Comparative Investigation of Fusion Reactions for Space Propulsion Applications

Abstract

A space propulsion system based on the acceleration of fusion ash is discussed by use of the energy balance equation and a hypothetic ash extraction and acceleration system. The fusion reactions D-T, D-3 He, p- 11B and 3 He-3 He are investigated under the condition of thermal generation of high energy ions and equal plasma system conditions in terms of Ti/Te relation and plasma beta. External plasma heating is defined by an equal efficiency concerning thermal energy conversion and energy transfer back into the plasma. There is no additional external heating applied to the fusion system. Power losses are based on neutrons, bremsstrahlung, synchrotron radiation and convection. We compare the plasma pressures, volumetric power densities, magnetic field strengths, heat waste, exhaust velocities and thrust density levels depending on the temperature and the hot ion mode. We show that, based on the fusion products, the exhaust velocity may reach several percent of speed of light in the case of 3 He-3 He. The temperature driven radiation losses of the 3 He-3 He reaction puts the purely aneutronic property into perspective. The mass flow rate densities of the considered fusion products are very low leading to very low thrust power densities. Considering the supposed system masses of a fusion based space vessel the thrust density levels are negligible and reach the order of 1 N/m 3 near the optimum in the case of 3 He-3 He. We conclude that a propulsion system based on the acceleration of fusion products or ash is unfeasible for typical manned missions e.g. to Mars.

Generalized Lawson criterion for magnetic fusion applications in space

“…Of the remainder 1 − f, a fraction 0 ≤ g ≤ 1 is assumed to be absorbed by the coolant within the blanket and may be used for thermal propulsion by expanding it through a nozzle. However, there are fusion propulsion systems conceivable which rely on ejection of fusion products only [11]. These resemble an open fusion reactor ejecting both products and reactants at a constant rate and the fraction g needs to be treated otherwise.…”

“…Another aspect the researches addressed was the qualification of different fusion reactions against typical requirements. The most pertinent reactions are D + T → n + 4 He, D + 3 He → p + 4 He, 11 B + p → + 3 4 He, 3 He + 3 He → 2p + 4 He.…”

“…Recent research [10,11] concerned the latter as well as the identification of the most promising fusion technology for application in space by elimination of options [10][11][12]. In this context the need of a more precise burn criterion enabling the study of various subsystems' impact had to be met.…”

Review of Nuclear Thermal Propulsion Systems

“…around 2025 [6]. A fusion NTP uses a thermonuclear fusion power source to heat up the working medium [19,[67][68][69][70][71][72]. Fusion is complementary to fission: instead of splitting one heavy atom core, fusion joins two lighter, separate cores into a single one.…”

“…Magnetically Confined Fusion Propulsion (MCFP) is a thermal propulsion concept currently investigated in Europe [19,[70][71][72]79]. The power is provided by the excessively hot magnetically confined fusion plasma.…”