Fundamental Plasma Physics Research Articles

Observation of plasma production in a multipole device

Plasma production is observed in a simple discharge model of one filament cathode and a multipole magnet anode with variable electrode separation. Two-dimensional velocity distribution functions of electrons and ions and two-dimensional spatial profiles of the potential and electron density are measured with a directional energy analyzer, an emissive probe, and a Langmuir probe. The electrode distance is found to affect the plasma production for isotropic velocity distribution, quiescent plasma, and homogeneous spatial distributions of the potential and electron density. The results may help to explain the fundamental plasma physics of a multipole double plasma machine.

Exploitation and development of particle beams at Culham Laboratory (invited)

Particle beams have been developed at the Culham Laboratory for many years, mainly for application to the production of high-temperature plasmas. These developments included demonstration of fundamental plasma physics such as particle trapping, heating, and current drive coupled to continuous advances in the physics and technology of ion beam production and transport. This work reached its zenith in production of multimegawatt high-proton fraction sources for the neutral beam injectors for JET. A new initiative is now coming for the development of negative ion based injectors. This wide ranging base of physics and technology provided a springboard for exploitation of beams in areas other than fusion. The last few years have seen increasing R and D at Culham in areas such as space, defense, surface treatment, and implantation. The applications have ranged from beams of H+ or H− to Xe+, from currents of less than 1 mA to currents of amperes and from energies of 50 eV to energies of hundreds of kilovolts. This paper describes some examples of these activities and relates them to the physics and technology base. Future areas of interest are also discussed.

Current Drive Experiments on the PLT Tokamak

Lower hybrid current-drive experiments have been carried out on the PLT Tokamak. Steady currents up to 175 kA have been maintained for three seconds and 400 kA for 0.3 s by the rf power alone. The principal current carrier appears to be a high energy (∼ 100 keV) electron tail, concentrated in the central 20–40 cm diameter core of the 80 cm PLT discharge. Effective current drive is observed only for n̄e ⩽ 8 × 1012 cm-3. This limitation may be a wave propagation phenomenon and not a fundamental plasma physics effect.

Large scientific releases

Mass-injection experiments in space plasmas have been conducted for the last twenty years. These injections trace or stain chemical or physical processes, facilitating diagnosis of the natural state of the space plasma; artificially perturb the space plasma away from equilibrium, isolating and controlling selected parameters; simulate natural or artificial states of space plasmas; and utilize the advantages of space as a laboratory to study fundamental plasma physics. We use the Lagopedo ionospheric-depletion experiments to illustrate the special operational aspects of active experiments, including weather, logistics, communications, and real-time diagnostics. The various objectives and techniques of mass-injection experiments are described by example. The CAMEO experiment, a thermite barium release from a satellite over the nightside polar cap, is an excellent example of the use of barium injections to trace upward ion acceleration. The Periquito Dos experiment provided a “snapshot” view of convection electric fields in the dayside polar cusp region. Project Waterhole, an artificial depletion of the topside auroral ionosphere, attempted to modify the equilibrium character of the field-aligned currents and apparently shut off the aurora in a small space-time volume. The Trigger experiment is another example of an active perturbation experiment, wherein the auroral ionospheric transverse conductivities were modified via a cesium injection. The Buaro experiment, a shaped-charged barium injection perpendicular to the local geomagnetic field, resulted in an ion-beam/background-plasma system being displaced from equilibrium, permitting diagnostics of collisionless coupling of the ion beam to the background plasma.