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(a) Magnetic field pulse and current pulse produced by the pulse power system, (b) Simulated magnetic field pulse and current pulse
Source publication
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 t...
Contexts in source publication
Context 1
... coil [19] , placed on the central anode copper plate of the transmission line near the plexiglass vacuum window, was used to mea- sure the discharging current. The magnetic field pulse was measured by a magnetic probe [19] put between the Helmholtz coil pair. The uncertainty of magnetic field strength given by the magnetic probe was ±10%. Fig. 3(a) shows the current pulse and the magnetic field pulse profiles. The magnetic field pulse presents a damped sinusoidal oscillation with a risetime of ap- proximately 230 ns, which is consistent with the profile of the current pulse. The peak current reaches 55 kA, which produces a peak magnetic field of about 7.5 T. The detailed 2D ...
Context 2
... field of about 7.5 T. The detailed 2D character of the pulsed magnetic field cannot be measured at present due to the difficulty in optical imaging of the small volume of the mag- netic field. Thus a 2D electromagnetic simulation us- ing the Ansoft Maxwell code was performed to explore the 2D profile of the pulsed magnetic field. As shown in Fig. 3(b), the electromagnetic simulation gives the same features in the current pulse and the magnetic field pulse at the center of the Helmholtz coil pair: 230 ns risetime, maximal 55 kA current and 8 T peak magnetic field strength, which agrees with the mea- sured result of 7.5 T in the error range of the magnetic probe. The other circuit ...
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Citations
... 14,15 Recently, a portable, noise-tolerant pulsed magnetic field was developed at the Gekko-XII laser facility. 16 At the University of Science and Technology of China (USTC), we built a compact 7T pulsed magnetic field generator of single turn coil 17 to study laser plasma expansion in external magnetic fields. 3,18 Unlike large-size solenoid-based devices, single-turn coil based pulsed magnetic field generators are portable to compatible with the laser facility and experimental requirement. ...
... It represented an upgrade to our original pulsed magnetic field generator intended for high vacuum environments. 17 The 2 kW high-voltage charging power supply (TD2202P100-2000 19 ′′ , Teslaman Technology Co., Ltd.) was controlled remotely via a fiber connector and LabVIEW software to isolate the control system from discharge-related electrical noise. The charging voltage and current could be adjusted in 0-100 kV and 0-16 mA, respectively. ...
A portable pulsed magnetic field generator for magnetized laser plasma experiments in low vacuum environments is presented. It is based on a classical high-voltage discharge pulsed power system. A 95 kA peak current was delivered at a 65 kV discharge voltage, which generated a quasiuniform magnetic field of 12T in a Φ8 mm × 8 mm volume. A compact, sealed design was developed to avoid short-circuit breakdowns caused by an ambient low-pressure gas medium. Design improvements were made to the vacuum feedthrough, the transmission line, and the magnetic coil. The system worked well in a low vacuum environment for a laser plasma experiment using a gas target. But at intermediate ambient gas pressure, the ambient gas was ionized around the surface of the coil at first and then the ionized gas diffused inward and outward slowly, which affected the laser plasma image in the coil. Experiments and simulations indicated that the ambient gas was ionized by the induced electric field. We developed analytical models of the induced breakdown of the ambient gas to guide the experimental design of a gas target. The analysis can also be used in the experimental design of a solid target in an intense pulsed magnetic field of hundreds of tesla that the induced breakdown along solid’s surface dominates the process.
... In a nondestructive approach, coils powered by capacitor banks have been widely used. Magnetic fields of several tens of tesla have been achieved, [8][9][10][11][12][13][14] but a large power source is required to generate a long-duration pulsed magnetic field. It is impossible to transport such power sources between experimental facilities owing to their huge mass and volume. ...
We have successfully developed a portable pulsed magnetic field generation system incorporating a number of techniques to avoid the effects of noise, including shielding, a self-power capability, and a high-capability semiconductor switch. The system fits into a cubical box less than 0.5 m in linear dimensions and can easily be installed in experimental facilities, including noisy environments such as high-power laser facilities. The system can generate a magnetic field of several tesla sustainable for several tens of microseconds over a spatial scale of several centimeters. In a high-power laser experiment with Gekko-XII, the system operated stably despite being subjected to a high level of electrical noise from laser shots of 600 J.
... In addition, we notice that strong magnetic fields on the order of a few tens of Tesla in a small volume can be generated by discharging a high-voltage capacitor through a small wire-wound coil in laboratories [35][36][37], and a pulsed non-destructive magnetic field above 100 Tesla was recently recorded in the Pulsed Field Facility at Los Alamos National Laboratory [38]. Such high magnetic fields are of great interest for controlling laser-plasma interactions [39,40]. Particularly, they could provide an alternative powerful means to control the ionization injection and modify the wakefield structure in the LWFA. ...
The effect of an external transverse magnetic field on ionization injection of electrons in a laser wakefield accelerator (LWFA) is investigated by theoretical analysis and particle-in-cell simulations. On application of a few tens of Tesla magnetic field, both the electron trapping condition and the wakefield structure changes significantly such that injection occurs over a shorter distance and at an enhanced rate. Furthermore, beam loading is compensated for, as a result of the intrinsic trapezoidal-shaped longitudinal charge density profile of injected electrons. The nonlinear ionization injection and consequent compensation of beam loading lead to a reduction in the energy spread and an enhancement of both the charge and final peak energy of the electron beam from a LWFA immersed in the magnetic field.
... We built up a magnetized laser plasma device [15] at University of Science and Technology of China (USTC) to explore the laser plasma expansion dynamics in strong external magnetic field. It is composed of a pulsed magnetic field generator and a Nd:YAG laser system. ...
... After laser irradiation that plasma is cooled to about 30 eV at 20 ns, the plasma without magnetic field keeps the same semi-spherical diffusion structure in figure 2(b). But the plasma with magnetic field forms a low-density plasma bubble and a convergence structure due to magnetic field pressure [15]. Our optical interferometry found that the density profile in external magnetic field has the same bubble and convergence structure [16]. ...
The evolutions of laser ablation plasma, expanding in strong (∼10 T) transverse external magnetic field, were investigated in experiments and simulations. The experimental results show that the magnetic field pressure causes the plasma decelerate and accumulate at the plasma-field interface, and then form a low-density plasma bubble. The saturation size of the plasma bubble has a scaling law on laser energy and magnetic field intensity. Magnetohydrodynamic simulation results support the observation and find that the scaling law (V max ∝ E p/B ², where V max is the maximum volume of the plasma bubble, E p is the absorbed laser energy, and B is the magnetic field intensity) is effective in a broad laser energy range from several joules to kilo-joules, since the plasma is always in the state of magnetic field frozen while expanding. About 15% absorbed laser energy converts into magnetic field energy stored in compressed and curved magnetic field lines. The duration that the plasma bubble comes to maximum size has another scaling law t max ∝ E p1/2/B ². The plasma expanding dynamics in external magnetic field have a similar character with that in underdense gas, which indicates that the external magnetic field may be a feasible approach to replace the gas filled in hohlraum to suppress the wall plasma expansion and mitigate the stimulated scattering process in indirect drive ignition.
... 为 6 mm、 线圈间距为 3 mm 的亥姆赫兹线圈放电, 产生峰值强度为 7.5 T、 上升沿为 230 ns 的一维均 匀脉冲磁场 [11] . 40 µm 厚的铝薄膜靶平行于磁力 ...
The nanosecond laser produced plasma expansion in an external transverse magnetic field is explored by using optical imaging of plasma self-luminescence, optical spectrum and optical interferometry techniques. The plasma displays bifurcation and focusing phenomena in a transverse magnetic field, which is different from the scenarios without external magnetic field significantly. We set up a simplified magnetohydrodynamics model according to the feature of experimental parameters. The theoretical results of the temporal evolutions of the plasma density and the temperature are in good agreement with the experimental results, which confirms the important role of the magnetic diffusion in the plasma evolution.
Magnetized laser plasma has attracted a lot of attention in recent years especially in magnetized inertial confinement fusion, laboratory astrophysics, and industrial application. Pulsed intense magnetic field device is the core equipment of magnetized laser plasma experiment. Here in this work, an inductively coupled coil is developed to optimize the pulsed intense magnetic field device. The primary coil of a multi-turn solenoid is used instead of a single-turn coil. Then the energy of the solenoid is delivered to the secondary coil via inductively coupled transformer, which increases the current density markedly. The current generates a stronger magnetic field in the single-turn magnetic field coil. The influence of the diameter and the number of turns of the primary solenoid of the inductively coupled coil on the magnetic field are explored in experiment and simulation. It is found that for a discharge system of 2.4 μF capacitance, the optimized parameters of the primary solenoid are 35 turns and 35 mm diameter. The optimized magnetic field is 3.6 times stronger than that of the conventional directly connected single-turn coil. At a charging voltage of 20 kV, the peak magnetic field reaches 19 T in a magnetic field coil of 5 mm inner diameter. The inductively coupled coil made of CuBe solves the problem of coil expansion in intense magnetic field, and a peak magnetic field of 33 T is obtained at a charging voltage of 35 kV. The present approach creates stronger magnetic field environments. At the same time, the inductively coupled coil reduces the requirements for system inductance, so that components such as energy storage capacitors and switch can be placed far from the coil, which improves the flexibility of the experiment setup.
In this work, the design of a pulsed magnetic field generator, with user-selective pulsed modulation frequency is described. The ability to operate at various frequencies (single-frequency below 10 MHz) makes the system valuable to several areas such as medical treatments and pulsed switching systems. In this work, the pulsed magnetic field generator is designed to create localized field effects in portable magnetic resonance systems. Users may operate at a Larmor precession frequency between 100 kHz - 10 MHz and can achieve high currents through the load. Certain tunability can also be obtained by varying the load inductance or switching device conditions. In summary, this paper will describe the design considerations and challenges for portable monophasic pulsed magnetic field systems.
Flute instability produced by laser plasma expanding in a 10 T external magnetic field was studied in experiments. The plasma was generated by a 0.3 J ns laser ablating an aluminum target. The external magnetic field of approximately 10 T was provided by a pair of Helmholtz coils aligned parallel to the target surface. Initially, the plasma plume expands freely. The external magnetic field confines the plasma plume and, finally, forms a plasma cavity with a sharp plasma–field interface. Flute instability was observed at the plasma–field interface, which presents a salient kinetic feature rather than classical fluid instability. In the initial linear phase, the growth rate of the perturbation has good agreement with Large Larmor radius instability, which is larger than ion gyrofrequency. In the later nonlinear growth phase, the flute instability shows an obvious “fishbone” structure of kinetic instability, and the initial short wavelength perturbation shifts continually to longer wavelength mode and, finally, close to the density scale length. Our experiment reveals a new region of parameter space that reproduces the flute instability in the space experiments of an active magnetospheric particle tracer experiment and a combined release and radiation effects satellite.
Thomson scattering (TS) is a powerful diagnostics for understanding the plasma conditions in high energy density experiments. With the aid of Monte Carlo simulation and statistical analysis, we demonstrated unreported high precisions of ne, Te, Ti, etc., via fitting the multiple-wavenumber spectra of ion-acoustic featured TS simultaneously. For instance, utilizing this method in the current typical conditions on SG-180kJ laser facility, the precisions of ne, Te would be better than 8% and 0.5%, respectively. We presented the fitting precisions at different cases and the chi-square trends of the single- and dual-branch TS. This diagnostic technique is found to be applicable within a wide range of plasma parameters and wavenumbers, which is practical to prompt much more precise plasma diagnostics in experiments.
The presentations on laser plasma physics at the first AAPPS-DPP conference covered topics of inertial confined fusion physics and technologies, laboratory astrophysics and high-energy density physics, laser plasma-based particle acceleration (electrons and ions) and radiation, fundamental laser plasma physics, and related high-power laser system development. This report summarizes the major advances in these topics presented at the plenary and oral sessions.
