Harry Dreicer

Kinetic Theory of an Electron‐Photon Gas

An extension of the Boltzmann equation for plasmas is presented, including interactions between the electrons and the photons which populate the radiation field. This development results in those electron‐photon collision integrals which are required to describe relaxation towards equilibrium of both particles and radiation field as a result of radiative interactions alone. Single‐photon emission and absorption as well as Compton scattering are treated. The equation derived is specialized to the case of electrons orbiting in a steady magnetic field, and is used to follow the relaxation of a test electron which is interacting with a thermal radiation field via the emission and absorption of cyclotron radiation. It is also used to study the saturation properties of the cyclotron radiation maser. In the case of Compton scattering by free electrons a clear separation between these electron‐photon collision terms and the usual electric field term in the Boltzmann equation is shown to exist. Collision terms are...

Formation of Drift Instabilities by Collisional Relaxation of High‐Energy Particles

The relaxation of a small group of fast test electrons as a result of two‐body Coulomb encounters with slow field electrons and ions orbiting in a magnetic field is investigated. The analysis is based upon an asymptotic form of the Fokker‐Planck equation which includes the slowing down in speed as well as the angular scattering of the test electrons. The derivation as well as the analytic solution of this equation is presented, and is used to illustrate a case where collisional relaxation of the test electrons alone is responsible for the formation of a second peak in the one‐dimensional electron velocity distribution. The maximum growth rate for the resulting electrostatic drift instability is calculated in the limit when the second peak is much smaller than the main peak, and is found to be proportional to the ratio of test to field particle density. The results are used to suggest an explanation of the several unstable current steps observed in the stellarator during its crowbarred relaxation phase.

High-power-density approaches to magnetic fusion energy: problems and promise of compact Reversed-Field Pinch Reactors (CRFPR)

Abstract If the costing assumptions upon which the positive assessment of conventional large superconducting fusion reactors are based proves overly optimistic, approaches that promise considerably increased system power density and reduced mass utilization will be required. These more compact reactor embodiments generally must operate with reduced shield thickness and resistive magnets. Because of the unique magnetic topology associated with the Reversed-Field Pinch (RFP), the compact reactor embodiment for this approach is particularly attractive from the viewpoint of low-field resistive coils operating with ohmic losses that can be made small relative to the fusion power. The RFP, therefore, is used as one example of a high-power-density (HPD) approach to magnetic fusion energy. A comprehensive system model is described and applied to select a unique, cost-optimized design point that will be used for a subsequent conceptual engineering design of the compact RFP Reactor (CRFPR). This cost-optimized CRFPR design serves as an example of a HPD fusion reactor that would operate with system power densities and mass utilizations that are comparable to fission power plants, these measures of system performance being an order of magnitude more favorable than the conventional approaches to magnetic fusion energy (MFE).

An intense source of positrons using a low energy proton beam

We will show that it should be possible to produce large fluxes of positrons using intense proton beams (100 mA CW) of modest energy (6−10 MeV). The basic idea is to use protons from an accelerator rather than neutrons from a reactor to produce B+ − unstable isotopes by the proton capture reaction.

Use of Radioactive Test Ions in the Measurement of the Spatial Distribution of Plasma Ion Drift Speeds

Radioactive test ions have been used to measure the axial ion drift speed distribution in a single‐ended Q machine. In the main plasma region these drift speeds are found to be significantly smaller than predicted by the sheath model.