Theoretical and experimental studies of the bell-jar-top inductively coupled plasma

The present paper describes a systematic study of argon plasmas in a bell-jar inductively coupled plasma (ICP) source over the range of pressure 5-20 mtorr and power input 0.2-0.5 kW, Experimental measurements as well as results of numerical simulations are presented. The models used in the study include the well-known global balance model (or the global model) as well as a detailed two-dimensional (2-D) fluid model of the system, The global model is able to provide reasonably accurate values for the global electron temperature and plasma density, The 2-D model provides spatial distributions of various plasma parameters that make it possible to compare with data measured in the experiments, The experimental measurements were obtained using a tuned Langmuir double-probe technique to reduce the RF interference and obtain the light versus current (I-V) characteristics of the probe. Time-averaged electron temperature and plasma density were measured for various combinations of pressure and applied RF power, The predictions of the 2-D model were found to be in good qualitative agreement with measured data, It was found that the electron temperature distribution T-e was more or less uniform in the chamber, It was also seen that the electron temperature depends primarily on pressure, but is almost independent of the power input, except in the very low-pressure regime. The plasma density goes up almost linearly with the power input.

Self-consistent kinetic modeling of low-pressure inductively coupled radio-frequency discharges

An efficient method for solving the spatially inhomogeneous Boltzmann equation in a two-term approximation for low-pressure inductively coupled plasmas has been developed. The electron distribution function (EDF), a function of total electron energy and two spatial coordinates, is found self-consistently with the static space-charge potential which is computed from a 2D fluid model, and the rf electric field profile which is calculated from the Maxwell equations. The EDF and the spatial distributions of the electron density, potential, temperature, ionization rate, and the inductive electric field are calculated and discussed. (C) 1996 American Institute of Physics.

Heating, current drive and confinement regimes with the JET ICRH and lhcd systems

During its 1990 operation, 2 large RF systems were available on JET. The Ion Cyclotron Resonance Heating (ICRH) system was equipped with new beryllium screens and with feedback matching systems. Specific impurities generated by ICRH were reduced to negligible levels even in the most stringent H-mode conditions. A maximum power of 22 MW was coupled to L-mode plasmas. High quality H-modes (tau-E greater-than-or-equal-to 2.5 tau-EG) were achieved using dipole phasing. A new high confinement mode was discovered. It combines the properties of the H-mode regime to the low central diffusivities obtained by pellet injection. A value of n(d) tau-E T(i) = 7.8 x 10(20) m-3 s keV was obtained in this mode with T(e) approximately T(i) approximately 11 keV. In the L-mode regime, a regime, a record (140 kW) D-He-3 fusion power was generated with 10 - 14 MW of ICRH at the He-3 cyclotron frequency. Experiments were performed with the prototype launcher of the Lower Hybrid Current Drive (LHCD) systems with coupled power up to 1.6 MW with current drive efficiencies up to < n(e) > R I(CD)/P = 0.4 x 10(20) m-2 A/W. Fast electrons are driven by LHCD to tail temperatures of 100 keV with a hollow radial profile. Paradoxically, LHCD induces central heating particularly in combination with ICRH. Finally we present the first observations of the synergistic acceleration of fast electrons by Transit Time Magnetic Pumping (TTMP) (from ICRH) and Electron Landau Damping (ELD) (from LHCD). The synergism generates TTMP current drive even without phasing the ICRH antennae.

The induction plasma chemical reactor: Part I. Equilibrium model

A mathematical model is presented for the numerical simulation of the flow, temperature, and concentration fields in an rf plasma chemical reactor. The simulation is performed assuming chemical equilibrium. The extent of validity of this assumption is discussed. The system considered is the reaction of SiCl4 and NH3 for the production of Si3N4.

The induction plasma chemical reactor: Part II. Kinetic model

A kinetic model has been developed for the prediction of the concentration gelds in an rf plasma reactor. A sample calculation for a SiCl4/H2 system is then performed. The model considers the mixing processes along with the kinetics of seven reactions involving the decomposition of these reactants. The results obtained are compared to those assuming chemical equilibrium. The predictions indicate that an equilibrium assumption will result in lower predicted temperature fields in the reactor. Furthermore, for the chemical system considered here, while differences exist between the concentration fields obtained by the two models, the differences are not substantial.

Numerical Simulation of Heat Transfer and Kinetics in the Bulk Growth of Silicon Carbide

The growth process of 2-inch silicon carbide (SiC) single crystals by the physical vapor transport method (or modified Lely method) has been modeled and simulated. The comprehensive process model incorporates the calculations of radio frequency (RF) induction heating, heat and mass transfer and growth kinetics. The transport equations for electromagnetic field, heat transfer, and species transport are solved using a finite volume-based numerical scheme called MASTRAPP (Multizone Adaptive Scheme for Transport and Phase Change Process). Temperature distribution for a 2-inch growth system is calculated, and the effects of induction heating frequency and current on the temperature distribution and growth rate are investigated. The predicted results have been compared with the experimental data.

Further acceleration of MeV electrons by a relativistic laser pulse

With the development of photocathode rf electron gun, electrons with high-brightness and mono-energy can be obtained easily. By numerically solving the relativistic equations of motion of an electron generated from this facility in laser fields modelled by a circular polarized Gaussian laser pulse, we find the electron can obtain high energy gain from the laser pulse. The corresponding acceleration distance for this electron driven by the ascending part of the laser pulse is much longer than the Rayleigh length, and the light amplitude experienced on the electron is very weak when the laser pulse overtakes the electron. The electron is accelerated effectively and the deceleration can be neglected. For intensities around 10(19) W(.)mu m(2)/cm(2), an electron's energy gain near 0.1 GeV can be realized when its initial energy is 4.5 MeV, and the final velocity of the energetic electron is parallel with the propagation axis. The energy gain can be up to 1 GeV if the intensity is about 10(21) W(.)mu m(2)/cm(2). The final energy gain of the electron as a function of its initial conditions and the parameters of the laser beam has also been discussed.

Photoionization of H atoms in few-cycle laser pulses

Photoionization of hydrogen atoms in few-cycle laser pulses is studied numerically. The total ionization probability, the. instantaneous ionization probability; and the partial ionization probabilities in a pair of opposite directions are obtained. The partial ionization probabilities are not always equal to each other which is termed as inversion asymmetry. The variation of asymmetry degree with the CE phase, the pulse duration and the pulse intensity is studied. It is found that the pulse intensity affects the asymmetry degree in many aspects. Firstly, the asymmetry is more distinct at higher intensities than that at lower intensities when the pulse duration exceeds 4 cycles; secondly, the maximal asymmetry in lower intensities varies with the CE phase visibly while at higher intensities riot; thirdly, the partial ionization probabilities equal to each other for some special CE phases. For lower pulse intensities, the corresponding value of CE phase is always 0.5 pi and 1.5 pi, while for higher pulse intensities, the corresponding value varies with the pulse intensity. Similar phenomena were observed in a recent experiment using few-cycle radio-frequency (RF) pulses.

Trapping of neutral Rb-87 atoms on an atomchip

We report an experiment of trapping of neutral Rb-87 atoms on a, self-made atomchip. The H-shaped atomchip is made by magnetron sputtering technology, which is different from the atomchip technology of other teams. We collect 3 x 10(6) Rb-87 atoms in the mirror magneto-optical trap (MOT) using the external MOT coils, and 1 X 10(5) Rb-87 atoms are transferred to U-MOT using U-shaped wire in chip and a pair of bias coils.

Quantum superchemistry in an output coupler of coherent matter waves

We investigate the quantum superchemistry or Bose-enhanced atom-molecule conversions in a coherent output coupler of matter waves, as a simple generalization of the two-color photoassociation. The stimulated effects of molecular output step and atomic revivals are exhibited by steering the rf output couplings. The quantum noise-induced molecular damping occurs near a total conversion in a levitation trap. This suggests a feasible two-trap scheme to make a stable coherent molecular beam.

A radio frequency field guide using field induced adiabatic potential

We study the behaviour of atoms in a field with both static magnetic field and radio frequency (rf) magnetic field. We calculate the adiabatic potential of atoms numerically beyond the usually rotating wave approximation, and it is pointed that there is a great difference between using these two methods. We find the preconditions when RWA is valid. In the extreme of static field almost parallel to rf field, we reach an analytic formula. Finally, we apply this method to Rb-87 and propose a guide based on an rf field on atom chip.

TWO-DIMENSIONAL ARRAY OF ION TRAPS ON A PLANAR CHIP

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for the scalable quantum information processor. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate, a combination of appropriate rf and DC potentials are applied to them for stable ion confinement, and the trap axes are located above the surface at a distance controlled by the electrodes' lateral extent and the substrate's height as discussed. The potential distributions are calculated using static electric field qualitatively. This architecture is conceptually simple and many current microfabrication techniques are feasible for the basic structure. It may provide a promising route for scalable quantum computers.

一种新型结构的单纵模光纤激光器

单纵模掺铒光纤激光器在光通信和光传感等方面有着广泛的应用前景。设计了一种新型的光纤激光器，在光纤环形镜中嵌入未抽运的掺铒光纤作为可饱和吸收体以抑制多纵模，用光纤环谐振腔作为滤波器抑制拍频噪声，用光纤光栅作为波长选择器件，最终得到了单纵模输出并消除了拍频噪声。使用零拍法测量其线宽小于频谱仪的低频极限5kHz。实验结果证明了可饱和吸收体和光纤环的功能。

声光调制光纤器件及其应用

综述了近年来光纤中声光耦合的研究及其一些应用。由PZT产生的弹性声波在光纤上传播，导致光纤周期性的微弯，引起光纤内模式耦合。其作用类似于长周期光栅，但又因为声波的频率、振幅随着施加的RF信号的频率和振幅的改变而改变，因而相对长周期光栅来讲有着灵活、可调的优点。根据声波对光纤共振波长的调谐特性，可以做出很多性能优异的光器件，如频移器，窄带和超宽带的可调滤波器，可调光衰减器，光开关等。

单长周期光栅迈克耳孙干涉仪特性研究

单长周期光栅迈克耳孙（Michelson）干涉仪是由尾纤端面蒸镀高反膜的单根长周期光纤光栅构成。入射光经长周期光栅后，部分被耦合到包层中传输。经过包层和纤芯传输的光信号经尾纤端面反射后，重新耦合回到长周期光栅中，在光栅区域形成干涉。通过理论计算分析了各种因素对其光谱响应的影响。从实验上得到了干涉光谱的谐振峰波长位移与光纤段温度变化成良好的线性关系，测得其温度系数为31．3pm／℃。表明这种结构可用于高温传感或作为波分复用滤波器。