Ignition condition and gain scaling of low temperature ignition targets

Abstract

The ignition and burn dynamics of low temperature ignition (LTI) targets are investigated by means of one dimensional (1-D) coupled transport-hydrodynamics simulations, in which the stagnation dynamics is appropriately taken into account. In this scheme, ignition takes place in the central region of the fuel and then the burn wave propagates outward owing to heating of the fusion products, without the production of a strong shock wave. The ignition condition in the LTI scheme is presented in terms of the usual ρR − T criterion and of the required implosion velocity. A scaling law for the limiting energy gain is proposed. It is shown that with enough fuel confinement (high ρR), higher energy gains can be achieved than those obtained in the previous model with volume ignited, uniformly compressed targets. (The limiting gain is about 1.5 times larger than that in the 'volume ignition' computations.) Without sufficient confinement, on the contrary, the bremsstrahlung loss during the stagnation phase increases rapidly, which significantly lowers the energy gain.

Single-event high-compression inertial confinement fusion at low temperatures compared with two-step fast ignitor

“…The following steps of our discussion are not so much the compression physics or the differences between volume and spark ignition, though it was shown that in detail there are clear differences (Hora et al 1998). Otherwise, it has been shown that the volume ignition bridges conditions of spark ignition (Basko 1990;Murakami 1997;Basko and Murakami 1998;Johzaki et al 1998) and -as mentioned (Nuckolls 2001) -the ignition of the spark is a volume ignition. The last case, however, is selecting very narrow ranges of parameters only, since the temperature for the fusion detonation wave has to be very carefully scaled as not too low and not too high.…”

“…The fast ignitor scheme would be a most interesting solution for the stagnationfree, classical nanosecond laser pulse compression of a plasma sphere of a few thousand times solid-state density, and with the then expected low temperature of a few hundred eV would receive additional heating (Yamanaka 1983;Campbell et al 2000) by deposition of the energy of a laser pulse of 500-fs duration into the compressed centre (Tabak et al 1994). Producing the necessary funnel into the compressed highly superdense plasma by relativistic self-focusing (Hora 1975) covering all additional dynamics such as ponderomotive self-focusing (Hora 1969b) and double-layer effects (Hora et al 1984;Eliezer and Hora 1989), it is clarified that the ps process is sufficiently short (Jones et al 1982) to provide self-focusing and to avoid hole boring only (see Fig. 12.9 of Hora 2000a) without focusing.…”

“…The threshold for this Linlor effect was measured to be at P = 10 5 to 10 6 W laser power only, as shown later (Hora 1969b) to coincide with the ponderomotive self-focusing threshold of the laser beams leading to the keV energies by nonlinear force acceleration (Hora 1969a) and Z-separation (Hora 2000a). Above the threshold of relativistic self-focusing (about 1000 times below the relativistic threshold of I r = 3.7 × 10 18 /λ 2 , where λ is the laser wavelength in micrometres, used only at this point of the paper for conventional scaling), the relativistic self-focusing (Hora 1975;Jones et al 1982) can cause a shrinking of the laser beam to a diameter δ = 0.6 times the wavelength. The subsequent very high laser intensities then accelerate the electrons and the double-layer attached ions to very high Z-separated energies, e.g.…”

“…Fusion reactions in a stationary low-density plasma with continuous emission of the bremsstrahlung need a minimum temperature of about 4.5 keV for DT to compensate the radiation loss by fusion-energy generation. This is no problem at the optimum reaction temperature of 17 keV for the (non-stationary) expanding and adiabatic cooling of a uniform reaction sphere (Hora 1964), from where (1.1) was derived (Hora and Pfirsch 1970;Kidder 1974). There were some attempts to achieve higher gains by lowering the optimum temperature, e.g.…”

“…After the simple burn of a DT plasma of an initial density n o (in relation to the solid-state density n s ), where energy E o was deposited as scaled by a break-even energy E BE , we arrived at an optimum (core) gain G: (Hora 1964;Hora and Pfirsch 1970) const n o R (Kidder 1974;Fraley et al 1974), (1.1)…”