ISSN 1063-7850, Technical Physics Letters, 2006, Vol. 32, No. 11, pp. 948–950. © Pleiades Publishing, Inc., 2006. Original Russian Text © E.Kh. Baksht, M.I. Lomaev, D.V. Rybka, V.F. Tarasenko, 2006, published in Pis’ma v Zhurnal Tekhnicheskoœ Fiziki, 2006, Vol. 32, No. 21, pp. 69–75. 948 Introduction. Previously, it was demonstrated [1–6] that the duration (defined as full width at half maxi- mum, FWHM) of an electron beam current pulse formed in gas diodes filled with various molecular or atomic gases at atmospheric pressure is ~100 ps. This circumstance allows relatively simple accelerators of subnanosecond electron beams to be created based on gas diodes driven by nanosecond high-voltage pulses. Recent experiments [7] showed that a relatively short (FWHM ~ 200 ps) beam current pulse duration remained unchanged when the working gas (helium) pressure was reduced to 300 Torr. However, beginning with a certain pressure, which was dependent on the particular gas (helium, neon, krypton), the beam cur- rent amplitude and FWHM value began to grow. It should be noted that the experiments with a helium- filled diode [7] were performed using a detection sys- tem with a temporal resolution of ~0.2 ns, while the measurements for neon and krypton were carried out with resolution on a level of ~1 ns. This Letter presents the results of experimental investigations of the formation of subnanosecond (FWHM ~ 0.1–0.3 ns) electron beam current pulses at low pressures of various gases and in a gas-filled diode driven by nanosecond high-voltage pulses. Experimental. The experiments were performed using a gas-filled diode with a design described in detail elsewhere [8]. The cathode had the form of a tube with a diameter of ~6 mm made of a 50-μm-thick steel sheet. The electron beam was extracted through a 45-μm- thick AlBe foil window. In high-current experiments, a 250-μm-thick copper foil was placed behind the AlBe foil, and the beam was extracted via a 0.56-mm-diame- ter hole made in the Cu foil on the diode axis. This aper- ture provided a decrease in the collector signal, which was necessary for measuring beam current densities in the experiments with high beam current amplitudes. The anode–cathode distance was the same (~14 mm) in all experiments. High-voltage pulses with an amplitude of up to ~220 kV, FWHM ~ 2 ns, and a front width of ~0.5 ns were produced by a generator of the RADAN- 220 type [9]. The electron beam current was measured on a col- lector, which was based on a metal cone forming (with a case) a transmission line with a wave impedance of 50 Ω . This line was connected to match a coaxial cable with the same wave impedance. The cone base facing the foil had a diameter of 20 mm. Signals from the col- lector were measured using a 6-GHz digital oscillo- graph (TDS-6604 at a sweep rate of 20 G/s), a broad- band coaxial cable, and 30-GHz attenuators of the 142-NM type (Barth Electronics). The time resolution of this detection system was 0.05 ns. The gas diode was initially evacuated by a mechanical pump and then filled with various gases. Results and discussion. Preliminarily, the beam current amplitude was studied as a function of the working gas pressure in various gases, including helium, hydrogen, neon, nitrogen, argon, methane, sul- fur hexafluoride, krypton, and xenon. In all cases, pulsed electron beams with FWHM ~0.1 ns were obtained at pressures within 0.3–1 bar. It should be noted that ultrashort avalanche electron beams (UAEBs) [10] with FWHM ~0.1 ns in helium, neon, nitrogen, argon, methane, sulfur hexafluoride, krypton, and xenon were observed for the first time (in [1-6], the High-Current-Density Subnanosecond Electron Beams Formed in a Gas-Filled Diode at Low Pressures E. Kh. Baksht, M. I. Lomaev, D. V. Rybka, and V. F. Tarasenko* Institute of High-Current Electronics, Siberian Division, Russian Academy of Sciences, Tomsk, Russia * e-mail: VFT@loi.hcei.tsc.ru Received May 10, 2006 Abstract—The formation of electron beams in a gas diode filled with various gases at low and medium pres- sures under the action of nanosecond voltage pulses has been studied. It is shown that subnanosecond pulses of the beam current in helium, hydrogen, neon, nitrogen, argon, methane, sulfur hexafluoride, krypton, and xenon can be obtained both at atmospheric pressure and at a pressure of several units or dozens of Torr. In particular, a beam current density above 2 kA/cm 2 behind the foil at a pulse duration (FWHM) of 250 ps has been obtained in helium-filled diode. On the passage from the regime of ultrashort avalanche electron beam formation to the vacuum diode regime, the beam current pulse amplitude decreases, while both the beam pulse duration (FWHM) and the pulse front width increase. PACS numbers: 85.30.Tv, 85.35.-p DOI: 10.1134/S1063785006110125