Experimental & Theoretical Plasma Physics

Fundamental Processes

Plasmas are rich in wave phenomena. Some plasma waves are very low frequency and analogous to sound waves while others are much higher frequency and analogous to radio or light waves. Waves can be a minor feature or can be the controlling feature. We have investigated many types of waves including drift, lower hybrid, Alfven, and whistler waves. A wave diagnostic concept we developed was successfully implemented by the Magnetospheric MultiScale Mission spacecraft cluster; this concept allows the wavelength and direction of a certain plasma waves to be measured using only a single spacecraft instead of the four spacecraft previously believed necessary.

Magnetic reconnection, a critical process in magnetized plasmas, provides the means by which a magnetically confined plasma can divide in two and the means by which two distinct plasmas can merge. An everyday analog is the blowing of soap bubbles. The detachment of the soap film to form a distinct bubble is analogous to the breaking and reconnection of a magnetic field to form a distinct magnetic structure. This process is important in the solar corona, the magnetosphere, and fusion plasmas. The breaking and reconnection process is complex and not well understood. It involves highly localized rapidly changing magnetic fields, associated large electric fields, acceleration of charged particles, and changes in magnetic topology. We observe reconnection as the culmination of a well-defined sequence in a plasma jet experiment. The sequence involves creation of the jet, the jet undergoing a kink instability such that the jet develops an exponentially growing corkscrew shape, ripples developing on the trailing side of the corkscrew, and then a breaking of the jet. The ripples result from the Rayleigh-Taylor instability because of the huge effective gravity associated with the exponentially growing corkscrew. Phenomena observed when the jet breaks include a dimming of the jet, a brightening of extreme ultraviolet light emission, radiation of high frequency waves, and a small distinct X-ray pulse. We are developing diagnostics to measure these phenomena and models to explain them. It is presumed that similar sequences of phenomena occur in solar and space plasmas.

Diagnostics include laser induced fluorescence, laser interferometers, Thomson scattering, X-ray scintillators, high-speed magnetic probe arrays, high speed movie cameras in the visible and EUV, and spectroscopy. These diagnostics are often designed and built in our lab as they are not commercially available.