Laser study into and explanation of the direct-indirect target concept

Abstract

Abstract. The idea of direct-indirect target is experimentally tested with planar targets from LPI made of low-density metal foam (nanosnow) or of nanoparticles (30%) in plastic aerogels. The laser experiments in BARC have shown that compared to plain targets the foams of/with nanoparticles demonstrate: 1) better x-ray emissivity ; 2) smoother energy distribution over the target surface; 3) material flow from low-density wall being slower and more uniform; 4) active transverse energy transport over the target plane. These properties could be useful for hohlraums and direct-indirect concept. DIRECT-INDIRECT TARGETS SCHEMESPlasma from foams has been studied for decades [1 and ref.], but Au and Bi are not studied enough. The design of direct-indirect target using a 0.25 m-thick outer gold shell was suggested in [2]. The advantage of this design was in the easy process of laser focusing. Disadvantages, such as low x-ray efficiency, necessity of short laser pulse duration and high velocity of Au-plasma were consequent.Another design shown in Fig. 1 was proposed by Yu.A. Merkul'ev [3]. This is a target with Au-lowdensity converter which allows easy laser focusing and long laser pulse. As the result, the Au-plasma motion is slower, but the x-ray efficiency is still low. One more design, shown in Fig. 2, was proposed in [4]. The target with low-density absorber-converter was invented for 2 MJ 5 ns laser pulses. Easy laser focusing, possibility of long laser pulse and high efficiency for 0.53 m wavelength are among its advantages. However with mixed interaction (both x-ray and thermal) taking place in this case, the cryogenic DT layer is difficult to keep.M.D. Rosen and J.H. Hammer proved [5], and observed experimentally [6], that x-ray temperature in gold low-density converter is higher than in ordinary Au-converter of indirect-drive targets.Au low-density converters of heavy ions energy to x-rays should have their density varying from 10 mg/cm 3 to 400 mg/cm 3 [7]. Unlike polymers, metal foams are heat conductive and allow cryo-layer formation in fuel capsule of the target by rapid cooling (quench).Low-density Au is being developed in LLNL and GA, USA, as well as in LPI (Russia). METAL FOAMS PRODUCTION FOR DIFFERENT DENSITIESNo universal fabrication methods exist for high-Z low-density metals in a wide density range. Various technology routes of metal low-density layers are realized for

Metal nano-particles modernized layers and those with polymers for laser thermonuclear targets

“…A multistep technological system of adding a metal cluster to the polymer is used [7]. Currently, similar studies are being continued and carried out based on the novel technological developments [8][9]. It is also noted that the parylene high-strength plastic (C 8 H 8 ) is used, as a rule, in the form of a micrometer-thick protective coating of micro-circuit inner surfaces.…”

Fabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments

“…The deuterated ratio of target materials is also important for an efficient fusion reaction [16]. For these purposes several targets have been developed, for example targets with a high deuterium concentration, metal foams and low-Z materials with transparency [17][18][19]. The type of tracer atom contained in the target depends on the purpose of the experiment.…”

Fabrication of Effective Low-Density Converter of Intensive Laser Radiation to X-Ray and Novel Measurement Method of Layer Density From Heavy Metal Nanoparticles

“…Баба в Индии и убедились, что коэффициент конверсии на малоплотном висмуте выше на 10%. [9]. Только отработав технологические приёмы и методы измерения плотности, мы перешли к изготовлению мишеней из малоплотного золота и поставке таких мишеней в эксперимент.…”