Cyclotron-resonance maser driven by magnetic compression of rarefied plasma

Conditions are found at which adiabatic magnetic compression of plasma confined in a mirror magnetic trap is accompanied by the accumulation of significant energy in a hot anisotropic electron tail with the subsequent release of this energy as a pulse of coherent electromagnetic radiation. The possibilities of creating THz radiation sources up to the GW power level are discussed.     

Simulation of Processes on a Target Induced by a Jet System and Laser Radiation

The mathematical model and the results of computer simulation of the processes of compression, heating, and energy release in a target under the hybrid influence of a system of pulsed plasma jets and intense laser radiation in magnetic inertial thermonuclear fusion are presented. The hybrid effects of intense energy flows on a single-layer cylindrical target are compared in the experimental and simulation conditions. The main radiation magnetic and gas dynamic parameters of the compressed and heated target plasma are evaluated as well.     

Gepulste UV-Strahlungsquelle zur Erzeugung eines hoch ionisierten Ausgangsplasmas niedriger Dichte

A 100 kV Z-pinch, pulse-filled with high-density xenon gas, is used as radiation source for photoionizing hydrogen or rare gases at filling pressures of 1–10 mtorr. This produces a homogeneous, magnetic field free, highly ionized (degree of ionization ≈10% in H₂ and ≈ 20% in Ar) plasma suitable for example, for collisionless shock wave experiments. Experimental and theoretical investigations have yielded information on the conversion of the stored electrical energy into radiation energy. As a result of fast magnetic compression and ohmic heating (the relatively low temperature of max. 6 eV due to multiple ionization of the xenon atoms being favourable) the xenon pinch absorbs 30% of the stored electrical energy. Investigation of the matching of the external circuit to theZ-pinch by means of the snowplow model shows that the energy transmission efficiency could be increased about 50% if the current half-cycle is made equal to the compression time. The suitability of the xenon pinch as a radiation source is due on the one hand, to the almost complete conversion of the absorbed energy into radiation and, in particular, to the spectral distribution of the radiation, which is favourable for the ionization of hydrogen. It is found that the radiation is mainly emitted in lines with maximum intensity at the same wavelength λ ≈ 700 Å as the maximum of the photoionization cross section owing to the low temperature of the xenon plasma.     

Effects of magnetic field and temperature on the nonrelativistic bremsstrahlung process in magnetized anisotropic plasmas

The magnetic field and thermal effects on the nonrelativistic electron-ion bremsstrahlung process are investigated in magnetized anisotropic plasmas. The effective electron-ion interaction potential is obtained in the presence of an external magnetic field. Using the Born approximation for the initial and final states of the projectile electron, the bremsstrahlung radiation cross section and bremsstrahlung emission rate are obtained as functions of the electron energy, radiation photon energy, magnetic field strength, plasma temperature, and Debye length. It is shown that the effects of the magnetic field enhance the bremsstrahlung radiation cross section for low plasma temperatures and, however, suppress the bremsstrahlung cross section for high plasma temperatures. It is also shown that the magnetic field effects diminish the bremsstrahlung emission rate in magnetized high temperature plasmas.     

Quasi-adiabatic compression of a plasma column by a longitudinal magnetic field

Approximate 1.5-dimensional MHD equations are derived that describe the quasi-adiabatic compression of a thin plasma column by a longitudinal magnetic field. The parameters of the compressed plasma are obtained analytically as functions of the initial conditions and longitudinal field. The stability of plasma compression against the Rayleigh-Taylor instability is investigated. It is shown that, in the Z-Θ-pinch geometry, increasing the longitudinal magnetic field makes it possible to achieve radial compression ratios of 20–30 without violating the cylindrical symmetry of the column. The possibility of thermonuclear ignition in a thin plasma column in a Z-Θ-pinch configuration is studied. The ranges of the initial plasma densities and temperatures and the initial lengths of the plasma column that are needed to achieve ignition in a plasma compressed by a factor of 20–30 are determined. The parameters of the electromagnetic energy source required to achieve such a high plasma compression are estimated.     

铝丝阵Z箍缩辐射产生机理初步研究

利用一维非平衡辐射磁流体力学程序研究了铝丝阵内爆过程中的能量转化规律和辐射产生机理.细致讨论了Z箍缩过程中脉冲功率驱动器电磁能馈入等离子体,等离子体动能转化为内能以及通过一系列原子过程电子内能转化为X射线辐射的能量转化机理.结合离子布居信息深入分析了Z箍缩过程中的辐射产生机理.结果表明,在内爆压缩阶段,电离和激发过程占优,线辐射占据总辐射的绝大部分.在滞止时,离子大都处于裸核离化度,连续谱辐射达到峰值.在滞止附近,线辐射出现两个峰值.在膨胀过程中,光电复合过程优于三体复合,线辐射占总辐射的份额逐渐下降.     

Disruption Mitigation Using Laser Ablation of High-Z Impurities in HL-1M Tokamak

Major plasma disruptions are considered to be a serious problem for development of tokamak fusion reactors. The preliminary experiment results in HL-1M presented here describe the methods of amelioration of plasma current quench in major disruptions using laser ablation of high-Z impurities, which support the design of next generation large tokomaks like ITER. Using injection of impurity with higher electric charge can produce resistive highly radiating plasma and increase the radiation cooling of plasma to make a safe termination of the disruption. It can be possibly a simple and potential approach to decrease significantly the plasma thermal energy and magnetic energy before a disruption then obtain a safe plasma termination. The magnetic energy can be dissipated by impurity radiation .     

The MAGO system (magnetic compression)

Results of experimental and theoretical investigations are presented in the frame of magnetohydrodynamic implosion conception MAGnitnoye Obzhatiye or magnetic compression (MAGO). This approach suggests magnetized deuterium-tritium (DT)-plasma preliminary heating and its subsequent adiabatic compression by liner imploded by a magnetic field. DT-plasma preliminary heating is performed using a special plasma chamber MAGO where magnetized plasma is accelerated in an annular nozzle up to velocities ~100 cm/μs and heated in arising collisionless shock waves. Subsequent plasma compression and bringing of its characteristics to the ignition can be realized using explosive magnetic generators with energy 100-500 MJ. This paper discusses the plasma chamber MAGO, physical effects essential for its operation, their relation with other plasma physics areas, as well as problems arising in the MAGO system. Due to its cylindrical symmetry with sole toroidal magnetic field component and essential role of magnetohydrodynamics, the MAGO system and its problems are similar to these in related systems, such as Z-pinches, plasma accelerators, and liner systems     

Numerical Simulation of the Effect of Radiation Injection Through Holes on the Comression Symmetry in Targets of the Laser-Greenhouse Type

A two-dimensional program code in Eulerian coordinates adopted to the spherical axisymmetric geometry is developed. The program package is intended to simulate plasma heating and compression under conditions of radiation injection into the target interior. Results of a series of calculation for targets of the laser-greenhouse type are presented. It is shown that allowance for the plasma outflow from holes leads to a 30–40 % energy loss and deterioration in symmetry of the target compression.     

等离子体中相对论电子的同步曲率辐射特性研究

根据同步曲率辐射理论推导了在等离子体环境中,不同磁场条件下的相对论性电子的吸收系数和发射系数表达式，计算了电子的发射强度，并且在此基础上研究了同步曲率辐射机制的脉泽效应.研究了两种磁场位型，第一种是强度均匀但弯曲的磁场，第二种是偶极磁场，结果发现了一些偶极磁场下特有的辐射特性.考虑到在天体的环境下电子具有的不同的能谱分布，分别选用了三种典型的能谱分布(幂率分布，高斯分布，热分布)进行了研究，通过计算负吸收和脉泽放大效应在发射强度上的表现后， 发现在某些天体物理环境中，同步曲率辐射在等离子体中的确存在脉泽放大效应.这些研究结果对太阳系中行星外层辐射的研究和宇宙中的射电高亮温度等问题的研究可能提供有益的帮助. 关键词： 同步曲率辐射 负吸收 脉泽效应     

Increase in radiation intensity in a quasi-spherical “double liner”/“dynamic hohlraum” system

A concept of the magnetic implosion of quasi-spherical liners, concentration of their kinetic energies, conversion of energy into thermal radiation, confinement of its energy in the cavity of an emitting plasma shell in the “double liner”/“dynamic hohlraum” system, and the irradiation of a spherical target is proposed for the physics of high energy densities and inertial confinement fusion. The radiation intensity on the target was shown to increase considerably due to capture of radiation in the process of converting the kinetic energy of the liner into radiation. The dynamics of the liners and the generation of radiation are simulated by the ZETA code using a physical model developed for a nonequilibrium plasma in a cylindrical geometry. The effect of the instability and inhomogeneity of the liners on confinement of radiation energy is estimated.     

Z箍缩等离子体磁重联现象

分析了磁重联对晕等离子体加速和能量平衡过程的影响。分析表明晕等离子体向轴心的加速过程分为两个阶段:第一阶段晕等离子体在磁压或热压(依赖于丝数)作用下向轴心运动;第二阶段晕等离子体由于磁重联过程被加速到阿尔芬速度,并到达轴心形成先驱等离子体。估算表明重联层的厚度与离子的惯性长度具有相同的数量级,电流片内电子运动和离子的运动是解耦合的。在内爆滞止阶段电荷分离产生强的径向电场,这个电场将磁能转化为等离子体轴向(z方向)动能,内爆动能和轴向动能共同转化为X射线辐射能,以此解释了X射线能量大于内爆动能这一观测结果。分析了磁重联电磁脉冲的性质,对于1 MA驱动条件,电磁脉冲的总能量可达kJ量级。     

Effects of drive current rise-time and initial load density distribution on Z-pinch characteristics

A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z-pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power.     

Formation of tight plasma pinches and generation of high-power soft x-ray radiation pulses in fast Z-pinch implosions

Argon K-shell plasma radiation source experiments were carried out on the GIT-12 generator [Bugaev, S.P. et al., 1997, Russian Phys. Journal, 40, 38] for a long (300 ns) implosion regime. The performance of a shell-on-solid-fill double gas puff was characterized in the experiments with and without an external axial magnetic field. The maximum Ar K-shell radiation yield registered in the experiments without an axial magnetic field was at the level of 1100 J/cm. This yield is consistent with the theoretically predicted yield for a short (100 ns) implosion regime. The experiments showed that the initial magnetic field which provides stabilization of the shell-on-solid-fill double gas puff was lower than that required for stabilization of a single annular gas puff. Satisfactory stabilization of the double gas puff was observed at an initial axial magnetic field of 1.4 kG. The maximum Ar K-shell radiation yield registered in the experiments with the axial magnetic field did not exceed 400 J/cm. A sharp reduction of the K-shell yield cannot be explained only by taking into account the energy losses associated with the compression of the axial magnetic field. Original Text ? Astro, Ltd., 2006.     

Z箍缩内爆过程中的能量转换机制研究

利用一维三温辐射磁流体力学程序对氖气和铝丝阵Z箍缩内爆过程中的能量转换过程进行了详细的数值研究，发现在内爆过程中离子和电子之间的碰撞能量交换是最主要的能量交换过程，其次是电子和光子之间的光电过程和轫致过程，而康普顿散射过程中的能量交换可以忽略不计；辐射出的x射线主要是在光电激发和光电复合过程中产生的，其次是在轫致辐射过程和康普顿散射过程中产生的.理论分析表明，辐射出的x射线能量可以超过，也可能小于其等离子体最大动能.数值模拟结果表明，在氖气Z箍缩中，辐射出的x射线能量没有超过其等离子体最大动能，而在铝丝阵列内爆中，辐射出的x射线能量超过了其等离子体最大动能，但小于磁压所做的功；在整个Z箍缩过程中欧姆加热能量是较小的. 关键词： Z箍缩 能量转换 x射线辐射     

Disruption mitigation using laser ablation of high-Z impurities in HL-1M tokamak

A preliminary experiment triggering a plasma current quench by laser ablation of high-Z impurities has been performed in the HL-1M tokamak. The injection of impurities with higher electric charges into tokamak plasmas can increase the radiation cooling of the plasma. Resistive, highly radiating plasma formed prior to the thermal quench can dissipate both the thermal and magnetic energies, which is possibly a simple and potential approach to reducing significantly the plasma thermal energy and magnetic energy before a disruption thereby a safe plasma termination is obtained.     

双等离子体团相互作用的磁流体力学模拟

利用商用磁流体力学模拟程序USIM对双等离子体团相互作用过程进行了数值模拟,分别考察和比较了双对流等离子体团在外加磁场和无外加磁场情况下,相互作用的物理过程.发现在外加磁场情况下等离子体团相互作用会伴随着磁重联(反向磁场)、磁排斥(同向磁场)以及一些不稳定过程.针对激光产生等离子体团错位相互作用实验,进行了标度模拟,发现外加磁场起着重要作用,进一步表明激光等离子体的磁化特征.研究结果为下一步在神光Ⅱ激光装置进行强磁环境下等离子体实验提供理论指导.     

Subnanosecond collapse and pinch dynamics at the plasma focus

Compression and pinch phase at the plasma focus were investigated by streak camera observations of the visible emission. The duration of maximum local compression provides no evidence for magnetic confinement of the focus plasma. With increasing hard X-ray intensity a decreasing of the temporal evoution of the pinch phase is observed, indicating enhanced diffusion of magnetic field energy into the locally compressed plasma.     

反场构型等离子体靶压缩过程中强磁场对α粒子能量的约束效应

基于一维弹塑性磁流体力学程序（SSS-MHD）,研究了反场构型（FRC）等离子体靶在磁驱动固体套筒压缩过程中强磁场对α粒子能量约束效应,分析了α粒子的非局域和局域自加热对FRC等离子靶压缩峰值温度的影响,以及α粒子能量在整个压缩过程中端部损失效应。等离子体部分采用多温单流体的模型,能量的计算中引入了DT离子、电子及α粒子多成分温度的能量方程,同时考虑了等离子体压缩过程热平衡下的核反应和非局域自加热问题。研究结果表明,磁化靶聚变等离子体在压缩过程中具有较好的稳定性,能够保持刚性转子的靶结构,压缩过程形成的强磁场能够将α粒子的能量约束在O点附近的区域,有利于等离子体靶的点火及燃烧;α粒子对等离子体的自加热效应主要集中在等离子体电流中心区,而非等离子体中心轴处;α粒子对DT等离子体局域和非局域自加热过程存在差异,局域自加热过程的功率大于非局域自加热过程的功率,FRC等离子靶压缩峰值状态温度相差0.5倍。在反场构型的刮离层区,α粒子的能量端部损失在FRC等离子体靶的压缩和膨胀过程中逐渐增大。     

基于MULTI2D-Z程序的Z箍缩动态黑腔形成过程模拟

对辐射流体力学程序MULTI-2D进行改造,增加磁场演化方程程序模块,自洽地在运动方程模块中增加洛伦兹力,在能量方程模块中增加欧姆加热,将它改造成辐射磁流体力学程序MULTI2D-Z.验证了新增磁场程序模块的可靠性,并发现温度和密度的增大会抑制磁场的扩散,负径向速度梯度的流体对流也会抑制磁场的扩散.利用改造好的MULTI2D-Z程序模拟了峰值为8 MA的脉冲电流驱动的钨丝阵Z箍缩动态黑腔形成过程.得到了X光功率(约30 TW)和能量(约300 k J)、泡沫辐射温度(约120 eV)、箍缩轨迹等模拟结果.在动态黑腔形成过程中,磁场主要分布在钨主体等离子体中;辐射向内传播,烧蚀泡沫柱而使它膨胀;辐射热波在被撞击的泡沫柱中传播,其传播速度比物质温度传播得快,当辐射热波传播到中心轴时泡沫柱中的辐射场变得比较均匀,并且除了冲击波处外辐射温度与物质温度基本上没有分离.这些模拟结果可增强人们对磁场扩散和对流规律以及动态黑腔形成机制的理解,同时表明了MULTI2D-Z程序可成为Z箍缩及其应用的新的程序模拟工具.