2009

Dubinov A. E.  On a widespread inaccuracy in defining the Mach number of solitons in a plasma  //  Plasma Physics Reports, 2009, Volume 35, Issue 11, Pages 991 - 993

RFNC - VNIIEF, Sarov, Russian Federation

An inaccuracy is considered in defining the Mach number of nonlinear acoustic waves in plasma - a frequent issue in the literature. It is shown that a correct definition of the Mach number is obtained by normalizing the wave velocity to its linear speed, which is to be obtained from the dispersion relation in a given, rather than arbitrary, plasma model.

Bulychev S. V., Vyalykh D. V., Dubinov A. E., Zhdanov V. S., Kornilova I. Y., L'vov I. L., Saikov S. K., Sadovoy S. A., Selemir V. D.  Study of high - power pulsed RF generators based on a hollow - cathode discharge  //  Plasma Physics Reports, 2009, Volume 35, Issue 11, Pages 941-961

RFNC - VNIIEF, Sarov, Russian Federation

Results are presented from studies of physical principles underlying operation of high - power pulsed RF generators based on a hollow - cathode discharge ( HCD ). Various types of instabilities that may occur in an HCD and lead to 100% RF modulation of the electrode voltage in the megahertz frequency range are discussed. The design, electric characteristics, and operating modes of HCD - based RF generators are described. Results of experiments aimed at increasing the power and duration of RF pulses are presented. It is demonstrated that such devices are capable of generating 10 to 220 MHz pulses with a power of up to 8 MW, duration of up to 10 µs, and repetition rate of 1 kHz. The discharge chambers of such generators are very simple in design, they have very high stability, and their efficiency reaches 35%.

Barinov M. A., Arapova E. Y., Vronskii M. A., Dolgoleva G. V., Ermolovich V. F.  Dependence of radiation from a laser-produced plasma on the plasma composition // Plasma Physics Reports, 2009, Volume 35, Issue 10, Pages 860 - 866

RFNC - VNIIEF, Sarov, Russian Federation

Results are reported from calculations of how the radiation spectrum from a laser - produced plasma depends on the gold concentration in a target made of a gold - copper alloy. Calculations were carried out with the SND code by using the photon absorption coefficients obtained from the THERMOS code. The experimental data are interpreted by comparing them with the calculated results.

Repin P. B., Selemir V. D., Selyavski V. T., Savchenko R. V., Orlov A. P., Repin B. G., Ibragimov M. Sh.  Study of the effect of preliminary wire explosion on X - ray generation during wire array Z - pinch implosion  //  Plasma Physics Reports, 2009, Volume 35, Issue 1, Pages 42 - 49

RFNC - VNIIEF, Sarov, Russian Federation

Results are presented from experimental studies and numerical simulations of the effect of preliminary wire explosion on the parameters of X - ray  emission generated during wire array Z - pinch  implosion. The wire array implosion was driven by a current pulse with an amplitude of 0,5 MA and a rise time of 0,5 µs, while the preliminary wire explosion was produced by a current pulse with an amplitude of 0,5 - 1 kA per wire, a rise time of 100 ns, and a full width at half maximum of 200 ns. The experiments showed that the current prepulse significantly impaired the parameters of  X - ray  pulses. In particular, along with a decrease in the amplitude and an increase in the duration of the X - ray  pulse, its spiky structure became more pronounced. The results of numerical simulations with the use of a one - dimensional radiative MHD code are in good agreement with the parameters of Z - pinch  emission in experiments with and without a current prepulse.

Donets E. D.,^a Donets E. E.,^a Syresin E. M.,^a Dubinov A. E.,^b Makarov I. V.,^b Sadovoy S. A.,^b Saikov S. K.,^b Tarakanov V. P.^c   Formation of longitudinal nonlinear structures in the electron cloud of an electron - string ion source  //  Plasma Physics Reports, 2009, Volume 35, Issue 1, Pages 54 - 61

^a  Joint Institute for Nuclear Research, Dubna, Moscow oblast 141980, Russian Federation
^b  RFNC - VNIIEF, Sarov, Russian Federation
^c  Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya ul. 13/19, Moscow 125412, Russian Federation

Accumulation of oscillating electrons in an electron - string ion source is simulated by the particle - in - cell method. The electrons are accumulated in a long trap into which an electron beam is injected. It is shown that a chain of alternating phase holes and squeezed states forms in the trap. The dynamical features of such a longitudinal structure, such as the double - pulse waveform and strong high - frequency oscillations of the accumulation current and the broadening of the electron distribution function, are qualitatively similar to those previously observed in experiments with the Krion - 2 ion source operating in the electron - string mode.

Annenkov V. I., Garanin S. G., Eroshenko V. A., Zhidkov N. V., Zubkov A. V., Kalipanov S. V., Kalmykov N. A., Kovalenko V. P., Krotov V. A., Lapin S. G., Martynenko S. P., Pankratov V. I., Faizullin V. S., Khrustalev V. A., Khudikov N. M., Chebotar V. S.  Laser stand for irradiation of targets by laser pulses from the Iskra-5 facility at a repetition rate of 100 MHz  //  Quantum Electronics, 2009, Volume 39, Issue8, Pages 719 - 722

RFNC - VNIIEF, Sarov, Russian Federation

A train of a few tens of high - power subnanosecond laser pulses with a repetition period of 10 ns is generated in the Iskra - 5  facility. The laser pulse train has an energy of up to 300 J and contains up to 40 pulses ( by the 0,15 intensity level ), the single pulse duration in the train being ~ 0,5 ns. The results of experiments on conversion of a train of laser pulses to a train of  X - ray   pulses are presented. Upon irradiation of a tungsten target, a train of  X - ray   pulses is generated with the shape of an envelope in the spectral band from 0,18 to 0,28 keV similar to that of the envelope of the laser pulse train. The duration of a single X - ray   pulse in the train is equal to that of a single laser pulse.

Bagdasarov V. Kh.,^a Garnov S. V.,^a Denisov N. N.,^a Malyutin A. A.,^a Dolgopolov Yu. V.,^b Kopalkin A. V.,^b Starikov F. A.^b  Laser system emitting 100 mJ  in Laguerre - Gaussian modes  //  Quantum Electronics, 2009, Volume 39, Issue 9, Pages 785 - 788

^a  A M Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow 119991, Russian Federation
^b  RFNC - VNIIEF, Sarov, Russian Federation

The optical scheme and radiation parameters of a neodymium glass laser system emitting high - power 40 - ns pulses in the first - third - order Laguerre - Gaussian modes of energy up to 100 mJ are described.

Starikov F. A., Volkov V. A., Gasparyan P. D., Roslov V. I.  Simulation of an  X - ray  laser in the transient gain-saturation regime  //  Quantum Electronics, 2009, Volume 39, Issue 9, Pages 825 - 829

RFNC - VNIIEF, Sarov, Russian Federation

By using the TRANS code, we performed three - dimensional calculations of amplified spontaneous emission ( ASE ) in X - ray  lasers on the 3p - 3s transition in Ne - like Ge ( λ = 19,6 nm ) and Ti ( λ = 2,6 nm ) operating in the transient regime upon irradiation of a flat target by a high - power picosecond laser pulse focused into a line with one or two nanosecond prepulses. The hydrodynamics and population kinetics of the active medium of  X - ray  lasers were calculated by using the SS - 9M  code. The pulse duration, the gain, the spatial structure of the laser beam and the type of influence of a « travelling pump wave » on the ASE brightness obtained in calculations are in agreement with the experimental data. The use of the « travelling pump wave » leads not only to the increase in the ASE brightness but also considerably reduces its angular divergence.

Pikulev A. A., Tsvetkov V. M., Sosnin P. V., Sinyanskii A. A.  Successive composition of two laser channels upon excitation of  He - Ar - Xe ( 2,03 µm ) and  Ar - Xe ( 1,73 µm )  mixtures by uranium fission fragments  //  Quantum Electronics, 2009, Volume 39, Issue 6, Pages 494 - 500

RFNC - VNIIEF, Sarov, Russian Federation

The operation efficiency of the scheme with successive composition of two laser channels upon excitation of the active medium by uranium - 235 fission fragments is studied experimentally and numerically. For the  He : Ar : Xe = 380 : 380 : 1 mixture ( at a pressure of 1 atm and the lasing wavelength λ  = 2,03 µm ) the maximum lasing power of a double channel ( 1 kW ) is almost twice that of a single channel ( 540 W ). Calculations show that in the case of ideal composition ( without losses on mirrors ) the lasing power of the double channel can be increased to 1,2 kW. For the Ar : Xe = 380 : 1 mixture ( the pressure is 0,5 atm, λ  = 1,73 µm ) the maximum lasing power of the double channel ( 620 W ) is slightly above that of the single channel ( 520 W ), which is caused by the losses on aluminum mirrors employed for channel doubling and by a negative effect of optical inhomogeneities. In the case of ideal composition, the lasing power can be increased to 830 W.

Zakharov N. G.,^a Antipov O. L.,^a Savikin A. P.,^a Sharkov V. V.,^a Eremeikin O. N.,^a Frolov Yu. N.,^b Mishchenko G. M.,^b Velikanov S. D.^b   Efficient emission at 1908 nm in a diode - pumped Tm : YLF  laser  //  Quantum Electronics, 2009, Volume 39, Issue 5, Pages 410 - 414

^a  Institute of Applied Physics, Russian Academy of Sciences, ul. Ul'yanova 46, 603950 Nizhnii Novgorod, Russian Federation
^b  RFNC - VNIIEF, Sarov, Russian Federation

Emission parameters at 1908 nm in a longitudinally - diode - pumped Tm : YLF  laser are studied. The laser parameters are optimised to obtain the maximal power of high - quality cw radiation. The output power of ~ 27 W is obtained at the slope efficiency of ~ 50% and total optical pump conversion efficiency of ~ 41%.