Signatures of hot electrons and fluorescence in Mo Kα emission on Z

Abstract

Recent experiments on the Z accelerator have produced high-energy (17 keV) inner-shell K-alpha emission from molybdenum wire array z-pinches. Extensive absolute power and spectroscopic diagnostics along with collisional-radiative modeling enable detailed investigation into the roles of thermal, hot electron, and fluorescence processes in the production of high-energy x-rays. We show that changing the dimensions of the arrays can impact the proportion of thermal and non-thermal K-shell x-rays.

Diagnostics of the plasma parameters based on the K X-ray line positions for various 4d and 4f metals

“…Moreover, in the future, these results for dysprosium can be useful in the interpretation of K X-ray spectra from the plasma produced by short-pulsed high power lasers irradiation in LULI, Palaiseau, France [16]. Our research for Mo will be also helpful for interpretation of K X-ray spectra from the plasma produced by X-ray generator Sandia Z-machine (Albuquerque, USA) [17]. The presented results may also be helpful for the interpretation of K X-ray spectra from the plasma generated by a plasma-focus device (e.g., PF-1000, Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland), high-power lasers PHELIX in GSI (Darmstadt, Germany), PALS (Prague, Czech Republic), and potentially relevant to diagnostics of laser-produced plasmas as studied in connection with the researches of National Ignition Facility.…”

Energy shifts of K- and L-lines as spectroscopic diagnostic of Z-pinch plasmas

“…For the pinch with the larger initial diameter (70 mm), the Kα radiation from both the pinch' core and part of the periphery, has higher photon energies than the Kα lines from cold Mo. This paper uses a simpler model for the pinch energetics than in Reference [1], and discusses the plasma's K-shell radiation expected from the ionization energy shift of the K-lines directly, along the lines of recent papers by our group [2,3,4,5,6]. More extensive computations of the ionization energy shift to the L x-ray lines of tungsten were essential for analysis in another paper [7].…”

“…A recent publication [1] presents x-ray spectra and other data for two molybdenum wire pinches imploded on the Z-machine at Sandia, for which detailed modeling of the radiation produced an estimate of the plasma conditions in the two pinches. The lower-energy x-ray spectrum, from the L-shell between 2 keV and 6 keV, is largely the same for the two pinches; in contrast, the x-ray emission around 17 keV is substantially different.…”

“…Therefore, the plasma must contain non-thermal electrons with energies not described by the thermal electron energy distribution; these are variously referred to as hot or beam electrons. The detailed collisional-radiative plasma modeling in Reference [1], which includes many interactions between the plasma's thermal electrons, Mo's L-shell and higher-lying shells, and the photons, can account for the radiation by assuming a stationary, higher-density central rod of plasma surrounded by a cylindrical shell, provided that a pinch of 60 keV electrons is added to excite the K-shell photons.…”

“…The K-shell x-ray spectrum from the two pinches, Figure 1 of Reference [1], is time-integrated but radially resolved, from the Mo Kα2 line close to 17.375 keV to just about 40 times ionized He-like Mo at 18.1 keV. For the pinch with the smaller initial diameter (50 mm), the energy of the Kα1 radiation in the outer shell remains close to the 17.480 keV value for cold Mo, and clearly distinct from the Kα2 emission; in the dense core the spectrum extends to higher photon energies.…”