Electrodeless discharge, one of the kinds of high-frequency discharge (or of pulsed discharge) in which the discharge gap is completely isolated from electrodes, and the discharge current may be either a displacement current (an E-discharge) or an induction current (an H-discharge). If a bulb containing a rarefied gas is placed between the plates of the capacitor of an oscillatory circuit, an E-discharge with a linear current is observed (Fig., a). When the bulb is placed inside the coil of the oscillatory circuit, an H-discharge with a ring current is observed (Fig., b). Of particular importance is an electrodeless discharge in a bulb shaped as a torus enclosing a turn of a pulse transformer, since the plasma obtained in such a bulb can be isolated from the walls by a magnetic field and, at a sufficiently large current, an almost completely ionised high-temperature plasma can be obtained. This arrangement underlies the tokamak — one of the types of magnetic traps used in research on controlled thermonuclear fusion. An electrodeless discharge can also be produced by placing a bulb containing a rarefied gas in a waveguide.
Arrangement for producing an electrodeless discharge — linear (a) and ring (b):
РК — the discharge bulb with the rarefied gas;
С — the capacitor of the oscillatory circuit;
L — the self-inductance coil;
Г — the generator of electromagnetic oscillations.
РК — the discharge bulb with the rarefied gas;
С — the capacitor of the oscillatory circuit;
L — the self-inductance coil;
Г — the generator of electromagnetic oscillations.