Two-Dimensional Kinetic Model for Fast Electron Transport in Compressed Core Plasmas

T. Yokota, Y. Nakao, T. Johzaki1), K. Mima1)

Department of Applied Quantum Physics and Nuclear Engineering, Graduate School of Engineering, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
1)Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan

In the scheme of fast ignition (FI) in inertial confinement fusion, an ultra-intense short-pulse laser is focused on pre-compressed fuel to heat it to ignition temperature. One of the key issues of this scheme is clarification of the compressed core-plasma heating by laser-produced fast electrons. However, in most of the previous studies[1] on ignition and burn of FI targets, the energy deposition process of fast beam particles was not explicitly taken into account. For precise examination, an explicit calculation of core heating is necessary. Since the collisions between the fast electrons and the plasma particles become significant in the dense core region, Fokker-Planck type calculation would be appropriate for analyzing the core plasma heating.
Recently we have developed a Fokker-Planck type transport model that can calculate the time- and space-dependent energy deposition rate of fast electrons in dense plasma.[2] The collision terms includes (a) short-range binary collisions with the plasma particles and (b) long-range collective effect, i.e. collisions between screened particles. The effect of self-generated electric field is taken into account by assuming a current neutrality condition. So far, however, the code has been written for one-dimensional planar coordinate system; the effect of magnetic field is not included. For more realistic examination of the core heating process, multi-dimensional (at least 2-D in coordinate space) calculations are indispensable.
In this paper, we first extend our 1-D kinetic model to 2-D one; the code is written in cylindrical coordinates with axial symmetry. Next, we examine the feature of energy deposition of fast electron beams (0.5∼5MeV) injected into compressed D-T plasmas. It is shown that the self-generated electric field shortens the penetration of the beam electrons into the dense plasma. On the other hand, the magnetic field pinches the beam electrons, enhancing the energy deposition rate around the beam axis.

References

[1]for example, S. Atzeni, Phys. Plasmas 6 (1999) 3316.
[2]T. Johzaki, et al., Fusion Sci. Technol. 43 (2003) 428; Y. Nakao, et al., to be published in Proc. of 19th IAEA FEC (Lyon, 2002).