A 7 T Pulsed Magnetic Field Generator for Magnetized Laser Plasma Experiments

A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma.A 40 kV pulsed power system delivered a fast(~230 ns),55 kA current pulse into a single-turn coil surrounding the laser target,using a capacitor bank of 200 nF,a laser-triggered switch and a low-impedance strip transmission line.A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter.The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam,a femtosecond probing laser beam and an optical Intensified Charge Coupled Device(ICCD) detector.The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field.     

Design,simulation and construction of the Taban tokamak

This paper describes the design and construction of the Taban tokamak, which is located in Amirkabir University of Technology, Tehran, Iran. The Taban tokamak was designed for plasma investigation. The design, simulation and construction of essential parts of the Taban tokamak such as the toroidal field(TF) system, ohmic heating(OH) system and equilibrium field system and their power supplies are presented. For the Taban tokamak, the toroidal magnetic coil was designed to produce a maximum field of 0.7 T at R?=?0.45 m. The power supply of the TF was a130 kJ, 0–10 kV capacitor bank. Ripples of toroidal magnetic field at the plasma edge and plasma center are 0.2% and 0.014%, respectively. For the OH system with 3 kA current, the stray field in the plasma region is less than 40 G over 80% of the plasma volume. The power supply of the OH system consists of two stages, as follows. The fast bank stage is a 120 μF, 0–5 k V capacitor that produces 2.5 kA in 400 μs and the slow bank stage is 93 mF, 600 V that can produce a maximum of 3 kA. The equilibrium system can produce uniform magnetic field at plasma volume. This system's power supply, like the OH system, consists of two stages, so that the fast bank stage is 500 μF, 800 V and the slow bank stage is 110 mF, 200 V.     

Low Energy Plasma Focus as an Intense X-ray Source for Radiography

Study on X-ray emission from a low energy (1.8 kJ) plasma focus device powered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175 kA by using a lead-inserted copper-tapered anode is reported. The X-ray yield in different energy windows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry is found to be (27.3±1.1) J and corresponding wall plug efficiency for X-ray generation is 1.52±.06%. X-ray emission, presumably due to bombarding activity of electrons in current sheath at the anode tip was dominant, which is confirmed by the pinhole images. The feasibility of the device as an intense X-ray source for radiography is demonstrated.     

用于Z箍缩诊断装置的快阀研制

Z箍缩实验滞止后期负载产生的微小碎片及其他飞溅物质会污染Z箍缩诊断系统内的光学器件,本文研制了一种基于电磁感应原理的快阀,其可用于遮断微小碎片及其他飞溅物质。根据能量守恒和电路方程,计算了快阀的运动速度、遮断时间及线圈放电电流等参数,并利用实验测量获得快阀运动速度为19 m/s,遮断时刻时间抖动为85 μs,实验测量与计算结果较为吻合。     

X-ray Emission from Plasma Focus: Envisioned by Various Competitive Detectors

A study of X-ray emission from a Mather-type plasma focus device by simultaneously employing various X-ray detectors like silicon pin diode, photoconducting detectors (PCDs)—CVD-diamond and gallium arsenide (GaAs), plastic scintillator coupled with photomultiplier tube with and with out optical fiber is presented. The pin diode and PCDs are masked with 10 μm thick cobalt filter. The device is energized by 9 μF capacitor bank charged at 18 kV (1.45 kJ), giving a peak discharge current of about 175 kA, with hydrogen as the filling gas. The optical fiber coupling is found to be beneficial in minimizing the electromagnetic noise generated during the system operation.     

Temporal Variation of the Current Sheet Inductance from PACO Plasma Focus Device

The temporal variation of the current sheet (CS) inductance in a plasma focus device can be calculated using the current derivative and the voltage signal acquired on the anode electrode, which are very common measurements in this type of device. The value of that inductance contains important information about the discharge performed including the CS lift-off from the insulator, voltage between the pinch extremes, maximum energy of the X-ray, energy delivered to the pinch and information about the actuating fusion mechanisms if the filling pressure is deuterium. This work discusses the values of the CS inductance extracted from several discharges of the Plasma Auto Confinado (PACO) plasma focus, installed in the National University of the Center of Buenos Aires—Argentina (2 kJ total energy, capacitor bank of 4 μF charged to 31 kV and a maximum current of 250 kA).     

Study the Output Characteristics of a 90 kJ Filippove-Type Plasma Focus

The output characteristics of a Filippove-Type plasma focus “Dena” (288 μF, 25 kV, 90 kJ) is numerically investigated by considering the voltage, current, current derivative, and maximum current as a function of capacitor bank energy in the constant Argon gas pressure and compared to the experiment. It is shown that increase on the bank energy leads to the increment on the maximum current and decrement on the pinch time.     

Solenoid-free Plasma Start-up in HIT-II and NSTX using Transient CHI

A new method of non-inductive startup, referred to as transient coaxial helicity injection (CHI), has been successfully developed on the HIT-II experiment. In this method, a plasma current is rapidly produced by discharging a capacitor bank between coaxial electrodes in the presence of toroidal and poloidal magnetic fields. The initial poloidal field configuration is chosen such that the plasma rapidly expands into the chamber. When the injected current is rapidly decreased, magnetic reconnection occurs near the injection electrodes, with the toroidal plasma current forming closed flux surfaces. On HIT-II, CHI-started plasmas outperform discharges initiated by induction alone and consume fewer volt-seconds. The method has now been successfully applied on NSTX for an unambiguous proof-of-principle demonstration of closed-flux current generation without the use of the central solenoid.     

A 20 kV, 5 A, 1 ns Risetime Pulsed Electron Beam Source

A 20 kV, 1 ns risetime pulsed electron beam source was developed using an extremely small gap （0.1 mm） diode driven by a sub-nanosecond risetime, 10 kV rectangular pulse generator. A beam current of 5 A was detected by using a fast response Faraday cup at a distance of 2 cm away from a grid anode. The shot to shot variation of the electron beam pulse was less than 10%.     

Pneumatically-Driven Fast Closing Valve System for Synchrotron Radiation Sources

A fast closing valve (FCV) system has been built to protect the vacuum of the electron storage ring against sudden vacuum failures during synchrotron radiation experiments. An electronic control detects the failure, and closes a 140 × 17 mm aperture within 32 ms with a guillotine blade driven by pneumatic pressure. This pressure is gated by a magnetic valve which is operated by an explosive charge from a capacitor bank. The design of the FCV itself is very simple; it is operated directly by a single pneumatic piston. The FCV system has a long operating lifetime and the blade can be readily rearmed in 0.5 s.     

Preliminary Results of the 115 kJ Dense Plasma Focus Device IR-MPF-100

This work summarizes the design and construction of the first Iranian 115 kJ Mather type plasma focus (PF) machine (IR-MPF-100). This machine consists of a 6.25 cm radius and 22 cm height brass made anode with a 50 mm height insulator which separates the anode and cathode electrodes. Twelve copper made 22 cm height rods play the role of cathode with 10.2 cm radius. Twenty four 6 μF capacitors were used with the maximum charging voltage of 40 kV (maximum energy of 115 kJ) as the capacitor bank and maximum theoretical current around 1.224 MA. The total inductance of the system is 120 nH. By using NE-102 plastic Scintillator, Rogowski coil, current and voltage probes, hard X-ray, current derivative, current and voltage signals of IR-MPF-100 were measured. The primary result of neutron detection by neutron activation counter represents approximately 10⁹ neutrons per shot at 65 kJ discharge energy while using deuterium filling gas. Also IR-MPF-100 PF has been tested successfully at 90 kJ by using the argon gas.     

Current-Step Technique to Enhance Plasma Focus Compression and Neutron Yield

A current-step technique is applied to the plasma focus by modifying the Lee Model code, incorporating a current-step bank to add current to the focus pinch at the time of the current dip. For a 50?kV, 1?MJ, 6?μs rise-time bank, the current-step from a 200?kV, 0.4?MJ, 0.8?μs rise-time bank maintains the pinch current at 2.2 MA, enhances compression by 1.9 and increases the neutron yield from 2.5?×?10¹² to 1.03?×?10¹³. The increase is attributed mainly to the step nature of the current which favorably shifts the end-point of compression; rather than to the scaling in terms of energy or current.     

Study of X-ray Emission from a Compact Diode Operated by a High-Inductance Capacitor Discharge

A compact diode comprising a flat plate anode and a sharp-edged cathode (a piece of razor blade) energized by 0.5 F capacitor charged to 30 kV is investigated for optimization of X-rays emission vis-à-vis separation between electrodes and width of the cathode, which is responsible for electron emission by impact of electric field. It is a high-inductance system, the parasitic inductance is found to be 353 ± 5 nH, and the recorded peak discharge current is just 35 ± 02 kA. The maximum X-ray emission is observed for a 2-mm-wide cathode with an interelectrode separation of 3 mm. The X-ray yield in 4-geometry is found to be 34 ± 3 mJ with a wall-plug efficiency of 0.015 ± 0.001%. The X-ray emission occurs about 200 ns after the application of high voltage, synchronized with the dip in current wave form. The low efficiency of the system for X-ray generation is attributed to high parasitic inductance.     

用压强法测量激光腔中能量沉积

用快响应压力传感器测量了激光腔中能量沉积，实验气体为氩、氪及氟化氪激光介质。实验中测到了在各种气体中由于能量沉积而产生的压强变化及压强随泵浦束能的变化情况，得到了激光腔中相应的能量沉积。测量结果与模拟计算结果基本一致。     

Experimental Study on Triggering Characteristics of a Surface Flashover Triggered Vacuum Switch

Triggering characteristics of triggered vacuum switch （TVS）, including the discharge delay time, delay jitter, range of operational voltage and peak of pulsed current, are investigated. Both structure and experimental circuit of TVS are presented. The results indicate that TVS, as a surface flashover triggering device with high dielectric permittivity material, is with excellent triggering characteristics. When the hold-off voltage reaches 120 kV, the minimum operational voltage is 1.3 kV, and the minimum discharge delay time and jitter are 100 ns and ?10 ns, respectively. The peak current is up to 240 kA when the operational voltage reaches 100 kV. TVS can well satisfy the main demands of high voltage and current applications, and can also be used under a multi-crowbar circuit.     

Design of Capacitor Blocks with Multi-Channel Switches for Linear Transformer Driver Stages

In the linear transformer driver technology, the low inductance energy storage components and switches are directly incorporated into the individual cavities (named stages) to generate a fast output voltage pulse, which is added along a vacuum coaxial line like in an inductive voltage adder. In this paper, we outline the detailed design concept and the basic parameters of four capacitor blocks with four different types of multi-channel gas switches. The 100 kV capacitor block #1 and #2 incorporate two parallel capacitors (40 nF, 100 kV) and multi-gap multi-channel gas switches with triggering plate or triggering cable. The 200 kV capacitor block #3 and #4 incorporate two capacitors (40 nF, 100 kV) in series and rail-gap gas switches with one triggering rail or two triggering rails. Operating principles of four multi-channel gas switches are illustrated by using the equivalent electrical scheme of each switch. The basic characteristics of four capacitor blocks are given. The effect of stray capacitances on the trigger pulses is also discussed.     

Initial Plasma Formation in the GLAST-II Spherical Tokamak

This paper reports the initial plasma formation in glass spherical tokamak (GLAST-II) with electron cyclotron resonance pre-ionization assisted startup. Initially, a plasma current of 3 kA has been produced for duration of about 0.5 ms after establishing optimum conditions for microwave absorption at 2.45 GHz. Plasma current is then enhanced up to 5 kA by applying a small vertical magnetic field that provides additional plasma heating and shaping. Applied vertical field is optimized experimentally and optimal value is found to be 40 Gauss for this experiment. Plasma current and loop voltage are monitored by using Rogowski coil and toroidal loop of wire. A fast framing camera (5000 fps) is used for temporal investigation of plasma during the discharge scenario. A fast photodiode (BPX-65) and USB4000 spectrometer are used to record the signature of plasma current and the impurity content (O₂, H etc.). Cross-sectional average electron temperature is also estimated from plasma resistivity and found to be 6.1 eV for maximum plasma current of 5 kA.     

Experimental Verification of Modified Lee’s Model Using a Newly Designed and Constructed Filippov-Type Plasma Focus Device

A new 20 kJ Filippov-type plasma focus device has been designed and constructed in Isfahan University. The paper reports on the design and construction of the Iranian Filippov-type plasma focus device (UIPFF1) using modified Lee’s model. A Rogowski coil has been used to measure the experimental discharge current. Equivalent electric circuit of the device is RLC circuit; therefore the discharge current has a sinusoidal shape which its amplitude decreases exponentially during the time. The current signal contains a set of data from physical processes in the device as well as discharge current characteristics. In a typical discharge experiment these values were obtained: the discharge current was 181 kA, period of current signal 7.9 µs, the total inductance of the device 132 nH and electrical resistance of the circuit 77 mΩ. By averaging from data obtained with a set of five experiments the calibration factor was obtained 121 kA/V. Temporal changes in plasma focus discharge current, confirmed the occurrence of pinch at a specific pressure of argon, neon and nitrogen gases. UIPFF1 has been tested between 15 and 25 kV and wide range of pressure for various gases. Experiments at various pressures and voltages have also confirmed reproducibility and stability of the plasma focus device.     

PIG Ion Source with Permanent Magnets: Model Based Anode Current Return Circuit

Ion sources are widely used in fusion technologies. A new high voltage pulsed power supply for use in penning ion gauge ion sources is proposed in this paper. To use discharge current, a diode-capacitor bank is included. The power supply is composed of 3 stages. A fast switching transistor is used as a single switch which is trigged by a pulse generator. A transformer is used to level up the voltage up to 2?kV without power loss. It is also used to isolate input and high voltage output. Also; the proposed high voltage power supply implementation uses a diode-capacitor bank whose capacitors are charged during plasma discharge. This system structure gives compactness and easiness to implement the total system which in combination with inexpensive commercially available components, makes the unit versatile and inexpensive.     

Impedance matching for repetitive high voltage all-solid-state Marx generator and excimer DBD UV sources

The purpose of impedance matching for a Marx generator and DBD lamp is to limit the output current of the Marx generator,provide a large discharge current at ignition,and obtain fast voltage rising/falling edges and large overshoot.In this paper,different impedance matching circuits (series inductor,parallel capacitor,and series inductor combined with parallel capacitor) are analyzed.It demonstrates that a series inductor could limit the Marx current.However,the discharge current is also limited.A parallel capacitor could provide a large discharge current,but the Marx current is also enlarged.A series inductor combined with a parallel capacitor takes full advantage of the inductor and capacitor,and avoids their shortcomings.Therefore,it is a good solution.Experimental results match the theoretical analysis well and show that both the series inductor and parallel capacitor improve the performance of the system.However,the series inductor combined with the parallel capacitor has the best performance.Compared with driving the DBD lamp with a Marx generator directly,an increase of 97.3％ in radiant power and an increase of 59.3％ in system efficiency are achieved using this matching circuit.