Review Report of The SACLA Detector Meeting
Dec. 9, 2011ndThe 2 Committee Meeting @ SPring-8
Date: Nov. 28-29, 2011
Committee Members:
Dr. Peter Denes, LBNL, U.S. (Chair of the Committee)
Prof. Yasuo Arai, KEK, Japan.
Prof. Andrew Holland, The Open University, UK.
Dr. Grzegorz Deptuch, Fermilab, US. (Absent)

Introduction
The SDAC (SACLA Detector Advisory Committee) has been chartered as a collegial
advisory committee (rather than a formal independent review committee) with the goalof sharing experience and advice in order to ensure that the SACLA Detector Team’sactivities maximize the scientific output of SACLA. The Mandate of the Committee as
presented at the 1st Committee Meeting is:
1. The following general issue.
1.1. Any Potential risk in the current on-going projects
1.2. Alternative approach to achieve the detector performance in short and longterm
1.3. Is there any need to add committee member? If so, what area of expertise do
we need?
1.4. Adequacy and balance of researchers’ own goal.
1.5. What Infrastructure do we need to invest in short and long term?
1.6. Strategic direction1.7. Any other suggestions.
2. The specific issues that the DAQ team is facing.
2.1. The list of the specific issues will be issued separately.
During our meeting, we were presented the state of the project, detector development,
and a discussion of an important application of the newly developed detectors incoherent imaging:
SACLA Project Status and Future Perspective – M. Yabashi
Imaging Science at SACLA – C. SongOverview of Detector Development Program – T. Hatsui
This was followed by detailed status reports on the MPCCD and MVIA developments, aswell as other topics:
MPCCD status overview – T. Kameshima
Status of CCD Sensor and Readout Electronics of MPCCD – T. Hatsui
MPCCD Octal Detector System – S. Ono

Upgrade of MPCCD Readout Electronics – Minglee Chu (Academica Sinica)
Multi-Via Detector Status – T.Hatsui
DAQ Front-End: Current Status and Future Perspectives – T. Ohata
In a change from the 1st Committee Meeting, the collection and transport of digital data,
referred to here as “DAQ”, is now the responsibility of the JASRI Controls and IT groups,
and no longer falls under the mandate of this committee.

Findings
Significant progress is continuing on the two principle current detector developments:

MPCCDThe MPCCD is an 8-port, 0.5k x 1k CCD in both single and octal (2k x 2k) formats. Theoctal detector was being prepared for first FEL light on the day after our Committee
Meeting. The CCD itself is being developed in four phases:
Phase 1 is a front-illuminated, partially-depleted device with 50 μm depletion depth fordirect X-ray detection. This is the device currently in use.
Phase 2 uses the same device, but with a phosphor. P46 has been selected as aphosphor, based on work done by the SPring-8 group, but light yield is low, and furtherevaluation is required to see if there is a science case match for such a detector.
Phase 3 would replace the Phase 1 CCD with a fully depleted CCD in order to achieve
lower noise and higher QE (quantum efficiency). Production of such a CCD is expected
to start shortly.
Phase 4 would be a thinned version of the Phase 3 sensor, optimized for soft X-rays.
This development is on hold, pending better definition of the science case requirements.
Specification
MeasuredNoise< 300 [e-]< 250 [e-]Peak signal
5 [Me-]
2.7 [Me-]
Frame rate
60 [Hz]30 [Hz]
Cross-talk< 1000 [ppm]< 3000 [ppm]
PSF< 50 [um]~ 21 [um]MPCCD specifications and measurements to date are shown in the table above.
Although several parameters meet or exceed specification, certain improvements areneeded, and are underway:
 The frame rate has not achieved the 60 Hz requirement. The cause has been
identified as a slew rate limitation due to high capacitive loading, and is being
addressed by the insertion of buffer amplifiers directly outside of the detector
chamber. 60 Hz operation is predicted to be achieved by summer 2012.
 Cross-talk between outputs is observed. While not fully understood, it isanticipated that improved layout of the kapton interconnect circuit can alleviate
this problem.



A discrepancy in the measured full well of MPCCD pixels remains between
measurements by the manufacturer, e2V – using their equipment, and SACLA –using the Meisei elecronics. At present, it is suspected that this difference is dueto the quality of vertical clocks.
Initial radiation hardness studies have been undertaken, although the resultspresented to us were somewhat inconsistent.

MVIA
MVIA is a medium-term development based on SOI (Silicon-on-Insulator technology)
developed in collaboration with KEK and Lapis Semiconductor. One pixel consists ofseveral charge collection diodes. One diode is connected to a high capacitance node, inorder to form a low-gain channel, and the other diodes are connected together to forma high-gain channel. The goal is a 500 μm thick detector with a full scale per pixel of
7x106 e− and a noise of 150 e− per 30 μm pixel, corresponding to a 16-bit dynamic range.
The final sensor design is 65 x 27 mm2, with 12 high-gain and 12 low-gain pseudodifferential ports. Power consumption is expected to be 1W average assuming a 10%
duty factor.
Since the last review, the pixel design has been significantly changed. Previously, agated integrator with op-amp input stage was used, which has been replaced with a 4T
design. In addition, due to 1/f noise, it has been concluded that correlated double
sampling is needed to meet the noise specification, so that 120 Hz frame rate readout isrequired.
In order to fabricate the desired sensor geometry, the group has worked with themanufacturer to develop a simple but effective stitching technique.
SOI is a relatively novel technology, and several process-related questions remain: Can one obtain suitable high-resistivity substrate material?
 Can the SOI structure achieve suitable radiation tolerance?
Active R&D by the larger SOI collaboration is under way in both of these areas.

Further topics
Detector requirements
Overall detector requirements remain unchanged from the 1st Committee Meeting:
1. Match the repetition rate of XFEL pulse (60 Hz for SPring-8 XFEL)
2. Single photon detection capability
3. Better quantum efficiency for 6-12 keV in short term. Wider range in longer term.
4. Higher peak signal. Higher delivers wider applications, and more opportunities toexplore.
5. Resistant to estimated 30 Mrad annual dose.

Mid-to-long term requirements have been slightly revised:
1. 1.Optical shielding
2. Higher photon energy (may be up to 20-30 keV)
3. Lower photon energy (may be down to 50 eV) (previously 200 eV)
Higher frame rate to record background up to 180 Hz (previous requirement, nolonger valid)
4. Higher frame rate to meet accelerator upgrade toward higher repetition rate,
probably 300 Hz in future. (was 120 Hz; 1 kHz eliminated) Then will start soft xray regime.
New collaborations
During the Committee meeting, a group from Academia Sinica presented plans toproduce a more compact readout for the MPCCD. Since the readout is mounted directlyon the endstation, this would be desireable.

Comments and Recommendations
MPCCD
The day after the Committee meeting, an Octal MPCCD took the first FEL images in thecoherent scattering chamber. The team is to be highly commended for thisaccomplishment.
As part of radiation tolerance studies, the use of thermal annealing in order to enhance
lifetime should be investigated.
Support effort in early operations should be carefully examined. In transitioning to user
operations, subtle problems – which require time from detector experts – often arise.

MVIA
In order to ensure delivery of the MPCCD, the MVIA was placed as 2nd priority. As theMPCCD development matures, the plan is to transfer knowledge to support staff, thusenabling the development team to focus on advancing the MVIA detector. The
Committee concurs with this approach, and notes that the MVIA is potentially a very
good technology match, especially considering the collaboration with KEK and Lapis.
Achieving the desired performance, independent of radiation hardness, will be very
challenging:A 16-bit pixel, if such performance is indeed achieved, is not trivial. With two gainstages per pixel, each pixel will require individual calibration. With a full-size detector of
4x107 pixels, consideration should be given to how such a detector will be calibrated.
The MVIA concept assumes uniform charge distribution over a (30 μm) pixel. With asuitable substrate, this assumption is not obvious. Simulation (at the device andnumerical level) together with measurements should be performed to confirm theviability of the concept.
Work should continue on the MVIA detector, but a set of minimum requirements
together with guidelines as to when they should be met should be developed.

Further topics
Collaboration
Defining useful collaborations can optimize resources. The collaboration with Academia
Sinica presents useful possibilities, but should be better defined and planned.
Data acquisition and Computing
Analysis, including algorithm development and on-line visualization, will make use of thestaff and facilities of the supercomputing center in Kobe. Together with the now
separate data acquisition group, good coordination is required – as efforts from all threeof these groups are required to validate, diagnose and improve detector performance.
Miscellaneous A long-term, time-phased road map of goals and requirements will be helpful todefine and prioritize future work.
 A “charge” for each Committee meeting, with specific topic(s), will help elicit
more targeted feedback.
 The group is encouraged to publish their detector developments, and to present
at appropriate conferences in order to maintain a high profile.
 Although on-site meetings are irreplaceable, for practical reasons short, focused“remote” (video, Skype, …) intermediate reviews should be considered.