kV Charging Voltage Research Articles

Short-pulse CO₂ laser with longitudinal tandem discharge tube.

We developed a longitudinally excited CO2 laser with a tandem discharge tube. The tandem scheme was constituted of two 30-cm long discharge tubes connected with an intermediate electrode. Two parts, each consisting of a charged capacitance and a 30-cm long discharge tube, were electrically connected in parallel and switched by a spark gap. The tandem scheme produced a short laser pulse like that of a TEA-CO2 laser with a charging voltage of -24.8 kV, which was smaller than the -40.0 kV charging voltage of our previous CO2 laser. At a gas pressure of 3.8 kPa, the spike pulse width was 145 ns, the pulse tail length was 58.8 μs, the output energy was 52.0 mJ, and the spike pulse energy was 2.4 mJ. We also investigated the dependence of the laser pulse and the discharge voltage on gas pressure.

Numerical experiments on neutron yield and soft x-ray study of a ∼100 kJ plasma focus using the current profile fitting technique

Numerical experiments using the Lee model were performed to study the neutron yield and soft x-ray emission from the IR-MPF-100 plasma focus using the current fitting technique. The mass sweeping factor and the current factor for the axial and radial phase were used to represent the imperfections encountered in experiments. All gross properties including the yields were realistically simulated once the computed and measured current profiles were well fitted. The computed neutron yield Yn was in agreement with the experimentally measured Yn at 20 kV (E0 ∼ 30 kJ) charging voltage. The optimum computed neutron yield of Yn = 1.238 × 109 neutrons per shot was obtained at optimum physics parameters of the plasma focus operated with deuterium gas. It was also observed that no soft x-rays were emitted from the IR-MPF-100 plasma focus operated with argon gas due to the absence of helium-like and hydrogen-like ions at a low plasma temperature (∼0.094 keV) and axial speed (8.12 cm µs−1). However, the soft x-ray yield can be achieved by increasing the charging voltage, using a higher ratio of outer anode radius to inner anode radius c or shorter anode length z0, or using neon as the operating gas.

ChargingE-perm for radon measurements

Recharging of commercial E-perm electret detectors used for radon measurement has been investigated. The E-perm was recharged using the poling charging method where a high voltage is applied on a metal nozzle to polarize the electret material. The optimum parameters to recharge the electrets were 5 kV charging voltage and 7 mm height of the nozzle from the electret surface and using an insulator while charging. Under these conditions, charging of E-perm carried out for 15 s attained required voltage and retained the charge for long durations. The response of recharged E-perm for radon activity measurements in a radon calibration chamber and in an open environment was compared with that of CR-39 detectors. Results showed close proximity in radon values.

Pulse generators based on air-insulated linear-transformer-driver stages

In this paper we present the design and test results of pulse generators based on air-insulated linear-transformer-driver stages that drive a vacuum transmission line. A custom designed unit, referred to as a capacitor block, was developed for use as a main structural element of the transformer stages. It incorporates two capacitors GA 35426 (40 nF, 100 kV) and a multichannel multigap gas switch. Two types of stages were developed: (1) stage LTD-20 with four modules in parallel and five capacitor blocks in each module (in tests of this stage current amplitude up to 850 kA with $\ensuremath{\sim}140\text{ }\text{ }\mathrm{ns}$ rise time was obtained on a $0.05\text{ }\ensuremath{\Omega}$ load at 100 kV charging voltage); (2) stage LTD-4 with two modules in parallel and two capacitor blocks in each module. Several installations were built on the base of these stages, including a linear transformer, consisting of two identical LTD-20 stages in series, and a high power electron accelerator on the base of LTD-4 stages. The design, tests results, and main problems are presented and discussed in this paper for these installations.

电激励重复频率非链式HF激光器

The repetitive-pulsed non-chain HF lasers initiated by e-beams and fast discharges were studied respectively.The e-beam initiated HF laser characterized by an all-solid-state generator was developed.A large area repetitive uniform e-beam was obtained and the Faraday cup was used to diagnose the uniformity of e-beam into the laser gas cell.The output characteristics of the laser were studied and the maximal energy of 4.8 mJ was obtained with gas mixture C2H6∶SF6=0.035.The e-beam initiated HF laser could operate at the repetition rate of 30 Hz.The discharge initiated non-chain HF laser was designed by using the technologies of peaking capacitor and UV pre-ionizing.The discharge characteristics and stability of SF6 gas in repetition mode were studied.The results show that the discharge includes main discharge(volume discharge) and arc discharge,between which the voltage maintains and no evident discharge is visible.The maximal output energy of 600 mJ is achieved under the condition of 28 kV charging voltage and 12 kPa gas pressure with 8% C2H6.Specific output energy of 8.5 J/l and laser electrical efficiency of 2.5% are obtained.In repetition mode,the laser can operate in the repetition rate from 1 Hz to 50 Hz.The first pulse energy is above 500 mJ,and the stable output energy of the laser at the repetition rate of 10 Hz is about 200 mJ.

“强光一号”加速器电路模拟与分析

The Qiangguang-Ⅰ accelerator is made up of linear transformer driver(LTD), water transmission line, water switch and diode. In this paper, parameters of the LTD, transmission line and water switch were estimated, and circuit models of nonlinear magnetic cores and pulse power drivers were established. In addition, properties of silicon steel magnetic cores were investigated by experiments, the results of which are perfectly in accord with the simulation ones of the LTD module and accelerator. The simulation shows that the magnetic cores was not saturated under current running status. And the output parameters would not alter for the LTD store capacitance changing from 2.8 μF to 4.0 μF with 35 kV charge voltage. These all would establish the basis for the enhancement of energy store and

A compact submicrosecond, high current generator

Pulsed current generator was developed for experiments with current carrying pulsed plasma. Main parts of the generator are capacitor bank, low inductive current driving lines, and central load part. Generator consists of four identical sections, connected in parallel to one load. Capacitor bank is assembled from 24 capacitor blocks (100 kV, 80 nF), connected in parallel. It stores 9.6 kJ at 100 kV charging voltage. Each capacitor block incorporates a multigap spark switch, which is able to commute by six parallel channels. Switches operate in dry air at atmospheric pressure. The generator was tested with an inductive load and a liner load. At 17.5 nH inductive load and 100 kV of charging voltage it provides 650 kA of current amplitude with 390 ns rise time with 0.6 ohms damping resistors in discharge circuit of each capacitor block. The net generator inductance without a load was optimized to be as low as 15 nH, which results in extremely low impedance of the generator (approximately 0.08 ohms). It ensures effective energy coupling with a low impedance load such as Z pinch. The generator operates reliably without any adjustments in 70-100 kV range of charging voltage. Jitter in delay between output pulse and triggering pulse is less than 5 ns at 70-100 kV charging voltage. Operation and handling are very simple, because no oil or purified gases are required for the generator. The generator has dimensions 5.24x1.2x0.18 m(3) and total weight about 1400 kg, thus manifesting itself as simple, robust, and cost effective apparatus.

40 GW Linear Transformer Driver stage for pulse generators of Mega-ampere range

AbstractLinear transformer driver (LTD) technology is actively developed at the Institute of High Current Electronics in Tomsk, Russia. This technology is being examined for use in high current high voltage pulsed accelerators. Recent development of high voltage low inductance capacitors and low inductance switches enabled to achieve ~100 ns rise time of the LTD output pulse. This technique allows one to eliminate intermediate pulse forming sections, used in the present accelerator technology, which would keep the footprint of an LTD accelerator small. LTD based drivers are currently considered for many applications, including future very high current Z-pinch drivers for inertial confinement fusion, medium current drivers with adjustable pulse length for isentropic compression experiments, and finally relatively low current accelerators for radiography and X-pinches. In this article, we present the design and test results for a new LTD stage, that operates at 100 kV charging voltage. Current amplitude up to 850 kA with ~140 ns rise time was obtained on a 0.05 Ω load. Stack of the LTD stages can be easily assembled in series or in parallel, thus providing voltage or current multiplication, respectively. Design of multi-mega-volt and multi-mega-ampere generators becomes straightforward with the LTD technology.

Three-electrode gas switches with electrodynamical acceleration of a discharge channel

High voltage, high current, and high Coulomb transfer closing switches are required for many high power pulsed systems. There are a few alternatives for closing switches, for example, ignitrons, vacuum switches, solid-state switches, high pressure gas switches (spark gaps), and some others. The most popular closing switches up to date are spark gaps due to relatively simple design, robustness, easily field maintenance, and repair. Main drawback of spark gaps is limited lifetime, which is related directly or indirectly to erosion of the electrodes. Multichannel switches and switches with moving arc have been proposed to prevent the electrodes erosion. This study investigates switches, where a spark channel is initiated in a three-electrode layout and then the spark accelerates due to electrodynamic force and moves along the extended electrodes. At a given current amplitude, the diameter of the extended electrodes allows to control the spark velocity and hence, the erosion of the electrodes providing the required lifetime. The first switch is designed for 24 kV charging voltage and approximately 4 C total charge transfer. This spark gap was tested at 25 kA peak current in 40 000 shots in a single polarity discharge and in 20 000 shots in bipolar discharge. Second spark gap is designed for 24 kV charging voltage and approximately 70 C total charge transfer. It was tested in 22 000 shots, at a current of 250 kA with a pulse length of 360 mus. In this paper, we present design of these spark gaps and trigger generator, describe the test bed, and present the results of the tests.

Mega-ampere submicrosecond generator GIT-32

The GIT-32 current generator was developed for experiments with current carrying pulsed plasma. The main parts of the generator are capacitor bank, multichannel multigap spark switches, low inductive current driving lines, and central load part. The generator consists of four identical sections, connected in parallel to one load. The capacitor bank is assembled from 32 IEK-100-0.17 (0.17 microF, 40 nH, 100 kV) capacitors, connected in parallel. It stores approximately 18 kJ at 80 kV charging voltage. Each two capacitors are commuted to a load by a multigap spark switch with eight parallel channels. Switches operate in ambient air at atmospheric pressure. The GIT-32 generator was tested with 10, 15, and 20 nH inductive loads. At 10 nH load and 80 kV of charging voltage it provides 1 MA of current amplitude and 490 ns rise time with 0.8 Omega damping resistors in discharge circuit of each capacitor and 1.34 MA530 ns without resistors. The net generator inductance without a load was optimized to be as low as 12 nH, which results in extremely low self-impedance of the generator ( approximately 0.05 Omega). It ensures effective energy coupling with low impedance loads like Z pinch. The generator operates reliably without any adjustments in 40-80 kV range of charging voltage. Maximum jitter (relative to a triggering pulse) at 40 kV charging voltage is about 7 ns and lower at higher charging voltages. Operation and handling are very simple, because no oil and no purified gases are required for the generator. The GIT-32 generator has dimensions of 3200 x 3200 x 400 mm(3) and total weight of about 2500 kg, thus manifesting itself as a simple, robust, and cost effective apparatus.

Catalytic action of β source on x-ray emission from plasma focus

The influence of preionization around the insulator sleeve by a mesh-type β source (Ni6328) for the x-ray emission from a (2.3-3.9 kJ) plasma focus device is investigated. Quantrad Si p-i-n diodes along with suitable filters are employed as time-resolved x-ray detectors and a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray emission in 4π geometry is measured as a function of argon and hydrogen gas filling pressures with and without β source at different charging voltages. It is found that the pressure range for the x-ray emission is broadened, x-ray emission is enhanced, and shot to shot reproducibility is improved with the β source. With argon, the CuKα emission is estimated to be 27.14 J with an efficiency of 0.7% for β source and 21.5 J with an efficiency of 0.55% without β source. The maximum x-ray yield in 4π geometry is found to be about 68.90 J with an efficiency of 1.8% for β source and 54.58 J with an efficiency of 1.4% without β source. With hydrogen, CuKα emission is 11.82 J with an efficiency of 0.32% for β source and 10.07 J with an efficiency of 0.27% without β source. The maximum x-ray yield in 4π geometry is found to be 30.20 J with an efficiency of 0.77% for β source and 25.58 J with an efficiency of 0.6% without β source. The x-ray emission with Pb insert at the anode tip without β source is also investigated and found to be reproducible and significantly high. The maximum x-ray yield is estimated to be 46.6 J in 4π geometry with an efficiency of 1.4% at 23 kV charging voltage. However, degradation of x-ray yield is observed when charging voltage exceeds 23 kV for Pb insert. From pinhole images it is observed that the x-ray emission due to the bombardment of electrons at the anode tip is dominant in both with and without β source.

Design and optimization of a compact, repetitive, high-power microwave system

The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate Marx generator for driving an high-power microwave (HPM) source are discussed. Benefiting from the large energy density of mica capacitors, four mica capacitors were utilized in parallel per stage, keeping the parasitic inductance per stage low. Including the spark-gap switches, a stage inductance of 55 nH was measured, which translates with 100 nF capacitance per stage to ∼18.5Ω characteristic Marx impedance. Using solely inductors, ∼1mH each, as charging elements instead of resistors enabled charging the Marx within less than 100 ms with little charging losses. The pulse width of the Marx into a matched resistive load is about 200 ns with 50 ns rise time. Repetitive HPM generation with the Marx directly driving a small virtual cathode oscilator (Vircator) has been verified. The Marx is fitted into a tube with 30 cm diameter and a total length of 0.7 m. We discuss the Marx operation at up to 21 kV charging voltage per stage, with repetition rates of up to 10 Hz in burst mode, primarily into resistive loads. A lumped circuit description of the Marx is also given, closely matching the experimental results. Design and testing of a low cost, all-metal Vircator cathode will also be discussed.

Neutron emission from a fast plasma focus of 400 Joules

The neutron emission from a small and fast plasma focus operating in deuterium is presented. The system operates at low energy in the hundred of joules range (880 nF capacitor bank, 38 nH, 20–35 kV, 176–539 J, ∼300 ns current rise time). The neutrons were measured by means of a silver activation counter, and the total neutron yield versus deuterium gas filling pressure was obtained. For discharges operating at 30 kV charging voltage, the maximum neutron yield was (1.06±0.13)×106 neutrons per shot at 9 mbar.

High-efficiency shock-wave generator for extracorporeal lithotripsy.

In extracorporeal lithotripsy, the electro-acoustic efficiency of electrohydraulic generators is limited by the inductance of the electrical discharge circuit. A new shock-wave generator is described that uses a coaxial discharge line enabling electro-acoustic efficiency to be greatly increased. The line is built using a para-electric ceramic with a relative dielectric constant of 1700, manufactured for use in high-voltage impulse mode. A coaxial spark gap, with minimal inductance, has been developed to obtain the triggered breakdown of the discharge line. Shock waves are created with a coaxial electrode plugged directly into the spark gap and immersed in an electrolyte of degassed saline. Electrode gap and electrolyte resistivity are adjusted to match the resistivity of the electrolyte volume between the underwater electrodes to the characteristic impedance of the line. The discharge line generates in the medium a rectangular current pulse with an amplitude of about 6000 A and a rise time of 50 ns. Compared with conventional generators, measurements of the expansive peak pressure pulse show an increase of 105% at 10 kV, 86.5% at 12 kV and 34.5% at 14 kV charging voltage. Electro-acoustic efficiency is found to be 11% instead of 5.5% for a conventional discharge circuit.

Experimental study of electron generation induced by a XeCl laser

The generation of photoelectrons by an incident XeCl laser beam of 4.02 eV photon energy on three different targets, Y, Zn, and Ge, having work functions of 2.9, 3.9, and 4.8 eV, respectively, has been studied. Considering that the laser pulse has a trapezoidal evolution time and a rectangular spatial dependence, the evolution of the target temperature at the laser spot has been calculated. Using the computer code egun, the output current picked up by the collector resulted only of 44%, 42%, and 37% of the effective current for Y, Zn, and Ge, respectively, at 3 kV charging voltage. By utilizing the generalized Richardson equation which governs the generated current density, the dominant process existing during the laser-matter interaction has been determined. During the electron extraction, plasma was formed on the target surface particularly at high laser energies and high accelerating voltages. This plasma introduces an impedance into the cathode-anode region which shifts the Child–Langmuir law.

Low-pressure 50-mJ KrF laser

Operation of a discharge-pumped KrF laser consisting of an all stainless steel chamber and using pure argon as the buffer gas at subatmospheric pressure is reported. The optimized pulse energy of [approximately]50 mJ was achieved from about 60 cm[sup 3] active volume and at [approximately]36 kV charging voltage. The optimized pressure of the gas mixture was about 800 mbar.

Control and command system for pulsed, high power fusion experiments

Abstract A Control and Command System (SECAM-4/5A) designed for the Plasma Focus Installation IPF-4/5A (1 MA plasma current and 40 kJ energy stored at 20 kV charging voltage) is presented.

High-energy output from a short-channel N2 laser

Abstract Optimization of electrode profile and discharge cross-section has led to the development of a compact low-pressure N 2 laser with a laser channel of only 10 cm length, capable to deliver 2.3 mJ at 17 kV charging voltage. The high output energy and the good efficiency of 0.065% are attributed to the optimized current density and to the preionization feature of the mesh electrodes.

An efficient high pressure XeCl discharge laser with UV pre-ionisation

The results from an improved simple UV pre-ionised XeCl discharge pumped laser are reported. Using an optimised pre-ionisation geometry and simple flat-profile electrodes, stable laser operation was obtained at a buffer gas pressure of 0.7 MPa with a specific energy extraction of 7.2 J l-1 at. 1.2% efficiency. An efficiency of 3.8% with 4.2 J l-1 energy extraction has been obtained at a buffer gas pressure of 0.7 MPa and 15 kV charging voltage.

Determination of the unsaturated losses and of the saturation intensity in the KrCl excimer laser

The unsaturated losses α, and the saturation intensityIs, were measured in an uv-preionized KrCl laser for optimized He and Ne based laser gas mixtures. The measurements were made as a function of the specific power loading and of the total pressure of the laser mixtures. Higher values for α andI s were found for the Ne-based laser mixture than for the He-based mixture. At 45 kV charging voltage and at 355 kPa of total pressure we measured α=0.053 cm−1 andI s =9.4MW/cm2 for the Ne based mixture, and α=0.035 cm−1 andI s =5.1MW/cm2 for the He based mixture.