COMPX^SM
Computational Modeling and Software Development

DTRAN Code

Description | Purpose | Algorithms | Results | Publications

Short Description

The Disruption TRANsport (DTRAN) code is a multi-species, 1-D (radially), magnetic flux surface averaged parameters, anomalous diffusive-convective macroscopic plasma transport code.

Date/Active Use

2019, under development

Author

A. Pigarov

Language

Purpose/Function/Special Features

Generation and kinetics of runaway electrons (RE) in plasma disruptions and in disruption mitigation events in tokamaks depend strongly on the rapid change in the plasma parameters, impurity plasma ion composition, and electro-magnetic properties, whereas the REs in turn have crucial impact on plasma current, plasma conductivity, ionization/radiation rates, and heating. For self-consistent plasma/RE studies, CompX is developing a DTRAN/CQL3D package, in which the kinetic Fokker-Planck code CQL3D is coupled to the macroscopic plasma transport code DTRAN. DTRAN is a multi-element, multispecies, 1-D (radial coordinate), magnetic flux surface averaged parameters, diffusive-convective transport code. The code solves a system of strongly coupled equations modeling the dynamics of plasma electrons, ions, parallel electric field, ionization states of various intrinsic and extrinsic impurity species, neutral atoms and molecules. The physics processes incorporated in DTRAN make it capable of simulating high-temperature plasma transport and its radiative collapse due to impurity pellet injection or MGI as well as the low-temperate partially-ionized plasmas, e.g., few-eV plasmas in RE-plateaus down to sub-eV plasmas in the afterglow phase. For self-consistent plasma/RE-beam studies the DTRAN code assumes a two-component electron distribution function (THE+RE). The first component is thermalized Maxwellian (THE), whereas the second component corresponds to a hot electron tail, as for example due to supra-thermal and RE electrons. Both components are accounted for in calculation collision rates and sink/sources associated with inelastic and elastic collisions of electrons with other particles. The modeled species include the following hydrogenic species: H(n), H+, H-, H2, H2+, H3+, H5+, H3-; and up to two impurity chemical elements (one intrinsic [i.e., C from chamber wall sputtering] and one extrinsic [e.g., He or Ar or Ne from pellet/MGI]) with all their charge and featured molecular states]. A chemical kinetics model in DTRAN incorporates the chains of various reactions leading to Molecular Assisted Recombination (MAR), interchange ion reactions, and increasing conversion for negative and positive ions (including creation of heavy Van-der-Waals clusters). The numerous cross-section data are from the CRAMD code (which includes the ADPAK code as well as ADAS and FLYCHK data) including the non-elastic collisions of runaway electrons with all species. DTRAN incorporates: (1) non-LTE, Collisional-Radiative kinetics involving electronically excited states for H, He, and Ar atoms and some ions; (2) effects of plasma radiation opacity of many hydrogen and impurity lines using the radiation escape factors calculated with line broadening models; and (3) “material” boundary conditions at the chamber walls, including various models for interactions of plasma and gas with graphite/metallic surfaces (e.g., hydrogen species recycling and production of intrinsic impurities).

Basic Algorithms

DTRAN uses a robust nonlinear ODE solver based on Runge-Kutta methods, with automatic time stepping (and switching to the Crank-Nicholson or Euler schemes in the cases when stability/accuracy criteria failed).

Coupled Diagnostics

DTRAN calculates view-chord-integrated signals mimicking various diagnostics on DIII-D, such as Filter Scopes, spectrometers (visible and UV spectra, Bremsstrahlung, and a number of impurity lines), CO2 interferometry, and CER.

Key Results

DTRAN tests have been used: (i) for better understanding physics of plasma cooling by multispecies multi-element impurities in tokamak plasma disruption mitigation experiments including the RE effects; (ii) for exploring the collisional-radiative kinetics of various atoms and molecules and ions in variety of low-T partially-ionized multispecies plasmas; and (iii) for studying the dynamics and properties of CQ RE-plateau and afterglow low-T plasmas.

Selected Publications

A.Y. Pigarov, R.W. Harvey, Y.V. Petrov (CompX) and E.M. Hollmann(UC, San Diego), "Development of Coupled DTRAN/CQL3D Codes for Runaway Electron Quench Studies", APS/DPP Meeting, For Lauderdale, FL, Oct. 21-25, 2019. Click here.