Spectroscopy of composite Z-pinches in the Angara-5-1 device

Results are presented from spectroscopic studies of a composite Z-pinch in the Angara-5-1 device. A load that was used to create the composite Z-pinch consisting of an outer annular gas (argon or propane) shell and a solid inner cylinder (fiber) made from a foamlike material (agar-agar with the addition of KCl or NaCl) with an initial density of ∼10^-2 g/cm³. In experiments, the intensity of line emission was measured for various shell compositions and for the shell mass per unit length from 3 to 60 μg/cm. The fiber mass per unit length varied from 55 to 80 μg/cm, and the weight content of salt additives varied from 30 to 57%. The measurements show that the temperature of a substantial fraction of the fiber material is comparable with the shell temperature. During compression, the electron density and electron temperature of the pinch (gas-jet and fiber) plasma reaches values of n_e ≈ 10²¹ and cm^-3 and T_e ≈ 1 keV, respectively. The spatially resolved spectroscopy shows that luminous regions of the gas-jet and fiber ions coincide with each other and occupy at most one-half of the pinch length (about 5 mm for Ar ions and 3-4 mm for K and Cl ions). The measurements of the electron temperature near the cathode (∼500 eV, which is lower than the electron temperature in the central part of the pinch) show the presence of a temperature gradient along the pinch axis. Possible mechanisms for fiber heating are discussed.