K-line spectra of warm, dense plasmas produced by intense pulsed electron beams

Summary form only given. Warm, dense plasmas can be produced at the tip of a plasmafilled rod-pinch diode (PFRP) on the Gamble II generator at the Naval Research Laboratory. The PFRP concentrates a high current (500 kA), 2 MeV, 60 ns electron beam at the pointed end of a 1 mm diameter tapered tungsten rod. At the time of maximum thermal energy density, the tungsten plasma parameters are estimated to be: 12 times ionized, near solid density (20 g/cm³), 25 eV, and 2.4 MJ/cm³.This paper reports the first measurements of K-line spectra from the PFRP, taken with a curved crystal transmission spectrometer that previously recorded spectra from dense laser-irradiated targets2. The radiation passes through two apertures onto the crystal, which diffracts the radiation in the K-line range and focuses it on the Rowland circle 1 m away, where an image plate records two symmetric spectra that allow a quantitative evaluation of absolute energies. With a quartz 30-31 crystal this system clearly resolves tungsten´s two K_α lines just below 60 keV, and even separates the K_β2 line from the K_β1-3 complex around 66 keV. Within the measurement uncertainty, the line shapes are identical to those from a cold calibration source; improved resolution is needed to see the approximately 0.05 keV shift in x-ray energy associated with the estimated plasma ionization. Besides tungsten, spectra have been obtained from materials such as Csl, Se and Lu by replacing the tungsten rod with a hollow aluminum tube and filling the end with the material of choice.