Discharge with an external magnetic field is promising for various applications of low-temperature plasmas from electric propulsion to semiconductor processes owing to high plasma density. It is essential to understand plasma transport across the magnetic field because plasma confinement under the field is based on strong magnetization of light electrons, maintaining quasi-neutrality through the inertial response of unmagnetized ions. In such a partially magnetized plasma, different degrees of magnetization between electrons and ions can create instability and make the confinement and transport mechanisms more complex. Theoretical studies have suggested a link between the instability of various frequency ranges and plasma confinement, whereas experimental work has not been done so far. Here, we experimentally study the magnetic confinement properties of a partially magnetized plasma considering instability. The plasma properties show non-uniform characteristics as the magnetic field increases, indicating enhanced magnetic confinement. However, the strengthened electric field at the edge of the plasma column gives rise to the Simon–Hoh instability, limiting the plasma confinement. The variation of the edge-to-center plasma density ratio (h-factor) with the magnetic field clearly reveals the transition of the transport regime through triggering of the instability. Eventually, the h-factor reaches an asymptotic value, indicating saturation of magnetic confinement.

For the generation of low-energy electron beam, the design and characteristics of channel spark discharge (CSD) operating at a low voltage are presented in this paper. The discharge voltage, discharge current, X-ray emissions, and electron beam current were experimentally determined. The effects of the applied voltage, working gas pressure, and external capacitance on the CSD and beam parameters were measured. At an applied voltage of 11 kV, an oxygen gas pressure of 25 mTorr, and an external capacitance of 16.45 nF, the maximum measured current was 900 A. The discharge current increased with the increase in the pressure and capacitance, while its periodic time decreased with the increase in the pressure. Two types of the discharge were identified and recorded: the hollow cathode discharge and the conduction discharge. A Faraday cup was used to measure the beam current. The maximum measured beam current was 120 A, and the beam signal exhibited two peaks. The increase in both the external capacitance and the applied discharge voltage increased the maximum electron beam current. The electron-beam pulse time decreased with the increase in the gas pressure at a constant voltage and increased with the decrease in the applied discharge voltage. At an applied voltage of 11 kV and an oxygen gas pressure of 15 mTorr, the maximum beam energy was 2.8 keV. The X-ray signal intensity decreased with the increase in the gas pressure and increased with the increase in the capacitance.

The indirectly heated cathode (IHC) Bernas source is used in plasma process devices as it can produce a high current of desired ion species. The formation of various ion species is associated with the complex electron production mechanism inside the source, including beam plasma interaction and energy relaxation. However, plasma diagnostics inside IHC sources has been limited by the assumption of a Maxwellian distribution. In this work, the discharge characteristics of IHC plasmas were investigated by analyzing the electron energy probability functions (EEPFs) under various conditions. The shape of the EEPF is dominantly affected by the voltage applied to the hot-cathode and repeller (i.e., cathode voltage), whereby the kinetic energy of the beam electrons is determined. With increasing cathode voltage, the EEPFs show a bi-Maxwellian-like distribution with the bulk and energetic electron groups. The thermalization among the two electron groups with increasing magnetic field makes the EEPFs to follow a Maxwellian distribution. The absolute value of the density and effective temperature of the electron are mainly governed by the bulk electron group with a relatively higher density, and the changes in the electric potentials are explained in the context of the confinement of the energetic electrons.

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