Koji Mori (University of Miyazaki) Y. Nishioka , S. Ohura , Y. Koura, M. Yamauchi ( miyazaki ),

1. Proton Radiation Damage Experiment on P-Channel CCD for X-ray CCD camera onboard the Astro-H satellite Koji Mori (University of Miyazaki) Y. Nishioka, S. Ohura, Y. Koura, M. Yamauchi (miyazaki), H. Nakajima, S. Ueda, H. Kan, K. Hayashida, N. Anabuki, H. Tsunemi (Osaka), T. Kohmura, S. Ikeda (Kogakuin), H. Murakami (Rikkyo)，T. Dotani, M. Ozaki (ISAS/JAXA), Y. Maeda (Miyazaki), and K. Sagara (Kyushu)

2. Contents • P-channel CCD for the Astro-H satellite • Proton radiation damage experiment • Comparison with other P-channel CCD experiments • Summary 2012-09-03/07 2012-09-03/07 PIXEL2012 PIXEL2012 PIXEL2012

3. X-ray CCD for Astronomical use “SUZAKU” 2005, 1700kg • A standard focal-plane detector with a 20-year history • ASCA (1993-2001): N-channel Front-Illuminated CCD • Suzaku (2005- ): N-channel Back-Illuminated CCD • Astro-H (2014- ): P-channel Back-Illuminated CCD “ASCA” 1993, 417kg “ASTRO-H” 2014, 2700kg electrode n-channel p-type Si n-type Si p-channel Cross-section of CCD PIXEL2012

4. New P-channel CCD for New Satellite • HAMAMATSU PHOTONICS K.K.-provided CCD-NeXT4 • frame-transfer type, fully-depleted BI CCD with a depletion layer thickness of 200 μm • 24 μm pixel size with a 1280x1280 format -> 640x640 after 2x2 on-board binning • 2 readout nodes used Imaging Area 31mm x 31mm Storage Area covered when installed PIXEL2012

5. Radiation damage in space • Cosmic-ray protons are the primary source for damage Pulse Height (Q) Stacking plot with 55Fe Y Frame image X Y • “Charge Transfer inefficiency (CTI)” is a measure of the radiation damage of CCD PIXEL2012

6. Mitigation of radiation damage • Charge-Injection technique • Charges are intentionally injected to selected rows which are regularly spaced • The injected charges work as scarifies to fill traps and following real X-ray-induced charges are transferred smoothly • Optimizing temperature • timescales of trapping and de-trapping depend on temperature • CCD type • It is reported that P-ch CCD is more radiation tolerant For space use, we need to know how radiation hard our new device is and how mitigation methods work http://heasarc.gsfc.nasa.gov/docs/suzaku/analysis/sci.html PIXEL2012

7. Contents • P-channel CCD for the Astro-H satellite • Proton radiation damage experiment • Comparison with other P-channel CCD experiments • Summary Inawashiro Fukuoka Narita Miyazaki PIXEL2012

8. Facility • Kyushu University tandem accelerator laboratory • performed from 2012 February 1st through 5th • Proton beam we used • Energy: 10.5 MeV • Intensity: 50nA - 1uA • guided into the scattering chamber http://www.kutl.kyushu-u.ac.jp/gaiyou.html PIXEL2012

9. Setup in the scattering chamber • Scattered beam is used • Direct beam intensity too strong for our purpose • Scattered beam is more spatially uniform • Carbon target is selected • The first excited state is about 4.4 MeV, allowing us to easily remove inelastic scattered protons with a thin filter • Incoming protons are mono-energetic, 6.7±0.5(HWHM) MeV PIXEL2012

10. We used two types of CCD • Large format CCD • installed in a camera body attached at the side of the chamber • working at -110 degree Celsius during beam-on • Mini-size CCD • same type as the large format CCD, just small • simply exposed inside the chamber, not working during beam-on • much closer to the scattering point, larger flux compared to the LF CCD PIXEL2012

11. Why 6.7 MeV? • 6.7 MeV protons penetrate 200 μm silicon CCD • Their dE/dx is more or less constant along the depth direction, damaging the chip uniformly in the depth direction. • The deposit energy is about 2.7 MeV Bragg curve of protons of various energy in Silicon PIXEL2012

12. Dose rate in orbit • Left: day-averaged radiation environment modeled in the orbit of the Astro-H satellite • ~100 MeV protons in SAA are the major source of damaging CCD • Right: Proton flux after passage of the camera body and Deposited energy spectrum • the camera body is simplified into Al 20mm in our calculation • The dose rate is 2.1x106MeV cm-2 day-1 or 260 rad yr-1 Mizuno et al. (2010, SPIE, 7732,105) PIXEL2012

13. Stacking plots without CI with CI • CTI is increased after irradiation • Activating the CI function mitigates the increase of CTI • A saw-tooth shape appears in stacking plots Before After PIXEL2012

14. Degradation without CI • The degradation of our new P-ch CCD in terms of CTI is comparable with that of the N-channel CCD onboard the Suzaku satellite, confirming its radiation tolerance enough for space use PIXEL2012

15. Degradation with CI • The same conclusion does apply also for the case with CI • Activating CI function surely mitigates CTI degradation PIXEL2012

16. Temperature dependence • performed after the radiation damage experiment • The cooler is the better • more than factor 2 improvement at -140 degree Celesius CI-off working temperature at the radiation test CI-on PIXEL2012

17. Contents • P-channel CCD for the Astro-H satellite • Proton radiation damage experiment • Comparison with other P-channel CCD experiments • Summary PIXEL2012

18. Comparison with other experimental results • Reported values of LBNL P-ch CCDs show higher radiation tolerance • Even considering differences in experimental setup (6.7 vs 12 MeV, -110 vs -145 degC), the difference appears to remain • Different manufactures (processing) might result in the difference PIXEL2012

19. Contents • P-channel CCD for the Astro-H satellite • Proton radiation damage experiment • Comparison with other P-channel CCD experiments • Summary PIXEL2012

20. Summary • We performed a proton radiation damage experiment on a new type of P-channel CCD for the Astro-H satellite • In comparison with the CTI measured in the N-channel CCD onboard the Suzaku satellite, our P-channel CCD has been proven to be radiation tolerant enough for space use • The comparable radiation tolerance with that of an N-ch CCD is different from the report on the LBNL P-ch CCDs PIXEL2012