| he possibility of bringing a spheromak plasma to the ignition threshold by ohmic heating alone is investigated using a zero-dimensional, two-region computational model. The model consists of solving a pair of time-dependent ordinary differential equations that describe a kinetic/thermal power balance in a core region and a balance of magnetic power terms for the entire plasma. The balance equations are written in terms of the temperature in the core region and the magnetic field at the edge, and include expressions for alpha heating, core ohmic power (considered a source), power losses due to radiation, non-radiative heat losses from the core, and the ohmic power in the edge region (considered a loss). We define the ignition threshold to be the time when the alpha heating power just balances the radiative power loss. Several energy confinement scaling mechanisms are considered in developing an expression for the non-radiative power loss term.;In the first portion of this work, the model is benchmarked against data from two experiments performed on the CTX spheromak device at Los Alamos National Laboratory. This application only exercises the model in the low-temperature, low-field regime and requires consideration of rapidly changing plasma variables (i.e., a plasma condition far from steady state). However, the model behaved as expected and the results of calculations are consistent with observed CTX characteristics.;The second part of the work consists of using the model to simulate the quasi-steady-state buildup of plasma thermal and magnetic energy to the point of ignition, as described above. Several parameters are studied including (i) scaling factors associated with energy confinement time expressions, (ii) time-dependent density functions, (iii) impurity radiation as represented by the parameter... |
