@misc{oai:repo.qst.go.jp:00082796,
 author = {N. Ryazantsev, S. and A. Pikuz, T. and A. Pikuz, S. and Kaji, T. and Tanabe, H. and Nakagawa, T. and Takafumi, Asai and Kanasaki, M. and Oda, K. and Yamauchi, T. and Jinno, S. and Taguchi, T. and K. Himeno and Iwasaki, K. and Hihara, T. and Sakai, K. and Minami, T. and Abe, Y. and Tokiyasu, A. and Kohri, H. and Kuramitsu, Y. and Sakawa, Y. and Yasuhiro, Miyasaka and Kotaro, Kondo and Akira, Kon and Akito, Sagisaka and Koichi, Ogura and Pirozhkov, Alexander and Masaki, Kando and Kiminori, Kondo and Tetsuya, Kawachi and Hiromitsu, Kiriyama and Yuji, Fukuda and Takafumi, Asai and Yasuhiro, Miyasaka and Kotaro, Kondo and Akira, Kon and Akito, Sagisaka and Koichi, Ogura and Pirozhkov, Alexander and Masaki, Kando and Kiminori, Kondo and Tetsuya, Kawachi and Hiromitsu, Kiriyama and Yuuji, Fukuda},
 month = {Apr},
 note = {Recently it was shown that injection of gas preliminary cooled down to cryogenic temperatures is a promising way to produce micron-scale clusters. For example, in hydrogen clusters with the size up to ≈2 μm were produced via a conical nozzle at 25 K, 6 MPa. Micron scale clusters can be also created with another pre-cooled gases, for example Ar or Kr, but for other temperature values.
 So large clusters diameter value becomes comparable with a waist width of a laser beam produced by the J-KAREN-P laser facility. As a result, an experimental case can occur, when most of the laser energy is absorbed in a single cluster. Such situation can be considered as an interaction of a laser pulse with matter, state of which is close to solid-state. 
In the presentation plasma X-ray spectra features indicating the described case of high-intensity laser and large-scale-cluster interaction are discussed. They were observed experimentally during irradiation of cryogenic (T = 140 K – 220 K) Ar flows by ultra-intensive (I = 10^22 W/cm^2) femtosecond laser pulses generated by the J-KAREN-P laser. Registered X-ray spectra of produced plasma contains Ar XVIII Ly-α and Ar XVII He-α of comparable intensities. It should be noted that the Ar XVIII Ly-α line has been for the first time observed in laser-matter interaction experiments. It indicates that the density of irradiated matter is high enough to provide a rate of impact ionization process, which is sufficient to create a significant amount of H-like Ar ions. It is a challenge to reach such condition for a pure gas or small clusters. Thus, the observed spectra are considered as an evidence of a large micron cluster existing in the beam waist region., International Conference on High Energy Density Sciences (HEDS2021)},
 title = {X-ray spectroscopy evidence of solid-density ultra-relativistic laser plasma in renewable micron-scale cryogenic clusters targets},
 year = {2021}
}