Computational Modeling and Software Development



Description | Purpose | Algorithms | Results | Publications

Short Description

Monte Carlo Guiding center Orbit code

Date/Active Use



R.W. Harvey, H. St.John, G. Sager



Purpose/Function/Special Features

MCGO was created to study the distribution of neutral beam injected fast ions in real tokamak geometry. Beam deposition is modelled using NFREYA. Circular equilibria are done analytically inside the code, and more complex geometries are taken from the equilibrium code EFIT. Pitch angle scattering, charge exchange, energy diffusion and Coulomb slowing down rates are simulated. Poloidal fast ion densities, beam beta, charge exchange flux, fast ion velocity distribution function, neutral beam current drive, and profiles of energy given to electrons and ions are determined. Power loading to the limiter due to fast ion loss processes is calculated. The code is routinely used to verify the extent to which the fast ion deposition profiles are in agreement with the deposition used in the ONETWO transport code (which uses simplified deposition methods).

Charge exchange diagnostic spectra are calculated based on the finite banana width fast ion distributions.

Basic Algorithms

Guiding center orbits are followed using a combination of stiff (Shampine-Gordon) and fast (Runge-Kutta) methods, with automatic sensing as to which method is currently more appropriate. The orbits are interrupted at times much less than the transit or bounce time and statistics from which the fundamental physical quantities are constructed are gathered.

Key Results

MCGO was used to confirm acceptable wall heat loading in DIII-D. The fast ion velocity distribution function was shown to be asymmetric in v-parallel due to finite banana width effects. The simulations were confirmed by charge exchange spectroscopy. The code is used as suport in several neutral beam related papers.

Selected Publications

  1. R.W.Harvey, D.K.Bhadra, and S.C.Chiu, Calculations of Neutral Beam Power Deposition for Doublet III. Poster 3B5, Sherwood Theory Meeting, Tuscon, 1980.
  2. H.E. St.John, R.W.Harvey, F.B.Marcus, and C.J. Armentrout, Finite Banana Width Effects on Charge Exchange Spectra, Bull. Amer. Phys. Soc. 8, Part II, poster 6T9, p. 1059, 1982.
  3. T.C.Simonen et al., Neutral-Beam Current-Driven High-Poloidal-Beta Operation of the DIII-D Tokamak, Phys.Rev.Lett., vol. 61, 1720 (1988).


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