Excimer laser development for fusion

Abstract

The future utility of inertial confinement fusion requires a new driver. Successful experiments coupling laser energy to targets, and our understanding of fuel capsule behavior strongly suggest that a Laboratory thermonuclear source is attainable and power production may be considered if a suitable driver with high efficiency, high repetition rate, and most importantly, low capital cost, can be identified. No adequate driver exists today; however, the krypton fluoride laser holds great promise (Rosocha et al. 1986). By the end of this decade, driver development can be brought to the point that a technically justifiable choice can be made for the future direction of ICF.The understanding we have gained through research on inertial confinement fusion (ICF) has led us to a rather well substantiated and stringent set of requirements. We now know, for example, that for ICF to represent a potential future large-scale energy source, we need: (1) a driver with a wall-plug efficiency (drive energy out compared to electrical energy input) of at least 7% at a repetition rate greater than 5 Hz, (2) a target gain such that the product of target gain and driver efficiency exceeds 5, and (3) a strong technical justification for eventual low capital cost. In fact these requirements depend on what other alternative power sources are available in the next century, but generally they represent a set of minimum criteria which must be met if ICF is to be an economically competitive source of energy.Although we have made great progress in our understanding of driver-target coupling and in the design of fusion capsules, we today have no driver capable of testing our high-gain designs, and certainly no proven driver which could be scaled to use in power production. One of the most promising drivers to be considered, the CO 2 laser, was indeed efficient, scalable, and capable of high repetition rate operation. However, detailed examination of the physics involved when high intensity long wavelength laser light irradiates target materials has shown that significantly shorter wavelengths than that obtainable from CO 2 lasers will be necessary as well. In fact, our data and calculations have shown that, to optimize the laser-target interaction process we would prefer to have a wavelength in the region of 200 nm.Ion drivers have been considered for some time, and such drivers have the immediate advantage of high efficiency. Light ion drivers offer low capital cost but have not been able to demonstrate either high power density, high repetition rate, adequate temporal history of the pulse, or sufficient stand-off distance between target and driver. Work continues at several laboratories to address and solve these problems, but we cannot be guaranteed of successful solutions today. Heavy ion drivers offer the potential of high efficiency and high repetition rate but at considerably higher cost than light ion drivers and the issues of obtaining adequate stand-off (beam propagation) and pulse shaping are still major questions.Lasers, with their ...

Spectroscopy and impurity behaviour in fusion plasmas

“…An experiment of the first type is the resistive inhibition of the hot electron current in a low-density Au layer, in which the electric field needed to drive the return current of cold electrons decelerates the supra-thermal electrons (Bond et al 1980(Bond et al , 1982. Preliminary measurements on the concept of 'vacuum insulations', to shield the pusher or fuel against hot electron heating, have been reported by Giovanielli (1982).…”

“…Spatial information on lateral transport, on the other hand, was obtained using special targets (half-plane layered targets or local high 2, disc tracers) and displacing the focal spot, by the relative emission contrast between weak low 2, emitters and stronger high 2, emitters. Although lateral remote energy deposition is important, particularly for 10.6 p m laser irradiation, it could be useful to symmetrise spherical targets, reducing asymmetryrelated hydrodynamic instabilities (Giovanielli 1982). (1980) and Mizui et a1 (1981) concluded that for their experimental conditions soft x-ray energy transport was the dominant mechanism, whereas Obenschain et a1 (1983) observed an initial sudden shock heating followed by hot electron heating.…”