Prospect of laser-driven particle beams for material science and space applications

Spacecraft are subject to harsh environments and their radiation resistance is one of the most important issues [1]. Therefore, radiation response of any components for use in space should be evaluated before their launch to predict their reliability and lifetime in space. For solar cells, electron and proton irradiation experiments are usually carried out to clarify their radiation degradation [2]. Although electrons/protons have energy spectra in space, electron/proton irradiation with mono-energy is used for ground testing due to the limitation of the capability of currently existing standard particle accelerators. Then relative damage coefficients (RDCs), which is a kind of conversion factors to understand degradation values to the standard electron/proton energy (1 MeV for electrons and 10 MeV for electrons), are estimated. Recently, multi-junction solar cells consisting of multilayer of sub-cells, such as InGaP/GaAs/Ge solar cells, are installed onto spacecraft. RDCs for multi-junction solar cells is not monotonic behaviors since their degradation strongly depends on the penetration depth of electrons/protons. Thus, they show large RDCs values when the penetration depth is close to pn junction for each sub cell. This indicates that it is necessary to make irradiation testing with many energies to clarify their degradation in space. If we can use electron/proton beams with energy spectra similar to space environment, the time and cost for the ground testing can reduce as well as radiation degradation of multi-junction solar cells can be predicted with high accuracy. We are expecting laser-driven particle acceleration technology to realized particle beams with energy spectra similar to space environments. Particle irradiation is a popular methodology for the functionalization of materials. For example, nitrogen-vacancy (NV) center in diamond is known as a spin defect which can be applied to the quantum technology, e.g. quantum bit (qubit) and quantum sensor. To create NV centers, we need to introduce vacancies and/or N atoms. Particle irradiation (N ion implantation) is a key technology [3]. For quantum sensing, the sensitivity improves with increasing amounts of NV centers. Thus, for realizing quantum sensing with high sensitivity, it is necessary to create the certain thickness of a NV center layer. Since particle (N ion) beams with energy spectra can introduce damage (N atoms) in diamond by one experiment, laser-driven particle beam acceleration technology is also useful from the point of view of material functionalization. [1] C. Morioka, et al., First flight demonstration of film-laminated InGaP/GaAs and CIGS thin-film solar cells by JAXA’s small satellite in LEO, Prog. Photovolt: Res. Appl., 19 (2011) 825. [2] M. Imaizumi, et al., Radiation degradation characteristics of component subcells in inverted metamorphic triple-junction solar cells irradiated with electrons and protons, Prog. Photovolt: Res. Appl., 25 (2017) 161. [3] Y. Yamazaki, et al., Chapter 4 “Color Centers in Wide-Gap Semiconductors for Quantum Technology” of Defect in Functional Materials, Edited by F. C-C Ling et al., World Scientific Publishing Co.Pte. Ltd (2020) 93.