1. Development of the Soft X-ray Large solid angle Camera onboard WF-MAXI
H. Tomida (ISAS/JAXA), S. Imai (Tokyo Tech, ISAS/JAXA)
N. Isobe, N. Kawai, Y. Yatsu (Tokyo Tech)
T. Kohmura, K. Tamasawa, Y. Ozawa, K. Yasuda (Tokyo Univ. of Science)
M. Arimoto (Waseda, Univ.), H. Tsunemi (Osaka Univ.)
T. Mihara, M. Serino (RIKEN), and the SLC team.
5th annual symposium of the innovarive area
2016/12/26

2. Soft X-ray Large solid angle Camera (SLC)
WF-MAXI/SLC on iSEEP/ISS
Mission instrument of WF-MAXI
Science goal:
Monitoring soft X-ray transients, especially counterparts of gravitational wave events.
Specifications
Energy range: 0.7 – 10 keV
Position localization: 0.1 deg
Field of View: > 10 % of the entire sky
60 deg x 60 deg (TBD)
Sensitivity: 100 mCrab in 100 s (5s)
Effective area: 293 cm2
Detector system
2 units of CCD arrays with 1-d coded masks (X and Y directions)
380 mm
Coded Mask
(Heritage of HETE-2)
250 mm
CCD chip (behind the mask)
5th annual symposium of the innovarive area
2016/12/26

3. Soft X-ray Large solid angle Camera (SLC)
CCDs for SLC
Fabricated by the Hamamatsu photonics
P-ch back-illuminated chip
16 CCDs in total (8 for each array)
Format: 2048 (H) x 3668 (V), 15 mm pixel
CCD operation
Flexible drive/read-out patterns with m- code
Read out in parallel sum mode
Read out time; 0.1 s
Heritage
MAXI/SSC: readout/drive electronics
ASTRO-H/SXI: CCD, m-code, camera
CCD cooling system: 2 options
Mechanical cooler
CCD temperature: -100 ℃
Flight proven
High cost
Radiator + peltier
CCD temperature: ≾−90 ℃
Low cost V
CCD
Flexible cable
Connector
SLC thermal design (Mechanical cooler)
-109
109
Temperature [℃]
CCDs: -100℃
5th annual symposium of the innovarive area
2016/12/26

4. Ground performance of the SLC CCD
55Fe CCD -90℃
Energy resolution
∼𝟏𝟖𝟎 eV for 5.9 keV
Similar to ASTRO-H/SXI (∼𝟏𝟔𝟎 eV, -110 ℃)
Further improvement is possible
Small pixel size
SLC: 15 mm
ASTRO-H: 24 mm
Fewer single pixel events
Binning parameters to be optimized
Mn Kα
Mn Kβ
Without radiation damage,
the SLC CCD exhibits a good performance at -90 ℃.
5th annual symposium of the innovarive area
2016/12/26

5. Radiation damage on the SLC CCDs
The CCD is expected to be degraded by radiation damage.
To check -90 ℃ performance.
Radiation damage test
HIMAC (Heavy Ion Medical Accelerator in Chiba)
1st round : 2015 Dec 9 – 19
ASTRO-H CCD (already reported)
2nd round : 2016 Feb 22 - Mar 2
WF-MAXI/SLC CCD
The CCD was irradiated with the scattered beam.
Direct beam: too strong
Scattered beam: spatially uniform.
The CCD was operated at -80 ℃, during proton irradiation.
The concept of “test like you fly”
Protons beam
Vacuum Chamber
Scattered Protons
Faraday cup
Incident proton beam
Energy: 6 MeV
Intensity: 70uA-400uA
Mini-type SLC CCD
5th annual symposium of the innovarive area

6. Results: Charge Transfer (In-)Efficiency (CTE/CTI)
one of the most impotent parameter to evaluate the CCD performance.
Before irradiation
SLC CCD: CTE ~100%
better than ASTRO-H CCD
After irradiation
The CTE of the WF-MAXI CCD is similar to that of ASTRO-H CCD (or possibly better)
-90 ℃
ASTRO-H CCD ( -110℃)
1.0 – CTE (CTI)
0.1year
1year
10year
Proton dose [cm-2]
note :
In orbit, the CTE/CTI correction is not applicable to the SLC CCD,
since the CTE/CTI is unable to be measured in the operation mode of the SLC CCD.

7. Results: Dark current -90 ℃
The MAXI/SSC has suffered from the increased dark current in orbit.
7 years operation
CCD temperature: -60 ℃
SLC CCD design
To minimize the dark current
Results of WF-MAXI CCD
8 years irradiation in the ASTROH orbit
CCD temperature: -90 ℃
0 week 1 week
1 month 6 month
1 year 3 years
8 years
dark current (e- s-1 4pix-1)
-90 ℃
time [s] after the beam irradiation
We confirmed that the dark current after the 8 years-operation
is very small, 2−3 e- s-1 4pix-1, as far as the CCD is cooled down to below -90 ℃ (possibly better than the ASTRO-H CCD -110℃)
is expected to have no significant impact on the energy resolution and dynamic range.

8. SLC Bread Board Model (BBM)
Electronics
SLC chamber
One CCD was installed
inside the SLC chamber
Plastic cover
The set up of the SLC BBM was completed last week.
The basic operation of the m-code in the drive electronics has been confirmed.
We plan to evaluate the performance of the CCDs using this SLC BBM, by the end of this fiscal year.
Cooler module
(non-flight item)
～1 m
5th annual symposium of the innovarive area
2016/12/26

9. Summary
The introduction to the WF-MAXI/SLC and its development status are presented.
SLC: CCD arrays + coded mask
Soft band (0.7 – 10 keV), good position localization (0.1 deg)
wide field of view (10% of the sky), high sensitivity (100 mCrab)
Heritages
MAXI/SSC: readout/drive electronics
ASTRO-H SXI:
HETE-2: coded mask
The radiation damage on the SLC/CCDs was evaluated.
The CCD performance without radiation damage was confirmed to be good.
The CTE and dark current -90℃) were measured as similar to (or even better than) those of the ASTRO-H CCDs
By using the BBM, we are on the way to demonstrate the SLC performance.
The flexibility of the CCD readout/drive patterns with the m-code was confirmed.
The evaluation is planed to be completed by the end of this fiscal year.
5th annual symposium of the innovarive area
2016/12/26