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Basics of Plasma-Focus


Plasma-Focus Device (PFD) is relatively inexpensive, non-radioactive, low voltage, compact, and very efficient source of plasma and radiation. With experienced guidance, it can be reproduced in experimental laboratories around the world for use as a non-radioactive source of X-Rays, plasma streams, electrons and ion beams, and neutrons for both applications and basic research.

The operation of PFD is based on the pulsed electrical discharge through gases contained between two coaxial electrodes separated with an insulator. High voltage applied to the electrodes immersed in a low pressure (of the order of few Torrs) gas causes an electrical break-down along the insulator. Fast rise of the current (with ~1-5 us time scale) leads to the formation of a plasma sheath, which, driven by jxB force, moves along the electrodes towards their open end. During this process, the plasma sheath accelerates to a velocity of 107 cm/s and the current rises up to ~0.7-3 MA (depending on a condenser battery power). After reaching the central electrode edge the sheath collapses toward the axis forming a dense (up to 1020cm-3), hot (~1 keV), elongated plasma structure called “pinch”. Rapid development of MHD instabilities causing disruption of the pinch is accompanied by an intense burst of ionizing radiation: soft and hard X-rays, electrons, ions and neutrons. The neutrons are from D-D reaction when deuterium is used as a filling gas. Fast (> 100km/s) plasma stream is also generated along the axis.

While the general features of phenomena occurring in the plasma-focus discharges have been known for several tens of years there is still no detailed understanding of mechanisms ruling the structure, dynamics and destruction of the current sheath which is responsible for anomalous impedance (caused by micro-instabilities) and subsequent generation of ion and electron beams which create then large yields of X-rays and neutrons. So, the plasma generated in the PF is a very interesting object for basic studies of current carrying plasmas.

Plasma-Focus Device: Principle of Operation

Launch movie in external player

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