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光は物質の構造や性質を探り，制御するツールとして，現代の科学と産業に欠かせないものとなっている。近年では，レーザー技術と加速器技術の発展と融合が，新たな展開を迎えつつある。その 1 つに「レーザー粒子加速 」 があり，電子やイオンが加速される．さらに２次粒子としてのガンマ線（X線），中性子を発生させることも可能であり，それらのマルチ量子ビームを同時に使えるという他の量子ビーム施設にはない大きな特長を持っている．本稿では，これらのマルチ量子ビーム発生の現状について解説する．

Beam charge control in the staging of laser wakefield acceleration (LWFA) is a crucial technique for developing full-optical jitter-free high-energy electron accelerators. Precise control of total charge in pre-accelerated electron bunches is necessary to achieve practical electron beam characteristics in the final acceleration stage(s). In contrast to the well-known cathode techniques in conventional accelerators, in LWFA the electron injection results from non-linear processes originating from plasma wave breaking. Therefore, the development of charge control requires a deep understanding of the electron self-injection processes and applications of non-trivial tools. The use of asymmetric gas-jet nozzles seems to be a promising way in developing charge control via tuning the target parameters such as plasma density, density slope, and acceleration length. Here, we demonstrate and characterize controllable electron self-injection, owing to a parametric resonance in slantwise density gas jets irradiated by 50 TW femtosecond laser pulses. The measured characteristics of the electron bunches, in which charge and energy distribution depend on the gas density and gas density gradient, agree well with those obtained by multidimensional particle-in-cell simulation and confirm the possibility of charge control.

Highly charged energetic ions generated by the high intensity short pulse laser interaction with the solid density targets attracts many fields of applications including next generation ion accelerators. Although extensive attempts have been carried out in around the world to produce better quality beams in a controllable manner in the past decades, there are still issues to be improved before realising many the applications. We have been investigating the ion acceleration performance from the irradiation of sub-micron solid density plastic and metal folis foils by using two different petawatt-class laser systems, J-KAREN-P at KPSI and Draco at HZDR, aiming at the optimizing ion acceleration performance in a controllable manner. We have achieved generated the energetic light ion acceleration (> 50MeV proton and > 30 MeV/u C6+) and the highly charged energetic heavy ions (Ag and Au) acceleration by controlling the laser temporal pulse condition. Hydrodynamic and 3D particle-in-cell simulation reveals that the laser temporal pulse shape plays an a vital role on in making tailored density conditions for the main pulse for theto undergo relativistic transparency, which as a result forms a transient space-charge field for the efficient ion accelerations. The robustness of the acceleration mechanism is confirmed by the similar ion acceleration performance achieved in the two laser systems. The results pave the way for the establishment of repetitive laser driven ion sources with high energy and high peak current applicable to radiobiology and material science., 光・量子ビーム科学合同シンポジウム2022

Highly charged energetic ions generated by the high intensity short pulse laser interaction with the solid density targets attracts many fields of applications including next generation ion accelerators. Although extensive attempts have been carried out in around the world to produce better quality beams in a controllable manner in the past decades, there are still issues to be improved before realising many the applications. We have been investigating the ion acceleration performance from the irradiation of sub-micron solid density plastic and metal folis foils by using two different petawatt-class laser systems, J-KAREN-P at KPSI and Draco at HZDR, aiming at the optimizing ion acceleration performance in a controllable manner. We have achieved generated the energetic light ion acceleration (> 50MeV proton and > 30 MeV/u C6+) and the highly charged energetic heavy ions (Ag and Au) acceleration by controlling the laser temporal pulse condition. Hydrodynamic and 3D particle-in-cell simulation reveals that the laser temporal pulse shape plays an a vital role on in making tailored density conditions for the main pulse for theto undergo relativistic transparency, which as a result forms a transient space-charge field for the efficient ion accelerations. The robustness of the acceleration mechanism is confirmed by the similar ion acceleration performance achieved in the two laser systems. The results pave the way for the establishment of repetitive laser driven ion sources with high energy and high peak current applicable to radiobiology and material science., International conference on high energy density sciences 2022

1. Introduction Burst Intensification by Singularity Emitting Radiation (BISER) [1] is the emission of coherent traveling waves by multi-stream flow singularities. Such singularities can be produced in relativistic plasma by high-power lasers, resulting in very bright coherent x-ray emission [2],[3]. 2. Experimental We have recently performed an experiment on BISER coherent x-ray generation with the Astra Laser at the CLF RAL, UK. We extensively optimized the experimental conditions, namely the plasma density and profile, and laser spot [4] and pulse, making use of substantial beam time. This resulted in a ~2 orders of magnitude higher BISER brightness compared to earlier experiments with 10 TW lasers. 3. Results In this presentation we discuss results from two soft x-ray spectrographs: a three-channel flat field spectrograph [5] in the forward direction (channels at −0.6, 0, and 0.8°) operating in the 17-34 nm range and a normal-incidence imaging spectrograph [6] in a 10° off-axis direction operating in the 12.4-20 nm range. Under optimum conditions, both spectrographs showed μJ and higher BISER pulse energies per shot in the corresponding spectral ranges and within their acceptance angles. This implies multi-100 μJ BISER pulses in the entire spectral range and within the full angular width. Acknowledgement We acknowledge support from the Astra Laser Group and the CLF Target Fab, Mechanical, and Electrical. Financial support: JSPS Kakenhi JP 19KK0355 and 19H00669, CLF, Russian Science Foundation (20-62-46050), IAP RAS, ELI-Beamlines, MŠMT by the project "Advanced Research Using High Intensity Laser Produced Photons and Particles" (CZ.02.1.01/0.0/0.0/16_019/0000789), High Field Initiative (CZ.02.1.01/0.0/0.0/15_003/0000449) from the European Regional Development Fund, and the QST Director Fund 創成的研究 #20. References [1]A. S. Pirozhkov, T. Zh. Esirkepov et al., "Burst intensification by singularity emitting radiation in multi-stream flows," Sci. Rep. 7, 17968 (2017). [2]A. S. Pirozhkov, et al. "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes" PRL 108, 135004 (2012). [3]A. S. Pirozhkov, et al., "High order harmonics from relativistic electron spikes" NJP 16, 093003 (2014). [4]A. S. Pirozhkov, et al. "Laser Requirements for High-Order Harmonic Generation by Relativistic Plasma Singularities," Quantum Beam Sci. 2, 7 (2018). [5]D. Neely, et al., "A multi-channel soft X-ray flat-field spectrometer," AIP Conf. Proc. 426, 479 (1998). [6]A. N. Shatokhin, et al., "High-resolution stigmatic spectrograph for a wavelength range of 12.5-30 nm," Opt. Express 26, 19009 (2018)., OPIC-2022 (ALPS-2022)

The generation of ~0.9 GGauss B-field was observed in the near-solid density plasma created by high-contrast ultra-relativistic J-KAREN-P laser pulses with specially designed sub-micron Si-rods targets. The B-field was measured by means of x-ray spectroscopic method based on the theory of Langmuir dips., International Conference on High Energy Density Science 2022

Acceleration of particles from the interaction of ultra-intense laser pulses of 1021 W/cm2 level with thin metal foils is investigated experimentally. To determine the laser-produced plasma condition is one of the keys to understand the physical processing and acceleration mechanism. For the purpose, an X-ray spectrometer with elliptical curved Germanium crystal is designed. The crystal was installed into a specific position which can collect the X-ray from the target and reflect the dispersive emission on the image plate. In the experiment, we observed the Au spectrum about 3-6 KeV range using 25-500 nm thickness Au foil targets. The Ni-like Au M-shell spectrum is recorded which is used to analyse the plasma temperature and density in this ultra-intense laser acceleration experiment. Together with the simultaneously measured data of X-ray single photon counting (SPC) system observing 2 to 20 keV energy range, estimate the plasma electron temperature and density using the spectrum data and compare them with theoretical calculated results under non-local thermodynamic equilibrium (NLTE) condition. We will present the detailed laser condition, diagnostic setup and experimental condition. The process between the plasma heating and particles acceleration in the different foil thicknesses will be discussed. showing that the high temperature solid density plasma condition achieved by the ultra-intense short-pulse laser at high intensity limit is crucial for producing highly charged high energy ion beam., OPIC2022

量研関西研では,レーザー駆動イオン加速機構によって生じる炭素ビームの横方向エミッタンスを明らかにすることに取り組んでいる。同時加速される陽子ビームから炭素ビームを弁別することが困難であるために，炭素ビームの横方向エミッタンスが評価された例はない。現在, 四重極磁石による核種の磁場弁別とダブルスリット法とを組み合わせた炭素ビーム横方向エミッタンス診断系の開発を進めている。 本発表では, 数理的な考えを診断装置に組み込むことによる, 観測誤差の低減に関して報告する予定である。, 第69回応用物理学会春季学術講演会

Burst Intensification by Singularity Emitting Radiation (BISER) [1] is the phenomenon of extremely bright coherent wave emission (constructive interference, N^2 effect) by singularities of multi-stream flows. High-power femtosecond lasers can produce such flows and corresponding relativistic plasma singularities in underdense plasma; these singularities emit very bright coherent x-rays [2]-[3]. We have recently performed an experiment on BISER coherent x-ray generation with the Astra Laser in the CLF RAL, UK. We observed BISER coherent soft x-rays with two spectrographs: a three-channel flat field spectrograph [4] in the forward direction (channels at -0.6, 0, and 0.8°) operating in the 17-34 nm range and a normal-incidence imaging spectrograph [5] in a 10° off-axis direction operating in the 12.4-20 nm range. Both spectrographs, in addition, provided data on the angular distribution of the BISER radiation. We took advantage of an extensive experiment term and long daily laser operation hours to optimize the laser (in particular, focal spot, which is a necessary prerequisite for BISER [6], and pulse width) and the experimental conditions (in particular, the density profile). These resulted in ~2 orders of magnitude enhancement in BISER photon number, providing >10^11 photons and >μJ energies per pulse in each channel at 7 TW laser power, the result which could previously be obtained at >100 TW laser power only. We acknowledge support from the Astra Laser Group and the CLF Target Fab, Mechanical, and Electrical. Financial support: JSPS Kakenhi JP 19KK0355 and 19H00669, CLF, Russian Science Foundation (20-62-46050), IAP RAS, ELI-Beamlines, the Ministry of Education, Youth and Sports of the Czech Republic by the project "Advanced Research Using High Intensity Laser Produced Photons and Particles" (CZ.02.1.01/0.0/0.0/16_019/0000789), and the QST Director Fund 創成的研究 #20. [1] A. Pirozhkov, T. Esirkepov et al., "Burst intensification by singularity emitting radiation in multi-stream flows," Sci. Rep. 7, 17968 (2017). [2] A. S. Pirozhkov et al. "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes" PRL 108 135004 (2012) [3] A. S. Pirozhkov et al., "High order harmonics from relativistic electron spikes" New J. Phys. 16, 093003 (2014). [4] D. Neely et al., "A multi-channel soft X-ray flat-field spectrometer," AIP Conf. Proc. 426, 479 (1998). [5] A. Shatokhin et al., "High-resolution stigmatic spectrograph for a wavelength range of 12.5-30 nm," Opt. Express 26 19009 (2018). [6] A. S. Pirozhkov, et al. "Laser Requirements for High-Order Harmonic Generation by Relativistic Plasma Singularities," Quantum Beam Sci. 2, 7 (2018)., Annual meeting of the JSAP

レーザー航跡場による電子加速では高出力短パルスのレーザーを集光光学系でガスに集光し電子を発生させる。この集光光学系の前に小さい開口のマスクを設置してビームサイズを制限し大きいF値を実現することで、電子ビームの品質および安定性が劇的に向上した。本講演ではこの内容について報告する。, 日本物理学会第77回年次大会

We report on an experimental study of optical transition radiation (OTR) from high energy electron bunches generated by laser wakefield acceleration (LWFA) using the J-KAREN-P laser at Kansai Photon Science Institute (KPSI), QST. A three-color OTR imaging system was built to monitor the electron bunch duration variation in a single shot. By the insertion of a blade, relatively stable electron beams were generated using the density transition injection regime. Obvious OTR signal difference was observed between the conditions of pure gas and mixture gas. This experiment suggest that the combination of a sharp density down-ramp and pure gas is beneficial for generating stable and high-brightness electron bunches and the realization of a compact x-ray free electron laser., 日本物理学会第77回年次大会

近年，炭素イオンなどを用いた重イオンビームによるガン治療は成功を収めている．一般的に，直線もしくはシンクロトロン型の粒子加速器が高エネルギー重イオンビーム生成のために使用されるが，それらの加速器は広く医療機関に行き渡らせるにはサイズが大きすぎるという問題を持つ．そのためコンパクトな加速器の実現が求められている．レーザー粒子加速器は，未来の加速器の候補の一つである． 量子科学技術研究開発機構では，高い治療効果が明らかになっている重イオンがん治療装置の高性能化・小型化を目指す“量子メス”プロジェクトを進めている．この次世代の小型重イオンがん治療装置は，重イオンビームの鋭いブラッグピークと，少ない内部散乱による腫瘍への高い線量集中性を持っている．これによって正常組織へのダメージを少なく抑え，より多くのがんを極めて短期間で治療できることが期待され、手術に代わる可能性を秘めている． 現在提案されている第５世代重イオンがん治療装置（量子メス）は，イオン入射器・超伝導シンクロトロン・ビーム輸送系・超伝導回転ガントリーから構成されている．装置を小型化するためには，体積の大部分を占める入射器とシンクロトロンの小型化が不可欠である．レーザー駆動イオン加速は非常に大きな加速勾配を持つことからこの小型化の要求に応える技術として期待されている．既存のイオン入射器をレーザー駆動方式で置き換えるためには，小型のレーザーモジュールの開発とそれを用いたレーザー駆動による数MeV/uの炭素イオンの加速が必要である．そこで，三次元電磁粒子コードによって実験に即したシミュレーションを実施することにより，加速炭素イオンの定量評価を行った．また，加速に有利な６価の炭素イオンを生成するためのレーザー条件を理論的に求め，シミュレーションによる妥当性評価を行った．, 日本物理学会第77回年次大会

超高強度短パルスレーザーと固体薄膜との相互作用により高エネルギーイオンを発生させる手法は、加速器の小型化をはじめとした様々な方面への応用が期待されている。 応用に資するために、発生するイオンビームを制御することが必要不可欠であり、我々はイオン加速性能を最も左右するレーザーの時間波形に着目し、これを制御することで発生するイオンの制御を行うことに挑戦してきている。 制御のためのノブを探るため、独立なペタワット級レーザーJ-KAREN-P（QST関西研）とDraco-PW （ドイツヘルムホルツ研究所）を用い、レーザーの時間波形の精密な制御を行い、同じ材質のターゲット、及びクロスキャリブレーションされた計測機器を用いることで、双方のイオン加速結果を詳細に比較し、同様のイオン加速結果を一致させる条件を得た。この背景にあるイオン加速メカニズムを調査するため、数百ピコ秒前からのレーザー波形を組み込んだ流体シミュレーション及び3D Particle In Cellシミュレーションを行った。イオンの高エネルギー化の背景にある加速メカニズムは、レーザーパルスの相対論的透過現象がカギを握り、レーザーからプラズマへの高効率エネルギー変換が起こっていることが判明した。本講演ではこれらの詳細に関して報告する。, 第77回物理学会年次大会

未来社会創造事業で進めているレーザープラズマ電子加速によるX線自由電子レーザー開発プロジェクトの紹介と理研播磨に設置されているレーザー電子加速プラットフォームで得られている電子、アンジュレータ放射光の成果と今後の展望について紹介する。

1.Why temporal diagnostics are necessary in LWFA 2.Electro-optic (EO) spatial decoding technique 3.EO spatial decoding on the Coulomb field of electron bunches from LWFA (Emission timing) 4.EO spatial decoding on the coherent transition radiation (CTR) from electron bunches in LWFA (Bunch duration, timing outside plasma) 5.Summary, 第５回 RIKEN-RAP and QST-KPSI Joint Seminar

本発表では，レーザー加速電子を用いたX線領域の前の実証段階として，極端紫外領域(Extreme ultraviolet, EUV)の自由電子レーザーの実証を中間の目的として挙げておりその計画の詳細と実験の現状について報告する。, レーザー学会 学術講演会 第42回年次大会

Laser wakefield acceleration (LWFA)1 has been studied intensively due to the inherent ultrashort bunch duration (fs) and large acceleration gradient (GV/cm) over conventional accelerators. For application such as pump-probe experiment, knowledge of not only the electron pulse duration, but also the emission time of electron bunches shot by shot are very important. Although it is of great importance, the emission time of the electron bunch from LWFA have barely been conducted in experiment. Electro-optic (EO) spatial decoding is a convenient technique widely used in THz study2. To measure the emission timing of electrons, we introduced the EO spatial decoding into LWFA. By setting the EO crystal very close to the gas target, we observed the spherical-wavefront coulomb field and derived a new formula describing the temporal mapping relationship3. We discovered that injection position of the electron beams became closer to the drive laser pulse with increased plasma density for Helium gas in the self-injection regime4. With superior data attainability and non-destructive single-shot characteristics, this method could be a candidate as electron emission timing monitor for LWFA experiments., 第25回産研国際シンポジウム

We have realized the removal of most pre-pulses with wedged optics and orders of magnitude enhancement of the pedestal with higher optical quality optics. We have successfully installed the plasma mirror system for further improvement.

We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute, National Institutes for Quantum Science and Technology. The reflectivity of the single plasma mirror system exceeded 80%. In addition, the temporal contrast was improved by two orders of magnitude at 1 ps before the main pulse. Furthermore, the laser near-field spatial distribution after the plasma mirror was kept constant at plasma mirror fluence of less than 100 kJ/cm2. We also present the results of investigating the difference and the fluctuation in energy, pulse width and pointing stability with and without the plasma mirror system.

We demonstrated the precise directional control of high-energy electron beams of several hundred MeV by moving a circular serrated aperture smaller than the laser diameter perpendicular to the laser propagation direction before the final focusing optics in a laser system. This technique is simple and effective because the direction of the electron beam can be precisely controlled without any additional manipulation of the optics in the laser system and the gas target. This will be a useful guideline and of great significance for the future development towards practical uses and applications of laser–plasma accelerators.

We have recently performed an experiment on BISER with the Astra Laser in the CLF RAL. Here we present some of the experiment highlights., 2021 Christmas Meeting of the High Powered Laser Science Community

We report on an experimental investigation of the jitter of electrons from laser wakefield acceleration. The relative arrival timings of the generated electron bunches were detected via electro-optic spatial decoding on the coherent transition radiation emitted when the electrons pass through a 100 μm thick stainless steel foil. The standard deviation of electron timing was measured to be 7 fs at a position outside the plasma. Preliminary analysis suggested that the electron bunches might have durations of a few tens of femtoseconds. This research demonstrated the potential of laser wakefield acceleration for femtosecond pump–probe studies.

We report on an experimental investigation of the jitter of electrons from laser wakefield acceleration. The relative arrival timings of the generated electron bunches were detected via electro-optic spatial decoding on the coherent transition radiation emitted when the electrons pass through a 100 μm thick stainless steel foil. The standard deviation of electron timing was measured to be 7 fs at a position outside the plasma. Preliminary analysis suggested that the electron bunches might have durations of a few tens of femtoseconds. This research demonstrated the potential of laser wakefield acceleration for femtosecond pump–probe studies.

We have experimentally improved the temporal contrast of the petawatt J-KAREN-P laser facility. We have investigated how the generation of pre-pulses by post-pulses changes due to the temporal overlap between the stretched pulse and the post-pulse in a chirped-pulse amplification system. We have shown that the time at which the pre-pulse by the post-pulse generates and its shape are related to the time difference between the stretched main-pulse and the post-pulse. With this investigation, we have found and identified the origins of the pre-pulses and have demonstrated removal of most pre-pulses by eliminating the post-pulse with wedged optics. We have also demonstrated the impact of stretcher optics on the picosecond pedestal. We have realized orders of magnitude enhancement of the pedestal by improving the optical quality of a key component in the stretcher.

The relativistic-flying mirror is a well-known plasma optic which further intensifies a reflected laser field through the Lorentz $\gamma$-factor of the mirror. A high-power laser pulse reflected and focused by a relativistic-flying parabolic mirror experiences the double Doppler effect and as a result its wavelength and pulse duration are shortened by a factor of $4\gamma^2$ in the relativistic limit of $\beta\rightarrow 1$. A laser focus travels with a relativistic speed of the mirror. The relativistic-flying motion of the laser focus makes electric and magnetic field distributions of the focus complicated, and the mathematical expressions describing the field distributions of the focus become of fundamental interest. We present analytical expressions describing the field distribution formed by an ideal flying mirror which has a perfect reflectance over the entire surface and wavelength range. The peak field strength of an incident laser pulse with a center wavelength of $\lambda_0$ and a beam radius of $w_0$ is enhanced by a factor of $\gamma^3(w_0/\lambda_0)$ in the relativistic limit. The electron-positron pair production is investigated in the context of invariant fields based on the enhanced electromagnetic field. The pair production rate under the relativistic-flying laser focus is modified by the Lorentz $\gamma$-factor and the beam radius- wavelength ratio $(w_0/\lambda_0)$. We show that the electron-positron pair can be created by colliding two counter-propagating relativistic-flying laser focuses, each of which is formed when a 180 TW laser pulse is reflected by a relativistic-flying parabolic mirror with a $\gamma= 12.2$, in vacuum.