Method for enhancing density of sub-nanosecond electron beam

FIELD: charged particle beam generation for quantum electronics, cathode-luminescent analyses, plasma chemistry, and other fields.

SUBSTANCE: proposed method for enhancing density of sub-nanosecond electron beam that can be used in studying interaction between charged particle flow and some material includes firing of volumetric high-voltage pulsed discharge in gas-filled gap between electrodes at reduced gas pressures P: Pmin ≤ P < 300 torr, where Pmin is minimal gas pressure at which beam current length is not over -0.25 ns and can be gradually varied within specified range between approximately 0.1 and 0.25 ns. Maximal current density and beam current value are approximately 2.2 kA/cm2 and 1 kA, respectively.

EFFECT: ability of varying gas pressure within specified limits.

1 cl, 1 dwg

 

The invention relates to the field of generating beams of charged particles and can be used to study the interaction of streams of charged particles with matter in quantum electronics, cathodoluminescence analysis of plasma chemistry and other fields.

A method of obtaining an electron beam in a gas discharge [1], which consists in the fact that a discharge gap serves nanosecond high-voltage pulses (up to 160-180 kV) with the duration of the leading edge is not more than 1 NS. The cathode used tungsten rods with hemispherical surface (radius of curvature 3-7 mm), and the anode is aluminum foil of a thickness of 8-15 μm. When a volume pulse discharge, and the foil is logged stream of high-energy electrons, resulting in the near-cathode region of the discharge. The main disadvantage of this method is that the flow of fast electrons is formed in conditions of high electric field strength sufficient to move the low-energy electron discharge mode of escape. This requires a bit high voltages. In addition, the current amplitude of the fast electron beam does not exceed ˜160 A.

The closest technical solution to the claimed method, taken as a prototype, is a method for subnanosecond elektronnogo beam [2]. The method consists in the fact that in the gas-filled space between electrodes implement volume pulsed high-voltage discharge formation in it subnanosecond (˜0.3 NS) electron beam. The discharge is carried out at a gas pressure of 300 Torr and above. The electron beam is formed at the stage of breakdown when reaching into parts of the gap located between the anode and front propagating from the cathode to the anode plasma, electric field intensity, enough to form a flow of the escaping electrons. When this plasma discharge, moving from the anode to the cathode, is formed by the preionization mode period of fast electrons, which appear due to the enhancement of the field at the cathode, and the cathode plasma formations. The disadvantage of the prototype is a low density value of the beam current (no more than tens of A/cm2).

The technical result of the invention is to increase the current density and beam current while maintaining subnanosecond pulse duration of the beam current.

This technical result in the implementation of the invention is achieved in that in the known method of obtaining an electron beam, namely, that in the gas-filled gap between the electrodes implement volume pulsed high-voltage discharge followed the formation in it of subnanosecond electron beam, according to the invention, the formation of electron beam in discharge is carried out at reduced pressure gas

Pmin≤P<300 Torr,

where Pmin- minimum gas pressure, in which the duration of the beam current does not exceed ˜of 0.25 NS.

This provides a significant increase (for helium ˜8 to ˜2200 a/cm2) current density of the beam while maintaining the subnanosecond pulse duration of the beam current at half-height (for helium pulse duration of the beam current increases with ˜120 PS - ˜250 PS). When this gas pressure P must not be less than the pressure (Pmin), where there is a noticeable increase in the pulse duration of the beam current. P-valuemindepends on gas and is ˜20-40 Torr for helium. Lowering the gas pressure also reduces energy losses of electrons in the beam due to the decrease in the frequency of collisions of beam electrons with atoms or molecules of the gas. At the same time to save subnanosecond pulse duration of the beam current of electrons (˜0.1-0.25 na) gas pressure P must be at least Pminbecause when R<Pminchanges the nature of the flow discharge, which leads to the formation of the electron beam with a duration of several nanoseconds, which is characteristic for the formation of the electron beam in a vacuum di is de [3].

Examples study the functional ability of the proposed technical solutions. The experiments were carried out using a gas diode, the cathode of which served as a tube made of steel foil having a thickness of 50 μm and a diameter of ˜6 mm electron beam extraction was carried out through the foil from AlBe, anode thickness of 45 μm. For foil from AlBe in experiments with large currents were installed copper foil with a thickness of 250 ám hole dia 0.56 mm on the axis of the gas diode. The beam current is output through the hole, thereby reducing the amplitude of the signal at the collector and to measure the current density of the beam modes with large amplitudes of the beam current. The distance between anode and cathode in all experiments was equal to 14 mm as a source of pulse voltage generator was used Radan-220, shaped voltage pulses with amplitude ˜220 kV, pulse duration at half-height ˜2 NS and a rise time ˜0.5 NS [3]. The current of the electron beam was measured using a collector. The collector consisted of a metal cone, which forms with the body line with a characteristic impedance of 50 Ohms. The line was connected with a coaxial cable having an impedance of 50 Ohms. The base of the cone facing the foil had a diameter of 20 mm For reception of signals from the collector were used digital oscillo the f TDS6604 (6 GHz, 20 GS/s). Used broadband coaxial cable and attenuators 142-NM firm Barth Electronics with a bandwidth of 30 GHz. The system resolution was reached 0.06 NS. Gas diode was pumped booster pump and filled with various gases. The dependence of the amplitude of the beam current from the pressure of the gas were removed in helium, hydrogen, neon, nitrogen, argon, methane, sulfur hexafluoride, krypton and xenon. All gases at pressures 250-760 Torr were obtained electron beams with duration ˜0.1 NS. When reducing the pressure of all the gases was registered an increase in the amplitude of the current of the electron beam at the foil. The pressure at which increased the amplitude of the beam current, dependent on the grade of gas. This pressure was the maximum for helium and decreased in the following sequence used gases: hydrogen, neon, nitrogen, argon, methane, sulfur hexafluoride, krypton and xenon.

The drawing shows the dependence of the maximum current density of the beam (J)registered by the collector, and the current pulse duration at half-height (τ1/2for helium. It is seen that the maximum beam current density >2 kA/cm2was obtained at a pressure of helium ˜23 Torr. The pulse duration at half-height was ˜0.25 NS. The amplitude of the beam current at low pressure helium exceeded ˜1 kA. With further decrease of the pressure of helium the current amplitude of the učka began to decline, and at a pressure less than 1 Torr mode diode corresponded to the mode of operation of the vacuum diode with a large gap. In addition, the drawing shows that by changing the gas pressure can be adjusted within certain limits the pulse duration of the beam current.

The sources of information used in the preparation of the application:

1. Lowthresh, Linguatula, Twico, Vasotran. / Fast electrons and x-ray radiation of nanosecond pulsed discharges in gases at pressures of 0.1-760 Topp // Journal of technical physics, 1974, .XLIV, B.3, s-568.

2. Sbeljaev, Vmouse, Vratarem. Patent RU No. 2244361 published 10.01.2005 in BI No. 1.

3. Fasiolo, Ascotan, Ughput, Jace, Mielonen. / RADAN - small-periodic-pulsed high-current electron accelerator // Pribory I Tekhnika eksperimenta, 1989, No. 2, p.146-149.

The method of increasing the density of subnanosecond electron beam in a gas discharge, namely, that in the gas-filled gap between the electrodes implement volume pulsed high-voltage discharge with subsequent formation it subnanosecond electron beam, characterized in that the formation of electron beam in discharge is carried out at a gas pressure: Pmin≤P<300 Torr, where Pmin- minimum gas pressure, in which the duration of the beam current does not exceed ˜of 0.25 NS.



 

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