puts priorities between newproposals and existing projects together with a selection committee.
• The DTP office should work with each project to set objective goals with a total budget
and development schedule. (No need to set yearly budget since we understand it is notpossible.) Project goals should be formulated to be beneficial for possible applications
without too specific to certain applications. Resource allocation (mainly budget) should
be made based on annual project reviews. Each project should be evaluated before
continuing beyond the initial term and budget.

• The DTP office (and/or KEK management) should allocate human resources for outreachand technology transfer. (KEK may take advantage of existing infrastructure for suchactivities.)

Response	
  from	  KEKDTP	  At the initial stage of the DTP startup, we did put significant effort to keep the R&D activities
in DTP generic and independent of any specific actual science projects as much as possible toextract maximum cooperation among the projects including the fields of HEP, NEP, photon
science, neutron science and so forth. We agree some DTP projects might show “lack of cleargoal” because of this initial goal.
DTP is now in the next stage after establishing some of the initial goal such as the local andexternal recognition of the importance of detector technology and should be ready to encourage
the projects to focus on several definite goals, which would be evaluated by the selection
committee with external members. It is noted, though, that the committee should consider not
only on which is the best planned proposal to realize but also what is the direction mostnecessary to KEK and the related communities.
As for the lack of human resources, KEK has provided one professor position devoted to DTP
from March 2013. Thus we have a well-experienced expert on semiconductor technology in theposition successfully. He has been working long to develop and apply the SOI technology toradiation sensor in OKI semiconductor. We expect he would play a leading role in not only
developments of the technology and also applications for industrial use.

Comments	
  from	  committee	
  The committee believes objective goals and schedule can be set even for generic development
without associating with any specific projects.

Silicon on Insulator (SOI)

General	  Findings	
  The SOI technology is an emerging technology to realize pixel detectors with highfunctionalities since it can realize CMOS circuits integrated with the fully depleted detector in amonolithic form. One of the main objectives of the SOI development is to solve the back gateeffect where the bias voltage applied to the detector affects the properties of MOS FETs. Oncethe back gate effect is resolved, the SOI technology has the great potential to be used in several
applications: high-energy physics, X-ray detection and others. This first 5 years have produced
proof of principle of the technology and it now looks mature to be implemented in some
applications as radiation detectors.
The group has demonstrated that the back gate effect can be mitigated by a buried P-well
implant with some side effects. A new technique employing a double SOI wafer is in progress toincrease immunity for a radiation dose, and to prevent the digital activity to interfere with thesensing volume.
The group has demonstrated full depletion of a significant fraction, estimated 170 µm, of a
500 µm float-zone handle wafer. This is enough for close to 100% absorption of X-rays at low
energy range as well as for the detection of Minimum Ionising Particles with good S/N ratio.
The group has also demonstrated it is possible to manufacture stitched sensors, although noresult was presentedSOI-1.
Good international consortium has been established. The KEK group manages two MPW
runs per year and, in 2013, it has reached its 10th run. Participants come from Asia, Europe andAmerica, demonstrating the reach of the technology.
The support from the foundry (LAPIS Semiconductor) seems to be very good, withcommitment for continuous improvement of the technology.

Concerns	
  and	
  Shortcomings	
  Leakage current remains still a serious limitation for spectroscopic use. It is of concern thatthe origin of the higher leakage current has not been understoodSOI-2.
With about 40 masks, this technology is fairly complex. Although this level is not unique inmicroelectronics technology, it is of concern, especially for the large area sensors that many
applications would require. Also, LAPIS is only now starting building its expertise in stitching.
The sensor manufactured so far only employs one-dimensional stitching and with fairly large(10 µm) buffer regions. This is not state-of-art, and, while there should be no showstopper toachieve state-of-art stitching, this would require further developments at the foundrySOI-3.
While the support from LAPIS is certainly exceptional, this SOI technology remains
restricted to a single vendor. As LAPIS is a commercial organization and every project needs
ultimately to find an economic justification, it is not clear what this justification is or if there is
any sound one. The SOI group has built an exceptionally good relationship with the foundry, but
for longer term stability it would seem important for the relationship to have a sounder financial
justification, i.e. through the start of production for at least one sensor in one application. In thefast paced field of microelectronics, where companies can change focus or disappear, the single
vendor relationship is a major risk and concernSOI-4.

The SOI group is understaffed, with a limited access to professional microelectronics
designer (most of the work is done by students or post-docs). This is particularly worrying now,where the project should shift its focus from technology development to design of full size
prototypes. This would require a level of expertise in microelectronics design which requires
years of experience. Retention of staff is a problem as this prevents the group from reaching
critical mass. To this respect, it is also not beneficial that the communication between the SOI
and the ASIC group is non ideal. It is also not clear if design reviews are routinely madeSOI-5.
The first 5 years were instrumental in developing the technology. It is now time for the
consortium to apply the technology successfully in some real applications. For this, we think it
would be beneficial for the group to place more efforts on the most promising applications,
identifying ‘low-hanging fruits’ and then building a portfolio of applications.SOI-6

Recommendations	  Stitching is of major importance for many scientific applications. The SOI group should
clearly demonstrate stitching at LAPIS works fine and also complete the development of thismodule by demonstrating 2D stitching is possible and achieving smaller buffer regionsSOI-7.
In order to share common design techniques and also to avoid common errors, design
reviews should be held for all SOI submissions with wide audienceSOI-8.
The group should also try to reduce the risk associated with the single vendor and try toestablish if it would be possible to have a similar technology with another vendor. In order toretain LAPIS and attract more vendors, the SOI group should focus on designing at least one
sensor that could be used for a real application. It should work on identifying early winners,
more than trying to demonstrate the technology for any possible applications. By doing this, it
could be useful for the consortium to do a more in depth review of other technologies, in order to
identify in which applications the SOI technology would be the optimum technology. It should
be noted that CMOS Monolithic Active Pixel Sensors (MAPS), have made progress and benefit
from a larger support from industrySOI-9.
If it hasn’t been already done, it would also be beneficial for the project to define theallocation of resources and draw a plan for the next 5 years, with a higher level of details for the
first 2 years. The SOI group should be reinforced with the addition of professional
microelectronics designers. Communications and collaborative work with the ASIC groupshould be increased. Design reviews jointly held by two groups could be the good first stepSOI-10.

Response	
  from	  the	
  group	  SOI-1: Although the yield of the stitched sensor is not yet so good, there are many stitchedsensors working well.
SOI-2: Leakage current changes depend on the wafer manufacturer and lots. Number ofmanufacturer for the 8” FZ wafer is not so many, and we will try to find the best wafer supplier.
In addition, we will continue to study structure of backside and bonding surface etc.
SOI-3: Now the yield of the small sensors is relatively high, so we don’t think the present
number of masks is critical. Of course, it is better to reduce the number of masks, but it needs
large re-works and causes other confusions. However, as for the large sensor which needs
stitching, we should re-define Design Rules and establish method to repair faulty circuits.

SOI-4: JAXA, Japan Aerospace Exploration Agency, is another main user of the Lapis SOI
process. Keeping the radiation hard electronics parts is primary concern of the JAXA. Thus
JAXA and KEK are asking Japanese government to identify the SOI process as a one of thecritical technology to keep in Japan. Of course, we will work hard to develop SOI sensor which
can be sold commercially.
SOI-5: We will continue to ask KEK management to increase our staff, but it looks very hardseeing present status of KEK. We are expanding SOI collaboration to many Universities andLaboratories where LSI experts exist.
SOI-6: Yes, we agree.
SOI-7: We think our first priority is to complete a sensor without the stitching. Thus thedevelopment of the stitching technology is low priority for the moment.
SOI-8: Yes, we agree.
SOI-9: Yes, but we are a group that started later in pixel detectors and have less staff. Then it is
our strength that we can use the Lapis process and their expertise like as our laboratory facility.
We would like to make use of this merit as much as possible.
SOI-10: Yes, we try to do.

Comments	
  from	  committee	
  Regarding SOI-9, the committee’s intention was to identify suitable applications for the SOI
technology by a in depth review of other technologies.

Micro-Pattern Gas Detector (MPGD)
General	  Findings	
  The development of MPGDs fits within the mission of KEK for conducting research withquantum beams, such as electron, photon, neutron, and muon beams because an MPGD isutilized in neutron science and photon science conducted at J-PARC and the PF. The KEK DTP
has developed a neutron detector using a boron-coated GEM and a hard X-ray detector using agold-plated GEM. It is notable that for neutron science, the DTP has demonstrated a nice TOF
measurement with 2D position resolution to resolve the microscopic lattice structure in a bulk
material instead of only a thin slice of the sample as with X-ray. The boron-coated GEM is
expected to be widely used in the community.
The collaboration in the DTP on the development of an ASIC and readout electronics for
MPGDs demonstrated that KEK has the best capability to develop the radiation detectors
efficiently. After the previous review, a working group was formed by KEK, universities, andother research institutions for not only sharing information on development and experience but
also conducting basic R&D of MPGDs. It is noteworthy that this group is developing MPGDs
with more robustness against discharges by using resistive materials and resistive electrodes,
though further testing and development are necessary. Their achievements have become more
widely known through international conferences and among the RD51 collaboration at CERN.

Concerns	
  and	
  Shortcomings	
  The current achievements are valued in general. However, the future roadmap is vague. For
example, in the oral presentation, it was expressed that the pixel readout will be developed someyears later. The detailed applications and their specifications were not shownMPGD-1.
Concerning the hard X-ray detector using a gold-plated GEM, a fine position resolution is
obtained thanks to the MPGD. However, lower efficiency compared with other technologies is aproblem for practical uses such as medical applicationsMPGD-2.
To share the information on development and experience in the community could accelerate thedevelopment. As described above, the DTP formed a group with researchers at other institutions.
However, it is unclear whether the DTP collaborates with MPGD R&D groups for upgrade of
projects in operation or future projects such as ILC. If not, such collaboration would create asynergy effectMPGD-3.

Recommendations	
  Since the DTP has fewer resources than what DTP members would like to do, the goals of the
project should be carefully chosen and focused. The presented roadmap seems to be based only
on personal intention. It is recommended to have a logical and reasonable roadmap to getexternal budgets and attract young students and postdocs. Applications should not be chosenfrom only the point of view of advantages over existing detectors. Disadvantages should also be
considered after clarifying the specifications and requirements for practical uses. Advices fromprofessionals in the corresponding fields would be helpful for choosing applications anddetermining development goals with consideration of usefulnessMPGD-4.
The developed MPGDs are suitable to be used in the fields of neutron science and photon
science. It is recommended that the DTP should collaborate further with scientists from thesefields and the developed MPGD should be commercialized. For commercialization of products,
the KEK management should support the DTP by securing the adequate number of office staffs
at the department of industry-KEK cooperation or work with RIKEN since they haveexperiences to commercialize neutron detectorsMPGD-5.
As mentioned above, a working group formed by the DTP, universities, and other research
institutions is achieving nice results on an MPGD with more robustness against discharges. The
KEK management should continue to provide financial support for their activitiesMPGD-6.

Response	
  from	  the	
  group	  MPGD-1: More efforts will be done to make R&D strategy clear.
MPGD-2: We hear the comment sincerely and will consider how to proceed with this R&D.
MPGD-3: Sharing the information with other groups has been done in various occasions, yearlydomestic workshop and other small meetings. More efforts will be done as one of activities of
MPGD R&D groups.
MPGD-4: More efforts will be done for getting advices from other professional people toproceed with MPGD projects.

MPGD-5: We have collaborated with some companies for the commercialization. The developed
ASIC chips and readout boards are commercially available. The company has sold the neutron
beam monitor, also. More products are followed. The recommendation is helpful for our moment.
MPGD-6: We are encouraged to continue developing new MPGD with more robustness against
discharges.

Superconducting Detector (SCD)
General	  Findings	
  Superconducting detectors (SCDs) provide unique sensing capabilities such as photon-noise
limited detection of millimeter waves, energy-resolving detection of visible light, high energyresolution of X-rays and particles and most sensitive searching capabilities for dark matterbecause superconductors require a lower excitation energy (typically 1/1000) compared to
semiconductors. Development of SCDs at KEK is expected to contribute also to related scientificdisciplines, such as astronomy/astrophysics and superconducting electronics.
Development of SCDs in KEK is very important and should be encouraged since SCDs will
become increasingly critical to the high-energy physics; KEK has correctly articulated this point,by for example the timely initiation of the LiteBIRD program to explore the high-energy state of
the early universe. This mission capitalizes on the rapid growth in the number of pixels insuperconducting detector arrays, which now exceeds 10,000 detector elements and continues togrow. LiteBIRD also provides a unique opportunity to the worldwide SCD community, because
it is one of the very few proposed observatories (along with SPICA) with an actively cooled
primary mirror, where ultra-sensitive SCDs with noise equivalent powers (NEPs) below 10-18 W
Hz-0.5 are required.
The SCD group focuses on two kinds of superconducting detectors, microwave kinetic
inductance detectors (MKIDs) and superconducting tunnel junctions (STJs). This is aninteresting combination because both of them can be used as pair-breaking quantum detectors,
and much of the underlying physical processes are common. For example, the ultimate
sensitivity of both detectors are set by the generation recombination (G-R) noise of quasiparticles,
unless the G-R noise is made lower than the photon noise. The two detectors probe the density ofquasiparticles in a different way, and therefore by having the two technologies side-by-side in
the laboratory could provide a complementary diagnosis of the device behavior. This should be
helpful in improving their performance.

Concerns	
  and	
  Shortcomings	
  The committee acknowledges that the SCD group are eager to, and capable of, coming up
with their original ideas, instead of simply following what has been demonstrated by othergroups. However, we also feel that some members may be overconfident and reluctant to learn
from previous developments, which may have negative effects on the realization of a functional
detector unit with competitive performance. Publishing in peer-reviewed journal provides a good
way to keep in touch with the external world.
In our view, the group makes the step from a new idea to device fabrication too quickly. To
give a few examples:• Lack of end-to-end system consideration
Example: STJs for infrared waves have been developed, without a conceptual idea of how tocouple light into the detector with sufficient quantum efficiency.
• Lack of contact with the broader community of the subject
Example: A rather new kind of readout scheme for mm-waves MKIDs has been developed,
based on a misunderstanding of the conventional scheme. This effort could have been
avoided if the group had been communicating with any group in the world with experiencein MKIDs.
• Lack of evaluation planning on the devices being developed
Example: Many different kinds of MKIDs have been fabricated, but the advance inunderstanding is relatively poor (or at least not presented). This includes the beam pattern of
the sinuous antenna and log-periodic antenna, the band-pass characteristics of the filters,
optical efficiency and so on.

Recommendations	  We recommend introducing following steps before starting to fabricate chips in the cleanroom:
1. Survey of existing technologies
We recommend a more careful technology survey of available and competitivetechnologies in Japan and in the world before starting the project and during the project.
2. Conceptual design phase
End-to-end system evaluation should be made based on a conceptual design to identify
potential risks and reduce the amount of unnecessary efforts for the final product. This
information is also essential to evaluate the feasibility of the instrument itself.
The conceptual design should include rough calculations and simulations of the expected
performance.
Design reviews should be conducted with experts from outside the SCD group with various
expertise before the fabrications.
3. Prototyping phase
Before fabricating devices, careful evaluation plans and milestones should be developed. It
usually helps to design experiments in such a way that each component can be evaluatedindependently (e.g., band pass characteristics of the antenna and filters.)
We recommend DTP office (and KEK) to increase their support to the development of SCDs,
along with other DTP activities. In particular, it is essential to assign dedicated scientific andtechnical staff to the currently understaffed development of SCDs, in order to bring thetechnological level up to where the SCDs developed by KEK can be considered as serious
candidates for missions such as LiteBIRD.
We recommend the SCD group to strengthen their interaction and collaboration with local(TIA-Nano and related institutes in Tsukuba), national (e.g., NAOJ, RIKEN, JAXA, anduniversities), and international (USA, Europe) institutions.

The SCD group obtained maximum internal resonator Q=106 and dark NEP=10-17 W Hz-0.5 at
0.3 K with MKIDs for CMB Observation. Device fabrication has been successfully improved.
We would recommend to evaluate the followings quantitatively:
1. Whether the experimental performance obtained at the present stage is sufficient from theviewpoint of the final goal and the rest of the project.
2. Expected improvement in NEP by replacing Al with TiN and thereby decreasing thevolume of the kinetic inductance elements.
Detecting alpha particles through phonons using the substrate as the absorber is interesting.
Though we understand the proposal to use lumped MKIDs for increasing the sensitivity, is it notclear if this is the only way to achieve the performance goal. We recommend to check
quantitatively whether the present sensitivity experimentally obtained agrees with the theoreticalprediction when taking into account of the ratio of volume (or surface area) of Al sensors and thesubstrates.
A distributed STJ is interesting for wider band operation than parallel-connected twinjunction (PCTJ) because the input impedance is in principle independent of frequency. However,resonant behavior was presented, indicating the frequency-dependent coupling between the
distributed junction and the antenna. In addition, a quantitative comparison of experimental
bandwidth between distributed STJ and PCTJ has not been carried out. This does means that theadvantage of the distributed STJ has not been verified. We would recommend evaluating thereason of this resonant regime and how to increase the bandwidth up to the expected value.
It is interesting to develop the integration technique of STJ on SOI. However, it is not clear
whether the noise and power consumption of MOS transistors on the SOI meet the requirementof the target system. We would recommend evaluating whether this approach is suitable.

Response	
  from	  the	
  group	  We are very happy to see that the committee recommends DTP office (and KEK) to increase
their support to the development of SCDs. We also appreciate that the committee thinks it
essential to assign dedicated scientific and technical staff to the currently understaffeddevelopment of SCDs, in order to bring the technological level up to where the SCDs developedby KEK can be considered as serious candidates for missions such as LiteBIRD. In the following,
we give our reply to each comment of the committee.
First, we recognize the importance of interacting with other groups that are also developing
SCDs. This review was a good opportunity for us to become acquainted with the reviewers andto interact with them for technical issues. We hope to continue interacting with a wider
community, both domestic and international.
Secondly, in the international review, we admit that our presentations should have included
more quantitative discussions. For example, the quality factor and NEP values obtained by ourgroup were not proved to be sufficient for the final goal for high-precision experiments such as
LiteBIRD. For the MKID design that employs Al side deposition, we are now discussing its
sensitivity more quantitatively along with the preparation of replies to reviewers of a paper wehave submitted. Please note, however, that the LiteBIRD working group includes the UC
Berkeley group who has been developing a wide-band receiver with the sinuous antenna and the
band-pass filters for multichroic millimeter-wave detection for the POLARBEAR-2 experiment.

Although the group uses TES bolometers, we think we will be able to apply the similar techniqueto the MKIDs.
Third, for phonon detections with lumped-element KIDs (LEKIDs), we have recently
confirmed that the LEKIDs have a better phonon sensitivity than the quarter-wavelength KIDs.
The improvement of the sensitivity is found to be comparable to the expectation obtained bytaking the ratio of the sensitive areas of the two types of KIDs. As for the distributed STJ, we
have designed the antenna-coupled STJs so that they have frequency-dependent coupling; suchdesign could be applied to the multichroic detections with frequency filters. The bandwidth ofthe distributed STJ is expected to be comparable to that of PCTJ. Details are given in the
Doctoral thesis written by Satoru Mima (written in Japanese). He observed the bandwidth that is
a few times wider than the expectations. He suggested it was due to multi-tunneling. We feel weneed further investigation to confirm that.
As for optical coupling between STJ and far infrared photon, an Infrared photon from cosmic
background neutrino decay will be received by a reflecting telescope with a main mirror of
15 cm diameter and 1m focal length, which will be loaded onto a research rocket, andtransmitted to an array of STJ pixels on the focal plane via collimators, secondary mirrors, band
pass filters and a diffraction grating device which covers the range from 40 μm to 80 μm in
wavelength and distributes photons into 50 STJ pixels per 0.8 μm. Each STJ pixel is supposed tohave 100 μm x 100 μm sensitive area to receive and detect an infrared single photon. Currently
we are measuring the quantum efficiency of Nb/Al-STJ by illuminating a laser pulse of aknown number of photons at single photon level in visible (470 nm) and near infrared (1.3um)
regions. We are establishing the principle of the quantum efficiency measurement of Nb/AlSTJ for visible photons, and targeting the measurement for middle infrared (10 μm) photons as anext step. We are considering conceptually the same techniques as anti-reflective coating withcommercially available dielectric film of the desirable thickness to improve the quantum
efficiency. Similar techniques are widely used for anti-reflective coating of infrared lenses for
astronomical observation fields.
As for SOI-STJ noise and power consumption issues, we have started noise measurement
using proto-type modules of SOI-STJ and we are also working on the circuit design
improvement to reduce the power consumption per channel from a few μW to sub μW order.

Noble Liquid Time Projection Chamber (LTPC)
General	
  Remarks	  Noble liquid TPCs are attracting much attention since they provide tracking and calorimetry
with high density and large volume (mass). They have high potential for experiments involving
weakly interacting particles such as neutrino and dark matter.
An astonishing aspect of R&D for noble liquid detectors is that small systems are nearly ascomplex as large systems. They require a complex infrastructure for cooling to cryogenic
temperatures, purification to sub-ppb level of impurities, charge measurements down to the subfC range, and light detection of single photon sensitivity. And these operation conditions have to
be stable for extensive time periods, sometimes several months. Given those requirements, theachievements of the Liquid TPC group are quite impressive. A very small group assembled
systems that produce some signals. However, there are still many technical issues to be solved orcorrected before the full potential of the detector can be explored. Several small and a few large
noble liquid detectors are operating in the world, and regular contacts with other groups in thefield could significantly reduce the development time and costsTPC-1.
Since LAr and LXe TPCs are not very different, it might make more sense to focus on one
technology now. After establishing one technology, DTP may resume development of the othertechnology taking advantage of techniques gain by thenTPC-2.

General	
  Remarks	
  for	
  Liquid	
  Xe	
  TPC	
  (LXeTPC)	
  LXeTPC group aims to develop a LXeTPC that can used for Positron Emission Tomography(PET) systems, taking advantage of three dimensional position measurements of charge signals
as well as fast timing signals of scintillation lights and good energy resolution in a compact
volume. Since PET is not one of the main interests of KEK, the committee is not convinced
whether it is the right goal for the LXeTPC projectTPC-3.
Although much progress has been made, there still are many issues to be solved before
practical use. Many of those problems are originated from support system problems that weresolved years ago by other groups, and they will take some time and efforts to be resolved due tolimited manpowerTPC-4.
It was proposed to replace the PMT now detecting the direct and the proportional scintillation
by MPGD in the form of gaseous photo multiplier (GPM). Such a read out would evensignificantly enhance the benefits of new read out scheme. Bringing the idea even further, it wassuggested to immerse the MPGD, GEM or ThGEM, into the liquid. The first observation of
proportional scintillation in a liquid filled ThGEM was recently reported from the Weizmann
Institute in Israel. This research might lead to TPCs of much larger size, higher performance, andat significantly lower costs. These detectors might then also be interesting for high-energy
physicsTPC-5.

Concerns	
  and	  Recommendations	
  for	
  LXeTPC	  The purity problem haunted all liquid xenon developments until continuous purification byrecirculation was introduced in the MEG experiment. Looking at other groups, nearly the same
components are used, except for the getter pump. And to keep the record straight much of theinnovative information concerning recirculation and also cooling originated in KEK. The single
most relevant problem is the recirculation rate. It is limited by the available cooling power to 1.2
standard liters per minute (SLPM) because the heat exchanger does not work efficiently. The
heat exchanger itself and it’s connecting lines have to be well insulated, preferably by a thermal
vacuum. This will increase the maximum rate to 5 SLPM, limited by the getter. This subject was
discussed with the KEK group 4–5 years ago, but it seems the importance was misjudgedTPC-6.
Unlike many LXeTPCs nowadays, the pulse tube refrigerator (PTR) is mounted directly inthe xenon gas. A much better way is to employ a copper cold-finger reaching through the wall of
the inner chamber. Only the Oxygen Free High Conductivity (OFHC) copper surface of the cold
finger is exposed to the xenon, while the other components, PTR, heater module, temperature
sensors, and cables are in the vacuum space. This arrangement also helps with purity since manypotentially 'dirty' parts, e.g. the heater module with large epoxy surfaces, does not come incontact with the xenon at all. Mounting the PTR remotely can help to mitigate the future problemof acoustic noise affecting the charge measurement. The high frequency noise stems from the He
steaming in the PTRTPC-7.
There are more minor points, e.g. the Teflon signal cables should have no jacket sincetrapped air will be released very slowly reducing the purity. After these the set up should allow
the study of the xenon detector, e.g. signal response, read out, etcTPC-8.
There are not many centers globally working on LXe detectors, but luckily most of thegroups are very open to discuss technical details. A more intense communication might avoid
similar problems in the future. In particular, they should work with other Japanese groups suchas MEG or XMASS since detailed communications and site visits are easier. Ironically muchinnovative information came the other way out of KEK, e.g. the recirculation, the model of thediaphragm pump, the idea to use a heat exchanger, and of course the pulse tube refrigerator(PTR) itself. Furthermore, it might be more efficient to use a proven LXe system as platform for
the TPC studiesTPC-9. Complete LXe test platforms can be acquired commercially, e.g. SHS
Vacuum, Shanghai. Four such systems exist so far internationally, and all were operating
satisfactorily right from the start. The present system would then be used to explore the aspectsof filling, recovery, purification and so onTPC-10.
The underlying principle of Dual Phase technology is Proportional Scintillation in the gas
phase. However, Proportional Scintillation also exists in liquid phase as the Doke group proved
35 years ago. At that time where was no advantage in using this read out scheme, but withtechnological advances now it seems to be very beneficial for large and very large detectors.
Research has started about 3 years ago, after a KEK seminar. The technique is underinvestigation at Columbia University and SJTU, Shanghai. The major difference to the small
TPC at KEK is the charge read out via proportional scintillation light instead of direct charge
measurement with integrating amplifiersTPC-11.
The committee recommends to re-align the LXe project with the recent research in new
detector structures and to take advantage of the synergy of the LXe project, the MPGD project,
and the ASIC developmentTPC-12. For such a road map, however, the LXe project might have tobe reinforced in manpower.

General	
  Remarks	
  for	
  Liquid	
  Ar	
  TPC	  (LArTPC)	
  
LArTPC group aims to develop a LArTPC that can be used for neutrino and dark matter
experiments, which is well aligned with objectives of KEK. The status of the LArTPC project ismore advanced and appears more successful. The test detectors show that the technology ismastered, and for some processes the development even goes further with detectors for somespecial applications. It was a good challenge to upgrade the Ar gas recirculation and the cryosystem to reduce the impurity level. The impurity level is demonstrated 0.3 ppb, from 0.8 ppb.

Concerns	
  and	  Recommendations	
  for	
  Liquid	
  LArTPC	  One of main issues of the project is whether a careful regeneration procedure for the filters isneeded. One of the important techniques to be established is how to replace exhausted filters tokeep the high purity level in the systemTPC-13.

It is more difficult to foresee the future for this project. Quality control of concrete is not oneof the main businesses of KEK. The most likely detector for high-energy or neutrino physics
would be a large detector in the 1–10 kton range. It is not clear whether the acquired expertiseand experience will be sufficient to develop a detector of this size. Presently the largest LAr
detector is the 600 ton Icarus, which is a product of the 1990’s technologies. Such large detectors
would require completely new technologies since the size of the detectors makes a huge
difference. For the cleaning and preparation of surfaces, new methods have to be developed
going far beyond the Icarus. The purification and signal read out also have to be adapted for the
new scaleTPC-14.

Response	
  from	  the	
  group	  TPC-1: We have communicated to foreign people regularly, however, we will consider the
possibility to have other communications (e.g.; Shanghai group) and/or to have deeper
communications.
TPC-2: We will also start considering the possibility to have common R&D items between LXeand LAr. In order to do this we pick up the common items at first, and then proceed with them ina timely manner.
TPC-3: Present target depends on interest of researchers involved with this R&D. Other targets
such as Dark matter and double beta decay are welcome.
TPC-4: Yes, we have noticed the importance of heat exchanger with vacuum insulation for fast
purification.
TPC-5: Thanks for this information. We see that such detection could increase the detection
efficiency as well as the cost performance.
TPC-6: Yes, we have constructed a prototype of the heat exchanger a few years ago. But, it has
never been operated because of “man power limit”. Also, it was pointed out that its location
should be moved to top of the cooler by an expert who has such experience at Subatech.
In this fiscal year, we initiated this effort with large modification as presented at this review. The
schematic of this system is appended, which has the heat exchanger and the second cooler in a
vacuum chamber. Even with this system, liquid Xe could be directly provided.
TPC-7: W agree with the remote location in future. Our next system explained above must be anintermediate stage.
TPC-8: We will replace them by ones with Kaptons which are commercially available as cables
for ultra vacuum application.
TPC-9: Yes, we have also developed based on the information. Several members are
participating in MEG and XMASS. So, such communication has no problem.
TPC-10: We will consider this possibility in next fiscal year. We would like ask you for the
information at the SHS Vacuum, Shanghai.
TPC-11: Apparently, we are very interested. We would like to know more especially the position
measurement accuracy in three dimensions.
TPC-12: Yes, there is no problem in such re-alignment in principle if there are enough staffs andinterested groups.

TPC-13: We skipped the item in the presentation, but we already established a regeneration
procedure with evacuation and H2 + Ar gas. Thus the regeneration itself is not an issue. If thefilters are put in parallel inside the purification system, we can replace the filter after theexhausting easily.
TPC-14: As mentioned during the review, building 1-10 kton level LAr detector is an issue
beyond the DTP. (because huge man power and budget are required.) To solve this, laboratory
and KEK wide supports are needed.

Ultra Fast Pixel Detector (FPIX)
General	  Findings	
  In order to conduct a time-resolved measurement by employing pulsed synchrotron X-rays,
the FPIX group has developed a frontend Application-Specific Integrated Circuit (ASIC). The
ASIC is fabricated with a 0.8 µm BiCMOS process from NJRC, which is compatible with a SiAPD with 2-ns pulse-pair resolving time. They assembled a 10-ns sampling system with a 64channel test board together with a 64-channel Si-APD from Hamamatsu Photonics, and tested
the assembly with the 8-keV X-ray beam at the Photon factory, KEK. Eventually theysuccessfully demonstrated that the detector could clearly record the time structure of X-rays
deriving from the electron-bunch filling of the PF ring. By upgrading the module to a 1-ns
sampling system, they have succeeded to distinguish the 2-ns interval of X-rays originating fromthe electron multi-bunch structure.

Concerns	
  and	
  Shortcomings	
  They need a new circuit designer for the fast BJT circuit, since the former designer is nolonger available. It takes many years to train a circuit designer for a radiation measurement
system.
Since the detail of the ASIC was not presented thoroughly at the DTP review, it is difficult
evaluate the circuit itself.
The power consumption of the above mentioned ASIC is 0.64 W per chip, which includes
only 4 identical signal channels. In order to cope with large number of APD pixels, it requires
special cooling devices to remove heat dissipated from the ASIC.

Recommendations	  The ASIC could be fabricated with a modern SiGe BiCMOS process to reduce power
consumption from the circuit, provided that an adequate designer is availableFPIX-1.

Response	
  from	  the	
  group	  FPIX-1: We will continue to search a new circuit designer and will try to gain a help from a
venture company. If we could obtain funds and a new designer for our project, we would
introduce a modern SiGe BiCMOS process for ASIC.

Application-Specific Integrated Circuits (ASIC)
General	  Findings	
  Demand for ASICs is growing in accelerator science. Twenty-one ASIC development
projects have been started in KEK for accelerator science. The ASIC chips that were developedby the DTP projects are actually used for many experiments including those for MPGD, PSD,
MPPC, DC and TPC projects. The QPIX project is a currently on-going project to develop an
ASIC with TDC, ADC and the LTCC flip-chip technology for gaseous detectors. An important
advantage of the QPIX is in-pixel ADC since the commonly used TIMEPIX chip does not havean on-chip ADC.
Increasing the number of researchers developing an ASIC is another objective for the ASIC
group. The ASIC group organized ASIC training courses since 2008 and the number of theattendees are increasing from 40 to more than 160. The committee recognizes that this is anextremely important activity to promote the ASIC developments for accelerator science. The
ASIC group also provided on the job training for young researchers in the experiments that
requires custom ASICs. Eleven projects successfully completed their ASIC developments andten projects are currently supported by the ASIC group. KEK should continue to support theeducation and development of ASICs.

Concerns	
  and	
  Shortcomings	
  Although ASIC development at KEK is very active, KEK should promote ASIC
development with extreme performance required for top accelerator science. The QPIX ASIC
being developed at KEK is unique and advanced compared with similar developments.
However, the performance of the QPIX still requires improvements. For instance, the thresholdof the QPIX chip is still high, which limits applications. Future plan presented at the review toimprove the threshold should be realizedASIC-1.
From the viewpoints of ASIC design efficiency and quality, ASIC design environment
should be improved. A mixed-signal simulation and design environment should be established toenable development of sophisticated ASICs.
For efficient and fast development of ASIC chips, developments of common IP libraries suchas analog amplifiers, ADC, DAC and functional logic circuits are also very important. However,
sufficient effort has not been made to promote such activitiesASIC-2.

Recommendations	  KEK should continue active roles on the ASIC developments and educations of researchers,
particularly, young researchers, and should make more efforts to establish sophisticated ASIC
design environment to enable ASIC developments for top accelerator science.
Building closer collaborations between the ASIC and other DTP groups such as SOI, MPGD
and TPC are desired for efficient design and advanced performance in ASICs and detectorsASIC-3.

Response	
  from	  the	
  group	  ASIC-1: Yes, we are/will be doing our best to improve QPIX performance.
ASIC-2: Although we already have amplifiers, DACs and slow ADC libraries on 0.18 μm
CMOS process, we understand it is not adequate resource for ASIC development for top
accelerator science. We will accelerate development of more sophisticated ASICs and spreading
those know-how to young researchers based on successfully launched education activity.
ASIC-3: Yes, we would like to do our best with KEK support.

Two-Phase CO2 Cooling system
General	  Findings	
  Demands for cooling systems have been increasing due to conflicts between higher power
consumption and low material requirements of (mostly) vertex detectors. Compared with airbased and single-phase liquid cooling, two-phase cooling is very attractive since it takes
advantage of the phase change mechanisms (evaporation and condensation) to absorb and emit
heat. Pumped two-phase cooling provides improved heat transport capability and reliability
compared with passive two-phase devices such as heat pipes.
Although perfluorocarbon (PFC) has been widely used as coolant in HEP detector systems
such as the ATLAS SCT, CO2 is consider to be better coolant due to much larger latent heat(approximately three times larger). In addition, we can use thinner cooling tubes for CO2 coolant
due to smaller evaporated vapor volume. Because of these advantages, the AMS tracker and the
LHCb-VELO has successfully employed two-phase CO2 cooling systems mainly developed by
NIKHEF, and CERN, FNAL and SLAC started R&D of two-phase CO2 cooling. Developmentof two-phase CO2 cooling system is also important for many industrial applications such as
refrigeration for bio-cells and foods.
It is reasonable to choose a gas compressor rather than a liquid pump to circulate CO2
because the former has many advantages theoretically. On the other hand, the gas compressor
requires an oil-free operation under a quite high pressure. This requirement is also widely needed
for some applications that use a pure-gas circulation system.
The gas pressure is higher than 1 MPa at almost all of the circuit. It is important from theviewpoint of industrial applications to develop a safe high-pressure gas circulation system. The
committee praises that this system has taken an inspection of safety regulations for high-pressure
facilities in spite of a small cooling capacity.

Concerns	
  and	  Recommendations	  Specifications of the cooling system are not shown in the report, in particular, the target sizeof the cooling system. Large-size system may require different design principlesCO2-1.
It is reasonable to utilize a commercial gas compressor as the first step, however, it is worth
considering a possibility to introduce an inter-cooling function to the compressor for the next
step. According to the phase diagram of CO2 circulation, the CO2 temperature at the outlet of thecompressor becomes about 150°C. It is effective that CO2 is compressed at a lower temperature
because its density is highCO2-2.
In the complicated cooling tube topologies, e.g. many vertical cooling paths, temperature
may not be uniform along the cooling tube. It is important to measure temperature and pressure
fluctuations at the exit of the cooling tubeCO2-3.
There is only one cryogenic expert in the group. Other members are physicists or electronics
engineers. It is better to have more cryogenic experts involving the project even as part-time
collaborators. For example, cryogenic experts may suggest adding a short-cut path between theinlet and outlet of the heat exchange as shown the figure to prepare for unexpected accidentsCO2-4.

Response	
  from	  the	
  group	
  CO2-1: The expected cooling capacity of the present test system is 800 W at +15°C and 260 W
at −40°C. Required capacity for the target system is 2 kW at +15°C and 500 W at −40°C. The
cooling capacity of the present system is limited by the capacity of the air compressor for gas
booster drive. Factor 2 –3 improvement of the cooling capacity can be achieved by replacing
the air compressor with more powerful one.
CO2-2: As the review committee pointed out, utilizing a gas compressor with inter-cooling
function is an interesting option. CO2 gas compressors developed for “ECO Cute” have suchfunction. We will investigate possibility of using such compressors.
CO2-3: It would be interesting to make a large scale dummy load and measure the temperatureand pressure non-uniformity. We would like to study it if allowed from the view point of safety.
CO2-4: We had one more cryogenic expert who worked as part-time. But after his retirement, wehave only one cryogenic expert. We are eager to involve more cryogenic experts, but KEK
cryogenic group is suffering from lack of manpower and we have not succeeded to get more
persons. We will do our best to increase the cryogenic experts in our group. We will include theshort-cut path suggested by the review committee in the next prototype.