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10Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2018
INTERPRETATION OF ION ENERGY SPECTRA DIRECTLY MEASURED IN THE INTERACTION VOLUME OF INTENSE LASER PULSES WITH
CLUSTERED PLASMA
S. G. Bochkarev1,5, A. Faenov2,3, T. Pikuz3,4, A. V. Brantov1,5, V. F. Kovalev1,5,6, I. Skobelev3,7, S. Pikuz3,7, R. Kodama2,4,8, K. I. Popov9, and V. Yu. Bychenkov1,5
1P.N. Lebedev Physical Institute, RAS, Moscow, 119991, Russia, bochkar@sci.lebedev.ru 2Open and Transdisciplinary Research Initiatives, Osaka University, Suita, Osaka, 565-0871, Japan 3Joint Institute for High Temperatures, RAS, Moscow, 125412, Russia 4Graduate School of Engineering, Osaka University, Suita, Osaka, 565-0871, Japan 5Center for Fundamental and Applied Research, VNIIA, ROSATOM, Moscow, 127055, Russia 6Keldysh Institute of Applied Mathematics, RAS, Moscow, 125047, Russia 7National Research Nuclear University MEPhI, Moscow, 115409, Russia 8Photon Pioneers Center, Osaka University, Suita, Osaka 565-0871, Japan 9University of Ottawa, Ottawa, ON K1N 6N5, Canada
The use of gas cluster media as a target for an intense femtosecond laser pulses is considered to be uniquely convenient approach for the development of a compact versatile pulsed source of ionizing radiation. Despite about 20 years of intensive investigations, a complete understanding of the interaction of short laser pulses with clusters is still far from clear. For example, the formation of very pronounced peaks in the contour of the OVIII Lya line
emitted by a CO2 cluster plasma created by the second harmonic of Ti:Sa laser light with an
18 2
intensity of the order of 1010 W/cm was observed [1]. It was found that while the laser of fundamental frequency creates commonly expected monotonic ion energy spectrum, frequency doubled laser radiation initiates energy spectra featuring of distinctive quasi-monoenergetic peaks. Conventional diagnostic methods fail to register highly charged ion states from a cluster plasma because of strong recombination in the ambient gas. In the paper we give the interpretation of high-resolution X-ray spectroscopy data and show that this method makes it possible to study energy spectra of highly charged ions created in the area of most intense laser radiation.
To interpret the experimental data, we adapt a numerical approach for studying a kinetic collisionless expansion of multispecies plasma clusters in a self-consistent electric field driven by laser-heated electrons [2] and the theory of the quasineutral adiabatic expansion of a hot macroscopic gas plasma [3] of the focal volume. We use both a simplified electrostatic kinetic numerical model and PIC simulations with the help of Mandor code [4] to model cluster expansion in the case where an ultrashort second-harmonic laser pulse interacts with CO2 clusters. Interpreting spectra using the developed theory and numerical simulations clearly show the prospects for such a diagnostic tool.
The theoretical part and interpretation of the experimental results were supported by the Russian Science Foundation (Grant No. 17-12-01283). The X-ray data measurements and analysis were performed by JIHT RAS and NRNU MEPHi team with support of the Russian Foundation for Basic Research (Grant No. 18-52-53033) and Competitiveness Program of NRNU.
1. Dobosz S. et al., JETP Letters 68, 454 (1998).
2. Popov. K.I., Bychenkov V.Yu., Rozmus, W., and Ramunno L., Phys. Plasmas 17, 083110 (2010).
3. Kovalev V. F., Bochkarev, S.G. and Bychenkov V.Yu., Quantum Electronics 47, 1023 (2017).
4. Romanov D.V. et al., Phys. Rev. Lett. 93, 215004 (2004).
