28 th ICPIG, July 15-20, 2007, Prague, Czech Republi Generation of powerful sub-nanosecond e-beams and X-rays in gas discharges under atmospheric pressure V.F. Tarasenko High Current Electronics Institute, Akademicheskii ave. 2/3,634055 Tomsk,Russia This paper reports on experimental studies on generation of sub-nanosecond electron beams and X-rays in gas discharges under atmospheric pressure. The properties of the runaway electrons and X-ray radiation produced using a nanosecond volume discharge are examined. An electron beam with amplitude of ~ 400 A has been obtained. Current pulse duration (FWHM) of the fast electrons beam formed in an atmospheric gas diode behind the foil is ~ 100 ps. A prepulse is found on the waveforms of the beam current of fast electrons, which advances the main peak by ∼200 ps. Three groups of the runaway electrons are formed in a gas diode under atmospheric air pressure, when nanosecond voltage pulses with amplitude of hundreds of kilovolts are applied. 1. Introduction The recent papers [1-3] (see also the review [4]) reported on supershort avalanche electron beams (SAEB [1]) with the amplitude of hundreds of amperes at pulse duration of hundreds of picoseconds (FWHM) generated in gas-filled diodes behind the metallic foil. SAEB was used for formation a volume discharge in CO 2 laser at atmospheric pressure [5] and cathodoluminescence excitation in various crystals [6]. The aims of this work were to study the optimal conditions of runaway electrons and X - ray radiation generation in atmospheric pressure gases. 2. Experimental setups Seven nanosecond pulse generators with different diodes and voltage pulse durations from 0.3 up to 15 ns were used in the experiments [1-6]. To measure the signals from a capacitive divider, a shunt and collectors, a digital oscilloscope TDS6604 (6 GHz, 20 GS/s) was used. Resolution of the recording method reached 0,05 ns. Integrated pattern of discharge glowing was photographed through a grid by an Olympus Camedia C-2020 Z digital camera. An exposure dose of X-ray radiation was defined by VICTOREEN (Model 541R) and Arrow-Tech, Inc (Model 138) radiation monitors, sensitive to radiation with quanta energy above 60 and above 16 keV, respectively. The X-ray radiation was determined by light striking RF-3 film, which was placed in black paper of ∼100 µm thickness and settled at various distances from gas diode edge (from grid and foil). The discharge gap is formed by a flat anode and a small-sized cathode, which provides an additional electric field gain in the near-cathode area. Figure 1 shows the gas diode and collector design. Fig. 1. Design of a gas diode and a collector: 1 – generator, 2 – cathode, 3 – anode, 4 – insulator, 5- collector, 6 – connector. 3. Result of measurements 3.1. Beam current duration and amplitude The waveforms of beam current taken from a collector behind an AlBe foil and a grid with transparency of 64 % are shown in Fig. 2. 2 1 0.4 ns 140 A Fig. 2. The waveforms of runaway electrons beam current in air. Electrons extraction was through a grid of 64% transparency (1) and the grid and Al foil of 20 µm thickness (2). SM-3NS generator.