*4.3. Research Results Using the Tandem Accelerator and the Synchrotron*

An AlGaN/GaN high-electron mobility transistor (HEMT) has a lot of advantages for space applications, such as having high efficiency, high power and being lightweight. In order to quantify the radiation tolerance of the HEMT in space environment, Sasaki et al. investigated the change in its device characteristics by using the 11.1 MeV, 20.6 MeV and 66.8 MeV proton beams from the synchrotron [22]. The irradiation was performed with the proton flux of 1.7 <sup>×</sup> <sup>10</sup><sup>8</sup> cm−<sup>2</sup> s <sup>−</sup><sup>1</sup> under off-bias (*V*gs <sup>=</sup> <sup>−</sup>5.0 V, *<sup>V</sup>*ds = 100 V) condition. No difference was observed in the breakdown voltage at any irradiation energy (Figure 11).

To study the DDD effect on the HEMT, the change in the output power due to the 2 MeV proton irradiation was also examined by using the tandem accelerator [22]. The 2 MeV proton beam flux was 7 <sup>×</sup> <sup>10</sup><sup>11</sup> cm−<sup>2</sup> s −1 . The output power at last decreased by <sup>−</sup>4 dB and <sup>−</sup>10 dB at fluences of 3 <sup>×</sup> <sup>10</sup><sup>14</sup> and 1 <sup>×</sup> <sup>10</sup><sup>15</sup> cm−<sup>2</sup> , respectively (Figure 12). Sasaki et al. have explained this irradiation effect as being due to the lattice defects produced by the proton irradiation. As the effect by proton fluence of 7 <sup>×</sup> <sup>10</sup>11/cm<sup>2</sup> roughly corresponds to the radiation damage of 10 years in the geostationary orbit, the experimental result indicates that this device has a sufficient margin for proton irradiation tolerance to operate in the geostationary orbit. They have also found that when the channel temperature was 125 ◦C, the output power was partially recovered by radio frequency (RF) operation or reverse bias stress (*V*gs = −5 V, *V*ds = 30 V).

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**Figure 11.** Normalized off-state (*V*gs = −5.0 V) drain breakdown voltage (*BV*ds) of HEMT under 11.1– 66.8 MeV proton irradiation. **Figure 11.** Normalized off-state (*V*gs = −5.0 V) drain breakdown voltage (*BV*ds) of HEMT under 11.1–66.8 MeV proton irradiation.

**Figure 12.** Change in output power of HEMT by 2 MeV proton irradiation. **Figure 12.** Change in output power of HEMT by 2 MeV proton irradiation.

### *4.4. Research Results Using the Tandem Accelerator 4.4. Research Results Using the Tandem Accelerator*

**Figure 12.** Change in output power of HEMT by 2 MeV proton irradiation. *4.4. Research Results Using the Tandem Accelerator* The Martian Moons eXploration (MMX) is a project of the Japan Aerospace Exploration Agency (JAXA) to explore the two moons (Phobos and Deimos) of Mars with a scheduled launch in the mid-2020s. A spacecraft will enter into the orbit around Mars and will collect scientific data and gather samples from the moons' surfaces. Unlike the Earth, Mars does not have a global magnetic field. Therefore, electronic devices attached to the MMX spacecraft orbiting around Mars and its moons will be exposed to interplanetary high energy protons with the wide energy range. Ozaki et al. have performed the experiments on irradiation resistance evaluation of CCD imagers, which is one of the important electronic devices installed to the MMX spacecraft, by using an 8 MeV proton beam from the tandem accelerator [23]. The irradiation effect has been observed as an increase in dark current. The Martian Moons eXploration (MMX) is a project of the Japan Aerospace Exploration Agency (JAXA) to explore the two moons (Phobos and Deimos) of Mars with a scheduled launch in the mid-2020s. A spacecraft will enter into the orbit around Mars and will collect scientific data and gather samples from the moons' surfaces. Unlike the Earth, Mars does not have a global magnetic field. Therefore, electronic devices attached to the MMX spacecraft orbiting around Mars and its moons will be exposed to interplanetary high energy protons with the wide energy range. Ozaki et al. have performed the experiments on irradiation resistance evaluation of CCD imagers, which is one of the important electronic devices installed to the MMX spacecraft, by using an 8 MeV proton beam from the tandem accelerator [23]. The irradiation effect has been observed as an increase in dark current. They have performed a similar experiment using a 70 MeV proton beam at another facility. From the proton energy dependence of the irradiation effect on CCD imagers, the ex-The Martian Moons eXploration (MMX) is a project of the Japan Aerospace Exploration Agency (JAXA) to explore the two moons (Phobos and Deimos) of Mars with a scheduled launch in the mid-2020s. A spacecraft will enter into the orbit around Mars and will collect scientific data and gather samples from the moons' surfaces. Unlike the Earth, Mars does not have a global magnetic field. Therefore, electronic devices attached to the MMX spacecraft orbiting around Mars and its moons will be exposed to interplanetary high energy protons with the wide energy range. Ozaki et al. have performed the experiments on irradiation resistance evaluation of CCD imagers, which is one of the important electronic devices installed to the MMX spacecraft, by using an 8 MeV proton beam from the tandem accelerator [23]. The irradiation effect has been observed as an increase in dark current. They have performed a similar experiment using a 70 MeV proton beam at another facility. From the proton energy dependence of the irradiation effect on CCD imagers, the experimental data are now being analyzed in terms of the total ionization dose (TID) and the non-ionization energy loss (NIEL).

#### They have performed a similar experiment using a 70 MeV proton beam at another facility. From the proton energy dependence of the irradiation effect on CCD imagers, the experimental data are now being analyzed in terms of the total ionization dose (TID) and the non-ionization energy loss (NIEL). *4.5. Research Results Using the Ion-Implanter*

perimental data are now being analyzed in terms of the total ionization dose (TID) and the non-ionization energy loss (NIEL). As perovskite solar cells have beneficial features as a high-power conversion efficiency as high as 24%, low-cost, thin-coating, lightweight, and large-area fabrication, they are expected for the application to the space industry. To confirm the irradiation effect on

perovskite type solar cells, Kanaya et al. performed the 50 keV proton irradiation with total doses of 1 <sup>×</sup> <sup>10</sup>13, 1 <sup>×</sup> <sup>10</sup>14, and 1 <sup>×</sup> <sup>10</sup><sup>15</sup> cm−<sup>2</sup> using the 200 kV ion-implanter [24]. To investigate the irradiation effect on the grain structure and lattice structure, three types of perovskite solar cells with different grain sizes (~240, ~340, and ~690 nm) were used and the irradiation effects were evaluated by a scanning electron microscope (SEM), X-ray diffraction (XRD), photoluminescence (PL), and time-resolved photoluminescence (TRPL). From the experimental results of SEM and XRD, they have concluded that there is little difference between the initial and irradiated samples in the grain structure or the crystal structure. The result of the TRPL spectrum measurements is shown in Figure 13. Even by the irradiation up to the fluence of 1 <sup>×</sup> <sup>10</sup><sup>14</sup> cm−<sup>2</sup> , the TRPL spectrum curve does not exhibit a significant decrease. After the irradiation with the fluence of 1 <sup>×</sup> <sup>10</sup><sup>15</sup> cm−<sup>2</sup> , the lifetime of TRPL spectrum decreases for each grain size. The experimental result shows that perovskite solar cells have a high radiation resistance against the proton irradiation up to the fluence of 10<sup>14</sup> cm−<sup>2</sup> . investigate the irradiation effect on the grain structure and lattice structure, three types of perovskite solar cells with different grain sizes (~240, ~340, and ~690 nm) were used and the irradiation effects were evaluated by a scanning electron microscope (SEM), X-ray diffraction (XRD), photoluminescence (PL), and time-resolved photoluminescence (TRPL). From the experimental results of SEM and XRD, they have concluded that there is little difference between the initial and irradiated samples in the grain structure or the crystal structure. The result of the TRPL spectrum measurements is shown in Figure 13. Even by the irradiation up to the fluence of 1 × 1014 cm–2, the TRPL spectrum curve does not exhibit a significant decrease. After the irradiation with the fluence of 1 × 1015 cm–2, the lifetime of TRPL spectrum decreases for each grain size. The experimental result shows that perovskite solar cells have a high radiation resistance against the proton irradiation up to the fluence of 1014 cm–2.

As perovskite solar cells have beneficial features as a high-power conversion effi-

perovskite type solar cells, Kanaya et al. performed the 50 keV proton irradiation with total doses of 1 × 1013, 1 × 1014, and 1 × 1015 cm–2 using the 200 kV ion-implanter [24]. To

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*4.5. Research Results Using the Ion-Implanter* 

**Figure 13.** Effect of 50 keV proton irradiation on normalized TRPL decay curves for small grain (~240 nm) sample, medium grain (~340 nm) sample, and large grain (~690 nm) sample. (Reprint Figure 2 in p. 6992 of S. Kanaya et al**.**, J. Phys. Chem. Lett. 10(2019) 6990–6995)**. Figure 13.** Effect of 50 keV proton irradiation on normalized TRPL decay curves for small grain (~240 nm) sample, medium grain (~340 nm) sample, and large grain (~690 nm) sample. (Reprint Figure 2 in p. 6992 of S. Kanaya et al., J. Phys. Chem. Lett. 10(2019) 6990–6995).

Triple-junction (InGaP/InGaAs/Ge) solar cells are typical successors for the space application and currently widely utilized due to their higher photovoltaic conversion efficiency and better radiation resistance compared to conventional single-junction silicon space solar cells. Imaizumi et al. investigated the effects of the fluence rate and the irradiation mode (defocused beam or scanned beam) of 50, 100 and 150 keV proton irradiation ground tests on the degradation of a triple-junction solar cell and a single-junction silicon solar cell using two accelerators: the ion-implanter at WERC, and that at the National Institutes for Quantum and Radiological Science and Technology (QST)-Takasaki. They Triple-junction (InGaP/InGaAs/Ge) solar cells are typical successors for the space application and currently widely utilized due to their higher photovoltaic conversion efficiency and better radiation resistance compared to conventional single-junction silicon space solar cells. Imaizumi et al. investigated the effects of the fluence rate and the irradiation mode (defocused beam or scanned beam) of 50, 100 and 150 keV proton irradiation ground tests on the degradation of a triple-junction solar cell and a single-junction silicon solar cell using two accelerators: the ion-implanter at WERC, and that at the National Institutes for Quantum and Radiological Science and Technology (QST)-Takasaki. They have found that the photovoltaic properties of both the solar cells are degraded irrespective of the fluence rate or the irradiation mode. The details are discussed in [25].

have found that the photovoltaic properties of both the solar cells are degraded irrespective of the fluence rate or the irradiation mode. The details are discussed in [25]. Finally, we mention the study of the proton irradiation effect on carbonaceous chondrites by Nakauchi et al. [33]. Although this study is not directly related to the irradiation Finally, we mention the study of the proton irradiation effect on carbonaceous chondrites by Nakauchi et al. [33]. Although this study is not directly related to the irradiation effect on space electronics, the result obtained by the ion irradiation at WERC is academically quite interesting and important in the field of the astrophysics.

effect on space electronics, the result obtained by the ion irradiation at WERC is academically quite interesting and important in the field of the astrophysics. Airless planetary bodies, from which carbonaceous chondrites (CCs) originate, have been mainly exposed to the irradiation with solar wind protons. To investigate the effect of solar wind protons on the surfaces of planetary bodies, Nakauchi et al. irradiated serpentine and saponite samples, which are two major components of CCs, with 10 keV H2+ Airless planetary bodies, from which carbonaceous chondrites (CCs) originate, have been mainly exposed to the irradiation with solar wind protons. To investigate the effect of solar wind protons on the surfaces of planetary bodies, Nakauchi et al. irradiated serpentine and saponite samples, which are two major components of CCs, with 10 keV H<sup>2</sup> + ions up to the fluence of 1.7 <sup>×</sup> <sup>10</sup><sup>18</sup> protons/cm<sup>2</sup> , and their reflectance spectra were measured in the wavelength range from 1.5 to 5.5 µm. As the 10 keV H<sup>2</sup> <sup>+</sup> molecule ion becomes two 5 keV proton ions at the sample surface by the Coulomb explosion process, the 10 keV H<sup>2</sup> + ion irradiation corresponds to the 5 keV proton irradiation. Figure 14 shows that the absorption strength for serpentine at the wavelengths of 2.85 µm and 3.0 µm

increases with increasing the proton dose. The absorption at 2.85 µm and that at 3.0 µm correspond to Si-OH and the total amount of OH and H2O, respectively. This experimental result is the first direct evidence of H2O formation at the surfaces of airless planetary bodies only by solar wind protons. with increasing the proton dose. The absorption at 2.85 μm and that at 3.0 μm correspond to Si-OH and the total amount of OH and H2O, respectively. This experimental result is the first direct evidence of H2O formation at the surfaces of airless planetary bodies only by solar wind protons.

ions up to the fluence of 1.7 × 1018 protons/cm2, and their reflectance spectra were measured in the wavelength range from 1.5 to 5.5 μm. As the 10 keV H2+ molecule ion becomes two 5 keV proton ions at the sample surface by the Coulomb explosion process, the 10 keV H2+ ion irradiation corresponds to the 5 keV proton irradiation. Figure 14 shows that the absorption strength for serpentine at the wavelengths of 2.85 μm and 3.0 μm increases

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**Figure 14.** Change in absorption strength at 2.85 μm and 3.0 μm as a function of proton dose for serpentine. (Reprint Figure 6 in p.6 of Y. Nakauchi et al., Icarus 355(2021) 114140). **Figure 14.** Change in absorption strength at 2.85 µm and 3.0 µm as a function of proton dose for serpentine. (Reprint Figure 6 in p.6 of Y. Nakauchi et al., Icarus 355(2021) 114140).

### **5. Summary 5. Summary**

The ion accelerator facility at WERC, which consists of three kinds of accelerators (the synchrotron, the tandem accelerator, and the ion-implanter), has been utilized for the ground tests of the irradiation-induced degradation of several space electronics such as space solar cells, radiation detectors, image sensors, and LSI circuits. The facility has also contributed to the fundamental study on the astrophysics. Through collaborations with several universities, private companies, and national institutes such as JAXA and QST, further research and development using the ion facility at WERC can be expected for the space industry. The ion accelerator facility at WERC, which consists of three kinds of accelerators (the synchrotron, the tandem accelerator, and the ion-implanter), has been utilized for the ground tests of the irradiation-induced degradation of several space electronics such as space solar cells, radiation detectors, image sensors, and LSI circuits. The facility has also contributed to the fundamental study on the astrophysics. Through collaborations with several universities, private companies, and national institutes such as JAXA and QST, further research and development using the ion facility at WERC can be expected for the space industry.

**Author Contributions:** Original draft preparation, writing and editing, S.H., R.I. and K.S. Final check of draft, K.K. All authors have read and agreed to the published version of the manuscript. **Author Contributions:** Original draft preparation, writing and editing, S.H., R.I. and K.S. Final check of draft, K.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding. **Funding:** This research received no external funding.

**Data Availability Statement:** The data presented in this study are available on request from the authors. **Data Availability Statement:** The data presented in this study are available on request from the authors.

**Acknowledgments:** The authors thank Yonetoku, Ogino, Takahashi, Yatsu, Arimoto, Yamaoka, Okumaya, Sasaki, Ozaki, Kanaya, and Nakauchi for their great help. The authors also thank T. Ohshima and M. Imaizumi for fruitful discussion. **Acknowledgments:** The authors thank Yonetoku, Ogino, Takahashi, Yatsu, Arimoto, Yamaoka, Okumaya, Sasaki, Ozaki, Kanaya, and Nakauchi for their great help. The authors also thank T. Ohshima and M. Imaizumi for fruitful discussion.

**Conflicts of Interest:** The authors declare no conflict of interest. **Conflicts of Interest:** The authors declare no conflict of interest.
