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)

Contents

P-channel CCD for the Astro-H satellite Proton radiation damage experiment Comparison with other P-channel CCD experiments Summary

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X-ray CCD for Astronomical use

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

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“ASCA” 1993, 417kg

“SUZAKU” 2005, 1700kg

“ASTRO-H” 2014, 2700kg

Cross-sectionof CCD

electroden-channelp-type Si

n-type Sip-channel

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

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Imaging Area31mm x 31mm

Storage Areacovered when installed

Radiation damage in space

Cosmic-ray protons are the primary source for damage

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X

Y

Y

Puls

e H

eig

ht

(Q)

“Charge Transfer inefficiency (CTI)” is a measure of the radiation damage of CCD

Stacking plotwith 55FeFrame image

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

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http://heasarc.gsfc.nasa.gov/docs/suzaku/analysis/sci.html

For space use, we need to know how radiation hard our new device is andhow mitigation methods work

Contents

P-channel CCD for the Astro-H satellite Proton radiation damage experiment Comparison with other P-channel CCD experiments Summary

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Inawashiro

FukuokaNarita

Miyazaki

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

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http://www.kutl.kyushu-u.ac.jp/gaiyou.html

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

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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

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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

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Bragg curve of protons of various energy in Silicon

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 2.1x106 MeV cm-2 day-1 or 260 rad yr-1

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Mizuno et al. (2010, SPIE, 7732,105)

Stacking plots

CTI is increased after irradiation Activating the CI function mitigates the increase of CTI

A saw-tooth shape appears in stacking plots

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without CI with CI

Before

After

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

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Degradation with CI

The same conclusion does apply also for the case with CI Activating CI function surely mitigates CTI degradation

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Temperature dependence

performed after the radiation damage experiment The cooler is the better

more than factor 2 improvement at -140 degree Celesius

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CI-on

CI-off

working temperatureat the radiation test

Contents

P-channel CCD for the Astro-H satellite Proton radiation damage experiment Comparison with other P-channel CCD experiments Summary

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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

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Contents

P-channel CCD for the Astro-H satellite Proton radiation damage experiment Comparison with other P-channel CCD experiments Summary

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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

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