Since the STARFIRE study, most tokamak reactor studies have been conducted under the assumption that non-inductive current drive was necessary for the reactor to be economically feasible. Unfortunately, the non-inductive current drives have proven to be extremely expensive (due to their relative inefficiency and elaborate hardware), perhaps exceeding the costs incurred by designing for the pulsed operation of an inductively-driven machine. The PULSAR study was initiated to investigate this trade-off.
The pulsed nature of PULSAR introduces several design issues that are not present in steady-state devices. These issues include: fatigue in the poloidal and toroidal field magnets, fatigue in any pumps and valves that must by cycled during each reactor pulse, thermal cycling of any component which undergoes temperature transients during each pulse, and fatigue in components which experience pressure fluctuations. The magnet fatigue, identified as a critical issue during this study, is dealt with elsewhere. With respect to the pumps and valves, a portion of the shield has been used to store heat between power cycles, thus minimizing the number of components which must undergo thermal and pressure cycles. This paper addresses the key remaining issue: thermal fatigue in the plasma-facing components (first wall and divertor).
There are two PULSAR engineering designs. PULSAR-I is a helium-cooled reactor built from SiC/SiC composite structural materials, while PULSAR-II is a lithium-cooled reactor built from a vanadium alloy structural material. In each of these designs, high-cycle fatigue is an important consideration for the 40,000 cycle life desired for each design and must be considered in the thermo-structural design of the plasma-facing components. Fatigue data is sparse for these materials, but in each case, data has been found for similar materials in order to assess the potential of these materials to withstand the loads expected in PULSAR, as well as to estimate the penalties that must be paid for using a pulsed device.