Entstehung und Eigenschaften des Halo bei PinchPl

Authors: Jürgen Freund

Publish Date: 1973/04/01

Volume: 258, Issue: 2, Pages: 108-125

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Abstract

In pinch discharges a second plasma regime called halo12 outside the central plasma column14 has been observed This surrounding plasma was investigated in the experiments with the 54 m long compression coil in the ISARI linear theta pinch because there it appears highly pronouncedThe development of the discharge was observed sideon stereoscopic with image converters and a streak camera It appears possible to resolve the spacetime behaviour of the plasma especially in the dynamic phase of the discharge where the halo shows a filament like structure by using highspeed color reversal film streak camera Furthermore the smear pictures show that after 6–8 μsec the halo region is frozen into the external magnetic field that is from this time the halo is characterized by a high electrical conductivity The boundary layer of the halo follows a magnetic flux tubeThe parameters of the halo such as electron densityn e 1015 cm−3 atomic temperatureT a and ion temperatureT i 15 eV were determined spectroscopically as a function of time and location from the broadening of the deuterium Balmer lines The absolutely measured line intensities do not allow direct calculation of the electron temperature since the excited levels of the investigated Balmer lines are mainly populated from the ground level By numerical solution of a system of rate equations describing the change of the levels a region for the electron temperature 5T e 10eV can be specifiedDifferent mechanisms such as photoionization ionization by electron impact in a time varying magnetic field ionizing collisions of high velocity neutral atoms with neutral gas at rest transport processes in the plasma across the magnetic field instabilities which may cause the development of the halo are discussed by means of the experimental results It is concluded that the halo region is caused by flute instabilities

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