Search

Abstract Many high power RF amplifiers, working at various frequencies are being used in ICRH group. High power RF output is obtained by amplification in stages i.e. 50 W, 2 kW, 20 kW, 200 kW. These stages are connected as chain and act as driver for the final stage amplifier of ∼1.5 MW. The high power tubes used in these amplifiers (e.g. Triodes, Tetrodes), need DC power sources up to few mega-watt working at ∼30 kV. The Triodes and Tetrodes that are in use are vulnerable to internal arc faults. To protect them from permanent damage, DC Voltages need to be removed within few tens of microseconds. The conventional power supplies that are being used are short circuited with a very fast switch known as crowbar switch. Ignitron based crowbar switches are widely in use but are being replaced because of the presence of large quantities of toxic Mercury. Further, above crowbar methods cause enormous stress (during the short circuit) of the power supply and can cause considerable disturbance in the power lines. With the development of solid state series switch such short circuits of conventional supplies can be avoided. It is envisaged that a series IGBT switch rated at 7 kV, 6 A would be suitable for HVDC power supply of 20 kW stage. This development involves complete switch design, selection of IGBTs, static and dynamic voltage balancing circuit design. Further, isolation level requirements of various circuits and components are analyzed and adequate isolation is provided. The 7 kV, 6 A series switch is fabricated and successfully tested. [ABSTRACT FROM AUTHOR]

This paper describes a low-cost ignitron-based switching scheme for transferring energy from capacitor bank to various loads, used in plasma physics and other pulsed power applications. Battery-operated driver modules have been designed to simultaneously trigger two ignitrons in parallel by using either transistor-transistor logic pulses or optical pulses using a fiber-optic interface with optical fibers of length up to 50 m, for applications prone to generate electromagnetic interferences. These driver modules are designed using insulated gate bipolar transistors as switches to deliver a pulse of amplitude of ~500 A and rise time of ~1.2 μs to the ignitor-cathode junction of their respective ignitrons. The modules are designed to facilitate triggering of multiple ignitrons required for large current applications. The feasibility of this scheme and the performance of designed circuit are characterized using a test setup. Statistical variation of triggering delay for single ignitrons is studied extensively, and the effect of trigger energy on statistical parameters is reported. Jitters of 63.5 and 85 ns, respectively, have been observed for triggering of each ignitron used in this scheme. Difference in triggering of two ignitrons connected in parallel is also studied, and a jitter of 150 ns is observed in the onset of current discharges through individual ignitrons. [ABSTRACT FROM PUBLISHER]

An investigation of the process of electrical strength recovery is performed using demountable devices and a TPI-10k/50 two-section, cold-cathode, sealed-off thyratron. The method of forced removal of the discharge burning products is used via a non-self-sustained discharge immediately after a breakdown in the thyratron. Measurements of the non-self-sustained discharge current allow estimating the time of the electrical strength recovery in the thyratron sections. [ABSTRACT FROM AUTHOR]

In this paper, a high current linear aperture radial multichannel Pseudospark switch (LARM-PSS) is reported which has been analyzed for its high current characteristics. In order to enhance hold-off voltage and support hollow cathode effect for the ignition of the discharge in this configuration, the field penetration analysis through circular and linear apertures of the electrodes has been carried out. The linear apertures in the electrodes increase the current handling capacity than that of circular aperture electrodes without significant compromise of the hold-off capacity. The developed LARM-PSS switch is capable to hold voltage up to 25 kV at gas pressure between 10 and 50 Pa for hydrogen. The switch has been operated using a 800 nF capacitor bank and conducted an effective charge up to 1.5 C with peak switch current ~20 kA at applied voltage 19 kV [ABSTRACT FROM AUTHOR]

An estimated 215,000 tonnes of mercury (Hg) have been emitted to the atmosphere from anthropogenic sources since the nineteenth century, igniting widespread environmental monitoring owing to its toxicity. The environmental fate of Hg is strongly determined by catchment characteristics, especially soil organic matter. In this study, concentrations and pools of Hg were determined for lakes and soils in upland peat-dominated catchments in Ireland to assess controls of aquatic Hg and soil response to changes in emissions. Headwater lakes in upland coastal regions were surveyed for water chemistry and total Hg (THg) during spring 2008. In addition, a sub-set of lakes ( n = 5) were repeatedly sampled during 2009–2011, and their surface soils collected for Hg analysis, including a short (30 cm) peat core to assess temporal Hg fluxes using radiometric 210Pb dating. Peat cores indicated a significant decrease in Hg deposition since the 1980s, in broad agreement with other ‘background’ regions. Total Hg was correlated with total organic carbon (TOC) in the survey and intensive study lakes (r = 0.70 and 0.45), indicative of the strong affinity of Hg to organic matter. At the intensive lakes, monomethylmercury (MMHg) made up 3.3 % of mean THg and exhibited a positive correlation with total SO 42− (r = 0.55). Further, both THg and MMHg were significantly correlated with conductivity (r = 0.48 and 0.54, respectively) potentially owing to marine inputs, and negatively correlated with pH (r = −0.59 and −0.56 respectively). Significant differences in THg (and MMHg) were observed between the five lakes, the highest concentrations (4.45 and 0.16 ng L −1, respectively) tended to be associated with TOC in lakes and occurred at sites in the northwest, characterized by higher levels of soil organic matter (peat) and soil moisture relative to the other sites. In contrast, surface soil pools of THg ranged between 13.6 and 20.8 μg m −2 across study sites and did not vary significantly, but were typical of global background regions. Nonetheless, the organic rich soils that dominate Ireland are a natural sink for THg, and peat harvesting for energy production may release long-term stores of Hg from deeper soil layers. [ABSTRACT FROM AUTHOR]

This paper describes a low cost, easy-to-implement circuit for triggering ignitrons in plasma physics experiments and other pulsed power applications. Using insulated gate bipolar transistors (IGBTs) for rapid switching, the circuit delivers >200~A peak current from a 0.1-\muF capacitor to the ignitron trigger pin with a rise time of \sim0.6~\mus. The trigger circuit is isolated from the ignitron by a pulse transformer. Details of the circuit design and practical considerations for working with IGBTs are discussed. Sources of inductance in the system are identified, and leakage inductance associated with the pulse transformer is shown to be the primary factor limiting the pulse rise time. [ABSTRACT FROM PUBLISHER]

A 10-MVA-scale resonant oscillator, powered by a pulse-forming network and switched with a pair of commutating mercury ignitrons, was developed for the MST reversed-field pinch plasma-confinement experiment. A novel feature of this circuit is its commutation mechanism, wherein each turning on of one ignitron causes a reverse voltage transient that turns off the other. Two of these oscillators are used in oscillating-field current-drive tests, in which they are capable of nearly 1MW net input power to the plasma, with resonant frequencies of a few 100 Hz for pulse durations of a few tens of ms, being precharged for immediate full amplitude. We describe the circuit and its operation, and discuss features that allow reliable, high-current commutation of the ignitrons and exploit their low switching impedance. [ABSTRACT FROM AUTHOR]

The Caltech spheromak experiment uses a size A ignitron in switching a 59-μF capacitor bank (charged up to 8 kV) across an inductive plasma load. Typical power levels in the discharge circuit are ∼200 MW for a duration of ∼10 μs. This paper describes the setup of the circuit and the measurements of various impedances in the circuit. The combined impedance of the size A ignitron and the cables was found to be significantly larger than the plasma impedance. This causes the circuit to behave like a current source with low energy transfer efficiency. This behavior is expected to be common with other pulsed plasma experiments of similar size that employ an ignitron switch. [ABSTRACT FROM AUTHOR]

Abstract: A new straw-tube gas chamber which is made of seamless straw-tubes, instead of ordinary wound-type straw-tubes is developed. Seamless straw-tubes have various advantages over ordinary wound-type ones, in particular, in terms of mechanical strength and lesser wall thickness. Our seamless straw-tubes are fabricated to be resistive so that the hit positions along the straw axis can be read by cathode planes placed outside the straw-tube chambers, where the cathode strips run transverse to the straw axis. A beam test was carried out at KEK to study their performance. As a result of the beam test, the position resolution of the cathode strips of is achieved, and an anode position resolution of is also obtained. [Copyright &y& Elsevier]

In this work, we report the ignition potential between an earthed spherical metal electrode and a charged insulating plate in hydrogen–air mixture. The test results indicate that it is very difficult to generate brush discharge when the surface potential of the plate center is less than −10 kV. And it is very difficult to ignite the hydrogen–air mixture when the surface potential of the plate center is less than −20 kV. The ignition can be generated when the range of the hydrogen concentration is 20–25%. [Copyright &y& Elsevier]

Presents a study which traced aspects of the history of power electronics from magnetic amplifiers, thyratrons and ignitrons to power semiconductors. Definition of power electronics; Goal of power electronics; Features of power electronics; Conclusions.

Describes the operation of small-scale capacitor discharge pulse generator. Use of thyristors in a Marx configuration; Comparison between sequential and simultaneous triggering; Design of the four-stage arrangement for ignitron firing application.