Analytic models of high-temperature hohlraums - art. no. 026410

A unified set of high-temperature-hohlraum models has been developed. For a simple hohlraum, P-S= [A(S)+(1 - alpha (W))A(W)+A(H)]sigmaT(R)(4)+(4V sigm a /c)(dT(R)(4)/dt), where P-S is the total power radiated by the source, A( S) is the source area, A(W) is the area of the cavity wall excluding the so urce and holes in the wall, A(H) is the area of the holes, sigma is the Ste fan-Boltzmann constant, T-R is the radiation brightness temperature, V is t he hohlraum volume, and c is the speed of light. The wall albedo alpha (W)e quivalent to (T-W/T-R)(4) where T-W is the brightness temperature of area A (W). The net power radiated by the source P-N = P-S - A(S)sigmaT(R)(4), whi ch suggests that for laser-driven hohlraums the conversion efficiency eta ( CE) be defined as P-N/P-Laser. The characteristic time required to change T -R(4) in response to a change in P-N is 4V/c[(1 - alpha (W))A(W)+A(H)]. Usi ng this model, T-R, alpha (W), and eta (CE) can be expressed in terms of qu antities directly measurable in a hohlraum experiment. For a steady-state h ohlraum that encloses a convex capsule, P-N={(1 - alpha (W))A(W)+A(H)+[(1 - alpha (C))A(C)(A(S)+A(W))/A(T)]}sigmaT(RC)(4), where alpha (C) is the caps ule albedo, Ac is the capsule area, A(T)equivalent to (A(S)+A(W)+A(H)), and T-RC is the brightness temperature of the radiation that drives the capsul e. According to this relation, the capsule-coupling efficiency of the basel ine National Ignition Facility hohlraum is 15-23 % higher than predicted by previous analytic expressions. A model of a hohlraum that encloses a z pin ch is also presented.