In the paper our type of GDT construction is shownwhere main body is metal instead ceramic which is conventionally used. The paper also presents the basic methods of measurements and determination of GDT properties with some measurement results at different filling gases. From the presented examples we will see that the prediction of results is very difficult and we need a lot of experiments and theoretical experience to reach the required properties of GDT.
COBISS.SI-ID: 24631847
Gasdischarge tube (GDT) surge protectors are known for many decades as passive units used in lowvoltage telecom networks for protection of electrical components from transient overvoltages (discharging) such as lightning. Unreliability of the mean turnon DC breakdown voltage and the runtorun 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 socalled 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 nanostructured 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
In this work we present basic principle of treecode (TC) method, its advantages and drawbacks in its applications for laboratory and fusion plasmas. Particular task done in this work was to create 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. The program is intended to be used in plasma-wall investigations of laboratory, technology oriented and fusion plasmas.
COBISS.SI-ID: 12612379
We present results obtained during a gas breakdown stage in a high pressure gas filled diode. The method is particle in cell (PIC) 2D-simulation performed with a particular choice of a simple external circuit presented by an ideal current generator. It is shown that within the diode gap extremely high local conductive and displacement currents develop, such that the external current may be neglected in comparison with them. Also, the first runs indicate appearance of torus like (convective) structures that require further theoretical research and code upgrades. Secondary electrons are mainly delivered from that localized part of cathode which is most frequently impacted by ions originated from the nearest local plasma-bunch. Such ”normal” situation appears only before the ion-rich plasma ”attaches” the cathode and after that the cathode ”spot” spreads over the cathode surface. Then strong electron and ion flux-bursts can be obtained with the total external current circuit for several orders of magnitude low and independent on time. That means that the conductive currents of particles inside the tube should be compensated by strong displacement currents. Our estimation of displacement currents has shown that the associated local self-generated magnetic field can be of the order of several tens of T. In addition the total energy that can be accumulated during the ionization front growth is estimated to be of the order of 1J within the volume of several cubic mm, and this can be released during the current burst in less than 1ns, yielding the power of emitted electromagnetic energy of the other of TW. However, although this phenomenon must not be so surprising for dense plasmas such as those in Plasma Focus and GDTs, more convenient results requires more precise physical model with corresponding simulation code. Unfortunately, available kinetic codes are in fact electrostatic one, i.e., they do not take into account self-generated magnetic electro-potential, i.e., corresponding field and therefore are not capable to calculate the local distribution Lorentz internal plasma self-force to particular particles, which could to certain extent dump described phenomena. Therefore we propose a full self-consistent set of Electrodynamics equations to be implemented into the XOOPIC code. For this the time-dependent a detailed calculation of local moments of velocity distributions (densities, average random and directional velocity components and related fluxes), together with scalar and vector fields components (with particle energy and heat fluxes components as a backside result) is proposed as a quite new approach in PIC simulations.
COBISS.SI-ID: 10155604
Quantification of hydrogen fraction in the gas mixture with inert gases kept in a small enclosure of the gas surge arrester (GSA) is a challenging task. Hydrogen greatly influences device properties, but as an omnipresent gas it represents also the background of any mass spectrometer. Hydrogen fraction in a particular GSA was quantified after its puncture in an evacuated batch inlet and subsequent introduction to a pumped chamber housing a quadrupole mass spectrometer (QMS). Its calibration was performed by an innovative in-situ calibration procedure which should yield high accuracy. In the first stage, a pure gas (Ar, Ne, H2) contained in a calibrated volume was set by a leak valve to flow into the UHV system. The pressure change reading of the capacitance manometer over time gives the flow rate which is directly correlated to the ion current of a specific mass peak in the span of 3 orders of magnitude. The extracted calibration curves of the QMS for each gas species are applied in the second stage of the calibration when known gas mixtures are prepared in the calibrated volume to verify the gas composition determination procedure based on the fractionation. Such procedure is revealed fairly accurate at high (above w6 _ 10_5 mbar L/s) flow rates, however a significant error appeared at lower flow rates. Possible explanations for erroneous hydrogen determination at very low fluxes by the QMS in the mixture with argon are presented.
COBISS.SI-ID: 1977191