HIGH-GAIN REQUIREMENTS AND HIGH-FIELD TOKAMAK EXPERIMENTS

Operation at sufficiently high gain (ratio of fusion power to external heating power) is a fundamental requirement for tokamak power reactor s. For typical reactor concepts, the gain is greater than 25. Self-hea ting from alpha particles in deuterium-tritium plasmas can greatly red uce n tau/temperature requirements for high gain. A range of high gain operating conditions is possible with different values of alpha-parti cle efficiency (fraction of alpha-particle power that actually heats t he plasma) and with different ratios of self heating to external heati ng. At one extreme, there is ignited operation, where all of the requi red plasma heating is provided by alpha particles and the alpha-partic le efficiency is 100%. At the other extreme, there is the case of no h eating contribution from alpha particles. n tau/temperature requiremen ts for high gain are determined as a function of alpha-particle heatin g efficiency. Possibilities for high gain experiments in deuterium-tri tium, deuterium, and hydrogen plasmas are discussed.