Optical Properties of Runaway Electron Preionized Diffuse Discharges and Their Applications for Excilamps and Lasers

Abstract

At the present time, high-pressure pulsed diffuse discharges find wide application in science and technology, in particular in designs of gas and plasma lasers. Diffuse discharges are produced using various preionization sources and discharge gaps with a homogeneous electric field. Since the late 1960s, the initiation of atmospheric-pressure diffuse discharges in various gases has been known to be possible even with no additional preionization [1, 2], for which short high-voltage pulses and discharge gaps with a cathode of small curvature radius are used. Atmospheric-pressure diffuse discharges were obtained in helium [1], in air [2], and later in SF6 [3]. A peculiar feature of this discharge type is the generation of X-rays [1, 2] and runaway electron beams [4]. Since 1990 the interest in this field has been lost. Apparently, this is due to the subnanosecond time of the processes occurring in the REP DD gap and thus to the complexity of nanosecond and subnanosecond high-voltage pulsers and measurements of discharge and runaway e-beam characteristics. In five recent years, interest in this discharge mode has been rekindled [5–13]. It was found that atmospheric-pressure discharges in an inhomogeneous electric field feature a number of unique properties; in particular the specific input power can reach ≈ 800 MW/cm at the gap center [6]. Another peculiarity of the runaway electrons preionized diffuse discharge (REP DD) is that its ignition is slightly affected by the polarity of a nanosecond voltage pulse [7]. A diffuse discharge with a voltage risetime of tens of nanoseconds was obtained in [8], and a diffuse discharge with a voltage of tens of kilovolts was realized in [6]. In the batch mode, the REP DD retained its properties at high repetition rate, e.g., up to 3 kHz [9]. However, this discharge type is still poorly understood and primarily due to the short