DISCUSSION OF RESULTS
Gas Gaps
The negative DC breakdown voltage gradient of the coaxial cylinder gap at 3. 5kg/cm2 pressure is approximately 150kV/cm according to the data in Fig.4. This voltage gradient is nearly 50 percent of the limiting breakdown voltage gradient. In this case, the total area exposed to the high field is nearly 0.15m2. On the other hand, the breakdown voltage gradient of a 150mm
diameter plane gap is 210kV/cm, whose exposed stressed area is 0.015m2t. This corresponds to 70 percent of the limiting value. This area effect is in agood agreement with the data given in the literature.(1) Such a breakdown far below the limiting value, as given above, is said to originate from the cathode surface microstructure and or from free particles attached on or moving near