Search

Electron extraction from a hollow cathode plasma discharge through a primary anode, biased with a dc accelerating potential, is modulated to produce pulsed or continuous electron beams without the interruption of the plasma cathode discharge. This is achieved with the addition of a secondary anode, within the hollow cathode. When this secondary anode is electrically connected to the primary anode, beam production ceases; when the secondary anode is electrically isolated, beam production resumes. Previous works demonstrated the utility and operation of this device; however, the precise physical principles allowing beam modulation were not well characterized. In this paper, we show that beam modulation can be understood in terms of changes in plasma potential within the hollow cathode that either promote or prevent the formation of an electron sheath at the exit of the hollow cathode, which is mediated by the electrical state of the secondary anode. Maintaining a plasma within the hollow cathode during a state change of the secondary anode depends on the secondary anode meeting the criteria for global nonambipolar flow. These effects are explored with both the Langmuir probe measurements within the hollow cathode during the steady-state operation, and the high-speed current and voltage monitoring during beam pulses. [ABSTRACT FROM PUBLISHER]

This paper presents an overview of some of the most enjoyable low-temperature plasma experiments I have carried out with my students over the course of my career. It begins with the connection between solitons and the Schrödinger equation, and continues with the discovery of cylindrical solitons. From moving structures, we progress to stable ones: sheaths and double layers. How can we measure double-layer potentials? This question leads to the development of emissive probe techniques. From there, we move on to the Bohm criterion and the first measurements of the full plasma potential variations of sheaths and presheaths in a single-species plasma, and later in two-ion-species plasmas. Finally, our recent measurements of double layers and presheaths in uniform helicon plasma are presented. [ABSTRACT FROM PUBLISHER]

Electron beams produced by the hollow cathode effect are studied in a compact gas filled 24-kV, 5-kA capillary discharge. The characteristics and role of electron beams on X-ray production are studied in order to better understand their impact on X-ray production. X-ray plasma emission is analyzed with a spectrometer, while wideband diodes and Faraday cup probe both electron beams and X-rays. Electron beams of >5 keV are observed early on the discharge and two types of electron beams are identified: a first beam of high energy and low current (with a speed of \sim 5 \times 10^7 m/s and a current density of \sim 4\times 10^\mathrm -2 A/cm ^2) enhanced by larger cathode apertures, and a second beam of low energy and high current enhanced by smaller cathode apertures. The use of a simple configuration of external magnets prevents X-ray fluorescence production, caused by electron beams, from reaching electronic detectors hence confusion when evaluating X-ray yield from the plasma source is avoided. This is particularly important in extreme ultraviolet lithography and soft X-ray production applications. Furthermore, the presence of the external magnets does not modify line emission, which is detected by means of spectrometry. Therefore, the use of external magnets provides a way to discriminate X-ray diode signals produced by source emitted X-rays and X-ray fluorescence from electron beams. [ABSTRACT FROM PUBLISHER]

We study the behavior of the generation efficiency and radiation spectrum of a three-cavity axial vircator as a function of the injected electron-beam radius, impedance, and energy homogeneity. We show that for each geometry of a three-cavity resonator, there exist optimal (maximizing the generation efficiency) values of these parameters and determine the range over which they may vary without losing the efficiency of generation. [ABSTRACT FROM PUBLISHER]

The performance of the electromagnetic wave with power of over 100 kW at 0.4 THz is very attractive in plasma diagnostics; the 0.4 THz second harmonic gyrotron is strict with the quality of the electron beam. The quality model of the electron beam is built in practical engineering in this paper. Based on the self-consistent nonlinear beam-wave interaction theory for gyrotrons, the relationship among the quality of the electron beam, the performance of the terahertz gyrotron from the aspects of the orbital-to-axial velocity ratio, the guiding center radius, the spread of the velocity, and the thickness of the electron beam of the designed gyrotron is studied. The results show that the gyrotron is insensitive to the voltage and current of the electron beam in a wide range, and sensitive to the orbital-to-axial velocity ratio and the guiding center radius of the electron beam. The efficiency decreases when the electron beam spread is deepening, and the deepening has a little improvement when both guiding center and velocity spreads are involved in the beam-wave interaction. [ABSTRACT FROM PUBLISHER]

The experimental results of a promising pulsed plasma source, producing electron beams with a current density of up to 10 kA/cm^2 are presented. The beam duration was up to \sim1~\mus , in an accelerating voltage of up to \sim350~kV , without shorting of the cathode–anode gap by the cathode plasma. This plasma electron source is proven to sustain hundreds of pulses without degradation in its emission properties. The cathode plasma electron density ne\,\leq\,10^{15}~cm^{-3} , electron Te\leq 13~eV and ion Ti\leq 4~eV temperatures, and expansion velocity Vpl\leq 1.6\times 10^6~\rm cm/\rm s were determined using time- and space-resolved spectroscopy and light emission. [ABSTRACT FROM PUBLISHER]

Central conductor is one of the key components of ion cyclotron ranges of heating antenna, which is usually formed by welding due to the complex structures. High level of welding seam quality and small deformation are very important to central conductor. Electron beam welding (EBW) is suggested as the central conductor welding. To meet EBW requirements and reduce the risk, complex and high level of the accuracy welding fixture have been designed for central conductor EBW. Some samples were manufactured to do test and examination for EBW qualification before central conductor welding. Based on the welding parameters, thermal analysis using finite element method for the welding seam have been carried out. One mockup of central conductor for EBW has been made for proving welding parameters. In addition, some postwelding process were employed after one central conductor EBW. Results of examination and inspection of one central conductor using EBW are presented in this paper. [ABSTRACT FROM PUBLISHER]

This paper illustrates the pseudospark discharge under nanosecond pulsed voltages in the condition of different breakdown voltages and pressures. The plasma images presented here indicate that the length of plasma-based electron beams vary with the changes in breakdown voltages and pressures. The length increases with the increase of the breakdown voltages and the pressures in a certain range. [ABSTRACT FROM PUBLISHER]

We report here the behavior of the atmospheric pressure plasma jet when passing through a dc electric field between two parallel plates. The deflection of the plasma plume was observed by using an intensified charge-coupled device camera. The external field affects both the length and the width of the plasma plume. The plasma jet first deflects toward the positive plate, then turns to the opposite direction. The result indicates that the plasma plume is induced by high-energy electron beam from the temporal cathode. [ABSTRACT FROM PUBLISHER]

Using the preionization of an electron beam of 13 keV, the electron avalanche process in argon at a high pressure of 20 kPa was studied. A bright conical plasma plume, which looks like an electron avalanche, is captured when electrons are accelerated by a dc voltage of 8 kV. [ABSTRACT FROM PUBLISHER]