Antiproton annihilation dynamics in the Gasdynamic Fusion Rocket

The use of antiprotons to initiate the fusion reactions in the Gasdynamic Fusion Rocket (GDFR) is examined as potential replacement of the neutral beam injection system often cited in connection with fusion power reactors. The effectiveness of this approach depends critically, however, on the ability of the antiprotons to penetrate the plasma and reach the center of the engine without undergoing many annihilation reactions along the way. Using expressions for the annihilation rate per unit distance and the stopping power of antiprotons in a fully ionized hydrogenous plasma we calculate the annihilation distribution and the fraction of antiprotons that reach the central region in a relatively cold deuterium-tritium plasma. We apply these results to a rocket engine 16 m in length and containing plasma with 1016 cm-3 density, and we find that well over 90% of the annihilations take place within a few centimeters from the midplane of the engine when the initial plasma temperature is 20 eV. Under these conditions we find that about 10-5 grams per second of antiprotons injected at an energy of about 4 MeV are required to ignite the plasma in this rocket engine. copyright 1996 American Institute of Physics