On the possibility of D-3He fusion based on fast - ignition inertial confinement scheme

Although nuclear fusion reactors adopting D3He fuel could provide many advantages, such as low neutron generation and efficient conversion of output fusion energy, the achievement of ignition is a difficult problem. It is therefore of particular importance to find some methods or schemes that relax the ignition requirements. In inertial confinement scheme, the use of pure D3He fuel is impractical because of the excessive requirement on driver energy. A small amount of DT fuel as 'igniter' is hence indispensable [1]. Our previous burn simulation [1] for DT/D3He fuels compressed to 5000 times the liquid density showed that substantial fuel gains (∼500) are obtained from fuels having parameters ρ RDT = 3 g/cm2, ρ Rtotal 14 g/cm2 and a central spark temperature of 5 keV. The driver energy needed to achieve these gains is estimated to be ∼30 MJ when the coupling efficiency is 10%; in this case the target gain is ∼50. Subsequent implosion simulation [2], however, showed that after void closure the central DT fuel is ignited while the bulk of the main D3He fuel is still imploding with high velocities. This pre-ignition of DT fuel leads to a low compression of the main fuel and prevents the DT/D3He fuel from obtaining required gain. These difficulties associated with the pre-ignition of DT fuel could be resolved or mitigated if other ignition schemes such as fast-ignition [3] and/or impact-ignition [4] are adopted, because in these schemes compression and ignition phases are separated. Furthermore, the reduction of driver energy can be expected. In the present study, we examine the possibility of D3He fusion in the fast-ignition scheme. Simulations until now have been made for a DT/D3He fuel compressed to 5000 times the liquid density by using FIBMET (2D fusion ignition and burning code) [5] and a newly developed neutron diffusion code. DT igniter was assumed to be placed at a corner of the compressed fuel. The ρ R values and temperature of compressed fuel were assumed as ρ RDT = 4 g/cm2, ρ Rtotal 12 g/cm2 and 0.2 keV. The coupling efficiencies of implosion and heating lasers were respectively taken as 10% and 30%. The work shows that it is possible to obtain sufficient target gains (∼60) with realistic driver energy below 10 MJ (∼8 MJ for implosion plus ∼0.3 MJ for heating). Crucial role of DT fusion neutrons in the D3He main fuel heating was clarified. The possibility to reduce the amount of DT igniter will be discussed. References: [1]. T. Honda, Y. Nakao, Y. Hnada, K. Kudo, H. Nakashima, Nucl. Fusion, 31, 851 (1991) ; Y. Nakao, T. Honda, H. Nakashima, Y. Honda, K. Kudo, Fusion Technol., 20, 66 (1992). [2]. H. Nakashima, M. Shinohara, Y. Wakuta, T. Honda, Y. Nakao, H. Takabe, Laser Part. Beams, 11, 137 (1993). [3]. M. Tabak, J. Hammer, M.E. Glinsky, W.L. Kruer, S.C. Wilks, J. Woodworth, E.M. Campbell, M.D. Perry, R.J. Mason, Phys. Plasmas, 1, 1626 (1944). {4]. M. Murakami, H. Nagatomo, H. Azechi, F. Ogando, M. Perlado, S. Eliezer, Nucl. Fusion, 46, 99 (2006). [5]. T. Johzaki, K. Mima, Y. Nakao, H. Nagatomo, A. Sunahara, Proc. of 3rd Int. Conf. on Inertial Fusion Sciences and Applications, Monterey, 2003, edited by B.A. Hammel, et al. (LLNL, 2004), p. 474