Gas-discharge tube (GDT) surge protectors are known for many decades as passive units used in low-voltage telecom networks for protection of electrical components from transient over-voltages (discharging) such as lightning. Unreliability of the mean turn-on DC breakdown voltage and the run-to-run variability has been overcome successfully in the past by adding, for example, a radioactive source inside the tube. Radioisotopes provide a constant low level of free electrons, which trigger the breakdown. In the last decades, any concept using environmentally harmful compounds is not acceptable anymore and new solutions were searched. In our application, a cold field electron emitter source is used as the trigger for the gas discharge but with no activating compound on the two main electrodes. The patent literature describes in details the implementation of the so-called trigger wires (auxiliary electrodes) made of graphite, placed in between the two main electrodes, but no physical explanation has been given yet. We present experimental results, which show that stable cold field electron emission current in the high vacuum range originating from the nano-structured edge of the graphite layer is well correlated to the stable breakdown voltage of the GDT surge protector filled with a mixture of clean gases.
COBISS.SI-ID: 25752615
This work has been devoted to plasma-wall investigations towards applications in laboratory, technology oriented and fusion plasmas. Special attention has been done to simulating the space charge effects that may play important role in secondary electron emission due to strong electric field appearing in Gas Discharge Tubes. We have developed a small but efficient PIC simulation program in order to obtain more data than currently possible with other such programs available today, and to compare results of our program with results obtained with other methods and packages. Our code is based on grid-free treecode (TC) method, which advantages and drawbacks in its applications to a general plasma diode with externaly controlable emitted electron influxes, have been presented.
COBISS.SI-ID: 12612379
Prediction of hydrogen isotopes interaction with W and their migration in devices designed for plasma-aided processes and reactions are very important, but still not enough understood, especially at the field of thermonuclear fusion experiments and applications. Solving this problem within fusion research activities, where the scope and severity of the problems is most demanding, gives automatically most of answers to similar problems that may appear in in laboratory, technology oriented and fusion plasmas, in particular in devices of Plasma Focus and gas arresters for overvolvoltage protection. A particular such problem concernes theoretically predicted traping of multiple H atoms exothermically, but their density and their potential influence on permeability has not been experimentally investigated yet. In our work, long-term hydrogen outgassing and permeation studies of structurally highly disordered tungsten films, deposited on 40 mm diameter highly permeable Eurofer substrates, using the Pulsed Laser Deposition technique have been realized. Permeability of W films having different thicknesses (1 and 10 micrometers) was initially extremely low, and was gradually increasing over a several-day campaign. The final values at 400 °C, lying between P = 1.46x10-15 mol H2/(m s Pa0.5) and P = 4.8x10-15 mol H2/(m s Pa0.5), were substantially lower than those known for well ordered films. Surprisingly, the 10 micrometer thick W film initially contained a very high amount of hydrogen, ~ 0.1 H/W, which was gradually releasing during the twenty-day campaign.
COBISS.SI-ID: 25978663