Search

We have developed a code for following the radial diffusion and slowing down of alpha particles from DT fusion. The partial differential equation is solved by a finite‐difference method. Ion as well as electron drag is included. Any given source function of radius, time, and energy width can be handled correctly. The code has been used to examine time waveforms, radial distributions, and energy spectra. The results can be used to model signals expected from the alpha charge exchange recombination spectroscopy and collective Thomson (‘‘gyrotron’’) scattering diagnostics. The code has also been used to calculate, as a function of diffusion coefficient, the flux of escaping fast ions that enters a lost‐ion detector, and thus to deduce from measurements an upper limit for the diffusion of fast charged fusion products.

A specialized method has been developed to maximize the two‐dimensional detail obtained from two perpendicular bolometer arrays. The technique relies on the assumption that poloidal variation exists only near the plasma surface. The cross section is divided into appropriate zones and the emittance is reconstructed by a numerical method. The position, intensity, and width of large features are clearly displayed. A marfe is tracked as it drifts around the plasma and evolves into a radiating shell detached from the limiter. A central peak, plus inner‐wall radiating layer, plus a marfe appear in a high‐density case reached by pellet injection.

A bolometer has been developed based on a thin, die‐cut platinum grid. It can survive high temperatures and the neutron and gamma radiation expected in the Toroidal Fusion Test Reactor (TFTR). The platinum resistance is measured with a square‐wave carrier system to minimize sensitivity to ambient electromagnetic interference. Electrical power fed back to the sensor holds its temperature constant and provides an output directly proportional to absorbed radiation power. With a bandwidth of 50 Hz the noise is equivalent to 100 μW/cm2. Methods are described for dealing with the background effects expected to contribute to bolometer heating.

For the past year we have been making use of a horizontally viewing 19‐channel array and a bolometer which views a narrow cross‐sectional slice of the plasma. More recently, we have also obtained results from a second, vertically viewing array. Software has been developed to translate the data from general plasma and array locations to plasma minor radius and to do the Abel inversion with an antisymmetrical term included. Experience has been obtained on the noise and response‐time characteristics, as well as the accuracy of total radiated power and radial profiles. Representative cases of radiated power profiles and local power balance are presented, as well as comparisons with other measurements of impurity concentration and trends with electron density and limiter coating. Although most of the ohmic‐heating input power leaves by radiation, most of this loss occurs near the outer part of the plasma. Also, the behavior of power profiles during neutral beam injection is discussed briefly.

Designing bolometers for Compact Ignition Tokamak presents difficult, perhaps insurmountable, challenges. Detector environment will be quite harsh, viewing access will be severely limited, and, most importantly, the heating of detectors by neutron and gamma radiation will be larger than that by the radiation losses to be measured. Furthermore, the radiation losses themselves will no longer be dominated by impurity radiation as in earlier machines, but will be a combination of impurity radiation, bremsstrahlung, and synchrotron radiation. Possible approaches to a design have been developed, based on optimizing the response to VUV‐ and x‐radiation, possible local shielding, subtraction of the n and γ heating, constant in situ calibration, and deployment of the detectors in a tangentially viewing array. The array makes it possible to cover the plasma cross section, as well as to see into the divertors. Estimates indicate that it should be possible to make successful measurements of the two‐dimensional radiat...