Electrostatic shock acceleration of ions in near-critical-density plasma driven by a femtosecond petawatt laser

Prashant Kumar Singh,Myung Hoon Cho,Chul Min Kim,Seong Ku Lee,Jae Hee Sung,Hyung Taek Kim,Il Woo Choi,Yong Joo Rhee,Jung Hun Shin,Hwang Woon Lee,Calin Ioan Hojbota ,Vishwa Bandhu Pathak,Victor Malka,Florian Mollica ,Kazuhisa Nakajima,Constantin Aniculaesei,Ki Hong Pae,Seung-Geun Lee ,Chang‐Mo Ryu ,Chang Hee Nam

doi:10.1038/s41598-020-75455-1

Abstract

With the recent advances in ultrahigh intensity lasers, exotic astrophysical phenomena can be investigated in laboratory environments. Collisionless shock in a plasma, prevalent in astrophysical events, is produced when a strong electric or electromagnetic force induces a shock structure in a time scale shorter than the collision time of charged particles. A near-critical-density (NCD) plasma, generated with an intense femtosecond laser, can be utilized to excite a collisionless shock due to its efficient and rapid energy absorption. We present electrostatic shock acceleration (ESA) in experiments performed with a high-density helium gas jet, containing a small fraction of hydrogen, irradiated with a 30 fs, petawatt laser. The onset of ESA exhibited a strong dependence on plasma density, consistent with the result of particle-in-cell simulations on relativistic plasma dynamics. The mass-dependent ESA in the NCD plasma, confirmed by the preferential reflection of only protons with two times the shock velocity, opens a new possibility of selective acceleration of ions by electrostatic shock.

Highlights

With the recent advances in ultrahigh intensity lasers, exotic astrophysical phenomena can be investigated in laboratory environments
Our observations demonstrated that such strong laser-bulk plasma interaction in a subcritical density medium can excite electrostatic shock, which opens another branch of applications for ultrashort, ultra-intense lasers to study collisionless shocks in laboratory-scale e nvironments[32]
The plasma density estimated from the side Raman scattering (n e = 2 × 1020 cm−3) showed a good agreement with the density estimated by the neutral gas density measurement

Summary

Introduction

With the recent advances in ultrahigh intensity lasers, exotic astrophysical phenomena can be investigated in laboratory environments. Collisionless shock in a plasma, prevalent in astrophysical events, is produced when a strong electric or electromagnetic force induces a shock structure in a time scale shorter than the collision time of charged particles. A near-critical-density (NCD) plasma, generated with an intense femtosecond laser, can be utilized to excite a collisionless shock due to its efficient and rapid energy absorption. Ultrahigh intensity femtosecond laser the electrostatic shock can be excited in plasma to reflect upstream ions via shock-acceleration. We applied, for the first time, a femtosecond petawatt (PW) laser to the generation of near-criticaldensity (NCD) plasmas for forming a collisionless electrostatic shock structure that accelerates ions transversally

Methods

Results

Discussion

Conclusion