Discharge Of Capacitor Bank Research Articles

A versatile power supply system for the central solenoid of the QUEST spherical tokamak

Here, a versatile power supply system, consisting of two current sources, insulated-gate bipolar transistor stacks, and a capacitor bank, is proposed for application in various operations of the QUEST spherical tokamak. The central solenoid coil in this system can carrying a maximum current and voltage of ±8 kA and ±375 V, respectively. In plasma start-up experiments based on ohmic heating through double flux swing, a plasma current of over 100 kA is stably obtained. Moreover, the feedback control of the thyristor power supply is utilized to control the plasma current, plasma shape, and position. The oscillating central-solenoid current applies a bipolar loop voltage at constant time intervals, and the capacitor bank discharge facilitates a co-axial helicity injection as well as amplifies the toroidal current.

Design and implementation of a versatile H-bridge power supply for experiments on the STOR-M Tokamak

An H-bridge power supply has been developed for different experiments on the STOR-M tokamak. Four insulated-gate bipolar transistors (IGBTs) are used to guide the current to the load from a capacitor bank discharge. The timing signal to the gates of the IGBTs is controlled by a field programmable gate array (FPGA). The power supply can be programmed to drive either a sinusoidal current waveform to an inductive load or a bipolar rectangular current waveform to a resistive load. The maximum frequency and current tested for the sinusoidal current waveform are 25 kHz and 2200 A, respectively. For bipolar current waveforms, the maximum current tested is 1500 A at 3 kHz. The sinusoidal current to a set of helical coils was used for the Resonant Magnetic Perturbation (RMP) experiments and the bipolar rectangular current waveform was used for both the electrode biasing experiments and the RMP experiments on the STOR-M tokamak.

Spark channel dynamics in railgun switches in unipolar and oscillatory discharges

AbstractSpark gaps are often used to commute energy in the discharge of a capacitive storage to a load. In some applications, a unipolar pulse is not feasible, and an oscillatory (underdamped sinusoidal) regime must be realized for the discharge of the capacitor bank. Spark gaps, which were developed for unipolar discharge, cannot be directly employed in an under-damped (oscillatory) regime since at the transition of the current through zero, the spark channel could stop motion and ignite in the following half period. This work has two main objectives: (i) To develop and test a simulation model of spark channel motion in linear rail geometry, which must be valid for both the oscillatory and unipolar regimes of capacitor bank discharge; and (ii) to investigate arc motion and electrode heating, depending on the current and charge transfer, over a wide range of operation. A self-consistent treatment of plasma motion and electrode heating (taking into account the radiation of a plasma channel) is applied in the present paper, and it is shown that radiation can significantly impact on the temperature of the electrodes. Electrode ablation and the temperature dependence of the main thermal parameters are also taken into account. Stainless steel (Cr/Ni/Ti 18/10/0.6÷0.8), copper (Cu), chromium (Cr), tungsten (W), and molybdenum (Mo) are used here as electrode materials since these materials are widely used for the manufacture of electrodes. The results of numerical calculations are compared with experimental results, and conditions are defined for reduced electrode erosion.

Numerical simulation of spark channel dynamics in railgun switches

Discharge of a capacitive storage on a load with unipolar pulse is employed for pumping of powerful lasers and also for feeding of electromagnetic launchers, and pulsed high magnetic field facilities. Spark gaps are often used to commute energy on a load. In some applications unipolar pulse is not feasible and oscillatory regime (underdamped sinusoidal) has to be realized for the capacitor bank discharge. Spark gaps, developed for unipolar discharge, cannot directly be employed in under-damped (oscillatory) regime, because at current transition through zero the arc channel could stop motion and ignite at initial place on the following half period. Two main objectives were pursued in this work: 1. develop and test simulation model of a the spark channel motion in linear rail geometry for the oscillatory regime of capacitor bank discharge; 2. Investigate arc motion and electrodes heating depending on the current and charge transfer in wide operation range.

Dynamics of quasi-empty rupture in the layer of cavitating liquid under SW-loading

The problem of formation and collapse of a quasi-empty rupture in the layer of a cavitating liquid under shock wave (SW) loading is considered. The SW-pulse is generated in the layer by electro-magnetic hydrodynamic shock tube in a result of high-voltage discharge of capacitor bank on a flat helical coil. The latter is located right up to the bottom (conducting membrane) of container with the layer of two-phase distilled liquid. The analysis of the experimental data shows that the rupture is shaped as a spherical segment, which retains its topology during the entire process of its evolution and collapse. It was shown that potential energy of maximum volume of rupture at its collapse is practically transformed in acoustical losses (SW-radiation) and rupture disappears. Dynamics of main parameters and an existence time of rupture were determined. The analysis of cavitating nuclei state in the form of thin layer on an entire interface of rupture shows that in the field of rupture collapse the thin cavitating layer is transformed to a cavitating cluster. The latter takes the form of a ring-shaped bubbly vortex floating upward to the free surface of the liquid layer. A р-к two-phase mathematical model was formulated, and calculations were performed to investigate the collapse of a quasi-empty spherical cavity (rupture model) in the unbounded cavitating liquid, generation of ultra-short shock wave and to discover the dynamic growth of micro-bubbles in a cluster by five orders of magnitude. [Work supported by RFBR Grant 15-05-03336.]

Tailored pressure distributions generated by vaporizing tailored metal foils

This study aimed to realize tailored pressure distributions by vaporizing metal foils. The foil specimen with two separate active areas can be fully vaporized at both tailoring positions using capacitor bank discharge. The shock pressure amplitude was revealed by free bulging test. The length effect of the foil specimen on generating shock pressure for the metal-forming work was firstly examined. Aluminum foil with an active length up to 300 mm was completely vaporized under a charging energy of 6 kJ. Using different combinations of process parameters including foil geometry and polyurethane plates, a variety of tailored pressure distributions were created. The pressure amplitudes at two separate positions can be varied by changing the process parameters used such as foil length and width and polyurethane thickness. Finally, the tailored pressure distribution was applied to sheet metal-forming process and a part with different forming depths was manufactured.

Overview of the Performance of Quench Heaters for High-Current LHC Superconducting Magnets

Quench heaters are an essential part of the protection of all high-current large hadron collider (LHC) superconducting circuits. About 2000 dipole and quadrupole magnets are equipped with quench heaters in order to protect them against development of excessive voltage and overheating after a resistive transition. The quench heaters are made of stainless steel foil partially plated with copper and connected to 900 V capacitor bank discharge power supplies. During Hardware Commissioning campaigns and machine operation every quench heater discharge event is carefully analysed to detect a possible failure or a precursor of a failure, which could lead to damage of the heater or to the superconducting coils in subsequent discharges. This paper will briefly describe two different ways of quench heater data analysis and will present the heaters performance during the years 2008-2015. A summary of the quench heater fatigue test performed on a spare LHC main dipole magnet will also be given.

Vaporizing foil actuator used for impulse forming and embossing of titanium and aluminum alloys

Electrically driven rapid vaporization of thin conductors is known to produce short-duration pressure pulses of high magnitude. This impulse can be used for applications such as high strain rate forming, shearing, collision welding, and springback calibration. Mechanical impulse was developed from aluminum foils of various thicknesses, which were vaporized using a capacitor bank discharge with a maximum charging voltage of 8.6kV. Peak current was delivered on the order of 100kA with rise times of about 12μs. In this work, polyurethane was used as a medium to transfer pressure from the aluminum foil vaporization zone to the workpiece. Fundamental experiments, where AA 3003-H14 aluminum alloy was formed into perforated plates, show that for a given foil thickness, a limit existed over which supplying higher electrical energy from a given capacitor bank did not necessarily result in higher pressure. The magnitude of generated pressure was proportional to the excess Joule heat deposited into the foil before it burst. Although the polyurethane layer helped spread the pressure pulse over a larger area, the resulting pressure distribution remained heterogeneous. Practical applications, such as forming into cavities and embossing into shallow dies, were possible with this method. Sheets of 0.508mm thick commercially pure titanium were nearly fully formed into a cellphone case die using a hybrid process that combined a quasistatic pre-forming step with a vaporizing foil forming step. Sheets of 0.508mm thick AA 2024-T3 aluminum alloy were embossed into a die with features of varying depths. Aluminum foils with straight and curved active sections were used as actuators. The curved-section foils resulted in higher conformation of the workpiece to the die in the center region, while the straight-section foils produced better conformity to the die features on the ends.

Magnetoresistance Relaxation in Thin La-Sr-Mn-O Films Exposed to High-Pulsed Magnetic Fields

Presented are the results of an investigation of colossal magnetoresistance relaxation in nanostructured La-Sr-Mn-O films after the removal of the magnetic field pulse. 400-nm thick films grown by the metal-organic chemical vapor deposition technique are studied in the magnetic field range of 2-10 T and a temperature range of 100-290 K using a pulsed magnetic field generator based on a capacitor bank discharge. A magnetic coil of special design with a nonmetallic outer casing made from polyamide materials allowed us to distinguish the relaxation processes occurring during three different time scales: ultrafast , fast ( ~ 100 μs), and slow ( ~ 1 ms). The dynamics of the fast relaxation is analyzed using the Kolmogorov-Avrami-Fatuzzo model, considering the reorientation of the magnetic domains into their equilibrium state. The slow relaxation is analyzed using the Kohlrausch-Williams-Watts model considering the short-range interaction of the magnetic moments in disordered grain boundaries having spin-glass properties.

Vaporizing foil actuator: A tool for collision welding

A method for implementing collision welding at moderate to small length scales has been developed. The flyer, instead of being driven by chemical explosives (explosive welding) or magnetic forces (magnetic pulse welding), is launched toward the target by the pressure created from the electrically driven rapid vaporization of a thin metallic conductor. Mechanical impulse is developed from 0.0762mm thick aluminum foils, which are vaporized using capacitor bank discharge with nominal charging voltage of 5.5kV and peak current on the order of 100kA delivered with rise times of about 12μs. Welding couples of copper–titanium, copper–steel, aluminum–copper, aluminum–magnesium and titanium–steel have been successfully created with the same input parameters such as foil geometry, input energy and standoff distance. Instrumented peel tests, lap shear tests and optical and scanning electron microscopy reveal a wide spectrum of both strengths and interface structures. Copper–titanium and copper–steel welds are strong and have characteristic wavy interfaces with little intermetallics or void formation. The other combinations are seen to have brittle interfaces with intermetallics and defects, with the collision welding parameters used presently. For the titanium–steel system, a thin nickel interlayer is introduced and all the layers are welded in a single experiment. Peel strength of the weld was observed to be quadrupled. Peak velocities of up to 560m/s were obtained for titanium flyer sheets.

Electrically driven plasma via vaporization of metallic conductors: A tool for impulse metal working

Forming, cutting and welding of metal by impulse has significant advantages, in that short time scales change the fundamental nature of the forming process and short duration impulses can enable much lighter and more agile equipment because large static forces do not need to be resisted. Impulse forming is most commonly executed using electromagnetic forming. However, the application of electromagnetic forming is limited at high energies and large numbers of operations by the availability of long-lived electromagnetic coils (or actuators, as they are sometimes referred to). Low-cost, disposable actuators have been suggested as one method to counteract this issue. Here we propose the use of low-cost foils or wires that are intentionally vaporized by a pulsed electric current, in order to create an intense mechanical impulse. Applications including cutting, forming, and dimensional calibration are demonstrated and discussed. The available literature that could provide design guidance is reviewed. A simple cutting and welding experiment using a vaporizing aluminum foil is demonstrated. Further experiments study the expansion of simple copper tubes using the impulse developed from copper and aluminum wires that are vaporized using capacitor bank discharge with nominal charged voltages between 3.4 and 6.7kV, and peak currents between 60 and 150kA delivered with rise times on the order of 20μs. This gives some guidance on how forming operations may be designed and, opens possible areas for further research.

Ionic collisions in metallic lattices under transient current pulses

A novel method for ionic collisions is presented based on a theoretical analysis of the long-standing wire fragmentation problem. Based on a Maxwellian approach of the transient electrodynamic forces we deduce a theoretical formula of the effective tensile force. A number of conducted experiments with low energy capacitor bank discharges are also reported with positive results. The new results show the possibility of building solid state ion colliders below the fragmentation threshold using high power electrical pulses with very low energy.

Modeling gas-dynamic processes in thunderstorms by powerful electric discharges

Conditions of using electric discharges for laboratory modeling of gas-dynamic processes in thunderstorms are considered. Methods of experimental modeling of lightning bolts by capacitor bank discharges are developed. Modeling criteria are obtained from the general equations describing the model and full-scale processes. Channel and blast-wave parameters were measured during powerful electric discharges in model experiments. Experimental data are compared with calculations of the explosion effect using various techniques. The TNT equivalents of the electric discharges modeling thunderstorms are determined. The lightning energy is estimated from its photographs, and the parameters of the blast wave in the near zone and acoustic perturbations at large distances in the air and ground are determined.

Solid-state power supply for gas lasers

A novel pulsed power supply for gas lasers is presented. The device uses only solid state components and is based on a capacitor bank discharge. Fast switching of the discharge is triggered by an insulated gate bipolar transistor. The terminal section of the power supply is a transformer designed to match the reactive capacitance of a gas discharge. Strokes up to 30 kV and 30 mA are achieved across the secondary windings of this transformer. The power supply delivers high voltage pulses with a duration between 0.5 and 50 μs and a repetition rate up to some kHz. The power supply has been tested on a longitudinal discharge quasi-cw regime CO2 laser. Laser pulses were generated with a duration down to the microseconds region, a peak power exceeding some kilowatts, and a repetition rate ranging from 200 Hz to a few kHz.

Experimental assessment of temperature in plasma wall interaction

The purpose of this paper is to study the temperature evolution during the interaction of a plasma with an insulating wall in polyethylene ((CH2) n ) and polyoxymethylene ((CH2O) n ). The plasma is initiated by means of a capacitor bank discharge in a copper fuse wire. Due to the energy release the ablation of the insulating wall produces some insulating vapours in addition to the copper vapours corresponding to the wire vaporization. Using neutral copper line intensity ratio assuming a Bo ltzmann distribution we obtain a temperature evolution from $\sim$ 11 000 K to $\sim$ 24 000 K in the first few hundreds microseconds of the discharge. For later times the copper lines are strongly self-absorbed and make impossible the diagnostic in a spectroscopic way. Hence the temperature is deduced from the comparison between the experimental and calculated electrical conductivity. So for the decrease of the current the temperature evolves from $\sim$ 21 000 K down to $\sim$ 6 000 K and depends on the p lasma density. The results and the reliability of the two methods are discussed.

Diagnostics of plasma channel for HIF transport

An alternate technique for heavy ion final transport, from the driver to the target, is by the use of the self-standing Z-pinched plasma channel. Experiments conducted at the Lawrence Berkeley National Laboratory have produced 40 cm long stable plasma channels with a peak discharge current of 55 kA in a 7 Torr nitrogen gas fill. These channels are produced using a double pulse discharge scheme, namely, a pre-pulse discharge and a main capacitor bank discharge. It is postulated that the channel's insensitivity to MHD instabilities within the time scale relevant to beam transport is due to the wall effect the pre-pulse discharge creates. This is accomplished by leaving a gas density depression on the channel's axis after hydrodynamic expansion. Since the pre-pulse discharge creates the initial conditions for the main bank Z-pinch, it is critical to understand how to control and engineer the pre-pulse. Here we present some of the results of ongoing experiments geared to understand the underlying physics of the LBNL Z-pinch plasma channel. Schlieren and phase contrast measurements show the radial propagation of a shock wave during the pre-pulse discharge and suggest indirectly the evidence of the on axis gas density depression, that is believed to be < 1 10 of the original gas fill pressure. For the main bank Z-pinch, interferometry show an integrated electron line density of 1.6×10 17 cm −2 for a 15 kV discharge on axis. These measurements coupled with Faraday rotation measurements will indicate ultimately the current density distribution in the channel. This data will be used to benchmark simulation codes.

Analytic Study on High-Voltage Crowbar System

Crowbar switches are largely used in plasma devices, such as field-reversed configuration (FRC) machines and tokamaks, to avoid energy return from the discharge coil to the capacitor bank. A method of identification of all resistances, inductances and currents involved in capacitor bank discharges using a crowbar is proposed based on the derivation of the general analytical form of the coil current. This analysis can also be used for optimization of the discharge, reducing the ripple amplitude inherent in the crowbar-switched current. Fitting results of the TC-1 UNICAMP FRC device are also presented in this work.

Preliminary observations on possible implications of new Bohr orbits (resulting from electromagnetic spin-spin and spin-orbit coupling) in “cold” quantum mechanical fusion processes appearing in strong “plasma focus” and “capillary fusion” experiments

The theoretical interpretation of recently observed “excess heat” (i.e. break-even) in low intensity electrolytic and discharge experiments (with both deuterium and hydrogen) as resulting from a new type of non-nuclear quantum phenomena (i.e. spin-spin and spin-orbit couplings added to the usual Coulomb potential in specially structured dense media) leads to the prediction that “fusion ashes” of deuterium (or deuterium compounds now in vanishingly small quantities) will grow with the current intensity input, thus increasing the excess energy output. To test this prediction one can study the dynamic of fusion reactions in simple capacitor bank discharges into deuterated media, both in plasma focus (PF) and capillary fusion (CF) type experiments.

Diamond production as a result of electrical explosions of graphite-containing samples

A method to achieve the region of thermodynamic stability of diamond is described. Pressures in the range 10–30 GPa and temperatures in the range 2000–4000 K may be obtained by current pulse heating of a special graphitecontaining sample. Numerical modeling of some regimes of capacitor bank discharge through the sample showed that this is possible by current pulses with a duration 2–10 μs and a magnitude of about 1 MA and higher. In doing so, the conductivity of the sample is of great importance. The analysis of numerical modeling results indicates that the best values of diamond synthesis parameters are achieved for metallic samples. Nonporous material containing small graphite particles having a size in the range of 10–100 μm was used. The best results are achieved when graphite constitutes no more than about 30% by volume of the sample. The method was tested under laboratory conditions. In these experiments, hexagonal diamond particles were obtained. The mean size of diamond crystallites was about 0.1–0.2 μm or smaller.

Dynamic Fracture of 6061-T6 Aluminum Cylinders

Radial expansion and subsequent fracture into segments of thin-walled cylindrical shells at large initial strain rates are studied analytically and experimentally. The theory of probability along with a description of relief wave propagation away from each fracture is used to formulate a theory which predicts the number of fractures and the distribution of fragment lengths. Eleven 6061-T6 Aluminum cylinders were expanded at strain rates of ∼104 s−1 by magnetic pressure pulses from a capacitor bank discharge, and these results are compared with predictions. Good agreement is shown between experimental results and predictions. In addition, the physical and material parameters to which the problem is sensitive are discussed.