Self-injection-locked magnetron as an active ring resonator side coupled to a waveguide with a delayed feedback loop

The theoretical analysis and numerical simulations of the magnetron operation with a feedback loop were performed assuming that the delay of the electromagnetic wave propagating in the loop is constant whereas the phase of the complex feedback reflection coefficient is varied. Results of simulations showed that by a proper adjustment of values of the time delay and phase of reflection coefficient that determines phase matching between the waves in the resonator and feedback loop, one can increase the magnetron's output power significantly without any other additional measures.Comment: 12 pages, 4 figure

Observation of the diocotron instability in a diode with split cathode

Diocotron instability has been observed in the pure electron plasma formed in a split cathode coaxial diode. This plasma consists of electrons, trapped in the longitudinal potential well between the two parts of the cathode. The mathematical model of the electron squeezed state, which allows calculation of the equilibrium plasma density, is presented. The model is applied in a comprehensive analysis of experimental data and the presence of the diocotron instability is unambiguously confirmed.Comment: Accepted for publication in Physics of Plasma

SUPERSONIC JET GENERATION BY UNDERWATER SUB-MICROSECOND ELECTRICAL EXPLOSIONS OF WIRE ARRAYS

Experiments in which supersonic water jets are generated by underwater sub-s timescale electrical explosions of cylindrical and conical wire arrays are presented. These are compared with previous experiments [Maler et al., Phys. Plasmas 28, 063509 (2021)] in which the generation of supersonic water jets was demonstrated using a s timescale generator. Although in the present experiments less energy is deposited into the wire arrays, the water jets acquire higher velocities compared to when the deposited energy is higher but the timescale is slower. That is, with a higher energy density deposition rate, faster radial wire expansion is induced resulting in a stronger converging shockwave and a faster waterflow behind its front. In addition, two dimensional hydrodynamic numerical simulations show that the formation of the water jet is the result of extremely high pressure at the axis of the shockwave implosion and the cumulative edge effect realized at the array output

Stationary striations in plasma, created by a short microwave pulse in a waveguide filled with a neutral gas

It was observed experimentally that after crossing a waveguide filled with a neutral gas, a short powerful microwave pulse leaves a periodic glow of plasma along the waveguide, persisting several tens of nanoseconds. A theoretical model is presented which in combination with numerical simulations proposes a possible explanation of this phenomenon.Comment: 15 pages, 9 figure

Generation of highly symmetric, cylindrically convergent shockwaves in water

We report on pulsed power driven, exploding copper wire array experiments conducted to generate cylindrical convergent shockwaves in water employing μs risetime currents >550 kA in amplitude and with stored energies of >15 kJ—a substantial increase over previous results. The experiments were carried out on the recently constructed Mega-Ampere-Compression-and-Hydrodynamics facility at Imperial College London in collaboration with colleagues of Technion, Israel. 10 mm diameter arrays consisting of 60 × 130 μm wires were utilized, and the current and voltage diagnostics of the load region suggested that ∼8 kJ of energy was deposited in the wires (and the load region close to the wires) during the experiments, resulting in the formation of dense, highly resistive plasmas that rapidly expanded driving the shockwaves in water. Laser-backlit framing images of the shockfront were obtained at radii 50:1. Framing images and streak photographs showed that the velocity of the shockwave reached ∼7.5 km s−1 at 0.1 mm from the axis. 2D hydrodynamic simulations that match the experimentally obtained implosion trajectory suggest that pressures >1 Mbar are produced within 10 μm of the axis along with water densities of 3gcm−3 and temperatures of many 1000 s of Kelvin. Under these conditions, Quotidian Equation of State suggests that a strongly coupled plasma with an ionization fraction of ∼0.7 would be formed. The results represent a “stepping stone” in the application of the technique to drive different material samples into high pressure, warm dense matter regimes with compact, university scale generators, and provide support in scaling the technique to multi-mega ampere currents

Intense electron emission from carbon fiber cathodes

We studied the emission properties of carbon fiber cathodes. These cathodes were made either of a single carbon fiber or of carbon fabric, or of an array of carbon fiber bundles. It was found that an intense emission of electrons occurs from a plasma which is formed on the carbon fiber surface as a result of a flashover process. In addition, the time delay in the appearance of the electron emission with respect to the start of the accelerating voltage pulse was found to depend strongly on the voltage growth rate. A simple model of the plasma formation is suggested