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Manuscript Title: ASPECT: an advanced specified-profile evaluation code for tokamaks.
Authors: D.P. Stotler, W.T. Reiersen, G. Bateman
Program title: ASPECT
Catalogue identifier: ACTL_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 81(1994)261
Programming language: Fortran.
Computer: CRAY-2.
Operating system: UNICOS, SUN OS.
RAM: 152K words
Word size: 64
Peripherals: disc.
Keywords: Plasma physics, Magnetic confinement, Thermonuclear fusion, Tokamak reactor, Specified Profile transport.
Classification: 19.9.

Nature of problem:
The 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 in 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.

Solution method:
For the steady-state portion of the calculation, the individual terms in the global power balance equation are estimated using user-specified radial plasma profiles. 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 temporal 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.

Although ASPECT is designed for use with tokamak reactors, it should be applicable to any toroidal reactor device. It is limited, however, in that it considers only closed flux surfaces; this implies that the cross-section of devices with separatrices are modelled approximately. The behaviour of the scrape-off layer plasma is not considered either. A limit of some sort on the total heating power resulting from plasma-wall interactions would be desirable [5]. The code is also restricted in that it cannot treat time-varying profiles.

Unusual features:
The steady-state calculation provided by ASPECT is considerably more flexible than that provided by similar programs. The ability to solve for the required auxiliary power within the time-dependent calculation is also note-worthy.

Running time:
1 - 7 CRAY-2 CPU seconds.