摘要:

We report the results of the recent implosion experiments performed with the uniformity‐improved GEKKO XII laser. A high quality plastic shell filled with deuterium gas was irradiated with the power‐balanced, smooth‐profile laser beams of 526 nm wavelength. The laser pulse was square‐shaped with a controlled prepulse in order to reduce the instability growth. The observed neutron yield under these conditions correspond to the 1‐D simulation value well within the stagnation phase. These results suggest that the implosion stability is now better controlled in comparison to previous experiments. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50397

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Investigation of the hot spark heating is now possible with a 10‐ps temporal resolution. Hot spark heating was improved with the increased stand‐off distance and RT stabilized implosion mode. Irradiation nonuniformities have been reduced by precise power balancing of the beams and by the partially coherent light technique. Improved spark heating in the deceleration phase resulted in enhanced neutron production up to the second bounce yield. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50387

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have investigated the hydrodynamic response of plastic and aluminum foils accelerated by a pulse formed by an x‐ray prepulse followed by the main laser pulse. This illumination scheme, so‐called indirect‐direct drive scheme, has been proposed as an alternative to the direct and indirect drive. The advantages of such a scheme are that it can contribute to solve the problem of uniformity of the direct drive and, at the same time, it can be much more efficient and use simpler targets than the indirect‐drive. Experiments about this hybrid drive scheme have been performed at Limeil with the PHEBUS facility and the standard experimental set‐up and diagnostics. The agreement between experiments and simulations is good for quantities such as the energy of the laser converted into x‐rays and the burnthrough time of the converter foil. To simulate the full hydrodynamic evolution of the converter and target foils separated a distance of 1 mm, 2‐D effects should be taken into account. The basic goals have been to check the simulation codes developed by the Institute of Nuclear Fusion and to determine the hydrodynamic response of the target foil to the hybrid pulse. These goals have been fulfilled. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50360

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

For achievement of ignition, one of the most important issue is uniform compression for which a nonsupported pellet is reported in this paper. The magnetic force to a Ni coat on a glass microballoon is clarified by theoretical analysis and model experiments. To introduce horizontal dumper, an LD is verified effective for horizontal dumper. The preliminary test of active dumper is done. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50369

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In order to prevent high‐Z plasma from filling in the hohlraum in indirect drive experiments, a low‐Z material, or tamper is introduced into the hohlraum. This material, when fully ionized is typically less than one‐tenth of the critical density for the laser light used to illuminate the hohlraum. This tamper absorbs little of the laser light, thus allowing most of the laser energy to be absorbed in the high‐Z material. However, the pressure associated with this tamper is sufficient to keep the hohlraum wall material from moving a significant distance into the interior of the hohlraum. In this paper we discuss measurements of the motion of the interface between the tamper and the high‐Z hohlraum material. We also present measurements of the effect the tamper has on the hohlraum temperature. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50414

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The second harmonic of 527 nm laser light was imaged by a Schwarzschild microscope. Obtained second harmonic images are compared with the x‐rays. The second harmonic originates from near the critical density, when laser light is absorbed via resonance absorption or ion acoustic decay instability. A plastic target coated with 1000 A˚ Al was irradiated with a 527 nm laser beam without any beam smoothing technique. The obtained second harmonic image at 263 nm was compared with an x‐ray pinhole picture with a proper filter to observe Al 1.8 keV emission. This comparison was taken as a proof of principle since the over all patterns between the second harmonic and x‐ray images show very close correlation. Then the second harmonic images were taken with random phase plate and partially coherent laser light. These images should show the absorption distribution at an early part of the irradiation laser pulse. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50425

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

DD‐produced protons are used to measure the imploded fuel‐shell areal density &rgr;&Dgr;Rof a cryogenic foam target. 12 green beams of the GEKKO XII laser directly imploded a cryogenic foamshell target containing a liquid or solid D2fuel. The proton emission is detected through a dipole magnet on a CR‐39 plate, whose energy shift from 3.02 MeV yielded the maximum &rgr;&Dgr;Rof 12 mg/cm2or the density of 8 g/cm3, in agreement with that from the secondary neutron method within a factor of 2. The proton energy spread is sensitive to the laser energy imbalance. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50427

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a multi‐imaging x‐ray streak camera (MIXS) technique and applied it to obtain time‐resolved x‐ray images of the laser‐imploded core plasmas. Temporal changes in the core structure of laser‐imploded targets were first observed with a temporal‐ and a spatial‐resolution of 10 ps and 15 &mgr;m, respectively. It has been found that these structures are dependent on the laser irradiation conditions. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50428

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Recent capsule implosions using indirect drive on NOVA have probed core and near‐core capsuleTe, &rgr; and mix structure using non‐trivial pulse shapes (i.e. with a foot). These experiments have been performed using smooth as well as artificially roughened capsules. They have been performed using basically 3 non‐trivial pulse‐shapes with 3 different types of capsules with correspondingly different growth regimes for Rayleigh‐Taylor instabilities. These experiments have employed time‐dependent spectroscopy, gated imaging andabsolutelycalibratedtime‐integrated imaging as x‐ray diagnostics. We compare nominal and ‘‘modified’’ 1D calculations with the spectroscopic and time‐integrated image results. We find that the coreTeis less than calculated (not surprising), but also that theTeof the inner pusher is substantially higher (at least 20%) than predicted, with perhaps some enhanced mix of the PVA layer towards the core. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50429

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Single‐mode experiments have been conducted on the Nova laser to examine the effect of perturbation shape on ablation front Rayleigh‐Taylor growth. The perturbations investigated had the same magnitude wave vectork=(k2x+k2y)1/2and the same initial amplitude. The shapes correspond to 2D &lgr;=50 &mgr;m, 3D squarekx=ky, and stretchedkx=3kyperturbations. We observed that the 3D perturbations grew more than the 2D perturbation. Numerical simulations in 2D and 3D are in agreement, showing the most symmetric modes growing the largest. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50430

出版商:AIP    

年代:1996

数据来源: AIP