Characteristics of double layers formed by a grid which is immersed in a large volume plasma (10 m3) are studied experimentally. Spatial variation of potential, velocity distributions of electrons and ions, fluctuation spectrum and negative resistivity and the relation between light intensity and electric potential, etc. are measured under the condition of low pressures. The argon pressure is mostly in the 10-5 torr range. The plasma density at the lower potential side is 2 to 8*106 cm-3 and the electron temperature is 2-3 eV. It is found that the plasma at the high potential side is created very efficiently by the accelerated electrons coming to both sides of the grid. Thus, the collisionless condition is well satisfied in the double layer. Discussion is made on the effect of ionization. Experimental data are compared with one-dimensional and two-dimensional collisionless theories to examine the possible parameters for the existence of double layers. Their stability against fluctuation is also studied.
Stationary potential jump on weak double layer in discharge plasmas