Plasma diagnostics from intensities of resonance line series of He-like ions
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MA DIAGNOSTICS
Plasma Diagnostics from Intensities of Resonance Line Series of He-like Ions S. N. Ryazantseva, b*, I. Yu. Skobeleva, c, A. Ya. Faenova, A. N. Grum-Grzhimailod, T. A. Pikuza, and S. A. Pikuza, c a Joint
Institute for High Temperatures, Russian Academy of Sciences, Moscow, 127412 Russia b Moscow State University, Moscow, 119991 Russia c National Research Nuclear University “MEPhI,” Moscow, Russia d Skobeltsyn Nuclear Physics Institute, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received May 4, 2016; in final form, June 21, 2016
Abstract—The possibility of using the relative intensities of the 1snp1P1–1s2 1S0 transitions with n = 3–6 in He-like multicharged ions to diagnose plasma in a nonstationary ionization state is considered. The calculations performed for F VIII ions show that, at electron temperatures of Te = 10–100 eV, the intensity ratios are sensitive to the plasma electron density in the range of Ne = 1016–1020 cm–3. The universal calculated dependences can be used to diagnose various kinds of recombining or ionizing plasmas containing such ions. DOI: 10.1134/S1063780X17040109
1. INTRODUCTION At present, there are a number of efficient X-ray spectral diagnostics allowing one to determine various parameters of high-temperature plasma (see, e.g., [1– 7]). These diagnostics are based the dependence of the plasma emission spectrum on the plasma parameters, which are determined by fitting the calculated emission spectrum to the measured one. Since the second half of the past century, the development of X-ray spectral diagnostics was mainly stimulated by studies in the field of controlled fusion research. Therefore, most X-ray spectral diagnostics employ the assumption that the plasma ionization state is close to the stationary state corresponding to a given electron temperature, as is the case in plasmas produced both in magnetic confinement facilities and under laser irradiation of spherical targets. However, in many practically important cases, the plasma ionization state is nonstationary. Moreover, the nonstationarity can be of the ionization or recombination type. Ionization nonstationarity occurs in the stage of fast plasma heating, when the ionization processes lag behind the processes of electron heating. Such nonstationarity take place, e.g., in the course of plasma heating by a long-wavelength СО2 laser, during solar corona flares, and in femtosecond laser plasma. Recombination nonstationarity usually occurs when the recombination processes are slower than the process of electron cooling. This type of nonstationarity can also take place when plasma is irradiated by
intense ionizing emission, which increases the degree of plasma ionization but slightly affects the temperature of free electrons. The ionization state of the rapidly expanding regions of laser plasma is almost always nonstationary. Due to fast cooling of electrons, plasma in these regions becomes overcooled, i.e., there appears recombination nonstationarity. Interest in studying such plasmas a
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