Secondary electrons are identified as a separate component within a plasma in a specifically modified multidipole device. It is shown that secondary electron emission at walls can be comparable to electron production by ionization. It is also shown that secondary electron emission can significantly change Langmuir probe characteristics.
Current disruptions may be excited spontaneously in a laboratory plasma when the electric current density along the magnetic field is large. This phenomenon is investigated in the plasma column of a triple plasma device with an inductive external electric circuit. Each current disruption then gives an inductive voltage pulse of several hundred volts over the plasma. and this potentia! drop is found to be concentrated at an electric double layer which forms in the plasma during the pulse. Most of the magnetic energy, initially stored in the circuit inductance. is transferred to the double layer during the period of current decrease and released there as particle energy.Simultaneously as the current decreases the potential level at a local potential minimum in the plasma is found to decrease. Reflection of electrons at this minimum is conjectured to cause the decrease of the current during a disruption.
The properties of double layers produced in current filaments have been studied. The experiments were performed in a magnetized triple plasma device in which the diameter of the central plasma column could be varied. The scaling of the double layer potential drop V dl with the parameter jd 2 , where j is the current density in the double layer and d is the double layer thickness, was determined for several values of the current filament radius Ro. For relatively large values of R o , the one-dimensional (Langmuir) scaling was obeyed, V dl -(jd 2 )213. WhenRo was decreased, a departure from the strictly one-dimensional scaling was observed, with V dl becoming less and less dependent on the parameter jd 2 •
The gamma-ray spectra that result from the capture of neutrons in resonances of Hg 199 , Pt 196 , W 183 , and Se 77 are measured. A least-squares fitting of the spectra gives relative values of partial widths for various sets of high-energy radiative transitions. These widths are treated as statistical samples drawn from populations governed by a x 2 distribution with v degrees of freedom. A technique of hypothesis testing that makes use of Monte Carlo calculations is used to derive unbiased values of v from the small samples of experimental widths. The over-all result of the analysis is ^=1.34db0.33±0.21. The previously reported partial radiation widths for resonances of Gd 155 , Yb 173 , Hf 177 , and Hg 201 are also analyzed. The result is v = 1.14±0.44=b0.21. Thus, both sets of data are in good agreement with the value v = l that is expected from the Porter-Thomas description of the distribution of the widths associated with a single exit channel.
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