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We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only

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

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.

The carbon thin film as a target for laser‐driven heavy ion acceleration has been developed using the carbonization of polyimide induced by the irradiation of a XeCl excimer laser. The relationship between the depth of the crater produced by the laser irradiation and the laser fluence were measured in order to clear the carbonization mechanisms of polyimide. The melting threshold of polyimide was estimated to 0.058 J/cm2. It is found that the carbonization is induced by the irradiation with the laser fluence around or under the threshold.

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

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

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

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.

関西光化学研究所の J-KAREN-P レーザーを CH または CHCl 薄膜ターゲットに照射し、 無衝突静電衝撃波イオン加速(ECS)の研究を行った。薄膜ターゲット(0.5~4.0μm)をプ レパルスまたはメインパルスの一部を取り出したイオンかパルスによりプラズマ化させる ことで初期プラズマを形成し、そこにメインパルス(プレパルスから数 ns 後)を入射する ことで ECS を生成した。ターゲットの厚さ、レーザーのスポット径、プレパルスとメイン パルスのコントラストなどを変化させることで初期プラズマを変化させて実験を行った。 計測にはトムソンパラボラ(加速イオン)、X 線分光器(プラズマ密度・温度)を使用した。, 第38回 プラズマ・核融合学会 年会

Laser ion acceleration has been intensively inves- tigated after the development of chirped pulse am- plification (CPA) technique. The accelerated ions are applicable for cancer therapy, radioisotope pro- duction, and fast ignition for inertial confinement fusion. To achieve higher ion energies, target thick- ness should be reduced. However, thinner targets can be easily broken by the pedestal or prepulse be- fore the main pulse arrival. We have developed a large-area suspend graphene (LSG) target, which is a single to multiple layered freestanding graphene sheet[3]. Graphene is the thinnest and the strongest material, hence LSG has the potential to be the best targets of laser ion acceleration. We have conducted several experiments with LFEX laser in Osaka University and J-KAREN-P laser in Kansai Photon Science Institute, National Institutes of Quantum Science and Technology. The LFEX laser irradiates on LSG targets with target normal angle. The maximum intensity is ∼ 4 × 10^18 W/cm^2. The J-KAREN-P laser is focused on LSG targets with 45 degree of incident angle at the intensity of ∼ 5 × 10^21 W/cm^2. We have tested the irradiation of non-relativistic laser inten- sity, < 10^18 W/cm^2, by putting the targets at defocusing positions of J-KAREN-P. Thomson parabola spectrometer and CR-39 stack are used to diagnose the accelerated ions. In the all experiments, no plasma mirrors are used. We have observed energetic ions with relativistic laser intensities, a0 ∼ 48 of J-KAREN-P best focus shots and a0 ∼ 1.8 of LFEX. Furthermore, MeV energy ions are also observed with non-relativistic laser intensity, a0 < 1, in defocused experiments of J-KAREN-P. These results imply that LSG has special features no other materials have. We discuss these specialities using particle-in-cell simulations., 第38回 プラズマ・核融合学会 年会

We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only

Recently, monoenergetic electron beams are obtained with intense, short-pulse laser interacting with tenuous (underdense), a few centimeters plasma via laser wakefield acceleration (LWFA) mechanism. Almost all the experiments utilize relatively long focal length focusing devices, of which the F-numbers (ratio of the focal length to the laser diameter) more than 10. We investigated experimentally highly nonlinear regime. The nonlinear regime is not well explored recently and the benefits of the nonlinear regime might be its high gradient and a capability to accelerate high current electrons., 5th Asia Pacific Conference on Plasma Physics

パルサーや高速電波バーストなどの高輝度天体現象で注目される誘導コンプトン散乱は実験的には未実証の物理過程である．本研究では誘導コンプトン散乱の実証実験を行い，散乱後の光子や電子にどのような影響を与えるのかを調べることを目的とする．本発表では2020年12月にJ-KAREN-Pレーザーを用いて行われた実験の報告と初期解析結果について紹介する．, 日本物理学会2021年秋季大会

超高強度レーザーはその強い電磁場により物質を瞬時にイオン化させ、非常 に高いエネルギー密度を持つプラズマを生成することが出来る。この高エネル ギー密度のプラズマの応用として、イオン加速や電子加速の研究が行われてき た。しかしこれらの研究では被加速粒子の計測に注力しており、加速電場を作 るプラズマの状態を計測する方法は限られている。そこで我々は超高強度レー ザーとプラズマの相互作用によって起こるトムソン散乱を用いてプラズマの状 態を診断した。本実験では関西光科学研究所の J-KAREN-P レーザーを用い て、トムソン散乱光のイメージとスペクトルの計測を行った。本発表ではこの 実験の解析結果について報告する。, 日本物理学会2021年秋季大会

Recent theoretical and numerical studies on laser-driven ion acceleration shows sub- relativistic ion acceleration with multistep acceleration schemes. The multistep acceleration with multiple laser pulses and multiple targets allow us to access the relativistic ion regime with the current and the future laser facilities. However, there is no relativistic ion detectors available in the field of laser ion acceleration. We have been developing energetic ion diagnostics using a combination of solid state nuclear path tracker and Thomson parabola, and scintillator base relativistic ion detectors commonly used in nuclear physics. We introduce our recent progress on the laser driven ion acceleration and the novel diagnostics., 日本物理学会2021年秋季大会

多価重イオンでプローブする高強度短パルスレーザーによるプラズマ中のダイナミクスについてＪ-ＫＡＲＥＮレーザーを用いた実験結果およびシミュレーション結果について発表する, レーザープラズマ原子過程シミュレーションオンライン研究会

超高強度レーザーを重金属に照射することで、極限的な高電離・高エネルギー密度プラズマを生成することができるが、その物性は未解明である。本研究では、衝突・電離・輻射過程を組み込んだプラズマ粒子シミュレーションコードPICLSを用いて、J-KAREN-Pに相当するレーザーパルスを銀薄膜に照射した場合の加熱・電離過程および輻射特性を調べた。平均電離度約40価、電子温度約10 keVまで加熱された銀プラズマ(図(a))は、パルス照射後にX線を輻射しながらピコ秒の時間スケールで数100 eV以下まで冷却されることが明らかになった(図(b))。重金属プラズマの輻射体としての特性を明らかにした本成果は、高輝度X線源の開発研究や天文学への応用にも繋がる。, OPTO2021

Ultra-high intensities open a way towards Terawatt and potentially Petawatt gamma-ray pulses in the so called Gamma Flare regime. We performed our first experiment towards this regime with the J-KAREN-P laser operating at intensities close to 10^22 W/cm^2. In this presentation I will overview the experiment, including very bright hard x-ray generation (sub-MeV to a few-MeV spectral range), high-order harmonic generation (30 to 70 eV), and multiple additional diagnostics revealing information on preplasma (properties of reflected 1st, 2nd, and 3rd harmonics and back-reflection). I will compare these results with the integrated HD and PIC simulations., OPTO-2021 Symposium on Photon and Beam Science

Atomically thin graphene is a transparent, highly electrically and thermally conductive, light-weight, and the strongest material. To date, graphene has found applications in many aspects including transport, medicine, electronics, energy, defense, and desalination. We demonstrate another disruptive application of graphene in the field of laser-ion acceleration, in which the unique features of graphene play indispensable role. Laser driven ion sources have been widely investigated for pure science, plasma diagnostics, medical and engineering applications. Recent developments of laser technologies allow us to access radiation regime of laser ion acceleration with relatively thin targets. However, the thinner target is the less durable and can be easily broken by the pedestal or prepulse through impact and heating prior to the main laser arrival. One of the solutions to avoid this is plasma mirror, which is a surface plasma created by the foot of the laser pulse on an optically transparent material working as an effective mirror only for the main laser peak. So far diamond like carbon (DLC) is used to explore the ion acceleration in extremely thin target regime (< 10 nm) with plasma mirrors, and it is necessary to use plasma mirrors even in moderately thin target regime (10-100 nm) to realize energetic ion generation. However, firstly DLC is not 2D material, and therefore, it is very expensive to make it thin and flat. Moreover, graphene is stronger than diamond at extremely thin regime, and much more reasonable for mass-production. Furthermore, installing and operating plasma mirrors at high repetition rate is also costly. Here we show another direct solution using graphene as the thinnest and strongest target ever made. We develop a facile transfer method to fabricate large-area suspended graphene (LSG) as target for laser ion acceleration with precision down to a single atomic layer. Direct irradiation of the LSG targets with an ultra intense laser generates energetic carbons and protons evidently showing the durability of graphene without plasma mirror. This extends the new frontier of science on graphene under extreme electromagnetic field, such as energy frontier and nuclear fusion.

We describe our experiment performed with the J-KAREN-P laser at the intensity approaching 10^22 W/cm^2. In particular, we present the results obtained with hard x-ray (0.1-3 MeV) spectrographs comprising 10 scintillators and a method to reconstruct the x-ray spectra., 3rd International Conference on Nuclear Photonics (NP2020)

At PW-class laser facilities pulse intensities of the order of 10^21 – 10^22 W/cm^2 can be reached by focusing high quality laser beams to spots of a few microns size. Under such conditions, during fs- time intervals a huge amount of optical energy is concentrated into a tiny volume and by the interaction with solid targets creates a plasma with high energy density. Such plasma can be sources of non-linear phenomena, among known and predicted by theory there is the acceleration to high energy of protons, ions, electrons and neutrons, generation of HOH and gamma-flare, creation of exotic states of hollow ions and WDM. The observed phenomena are defined by the type of target, laser energy and strongly depend on the prepulse condition. Achieving highly ionized states for elements with medium Z allows to effectively perform x-ray diagnostics of plasma parameters and preplasma conditions by means of high-resolution spectroscopy based on the analysis of spectra of H-like and He-like ions. Here we l present a review on the recent results on application of x-ray spectroscopic diagnostics of plasmas generated in the interaction of J-KAREN-P ultra-high intensity laser pulses with solid and clusters targets under conditions of different intrinsic laser contrast and under the cases of specially incorporated prepulse for controlled preplasma formation. Plasma parameters were evaluated by means of time integrated x-ray spectroscopic measurements and kinetic modeling using the code PrismSPECT. Certain line intensity relations, including the relations (Ly_a / He_b), (Ly_a / Ly_a satellites), relation between Ly_a satellites, as well as broadening and the shape of line, were used as the main tools for evaluation of plasma parameters. Each of the tools has preferred dependences on plasma electron temperature, electron density, electric and magnetic field strength. Four types of experiments are under consideration., 3rd International Conference on Nuclear Photonics NP2020

We present multi-diagnostic results from laser-plasma experiment at ~10^22 W/cm^2, including optical and high-order harmonics, back-reflection, soft x-rays, keV x-rays, and sub-MeV to MeV x-rays, simultaneously with important laser parameters. We discuss methods to find at-focus target position and compare intensity dependences., OPTICS & PHOTONICS International Congress 2021

After recent upgrade of the Petawatt-class J-KEREN-P laser system the experiments with on-target relativistic intensity up to 10^22 W/cm^2 (pulse energy ~10 J, pulse length ~40 fs, focal spot down to 1.5 um) are routinely carried out at KPSI, QST. In general, for solid targets the plasma formation threshold is of ~10^10-10^12 W/cm^2, therefore the long ASE prepulse, short and ultrashort pedestal intensity crucially impact the formation of plasma conditions and the observed phenomena. It was demonstrated that there exists a strong dependence of the degree of Fe ionization on a laser prepulse, and that an effective generation of energetic, multiply-charged moderate- and high-Z ions can be driven only with laser pulses of ultra-high contrast. Here we report on the new experiments performed at J-KAREN-P laser with the tailored plasma density profile created by specially incorporated prepulse. For the prepulse the ~1/100 of the main pulse power was picked up and delivered to the target with controlled sub-nanosecond time interval prior to the main pulse. The prepulse was focused: (1) on the front of a stainless steel foil for the formation of downstream preplasma with conditions aiming the efficient generation of x-ray flare and high-order harmonics (experiment led by A.S. Pirozhkov); and (2) on the rear-side of a 4-Chlorosterene foil mimicking upstream preplasma, which has the necessary density profile for collisionless shock ion acceleration, when the main pulse is irradiated (experiment led by Y. Fukuda and Y. Sakawa). For both experiments, we present the detailed analysis of plasma parameters provided by means of high-resolution x-ray spectroscopic methods, based on emission characteristics of plasma in the spectral range of Ne-like Fe and H-like Cl ionization states, respectively., International Conference on High Energy Density Sciences (HEDS2021)

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)

超高強度レーザーを用いたイオン加速の研究に関して発表する, 2021年春の物理学会年会

量研・ 関西研では 、超電導シンクロトロンとレーザー駆動炭素インジェクターを組み合わせた重粒子線治療装置の量子メスの開発を進めている。この開発では、 TNSA 法 により、4MeV/ 核子の炭素を発生させ入射することを目標としているが、レーザー駆動加速イオンの特徴であるピコ秒領域の極短パルス大電流という炭素ビームが「ビーム輸送系を介して超伝導 シンクロトロン のアクセプタンスに入射できるのか」という点については十分な検討がされていない。そこで、ビーム診断系および輸送系コンポーネント（磁石、静電レンズ）通過時 に生じる磁場および電場（空間電荷効果以外の外力）による 非線形性の増大に関して計算できるように整備した。今回はそれらの 結果と、量子メス実験用プラットホームでペッパーポット式のエミッタンスモニタで求めた数十keV級低エネルギーのイオンビームのエミッタンス量の結果を比較検討したので報告する。, 日本物理学会第76回年次大会

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 is generated by the post-pulse 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 the 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.

We demonstrate the removal of the pre-pulses based on the exploration of the generation of pre-pulses by post-pulses through the nonlinear process associated with the B-integral in the laser chain of the petawatt facility J-KAREN-P.

International audience; LIPAc is the Linear IFMIF Prototype Accelerator developed within the framework of the IFMIF project under the Broader Approach (BA) agreement signed between EURATOM and the Japanese Government in 2007. The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity neutron fluxes with appropriate energy spectrum in order to characterize materials envisioned for future fusion reactors. Because the IFMIF accelerator has to reach unprecedented performances, the feasibility is being tested through the design, manufacturing, installation, commissioning and testing activities of a 1:1-scale prototype accelerator, namely LIPAc, from the injector to the first cryomodule together with the High Energy Beam Transport line and the High Power Beam Dump. After outstanding results obtained in 2019, the LIPAc project has entered 2020 in the preparation of the third commissioning stage, i.e., validation in continuous-wave mode of the complete accelerator up to 5 MeV with its final beam dump. The validation until the nominal energy of 9 MeV will be made after the completion of cryomodule assembly. After a brief overview of the goals already achieved in the framework of the IFMIF/EVEDA program, this paper will present a synthesis of the results that have been obtained so far with the LIPAc accelerator as well as the future developments planned beyond 2020.