Status of the laser stripping of H beam at J-PARC RCS

Saha, P. K.; 原田 寛之; 米田 仁紀*; 道根 百合奈*; 佐藤 篤*; 柴田 崇統*; 金正 倫計

Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.59 - 63, 2023/11

https://www.pasj.jp/web_publish/pasj2023/proceedings/PDF/WEOB/WEOB5.pdf

To overcome the issues and practical limitations associated with the stripper foil used for the charge-exchange injection (CEI) of H beam for high-intensity proton accelerators, we are studying a foil-less H CEI by using only lasers at J-PARC RCS. To establish our principle, we are preparing for a POP (proof-of-principle) demonstration of 400 MeV H stripping to proton by using lasers. We will use both IR and UV lasers in the process of H stripping to protons. A prototype YAG laser system has been developed through experimental studies of 3 MeV H neutralization. We have also developed a multi-reflection laser cavity system to sufficiently reduce the seed laser energy. We have succeeded for 32 reflections to gain on the laser energy up to 16 to obtain a neutralization fraction of 25%. To realize a perfect benefit of the cavity, we also recently developed higher efficient vacuum windows by which we can achieve the laser energy gain to almost 32, proportional to the number of reflections. As a result, the average power of the seed laser can be reduced to 1/32, which is more useful for the UV laser. The laser setup at the 400 MeV beam line is in progress to start POP experimental studies in 2024.

Recent progress of laser stripping POP demonstration study at J-PARC RCS

Saha, P. K.; 原田 寛之; 米田 仁紀*; 道根 百合奈*; 渕 葵*; 佐藤 篤*; 柴田 崇統*; 金正 倫計

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.656 - 660, 2021/10

https://www.pasj.jp/web_publish/pasj2021/proceedings/PDF/WEP0/WEP020.pdf

We have significant progress on the preparation of POP (proof-of-principle) demonstration of 400 MeV H stripping to proton by using only lasers at J-PARC RCS. The motivation of this research is to establish H charge-exchange injection by using lasers instead of a stripper foil conventionally used at present. A short foil lifetime and residual radiation caused by the foil scattering beam loss are extremely serious issues, especially at high-intensity operation. The R&D of the laser system is in good progress through experimental studies for 3 MeV H beam at present. We developed a multi-reflection laser cavity system to reduce the seed laser power, which was also successfully tested for 3 MeV H beam neutralization in July, 2021. Further development of the whole laser system is continued to start the POP demonstration study in 2022.

Studies of laser power reduction for the laser stripping of 400 MeV beam at J-PARC RCS

Saha, P. K.; 原田 寛之; 金正 倫計; 米田 仁紀*; 道根 百合奈*; 渕 葵*; 佐藤 篤*; Liu, Y.*

JPS Conference Proceedings (Internet), 33, p.011025_1 - 011025_7, 2021/03

BB2019-1158.pdf:0.7MB

https://doi.org/10.7566/JPSCP.33.011025

We proposed and also preparing for a POP (Proof-of-Principle) demonstration of a completely non-destructive H stripping method by using only lasers at J-PARC. To reduce the laser power, which is one of the critical issues in this case, we have studied an extensive manipulations of the H beam as well advanced uses of the lasers in this research. These includes utilizing a dispersion derivative of the H beam to cope with its large momentum spread, while multi-pass laser system to utilize multiple interactions of the H beam with lasers. We have estimated that the laser power can be reduced to more than one order of magnitude by applying a combination of these two methods. The detail simulation and experimental results of the H beam manipulations as well as development status of the multi-pass laser system are presented in this paper.

Status of the proof-of-principle demonstration of 400 MeV H laser stripping at J-PARC

Saha, P. K.; 原田 寛之; 米田 仁紀*; 道根 百合奈*; 渕 葵*; 佐藤 篤*; 柴田 崇統*; 金正 倫計

Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.436 - 440, 2020/09

https://www.pasj.jp/web_publish/pasj2020/proceedings/PDF/THPP/THPP02.pdf

A proof-of-principle (POP) demonstration of 400 MeV H stripping to proton by using only laser is under preparation at J-PARC. We aim to establish a non-destructive H charge-exchange injection by using lasers instead of stripper foil used for that purpose. A short foil lifetime, unexpected failure and also high residual radiation due to foil scattering beam losses are serious issues for high-intensity operation. In our three steps method, the H is first neutralized to H by using an YAG laser, the H is excited to the upper states (H) by using a UV laser, and finally the H is stripped to proton by the YAG laser. The YAG laser system will be tested first for 3 MeV H neutralization at the end of 2020, while the UV laser is under development. The H beam manipulations to match with laser parameters are also being continued. The present experimental status for the POP demonstration of H laser stripping is presented.

Progress status of proof-of-principle demonstration of 400 MeV H laser stripping at J-PARC 3-GeV RCS

Saha, P. K.; 原田 寛之; 金正 倫計; 三浦 昭彦; 吉本 政弘; 岡部 晃大; 菅沼 和明; 山根 功*; 入江 吉郎*; Liu, Y.*; et al.

Proceedings of 15th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.806 - 810, 2018/08

https://www.pasj.jp/web_publish/pasj2018/proceedings/PDF/THP0/THP016.pdf

To ensure stable operation of J-PARC RCS at 1 MW beam power and beyond, an alternative H stripping injection method other than using stripper foil has to be implemented. A short life time of the foil due to foil degradation caused by high intensity beam irradiation as well as an extremely high residual radiation at the injection area caused by the foil beam scattering beam loss are two serious issues not only to maintain a long-term stable operation, but also for the facility maintenance. The laser stripping of H holds the promise of overcoming and eliminating the above issues, as it has no lifetime issue as well as completely nondestructive. To establish and develop the new method for the RCS operation, a POP (proof-of-principle) demonstration of 400 MeV H stripping by using only laser has to be carried out first. The progress status of the POP experiment, which includes recent beam study and simulation results for the H beam manipulations to reduce the laser power is presented.

Status of proof-of-principle demonstration of 400 MeV H- stripping to proton by using only lasers at J-PARC

Saha, P. K.; 原田 寛之; 金正 倫計; 三浦 昭彦; 吉本 政弘; 入江 吉郎*; 山根 功*; 米田 仁紀*; 道根 百合奈*

Proceedings of 61st ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2018) (Internet), p.422 - 427, 2018/07

https://doi.org/10.18429/JACoW-HB2018-THP1WC02

The laser stripping of H is the most advanced application of the laser manipulations of H beams, especially at high intensity accelerators like J-PARC. The first stage of the present research includes non-destructive beam measuring as well as online morning by using lasers, which is highly essential at J-PARC as the beam power is approaching to 1 MW and beyond. In addition, it is also highly required to replace the stripper foil by lasers used for multi-turn H charge exchange injection in RCS. Extremely high residual radiation due to beam losses caused by the foil-beam interaction and short lifetime of the foil are serious issues for facility maintenance and stable operation. To overcome the issues and limitations associated with foil, in the present research we will perform a proof-of-principle demonstration of H stripping to protons by using lasers, which is essential not only at J-PARC, but also for similar existing and proposing high intensity proton accelerators worldwide.

High-precision measurement of the spectral width of the nickel-like molybdenum X-ray laser

長谷川 登; 河内 哲哉; 佐々木 明; 山谷 寛; 岸本 牧; 越智 義浩; 田中 桃子; 錦野 将元; 國枝 雄一; 永島 圭介; et al.

Journal of Physics; Conference Series, 163(1), p.012062_1 - 012062_4, 2009/06

https://doi.org/10.1088/1742-6596/163/1/012062

X線レーザーは高密度の多価イオンを媒質としている。X線レーザーは線幅が非常に狭いため、その波長及び線幅の精密な計測結果は、原子過程の計算、特に衝突励起及び脱励起の計算の指標となる。しかし、非常に高い分解能が必要なため、特に線幅についての計測例はほとんど報告されていないのが現状である。今回われわれは、ニッケル様モリブデンを増幅媒質とするX線レーザーの線幅計測に成功したので、それを報告する。

強磁場によるX線レーザーの偏光制御について

長谷川 登; 河内 哲哉; 佐々木 明; 岸本 牧; 田中 桃子; 越智 義浩; 錦野 将元; 國枝 雄一; 岩前 敦*; 米田 仁紀*

no journal, , 

本研究ではプラズマX線レーザーの発振過程を利用し、強磁場を印加することで円偏光の選択的な抽出を行う方法を開発している。今回対象としたX線レーザー遷移はNi様イオンの4p(J=1)-4d(J=0)であり、下準位(4p)は磁気量子数m=-1,0,+1の3つの準位が縮退しているものを選んでいる。m=-1の遷移線では量子化軸の方向に右回りの円偏光、m=+1の遷移線では量子化軸の方向に左回りの円偏光、m=0の遷移線では量子化軸と垂直な方向に直線偏光の輻射が行われるため、量子化軸を外部磁場により決定することで特定の偏光状態の選択が可能となる。実験では小型パルスパワー装置により約20Teslaの磁場をプラズマX線利得媒質部に与え、この制御を試みたのでこれを報告する。

レーザー荷電変換入射に向けた原理実証実験

原田 寛之; Saha, P. K.; 米田 仁紀*; 道根 百合奈*; 渕 葵*; 佐藤 篤*; 金正 倫計

no journal, , 

大強度陽子加速器では、線形加速器で加速された負水素イオンの2つの電子を円形加速器の入射点に設置された荷電変換用炭素膜にて剥ぎ取り、陽子へと変換しながら多周回にわたり入射することで、大強度陽子ビームを形成している。この入射手法は、大強度の陽子ビームを生成できる反面、周回する陽子ビームが膜への衝突を繰り返すことで、ビーム自身が散乱され制御不能なビーム損失が原理的に発生する。加えて、大強度出力ではビームの衝突時の熱や衝撃による膜の破壊が生じる。大強度陽子ビームの出力や運転効率は、このビーム損失による残留線量や膜の寿命による制限が懸念される。そのため、さらなる大強度出力には炭素膜を用いた荷電変換入射に代わる新たな入射手法が必要となる。J-PARCでは、さらなる大強度化に向けて、レーザーにて電子剥離を行う「レーザー荷電変換入射」を新たに考案した。その原理実証実験に向けて、レーザーシステムの開発を進めている。本発表では、レーザー荷電変換入射の概要を紹介し、レーザーシステムの開発状況を報告する。

J-PARCにおけるレーザー荷電変換実験のための高繰り返しレーザー開発

渕 葵*; 米田 仁紀*; 道根 百合奈*; 原田 寛之; Saha, P. K.; 佐藤 篤*; 柴田 崇統*; 金正 倫計

no journal, , 

大強度陽子加速器J-PARCでは、リニアックからシンクロトロンに負水素イオンを入射する際に陽子へと荷電変換をしている。現在は炭素膜を用いた手法が用いられているが、さらなる大強度化に向け、レーザーを用いた荷電変換を行うことを目指し、レーザー光源及び原理実証実験を進めている。この方式では、ドップラー効果と多段階の電子電離プロセスを考えており、高出力レーザー開発が比較的容易な波長のレーザーとその5倍波のパルスレーザーを利用することを想定している。さらに、パルスあたりのエネルギーを下げるには、光の有効利用率を高めなければならない。そのため、折り返し像転送光学系やビームシェーパーの開発を進めている。本発表では、現在開発中の高繰り返しレーザー光源や像転送光学系について報告する。