San Diego, California, 17-19 June 2002

Some problems related to heating the compressed fuel through the cone

M.L.Shmatov

Ioffe Physical Technical Institute, 194021 St. Petersburg, Russia

M.Shmatovpop.ioffe.rssi.ru

In some of the proposed scenarios of ignition of thermonuclear microexplosions the compressed fuel is being heated through the cone(s) by the ions generated by the ultrahigh-intensity laser beams [1] (see also Refs. [2,3]). One of the requirements on the intensity of irradiation of the foil being used as a source of the ions is that the ranges of the ions in the compressed fuel should not be too large (see Refs. [1,3]). Therefore the intensity I_i0 of the ion flux near the foil will probably be too low to provide fast ignition. If the ion flux is focused, the intensity I_bomb of bombardment of the hot spot can be greater than I_i0 [2]. However, the efficiency of such focusing will be sufficiently high for IFE applications and ICF scientific experiments only if a decrease in I_bomb due to spread of the ion energies is not too strong (see Ref. [2]). The model according to which this condition can be satisfied at heating the compressed D-T fuel by the Be⁺⁴ ions will be presented. The model is based on assumptions about formation of the ion flux from Ref. [3], requirements on heating the fuel from Ref. [4], and the requirements on the bombarding ion energies from Refs. [1,3] (namely, it is assumed that the fuel is compressed to the density of 300 g/cm³ , the hot spot with the radius of about 16.7 microns should be heated to the temperature of 12 keV during the time of about 13.3 ps, I_bomb should be about 6.8 10¹⁹ W/cm² , the typical ion energy should be about 41.2 MeV). The model yields that if the special measures to reduce the spread of the ion energies are not taken, the distance between the foil and the hot spot should be about 40 — 90 microns; it is supposed that the wavelength of the ultrahigh-intensity radiation equals to 1 micron.

In the experiments with the use of the cones, especially at the indirect compression of the fuel, the difficulties caused by formation of the cumulative jets [5,6] or the so-called "striking cores" can arise, because these objects can damage the focusing optics and other experimental equipment. Probably, at the indirect compression of the fuel formation of rather dangerous cumulative jets or striking cores is possible even if the energy delivered by the driver inside the hohlraum is of the order of 1 — 10 kJ and the ignition of microexplosion does not occur. Elimination of the cumulative jets, their fragments, and striking cores in flight by the laser beams may be necessary (see also Refs. [5,6]).

The problems related to heating the compressed "advanced" fuels (i.e., fuels without tritium) by the D-T microexplosions will also be considered. The necessity to realize such scenarios may arise due to the very high energetic requirements on heating the "advanced" fuels (see Refs. [1,5]).

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

2. M.Roth et al., Phys. Rev. Lett. 86, 436 (2001).

3. V.Yu.Bychenkov et al., Fizika Plazmy 27, 1076 (2001) [Plasma Physics Reports 27, N 12

(December 2001)].

4. S.Atzeni, in: Atoms, Solids, and Plasmas in Super-Intense Laser Fields, ed. by D.Batani et al., p. 119, Kluwer Academic / Plenum Publishers, New York (2001).

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

6. M.L.Shmatov, Fusion Eng. Des. 60, 65 (2002).