ASPECT: An advanced specified-profile evaluation code for tokamaks

Abstract

•A specified-profile, global analysis code has been developed to evaluate the performance of fusion reactor designs. Both steady-state and time-dependent calculations are carried out; the results of the former can be used in defining the parameters of the latter, if desired. In the steady-state analysis, the performance is computed at a density and temperature chosen to be consistent with input limits (e.g., density and beta) of several varieties. The calculation can be made at either the intersection of the two limits or at the point of optimum performance as the density and temperature are varied along the limiting boundaries. Two measures of performance are available for this purpose: the ignition margin or the confinement level required to achieve a prescrib.ed ignition margin. The time-dependent calculation can be configured to yield either the evolution of plasma energy as a function of time or, via an iteration scheme, the amount of auxiliary power required to achieve a desired final plasma energy. Number of bits in a word: 64Number of processors used: 1 Peripheral used: disk Number of lines in distributed program: 7923Keywords: thermonuclear fusion, tokamak reactor, specified-profile transport Nature of physical problemThe purpose of this code is to provide a quick, if largely empirical, assessment of the performance of a tokamak fusion reactor [1,2]. ASPECT first performs a steady-state analysis at a point irl the density -temperature operating space determined according to a set of user-specified criteria. The code then carries out a time-dependent calculation which can be used to address, for example, auxiliary heating requirements and helium ash buildup. Method of solutionFor the steady-state portion of the calculation, the individual terms in the global power balance equation are estimated using user-specified radial plasmaprofiles. An expression for the energy confinement time is required; a number of popular forms are included in the code. The power balance equation is solved using a Brent algorithm subroutine [3]. The reactor performance is quantified using either the ignition margin parameter or the level of confinement required to achieve a specified ignition margin.For the time-.dependent calculation, the tempor__l variation of the device parameters, the relative plasma density, and the relative auxiliary power must be input. A feedback procedure for limiting the total heating power in the plasma is available. Helium ash accumulation can be included with an adjustable global confinement time. The time-dependent global plasma evolution equations are integrated using Hindmarsh's LSODE algorithm [4]; this yields the plasma energy as a function of time. The integration can be iterated (via the Brent algorithm subroutine [3]) to determine the level of auxiliary input power required to reach a specific plasma energy at a certain time.Restrictions on the complexity of the problem Although ASPECT is designed for use with tokamak reactors, it should be • applicable to any toroidal reactor dev...