Development of Density and Temperature Boundary Condition Models in L-mode Tokamak Plasmas

Abstract

Models for predicting temperature and density at the edge of Low Confinement mode (L-mode) plasmas are developed. It is assumed in this work that the temperature and density at boundary of L-mode plasma are functions of plasma engineering controlled parameters,
including plasma current, toroidal magnetic field, total heating power, line averaged density, hydrogenic mass, major radius, minor radius, inverse aspect ratio and elongation. A multiple regression technique is used to analyze 86 experimental data points of L-mode from AUG and
JT60U tokamaks obtained from the latest public version of the International Pedestal Database (version 3.2). The RMSEs of temperature and density boundary models are found to be 24.41% and 14.27%, respectively. Self-consistent simulations of L-mode plasmas in DIIID and TFTR tokamaks are carried out using BALDUR 1.5D integrated predictive modeling code. The combination of anomalous Multi-Mode (MMM95) and Mixed Bohm/gyro-Bohm
(Mixed B/gB) transport models, together with the developed boundary models, are used to simulate the time evolution of temperature and density profiles for 13 L-mode discharges from DIII-D and TFTR tokamaks, including systematic scans over gyro-radius, plasma power,
plasma current and plasma density. Statistical analysis is carried out to evaluate the agreement. For example, it is found that the average relative root mean square (RMS) deviation for each model and each kind of profile is less than the scatter within each transport model from one discharge to another. The RMS deviation of all discharges from either using MMM95 model or using Mixed B/gB model for the electron density profile varies from 2.00% to 16.41%, while the electron temperature profile varies from 3.34% to 27.94%, and the ion temperature profile varies from 4.17% to 38.87%. It is shown that the simulations using the MMM95 model tend to agree better with experimental data than those using the Mixed B/gB model, especially the ion and electron temperature profiles. In addition, these boundary conditions are used to simulate the plasma profiles in L-mode of ITER. It is found that the plasma performance in ITER is predicted to be in the range of Fusion Q and is approximately 4 for the L-mode condition (4.12 for MMM95 model and 3.59 for Mixed B/gB model).