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Laser and heavy ion compression physics

1. Theoretical and experimental investigation of hydrodynamic instabilities under inertial fusion energy conditions.

An investigation of some basic phenomena to predict the multimode hydrodynamic instabilities was performed experimentally and theoretically. This study was carried out for Richtmyer-Meshkov (RM) instability in two pairs of gases: Ar-Xe, Mach number 3.5; and He-Xe, Mach number 2.5. The following simple forms of initial contact boundary perturbations were chosen: single cosine-type perturbation with different wavelength ( and initial amplitude a0, and the combinations (( = 8, 12, 18, 36, and 72 mm; a0 = 5-10 mm).

Experiments have shown that the presence of the short wavelength component with the large curvature (a0/( ( 1) in the complex perturbation leads to the more early transition into a turbulent stage and, so to the approximately 30% decrease of a growth rate of the long wave part of perturbation spectrum. This fact is in a good agreement with a proposed evolution theory of a mixing layer development, and 2D numerical simulations performed by means of Eulerian code "NUT".

2. Intense heavy ion beams compression and propagation.

The study of the non-linear effects in the dynamics of charge-neutralized beams in long transport channels has been carried out by means of computer simulations. The results have shown some growth of the phase volume, which, nevertheless, allowed to obtain the needed beam focal spot size on the thermonuclear target surface.

The next important problem is the ion beam compression.
Presently, a work has been initiated to investigate the possibility of compressing the bunched beam according to the target requirements by varying the main parameters of the RF field. This work is carried out under the assumption of full charge neutralization without beam telescoping. When the beam telescoping is employed, the required power profile can be generated by varying the degree of longitudinal compression from one isotope to another. Without beam telescoping this should be accomplished by adjusting the parameters of the RF system.

3. Proposal of greenhouse target designs for laser fusion.

The problems of compression, ignition and burn of the Laser greenhouse target, provided that the non-uniformities of laser energy deposition in low density absorber are smoothed, were investigated. The masses and sizes of the target layers were optimized on the base of numerous 1D "DIANA" code and a few 2D "ATLANT" code calculations. For laser energy of 100 kJ, wavelength ( = 0.351(m and pulse duration of 3 ns the following parameters are found for the optimized target: the radius of massive external Cu-container is 1533 (m, the thickness of porous polystyrene (CH) absorber (density 10-3 g/cm3) is 500 (m, and the radius of thermonuclear capsule is about 1000 (m. The thermonuclear gain of this optimized target is in the range of 1-3.

4. Proposal of reactor size and ignition size indirect-drive targets for heavy ion fusion.

A hohlraum target able to achieve ignition conditions with a heavy ion pulse of 3 MJ has been designed within the HIDIF study group. Two converter elements are located axially at oposite sides in which the incident ion beams deposit their energy heating the hohlraum to a temperature of 250 eV. Simulations were carried out with the MULTI-2D code.

The decrease of the ion beam energy from Eo ( 10 MJ in the Russian Project to the energy Eo ( 3 MJ in the European Heavy Ion Ignition Facility was also considered. It was found that the ignition is possible but the threshold is sensitive to the focusing capability of the beam transport system: in the ``conservative'' single-charge scheme the ignition threshold was estimated as Eo ( 4 MJ, whereas in the charge-neutralized scheme it can be as low as Eo ( 3 MJ.

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