Evidence for separatrix formation and sustainment with steady inductive helicity injection

The first sustainment of toroidal plasma current of 50 kA at up to 3 times the injected currents, added in quadrature, using steady inductive helicity injection is described. Separatrix currents-currents not linking the helicity injectors-are sustained up to 40 kA. Decreases in the n=1 toroidal mode of the poloidal magnetic field at higher current amplifications indicate more quiescent, direct toroidal current drive. Results are achieved in HIT-SI (with a spheromak of major radius 0.3 m) during deuterium operations immediately after helium operation. These results represent a breakthrough in the development of this new current drive method for magnetic confinement fusion.     

New mode of operating a magnetized coaxial plasma gun for injecting magnetic helicity into a spheromak

By operating a magnetized coaxial plasma gun continuously with just sufficient current to enable plasma ejection, large gun-voltage spikes (approximately 1 kV) are produced, giving the highest sustained voltage approximately 500 V and highest sustained helicity injection rate observed in the Sustained Spheromak Physics Experiment. The spheromak magnetic field increases monotonically with time, exhibiting the lowest fluctuation levels observed during formation of any spheromak (B/B>/=2%). The results suggest an important mechanism for field generation by helicity injection, namely, the merging of helicity-carrying filaments.     

Increasing the magnetic helicity content of a plasma by pulsing a magnetized source

By operating a magnetized coaxial gun in a pulsed mode it is possible to produce large voltage pulses of duration approximately 500 mus while reaching a few kV, giving a discrete input of helicity into a spheromak. In the sustained spheromak physics experiment (SSPX), it is observed that pulsing serves to nearly double the stored magnetic energy and double the temperature. We discuss these results by comparison with 3D MHD simulations of the same phenomenon.     

Chaotic scattering and self-organization in spheromak sustainment

Flux core spheromak sustainment by electrostatic helicity injection is studied in resistive MHD. The geometry has magnetized electrodes at the ends held at a potential difference V. For V>V(c) the central current column is kink unstable. The nonlinear state with V just above V(c) has a large volume of flux surfaces, with rotational transform provided by the helical kinking of the column. As V increases the kink becomes stronger, the tori are destroyed, and the field lines exhibit chaotic scattering. The distribution of field line lengths L, related to confinement and parallel current density, is studied. At larger V or larger Lundquist number S, a limit cycle appears.     

Force-free magnetic relaxation in driven plasmas

Taylor relaxation in a driven plasma with normal magnetic field intercepting the boundary is described by the Jensen-Chu theory, which predicts infinite energy and helicity barriers that constrain the accessible relaxed states to system scale. For a partially relaxed force-free (j=kB) plasma where k is a field line constant, nonlinearity regularizes the Jensen-Chu singularities and new branches of relaxed state become accessible, such as the flipped spheromak and other high k states.     

Demonstration of plasma startup by coaxial helicity injection

The first successful results on the transfer of a coaxial helicity injection (CHI) produced discharge to inductive operation are reported. CHI-assisted plasma startup is more robust than inductive only operation. After hand off for inductive operation, the initial 90 kA of CHI-produced current drops to 40 kA, then ramps up to 170 kA, using only 30 mV s, more than 30% higher than that produced by induction alone. These significant performance enhancing results were obtained on the HIT-II spherical torus experiment (major/minor radius of 0.3/0.2 m).     

磁螺度(helicity)注入电流驱动实验的平衡反演

磁螺度注入是一种国际上正处于探索性研究阶段的极富吸收力的电汉驱动方案,尤其对于球环堆芯更具有至和关重要的意义。对磁螺度注入电流驱动实验进行平衡反演工作,将实验数据进行理论分析研究,拟合所有的测量数据以确立实际的等离子体位形,平衡的磁拓扑结构以及环向电流的空间分布,从而确定闭合橛面区的驱动电流大小以及等离子体的性质,计算结果表明等离子体具有托卡马克型ｑ分布,环向电汉分布呈中空形,磁面结构为有三角形变     

叶尖喷气影响低速离心压气机特性的数值分析

本文采用数值模拟方法研究了进口叶尖喷气对低速离心压气机稳定工作范围的影响。计算讨论了机匣开缝和机匣安装喷嘴两种喷气方案,通过改变喷气量、喷气角、气流偏角以及喷嘴的周向布置研究不同喷气形式对压气机特性的影响。结果显示两种喷气方案均可起到拓宽压气机稳定工作范围的作用,各参数间存在最优组合使喷气的扩稳效果最佳。     

Energy Efficiency Analysis of the Discharge Circuit of Caltech Spheromak Experiment

The Caltech spheromak experiment uses a size A ignitron in switching a 59-$ muhbox{F}$ capacitor bank (charged up to 8 kV) across an inductive plasma load. Typical power levels in the discharge circuit are $sim$200 MW for a duration of $sim!! 10 muhbox{s}$. 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.      

Oscillating-field current-drive experiments in a reversed field pinch

Oscillating-field current drive (OFCD) is a steady-state magnetic helicity injection method to drive net toroidal current in a plasma by applying oscillating poloidal and toroidal loop voltages. OFCD is added to standard toroidal induction to produce about 10% of the total current in the Madison symmetric torus. The dependence of the added current on the phase between the two applied voltages is measured. Maximum current does not occur at the phase of the maximum helicity injection rate. Effects of OFCD on magnetic fluctuations and dissipated power are shown.     

Whistler modes with wave magnetic fields exceeding the ambient field

Whistler-mode wave packets with fields exceeding the ambient dc magnetic field have been excited in a large, high electron-beta plasma. The waves are induced with a loop antenna with dipole moment either along or opposite to the dc field. In the latter case the excited wave packets have the topology of a spheromak but are propagating in the whistler mode along and opposite to the dc magnetic field. Field-reversed configurations with net zero helicity have also been produced. The electron magnetohydrodynamics fields are force free, have wave energy density exceeding the particle energy density, and propagate stably at subelectron thermal velocities through a nearly uniform stationary ion density background.     

Experiments on the interaction of current channels in a laboratoryplasma: relaxation to the force-free state

A series of experiments on the dynamic interaction of two current channels has been performed in the large plasma device, a laboratory device at UCLA. The two current channels are formed by coating the cathode source nonuniformly and then biasing it with respect to an anode 10 m away. The experiment consists of two phases, one in which a net current is drawn through the plasma, and one in which the net current is zero. The current channels twist about each other, merge, and evolve toward a force-free state when a net current is drawn through the plasma. When the net current is zero the interaction between the channels is greatly reduced. The dynamics of the system are dominated by electron pressure and associated electrostatic fields. However, as the currents twist, a small amount of magnetic helicity is generated. The helicity and its temporal rate of change are computed and found to compare within experimental uncertainty to the predicted rate     

Fluid simulation of the pulsed bias effect on inductively coupled nitrogen discharges for low-voltage plasma immersion ion implantation

Planar radio frequency inductively coupled plasmas(ICP) are employed for low-voltage ion implantation processes,with capacitive pulse biasing of the substrate for modulation of the ion energy. In this work, a two-dimensional(2D) selfconsistent fluid model has been employed to investigate the influence of the pulsed bias power on the nitrogen plasmas for various bias voltages and pulse frequencies. The results indicate that the plasma density as well as the inductive power density increase significantly when the bias voltage varies from 0 V to-4000 V, due to the heating of the capacitive field caused by the bias power. The N+fraction increases rapidly to a maximum at the beginning of the power-on time, and then it decreases and reaches the steady state at the end of the glow period. Moreover, it increases with the bias voltage during the power-on time, whereas the N_2~+ fraction exhibits a reverse behavior. When the pulse frequency increases to 25 kHz and40 kHz, the plasma steady state cannot be obtained, and a rapid decrease of the ion density at the substrate surface at the beginning of the glow period is observed.     

Non-existence of Goldstone bosons with non-zero helicity

In a local relativistic quantum field theory a conserved covariant tensor current may lead to a spontaneously broken symmetry if it generates zero mass states from the vacuum (Goldstone theorem). Here it is shown that in addition it is necessary that these massless states have helicity zero if the underlaying state space has a positive metric.     

Classical perfect diamagnetism: expulsion of current from the plasma interior

The vanishing of generalized helicity is shown to be the necessary and sufficient condition for a perfect conductor to display perfect diamagnetism, considered to be the defining attribute of a conventional superconductor. Although conventional superconductivity is brought about by quantum correlations in classical systems, prepared in the state of zero initial helicity (helicity is a constant of the motion for a perfect conductor), it can mimic the superconductor's behavior.     

Near field and far field power distributions in a multimode graded fibre

It is shown in this paper that the near field and far field power distributions corresponding to any distribution of rays in an arbitrary graded fibre, reach a steady state along the fibre. This steady state is usually a function of the input distribution of rays and of the refractive index profile of the fibre. The case of parallel beam injection is considered and an analytical expression for the near field power distributions for any arbitrary profile is found. This suggests a new method of refractive index profile measurement which is free of leaky ray corrections and can be very sensitive near the optimum profile for time dispersion.     

两路双包层光纤激光器互注入锁相实验研究

提出了一种利用45°半透半反分束镜和角锥反射器实现两路光纤激光器的能量相互注入,从而获得相干合成激光输出的新方法,分析了其锁相原理.在实验上成功实现了两路独立振荡双包层光纤激光器的互注入锁相输出,在远场观察到了清晰稳定的干涉条纹（可见度约0.57）,获得了超过10W的相干合成激光输出,功率合成效率约为76%.实验表明,这种互注入锁相方法可以在更高功率条件下运行,是光纤激光相干合成领域一种有前途的新技术. 关键词： 光纤激光器 相干合成 互注入锁相     

固态化高功率长脉冲驱动源关键技术

基于固态化磁开关、低阻抗脉冲形成网络和感应电压叠加等关键技术,提出了一种固态化高功率长脉冲驱动源技术方案,该方案充分利用了绝缘规律,可实现模块化设计,具备提高系统稳定性、可靠性、重复频率和长时间运行的潜在优势。目前,针对系统方案进行了电路模拟计算,研制了各关键子系统,开展了全系统的初步联合实验,在假负载上输出了功率2.1GW、脉宽约170ns的高压脉冲,验证了技术方案的合理性。     

Symmetry and some consequences for spin-particle reactions

On the basis of general spacetime and crossing symmetry, the general structure for amplitudes describing spin-particle binary reactions is considered. Using the knowledge of the kinematic structure of helicity amplitudes in the dynamical amplitude approach, we can get as model-independent general consequences about observable quantities, as some asymptotic relations between polarization parameters on the basis of a “kinematic hierarchy” assumption.     

Group properties of linear equations

A method of determining the symmetry algebra of a linear homogeneous equation is proposed. The Schrödinger equation that describes the steady state of a particle in a potential field is used as an example. The symmetry operators of this equation, which are second-order differential operators, are studied.