Modern technology often involves heating matter to very high temperatures to one million degrees or more. Under such conditions, the atoms become highly ionized and the resulting plasma radiates profusely. To elucidate the basic physics in these processes, Auburn scientists accurately measure the spectra, the time-dependence, and the total flux of the emitted radiation.
One technique for bringing matter to this exotic state is the vacuum spark discharge. It was first proposed as a source of x-ray radiation in 1897 by R.W. Wood. Since then, it has been an arena for the study of hot (electron temperatures = 100 - 1000 eV), dense (electron density = 10^20 -10^25 1/cm^3) plasmas. At Auburn, we have pioneered the technique of using a laser beam to initiate the vacuum spark and thus achieved more reliable operation. A variety of diagnostic techniques and instruments are used to study the vacuum electrical breakdown and the emission from the vacuum spark plasmas. Rogowski coils are used to measure dI/dt and this signal is integrated to give I(t). PIN diodes and photomultiplier tubes are used to obtain the strength and temporal evolution of the x-ray emission. Radiation pulse lengths are measured in nanoseconds. A 75 mm flat crystal spectrograph detects the time-integrated x-ray spectrum. A 100 MW ruby laser is used to measure electron density with holographic interferometry.
Discovering the basic physics that controls the dynamics of this exotic state of matter is a complex but exciting task. A vital tool in this pursuit is the interpretation of the line-shapes in the observed spectra. Faculty and students at Auburn are now actively engaged in developing new models and comparing them with experimental measurements to help unravel some of the mysteries of highly ionized matter.
The electromagnetic acceleration of projectiles is accomplished by passing a high current through a moving plasma armature and channeling the jxB force along the bore of the rail gun. Many of the same techniques that have been applied to the study of vacuum spark discharges have proven to be quite useful in the study of how to achieve very high speeds (1- 8 km/sec) in such devices.