San Diego, California, 17-19 June 2002

The measures to provide survival of the direct drive targets in the reactor chamber

M.L.Shmatov

Ioffe Physical Technical Institute, 194021 St. Petersburg, Russia

M.Shmatovpop.ioffe.rssi.ru

Power production utilizing the direct drive laser thermonuclear fusion will be possible only if the technical measures to provide survival of the target in the high-temperature reactor chamber are developed [1,2]. For example, these measures can be following:

1. The use of the multilayer ablator consisting of two or more layers separated by vacuum or low density gas [3]. The layers can be connected by the plastic foils that are parallel to each other and are being crumpled at the target implosion. The foil thickness of several hundred angstroms is compatible with the requirements of both target acceleration and implosion symmetry. The multilayer ablator is especially convenient for the ignition scenarios with the direct compression of the fuel and heating the compressed fuel through the cone(s) (see, e.g., Refs. [3-5]) because of the reduced requirements on the implosion symmetry and possibility to use the cone(s) as the additional part(s) connecting the layers of the ablator. Besides, a sufficiently wide cone can serve as a "wake shield" protecting the forward target surface from the reactor chamber environment.

2. Protection of the target by the container totally isolating it from the reactor chamber environment during the sufficiently long time (for example, this time can be about 80 — 90 % of the total time of the target flight in the reactor chamber) and being opened by the ablation pressure, created by the auxiliary laser beams, before the target irradiation [3]. This is similar to the use of the sabot protecting the target not only during the acceleration but also in the reactor chamber (see Ref. [1]). However, the container optimized to protect the target in the reactor chamber may be so fragile that it cannot serve as a sabot for the acceleration (in such a case a sabot will also be necessary). Therefore the use of the containers and sabots can be considered as the different measures. The ablation pressure, generated by the auxiliary laser beams, can also remove the container opened from the rear end (such container can be considered as a version of a wake shield)[3]. If necessary, the protective containers can be coated with the frozen gas (see also Ref. [1], where deposition of the frozen gas on the target itself was proposed).

The use of the multilayer ablator is compatible with all other measures to provide survival of the target. The use of the containers being opened or removed by the ablation pressure is compatible with a number of other measures, for example, with deposition of the gold coating increasing the target albedo (see Ref. [6]).

1. W.R.Meyer, Fusion Eng. Des. 25, 145 (1994).

2. K.R.Schultz et al., General Atomics Report GA — A23379 (2000).

3. M.L.Shmatov, Preprint of Ioffe Physical Technical Institute N 1749 (2000).

4. L.P.Feoktistov, in: Budustchee Nauki [Future of Science], N 18, p. 168, Znanie, Moscow (1985) [in Russian].

5. S.Yu.Gus’kov, Kvantovaya Elektronika 31, 885 (2001) [Quantum Electronics 31, 885 (2001)].

6. S.E.Bonder et al., Phys. Plasmas 7, 2298 (2000).