San Diego, California, 17-19 June 2002

Wake Shields for Protection of IFE Targets During Injection *

E.I. Valmianski, R.W.Petzoldt, and N.B.Alexander

General Atomics, P.O.Box 85608, San Diego, California 92186-5608
valmiansfusion.gat.com

Cryogenic DT targets must be injected into a high-temperature chamber in an inertial fusion energy power plant. Heat flux from both gas convection and chamber radiation on a direct drive target must be limited to about 1 W/cm to avoid target damage from excessive DT temperature increase. A wake shield flying in front of the target can assist in protecting the target from gas convection heating. A shield will also reduce drag force on the target, thereby facilitating target tracking and position prediction. Using the Direct Simulation Monte Carlo (DSMC) approach we have analyzed the protective properties for various shield shapes. We analyzed pressures from 0.005 Torr to 0.5 Torr in the chamber and speeds from 200 m/s to 1,000 m/s, as well as for different angles subtended by the wake shield (17°and 25° half angles — maximum is limited for laser access). The temperature in the chamber gas was assumed to be 1000 K to 1500 K.

The analyses show:

ý The shield forms a wake region with reduced temperature and flow velocity.

ý The protective properties only slightly depend on the shield shape, 10%—15% on the average.

ý The shield can reduce the convective heat flux and the drag force by a factor of 2 to 5 depending on pressure, temperature, and velocity.

Additional calculations to be made and discussed are aimed at finding the optimal initial distance between the shield and the target, the optimal mass and diameter of the shield as well as evaluating more complex shields.