@misc{oai:repo.qst.go.jp:00075736,
 author = {ドーバー, ニコラス ピーター and Nishiuchi, Mamiko and Kevin Koga, James and Sakaki, Hironao and Kondo, Kotaro and Kiriyama, Hiromitsu and Miyahara, Takumi and Ogura, Koichi and Pirozhkov, Alexander and Sagisaka, Akito and Kando, Masaki and Kondo, Kiminori and Dover, NicholasPeter and Nishiuchi, Mamiko and Kevin Koga, James and Sakaki, Hironao and Kondo, Kotaro and Kiriyama, Hiromitsu and Miyahara, Takumi and Ogura, Koichi and Pirozhkov, Alexander and Sagisaka, Akito and Kando, Masaki and Kondo, Kiminori},
 month = {Apr},
 note = {State-of-the-art high power laser facilities present numerous potential applications, including the generation of ultra-short and low emittance ion beams. Understanding the underlying laser-plasma interaction physics and resulting scaling to ultra-high intensities is of great importance for optimising such sources. We therefore present experimental data of proton acceleration in a sheath field using the ultra-high intensity J-KAREN-P laser (10 J, 40 fs, 5x1021 W/cm2), allowing investigation at the high-intensity frontier.
A repetitive tape target was used to generate proton beams at a 0.1 Hz repetition rate limited only by the laser, allowing a systematic and comprehensive scan over laser parameters. Our laser-target system is able to regularly produce protons in excess of 40 MeV at the full repetition rate. We will demonstrate a slower than expected increase in proton energy with decreasing focal spot size, show that this is due to a reduced sheath lifetime for tight focal spots, and propose a new model which successfully predicts proton energies over a large range of focal spot sizes.We demonstrate that the laser accelerated electron temperature depends not only on laser intensity but also on focal-spot size, in which the restriction of the transverse acceleration distance causes saturation of the electron temperature at increasingly small foci. However, the accelerated electron beam profile becomes more collimated and asymmetric with small focal spots. Measurements of the proton beam show only limited benefit to using increasingly small focal spot sizes, and the best scaling for achieving higher maximum proton energies from sheath acceleration is achieved with increasing the pulse energy, rather than reducing the spot size or pulse length., Optics & Photonics International Congress 2019 (HEDS2019)},
 title = {Experimental investigation of sheath-driven proton beam parameters in the ultra-short pulse, ultra-high intensity regime},
 year = {2019}
}