MAGNETIC FIELD DYNAMICS IN PLASMA OPENING SWITCH

Computer simulations for magnetic field penetration into plasma of plasma opening switch (POS), and current loop formation in it are presented for various initial plasma densities, currents, and POS geometries. It is shown that the current loop dynamics in the POS is determined by the fast magnetic field penetration in plasma due to the Hall effect. The strong dependence of the current loop longitudinal velocity on the transverse coordinate, together with the influence of the boundary conditions at the POS cathode and anode, lead to the formation of the narrow S-shaped current loop even in a homogeneous plasma. It is shown that the control parameters influencing the dynam-ics of the magnetic field and the motion of the current loop in the POS are the initial plasma density, driving current and cathode radius. The POS resistance is calculated for wide range of initial plasma densities, currents, and cath-ode radiuses. It is shown, that POS resistance is proportional to the total current, inversely proportional to plasma density, and is in the range 10-3…1 Ω for plasma densities 1012…1015 cm-3.

Some issues of the operation of plasma opening switches

The paper analyzes some processes in a plasma opening switch with a conduction time of ~ 100 ns. Relations are derived for assessing the evolution of the ion current to its space charge-limited state and for estimating its maximum possible density. It is shown that the ion current density reaches its extremum before electron magnetization. Estimates for the electromagnetic energy delivered to the switch are also presented demonstrating that this energy is spent equally for creating a magnetic field in the plasma volume and for its ohmic heating.

Picosecond semiconductor generator for capacitive sensors calibration

The paper describes a semiconductor picosecond pulse generator that can be used to calibrate capacitive high voltage sensors of MV range. The generator is designed as a base unit, to which external pulse converters are connected. In the base unit, semiconductor devices – first a semiconductor opening switch (SOS) and then a semiconductor sharpener (SS) – generate an output pulse with a rise time of 220 ps and a subsequent flat-top of 2 ns in duration. The pulse amplitude is around 1 kV across 50 Ω load. An external diode sharpener generates a pulse with 120 ps rise time and 500-ps flat-top at the amplitude of 850 V. To switch the semiconductor sharpeners to the conducting state, the shock-ionization wave mode is used. Additional pulse converters make it possible to generate output pulses across 50 Ω load with the rise time of 70-150 ps, the pulse duration of 135-310 ps, and the amplitude of 130–480 V. The electrical diagram of the generator and waveforms of the output pulses are presented. An example of the calibration of capacitive sensors of a multi-gigawatt picosecond generator is also shown.

CURRENT FLOW DYNAMICS IN PLASMA OPENING SWITCH

The electromagnetic fields and processes of current flow in the plasma channel of the plasma opening switch were considered in the electron hydrodynamics approximation. Taking into account the nature and features of the current flow through the plasma filled region of plasma opening switch allowed to obtain the structure of the current channel and its dynamics along the plasma. The current flow is a wave process. When this wave reaches the boundary of plasma it seems to be the break of current at this moment. The criterion of this break is obtained.

PLASMA DYNAMICS IN ACCELERATOR WITH PLASMA OPENING SWITCH

Plasma propagation in the pulse electron accelerator chamber with a plasma opening switch is investigated. Output beam and X-ray radiation parameters are shown to vary depending on the plasma channel location at the moment of current breaking. Experiments showing plasma compression into channels during the conductive phase of the plasma opening switch operation have been performed.