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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

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

超高強度J-KARENレーザーを用いた重イオン加速におけるイオン化メカニズム及びターゲット中のダイナミクスについて発表する。, 光・量子ビーム科学合同シンポジウム2020（OPTO2020)

Motivated by the development of next-generation heavy ion sources, we have investigated the ionization and acceleration dynamics of an ultra intense laser-driven high-Z silver target, experimentally, numerically and analytically. Using a novel ion measurement technique allowing us to uniquely identify silver ions, we experimentally demonstrate generation of highly charged silver ions (Z=45+2 ????2) with energies of >20 MeV/nucleon (>2.2 GeV) from sub-micron silver targets driven by a laser with intensity 51021 W/cm2, with increasing ion energy and charge state for decreasing target thickness. We show that although target pre-expansion by the unavoidable rising edge of state-of-the-art high power lasers can limit proton energies, it is advantageous for heavy ion acceleration. Two-dimensional particle-in-cell simulations show that the Joule heating in the target bulk results in a high temperature (10 keV) solid density plasma, leading to the generation of high particle number highly charged ions (Z=40+2 ????2 , &10 MeV/nucleon) via electron collisional ionization, which are extracted and accelerated with a small divergence by an extreme sheath eld at the target rear. However, with reduced target thickness this favorable acceleration is degraded due to the target deformation via laser hole boring, which accompanies higher energy ions with higher charge states but in an uncontrollable manner. Our elucidation of the fundamental processes of high intensity laser driven ionization and ion acceleration provides a path for improving the control and parameters of laser driven heavy ion sources, a key component for next-generation heavy ion accelerators.

Retrieving the spectrum of physical radiation from experimental measurements typically involves using a mathematical algorithm to deconvolve the instrument response function from the measured signal. However, in the field of signal processing known as "Source Separation", which refers to the process of computationally retrieving the separate source components that generate an overlapping signal on the detector, the deconvolution process can become an ill-posed problem and crosstalk complicates the separation of the individual sources. To overcome this problem, we have designed a magnetic spectrometer for inline electron energy spectrum diagnosis and developed an analysis algorithm using techniques applicable to the problem of Source Separation. An unknown polychromatic electron spectrum is calculated by sparse coding using a Gaussian basis function and an L1 regularization algorithm with a sparsity constraint. This technique is verified by a specially designed magnetic field electron spectrometer. We use Monte Carlo simulations of the detector response to Maxwellian input energy distributions with electron temperatures of 5.0, 10.0 and 15.0 MeV to show that the calculated sparse spectrum can reproduce the input spectrum with an optimum energy bin width automatically selected by the L1 regularization. The spectra are reproduced with high accuracy of less than 4.0 % error, without an initial value. The technique is then applied to experimental measurements of intense laser accelerated electron beams from solid targets. Our analysis concept of spectral retrieval and automatic optimization of energy bin width by sparse coding could form the basis of a novel diagnostic method for spectroscopy.

On the experiment for laser-driven ion acceleration at J-KAREN-P[1] with pulse repetition rates of 0.1 Hz, the angular distribution of electron spectrum is diagnosed by multiple electron spectrometers. The electron spectrometer with comprising a bending magnet, a CCD camera and a scintillator is placed in the main vacuum chamber. When the laser focus on the target, many radiations generated in the main vacuum chamber, therefore, CCD camera is exposed to the radiation and distorted the measured images. We need to develop a new technique for removing noise (denoising) from a noisy image and recovering a true measurement image. In recent years, with the development of machine learning methods such as Deep-Learning, "Deep-Learning based Feature filtering" that uses a feature value of an image obtained from machine learning as a base and reproduces a true image from a noisy image is developed[2]. This filtering technique is a new technique of reconstructing a denoising image by separating noise and true data with the feature value of the true-image data. This technique expectes to be effective for the denoising of radiation. In order to demonstrate the feature filtering method, we make a pseudo-measured image generated from an ideal simulation of electron spectroscopy (using as the true-image data), and the noise-image data which make from the measured radiation noise convoluted with the pseudo-measured image (using as the noise-image data). Then, the ideal feature base is obtained by machine learning from the true-image data and the noise-image data, the feature filtering of the actually measured data is verified by using these the ideal feature base. In this report, we show the denoising performance of the feature filtering compared with "median filter" which is generally used for filtering of radiation noise., HEDS2020

We report on femtosecond petawatt laser pulses at 0.1 Hz that combine both Ti:sapphire chirped-pulse amplification (CPA) and optical parametric CPA (OPCPA) techniques. High temporal contrast of 1012 prior to the main pulse of 10 J output energy has been demonstrated with a cleaned high-energy seeded low gain OPCPA preamplifier. Intensities as high as 1022 W∕cm2 on target have been achieved by focusing a wave-front corrected 0.3 PW laser by adaptive optics and reflective-type optics with an f ∕1.3 off-axis parabolic mirror. We describe the origins of the pre-pulses generated by the post-pulses through non-linear processes and demonstrate the removal of the pre-pulses by switching to optical components with a small wedge angle at our petawatt laser facility. We also briefly introduce some experimental results. Exploration of new regimes in high field science is now possible with the unprecedented laser intensity levels of the J-KAREN-P laser.

In the high energy, high density plasmas formed by the interaction of an ultra-short pulse laser with a ~100nm-1µm target foil, ions are generated by Target Normal Sheath Acceleration (TNSA). TNSA and specifically the formation of the sheath field on the rear surface of the target needs to be better understood in order to optimize laser driven ion beams for applications such as medical hadron therapy. An understanding of the electron dynamics that control formation of the sheath field in the target is essential and studying x-ray emission from the interaction region provides valuable information about the electron population. For this purpose, preliminary measurements of the spatial and spectral characteristics of the interaction region generated by the irradiation of ultra-thin foil targets by the 1022W/cm2 J-KAREN-P laser have been made via penumbral imaging of the x-ray source and continuum x-ray spectroscopy., OPTO Symposium on Photon and Beam Science

At upgraded petawatt-class J-KARENP laser experiment, we have demonstrated the high charge-states heavy ions to high energies through the interaction of an intense and short laser pulse with a solid target. Petawatt-class laser-solid interaction experiments produce to ion species from the base metal, include contamination ions, with the energy spectrum ranging from a few MeV/u to a few tens MeV/u. And these ion beams have peculiar characteristics; good emittance, high charge-states, and particle flux. Several possible applications of these ion beams have been suggested as injectors for heavy ion accelerators and in the hadron therapy . In order to achieve these applications in the future, it is required to control the ion beam parameters using some scaling models which are made from obtain spectra of each ions. The laser-solid interaction experiments generally use to get the ion spectrum the Thomson parabola and photostimulable phosphor detector (Imaging plate). The imaging plate has a wide dynamic reigns and few tens micrometer resolution. It diagnose a single ion track which made from the deposited energies on the imaging plate. Therefore, from the information of the ion track, an identification of ion species should be possible. Details of an identification of ion species from the single track on the imaging plate will be discussed., International Conference on High Energy Density Science 2019

Petawatt class laser-solid interaction experiments [1] are conducted at the ultra-short pulse (40fs), ultra-intense (10^22 W/cm^2) J-KAREN-P laser system[2]. An electron spectrometer (ESM) that can detect up to a maximum electron energy of 30 MeV was used for measurement of the temperature of the hot electron population emitted by the laser-driven plasma. The ESM consists of a 1.0 T magnet, scintillator (DRZ-high) and CCD camera which were placed in the vacuum chamber in order to make real-time measurements. Not only electrons and x-rays emitted by the plasma, but also secondary electron and x-ray emission generated in the vacuum chamber are detected by the ESM. This secondary emission creates background noise which is randomly scattered over the whole of the observed ESM image. Recently, Statistical-Learning methods for analysis of “big data” have progressed rapidly allowing a novel denoising technique, known as the Denoising Auto Encoder (DAE) [3], to be established. The DAE is based on a Convolution Neural Network that transforms features extracted from the raw image to produce a processed image in which the unwanted noise component has been digitally removed. This technique has been shown to be suitable for processing the ESM images for the purpose of denoising. In this report, we compare conventional denoising methods with the DAE., HEDS2019

QST関西研では、レーザー駆動イオン計測において電場・磁場を同時に垂直にかけて電荷質量比Q/Aに応じた軌跡にてイオンエネルギーとイオン価数を弁別するトムソンパラボラ分光器と、その検出器として輝尽性蛍光体検出器（市販イメージングプレート：IP）を組み合わせたものをHIMACのビームを利用して開発している。その成果を報告する。, HIMAC成果報告会

超高強度レーザーと薄膜との相互作用によって、高エネルギーのイオンが加速されることが知られており、このイオンビームの持つ類希な特徴によって、いろいろな応用先が提唱されている。その一つとして医療応用があるが、量研機構においても炭素線の粒子線治療器のインジェクターへの応用開発が進められており、安定した、より高いフラックス、高エネルギーのイオン線の発生が求められている。 量研機構における高コントラスト超高強度短パルスレーザーJ-KARENを用い、レーザーパルスエネルギー15J、パルス幅30fs、集光径1.5x1.5m2、最大5x1021Wcm-2の集光強度でイオンの加速実験を行った。ターゲットとして、high-Z（銀）の薄膜のターゲットを用いることで、厚みをシステマティックに変化させ、表面不純物層より加速される陽子線・炭素線及びバルクからの銀イオンのエネルギーと価数分布を調査した。サブミクロン厚のターゲットを用いた際には陽子・炭素線共に高エネルギーまで加速される（最高40MeV, 15MeV/u）が、厚みがうすくなるほど最高エネルギーは減少する傾向にあったが（最高20MeV, 10MeV/u）、バルクからの銀イオンに関しては、最高エネルギーは薄いターゲットの方がエネルギー価数共に高く最大で少なくとも45価にまでイオン化された多価イオンが30MeV/uまで加速されていることを確認した。本講演においてはこれらのイオンのイオン化及び加速メカニズムについて報告する。, 第74回年次大会

The interaction of high-intensity laser pulses with solid targets can be used as a highly charged, energetic heavy ion source. Normally, intrinsic contaminants on the target surface suppress the performance of heavy ion acceleration from a high-intensity laser–target interaction, resulting in preferential proton acceleration. Here, we demonstrate that CW laser heating of 5 μm titanium tape targets can remove contaminant hydrocarbons in order to expose a thin oxide layer on the metal surface, ideal for the generation of energetic oxygen beams. This is demonstrated by irradiating the heated targets with a PW class high-power laser at an intensity of 5 × 10^21 W/cm2, showing enhanced acceleration of oxygen ions with a non-thermal-like distribution. Our new scheme using a CW laser-heated Ti tape target is promising for use as a moderate repetition energetic oxygen ion source for future applications.

High power laser systems are an attractive driver for compact energetic ion sources. We demonstrate repetitive acceleration at 0.1 Hz of proton beams up to 40 MeV from a reeled tape target irradiated by ultra-high intensities up to 5 × 1021 Wcm−2 and laser energies ≈ 15 J using the J-KAREN-P laser system. We investigate the stability of the source and its behaviour with laser spot focal size. We compare the scaling of proton energy with laser energy with a recently developed analytical model, and also demonstrate that it is possible to reach energies up to 50 MeV on a single shot with a lower laser energy ≈ 10 J by using a thinner target, motivating development of high repetition targetry suitable for thinner targets.