High-power terahertz optically pumped NH 3 laser for plasma diagnostics
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HighPower Terahertz Optically Pumped NH3 Laser for Plasma Diagnostics V. A. Mishchenko, Yu. V. Petrushevich, D. N. Sobolenko, and A. N. Starostin Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 Russia Received November 21, 2011
Abstract—The parameter of a terahertz (THz) laser intended for plasma diagnostics in electrodynamic accelerators and tokamaks with a strong magnetic field are discussed. Generation of THz radiation in an ammonia laser under the action of highpower pulsed optical pumping by the radiation of a 10P(32) CO2 laser is simulated numerically. The main characteristics of the output radiation, such as its spectrum, peak inten sity, time dependence, and total energy, are calculated. DOI: 10.1134/S1063780X12060074
1. INTRODUCTION Lasers with optical pumping of the gain medium (ammonia) by the radiation of a pulsed СО2 laser have been actively used in various applications for many years. An important application of this laser is plasma diagnostics. In the present work, we study the param eters of an optically pumped ammonia terahertz (THz) laser for plasma diagnostics in electrodynamic plasma accelerators and tokamaks with a strong mag netic field, such as T14, Alkator, and Ignitor. Electrodynamic plasma accelerators are widely used in various fields of science and engineering. They have found application in electric propulsion systems, surface processing and film deposition technologies, plasma chemistry, systems for plasma injection in magnetic fusion facilities, etc. At the Troitsk Institute for Innovation and Fusion Research, various types of highpower pulsed plasma accelerators have been designed and continue to be developed [1]. Experi ments with such accelerators are intended to study physical processes that take place during the accelera tion and transportation of plasma flows and their interaction with solid surfaces, as well as during the collision of counterpropagating plasma flows. In view of the variety of operating conditions, the parameters of the plasma produced in such accelera tors vary in a wide range [2, 3]. The plasma density is 1013–1018 cm–3, the electron temperature varies from 10 eV to 2 keV, and the ion kinetic energy is in the range of 0.1–3 keV. The diameter of the plasma flow is 5–20 cm, and its length is 100–1000 cm. The plasma velocity varies in the range of 106–108 cm/s, its life time is 10–500 µs, and the external magnetic field is up to 3 T. In tokamaks with a strong magnetic field of up to 14 T, the plasma density reaches 1013–1016 cm–3, the electron temperature is on the order of 10 keV, the
size of the plasma column is up to 1.5 m, and the plasma lifetime is about 1 s. To better understand the processes occurring in electrodynamic plasma accelerators when the plasma flows interact with one another or with a solid surface, it is necessary to know the most important plasma parameters, such as the values and spatiotemporal dis tributions of the electron density and temperature. By now, a large number of pl
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