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Low-temperature absorption spectra at temperatures of range of 7.2–300 K in MgF2 and LiF-O,OH crystals were studied to investigate the electron-phonon interaction of radiation-induced color centers in these crystals. The coupling strength (S) with the phonons of the lattice of electronic-vibrational transitions was determined from the ratio of intensities in the zero-phonon line and the integrated absorption band. The nature of the color centers associated eith the absorption band at 390 nm and the emission at 490 nm in LiF-O,OH crystals and for the absorption band at 370 nm and the emission at 420 nm in MgF2 crystals was determined from value of S.

Two types of thermally unstable U1 centers are created in LiF:Mg,OH crystals by γ−irradiation at low temperatures. One of them is influenced by impurity complexes containing magnesium ions Mg2+. Another type of U1 center is perturbed by impurities of OH¯ ions. Temporal dynamics of conversion of U1 centers and F2+ and F2+** color centers after crystal was heated from temperature of 80 K to 300 K is presented.

Experimental results on rotation coupling between the m = 2, n = 1 and m = 3, n = 2 tearing-modes in the T-10 tokamak are presented. In the specially chosen T-10 regime, these two modes are observed simultaneously, no modes other than these two ones being detected. For each of the two tearing-modes, a rotation irregularity expressed as frequency modulation is analyzed. The characteristics of the frequency modulation are used to identify the effect of each mode on the oscillations of the other one. According to the experiment, the frequency modulation of each mode consists of two components if the two modes are present simultaneously. The first component is related to the effect of static Error Field and the second one arises due to the mode coupling. For the modes in question with different toroidal numbers, the natural explanation of this coupling is related to the effect of plasma viscosity. The nonlinear visco-resistive TEAR-code is used for simulation and parametric analysis of the experimental data. The simulation results confirm the assumption that the observed coupling between tearing-modes with different toroidal mode-numbers can be attributed to plasma viscosity.

The results of calculations and parametric analysis of the plasma rotation reversal subject to the tearing mode under magnetic perturbation of the same helicity are presented. The TEAR code used for the calculations is based on the visco-resistive MHD approximation that gives coupled diffusion-type equations for the magnetic flux perturbation and for the plasma rotation velocities in toroidal and poloidal directions. The resonant magnetic perturbation consists of both the traveling perturbation induced by eddy current in the vacuum vessel and an artificially applied nonrotating magnetic perturbation produced by a current layer outside plasma. The main attention is paid to conditions necessary for the plasma velocity reversals separately in toroidal and poloidal directions, as well as for the concurrent changes of both velocity directions. The dynamics of the plasma toroidal and poloidal rotation-profile variations are also presented.

Results of simulation and parametric analysis of magnetic island production by helical magnetic perturbation generated under non-axisymmetric halo current are presented. Predictions are made for a cylindrical ITER-size plasma in conditions of disruption. Calculations are carried out with the TEAR code based on the visco-resistive MHD approximation. The radial distribution of the magnetic flux perturbation is calculated with account of the external helical field produced by halo current. The equations for the magnetic flux perturbation describe the dynamics of the tearing mode depending on plasma rotation. In sequence, this rotation is affected by electromagnetic forces depending on the tearing mode magnetic field and external magnetic perturbation. The coupled diffusion-type equations for the helical flux function and for the plasma rotation velocity are numerically treated in a similar way. The magnetic island behavior is analyzed for different plasma parameters expected at the Current Quench stage of di...

Ion interpenetration, stagnation, and energization processes are studied in colliding laser‐produced plasma configurations relevant to Trident [R. G. Watt, Rev. Sci. Instrum. 64, 1770 (1993)] experiments using four different numerical methods: one‐dimensional Monte Carlo and Lagrangian multifluid codes, and one‐ and two‐dimensional hybrid (particle ions, fluid electrons) and single‐fluid Lagrangian codes. Results from the four methodologies are compared for plasmas generated with gold and deuterated polyethylene (CD2) targets. Overall, the various codes give similar results concerning the initial expansion of the plasmas and their collisional interaction, the degree of stagnation, stagnation time, and amount of ion thermalization for gold targets, while multispecies techniques indicate a much softer stagnation for CD2 plasmas than the single‐fluid model. Variations in the results of the calculations due to somewhat different initializations and parameters, as well as to different physics in the codes, are discussed.

Experimental comparison of the m = 2, n = 1 mode and plasma rotation velocities at q = 2 magnetic surface in a wide range of the mode amplitudes is presented. Phase velocity of the mode rotation is measured with a set of poloidal magnetic field sensors located at the inner side of the vacuum vessel wall. Plasma rotation velocity at the q = 2 magnetic surface in the direction of the mode phase velocity is measured with the heavy ion beam probe diagnostics. In the presence of a static Resonant Magnetic Perturbation (RMP), the rotation is irregular that appears as cyclical variations of the mode and plasma instantaneous velocities. The period of these variations is equal to the period of the mode oscillations. In the case of high mode amplitude, the rotation irregularity of the mode is consistent with the rotation irregularity of the resonant plasma layer. On the contrary, the observed rise of the mode rotation irregularity in the case of low mode amplitude occurs without an increase of the rotation irregula...

Simulation of the magnetic island evolution under Resonant Magnetic Perturbation (RMP) in rotating T-10 tokamak plasma is presented with intent of TEAR code experimental validation. In the T-10 experiment chosen for simulation, the RMP consists of a stationary error field, a magnetic field of the eddy current in the resistive vacuum vessel and magnetic field of the externally applied controlled halo current in the plasma scrape-off layer (SOL). The halo-current loop consists of a rail limiter, plasma SOL, vacuum vessel, and external part of the circuit. Effects of plasma resistivity, viscosity, and RMP are taken into account in the TEAR code based on the two-fluid MHD approximation. Radial distribution of the magnetic flux perturbation is calculated with account of the externally applied RMP. A good agreement is obtained between the simulation results and experimental data for the cases of preprogrammed and feedback-controlled halo current in the plasma SOL.

The 90°-light scattering on domain walls was probed in various strontium barium niobate (SBN) crystals for studies of the ferroelectric switching under pulsed fields. The validity of this optical method is proved by a good agreement of the switching parameters deduced from optical scattering data with those obtained with electric methods. Scanning of the scattering over the crystal bulk revealed local specialities of the switching, particularly, a marked distribution of the domain wall density D along the polar axis with a maximum close to the negative electrode. In compliance with these in situ observations, the electro-optic coefficient rc reveals a position dependence in all SBN crystals poled in the ferroelectric phase, rc decreasing from the positive to negative electrode. This regularity is interpreted in terms of the domain density distribution D(z) and accounted for by an asymmetry of the domain nucleation.