The effects of the operational parameters of the reactor on ECR plasma characteristics

A two-dimensional axis-symmetric model is adopted to investigate the characteristics of an electron cyclotron resonance plasma. The mass conservation equations of electrons, positive ions, and metastable atoms, the electron energy equation, and the Poisson equation are used in this multi-component system. The magnetic field generated by coils was computed numerically. The distributions of temperature and density of electrons are calculated by the finite difference method. The results of the numerical simulation for argon plasma shows that, in the phase of a long-time discharge, the electron temperature in the resonance chamber is higher than that in the reactor chamber, and electron density in the resonance chamber is lower than that in the reactor chamber. In addition, the effects of pressure on the two distributions are illustrated and discussed.     

A superconducting electron spectrometer

The set-up and tests of an electron spectrometer for in-beam conversion electron measurements are described. A superconducting solenoid is used to transport the electrons from the target to cooled Si(Li) detectors. The solenoid is designed to produce either a homogeneous axially symmetric field of up to 2 T or a variety of field profiles by powering the inner and outer set of coils of the solenoid separately. The electron trajectories resulting for various field profiles are discussed. In-beam electron spectra taken in coincidence with electrons, gammas and alpha-particles are shown.     

The Inchworm as a precision translator in a high magnetic field and uhv environment

A new set-up has been designed and tested for on-line, high-precision mass measurements of short-lived radioactive isotopes via a determination of the ion cyclotron resonance. Ions delivered by the on-line isotope separator ISOLDE at CERN/Geneva are stored in a Penning trap installed in a superconducting solenoid. Due to severe space limitations in the bore of the solenoid, it is impossible to use conventional mechanical feedthroughs for the necessary manipulations inside the uhv chamber. Instead, a number of Inchworms, a high-precision positioning device based on the piezo-electric effect are employed. This publication reports on the first application of this device in a uhv environment at a magnetic field of nearly 6 T.     

Characterization of spatial plasma distribution in a divergence-type ECR-PECVD system

The spatial distribution of electron cyclotron resonance plasma in ECR-PECVD reaction chamber is diagnosed by a Langmuir probe and the effect of the magnetic field is also investigated. The results show that the ECR plasma in the upper region has poor radial and axial uniformity, whereas the plasma in the downstream region has fine radial uniformity. Changing of magnetic coil currents does not distort the characteristics of spatial distribution in the reaction chamber.     

Control of the electron temperature by varying the resonance zone width in ECR plasma

The electron temperature (T_e) in an electron cyclotron resonance plasma is clarified to depend on the spatial profiles of the microwave-power absorption by both the electromagnetic-waves measurement and the simulation of microwave power absorption. It is found that T_e is controlled by varying the magnetic field configuration and/or the microwave frequency since the power absorption profile is influenced by the effective resonance width. In fact, T_e is observed to decrease with decreasing the magnetic field gradient at the resonance point for N₂, Ar and O₂/Ar plasma.     

Modeling of wave propagation and absorption in electron cyclotron resonance ion source plasmas

The performance of electron cyclotron resonance ion sources (ECRIS) is critically dependent on the resonant absorption of microwave power. However, currently there is little understanding of the propagation and absorption of electromagnetic waves in these ion sources. Measurement of the electromagnetic fields in a source is difficult without perturbing the plasma, and theory is hindered by the complex interaction between the waves, the plasma, the walls of the device, and the magnetic field. In this paper we present the results of quantitative 1D and qualitative 3D simulations of wave propagation and absorption in an electron cyclotron resonance ion source. The 1D simulations use the hot plasma dielectric tensor, which has not previously been applied to ECRIS modeling. The 3D simulations are the first attempt to include absorption by the plasma in calculating the structure of the electromagnetic fields in an ECRIS. These simulations demonstrate that the wave propagation and absorption is strongly dependent on the plasma. The results of the simulations are compared to experimental measurements of the mode structure, energy absorption, and frequency scaling.     

新型微波ECR-PECVD装置的研制

介绍一台新型的ECR-PECVD装置.这一装置设计和采用了一种由单个电磁线圈和永磁体单元组合的新型磁场,使整个装置结构明显简化.为提高装置的微波转换效率,通过计算机仿真微波场在等离子体室的分布,选择和采用了一种新型的矩形耦合波导.应用这一装置分解H2稀释的SiH4气体以沉积a-Si:H薄膜,获得了2 nm/s以上的高沉积速率.     

Two-Fraction Electron System on a Thin Helium Film

A systematic theoretical investigation of microwave absorption of 2-dimensional electron systems above a thin helium film in the presence of a cyclotron resonance magnetic field is presented. To explain the measured data, a two-fraction structure of the electron system is introduced. One component corresponds to the free electron motion, the second one takes into account electron localization near the potential minimum caused by the roughness of the substrate. Within this model the general dependence of microwave absorption becomes understandable. The details of the observed cyclotron resonance line-shift are discussed.     

Microwave absorption/reflection and magneto-transport experiments on high-mobility electron gas

We have performed simultaneous measurements of microwave absorption/reflection and magneto-transport characteristics of a high-mobility two-dimensional electrons in GaAs-AlGaAs heterostructure in the regime of microwave-induced resistance oscillations (MIROs). It is shown that the electrodynamic aspect of the problem is important in these experiments. In the absorption experiments, a broad cyclotron resonance line was observed due to a large reflection from the highly conductive electron gas. There were no additional features observed related to absorption at harmonics of the cyclotron resonance. In near-field reflection experiments, a very different oscillation pattern was revealed when compared to MIROs. The oscillation pattern observed in the reflection experiments is probably due to plasma effects occurring in a finite-size sample. The whole microscopic picture of MIROs is more complicated than simply a resonant absorption at harmonics of the cyclotron resonance. Nevertheless, the experimental observations are in good agreement with the model by Ryzhii et al. involving the photo-assisted scattering in the presence of a crossed magnetic field and dc bias. The observed damping factor of MIROs may be attributed to a change in the electron mobility as a function of temperature.     

Special Coils Development at the National High Magnetic Field Laboratory in Toulouse

The Laboratoire National des Champs Magnétiques Intenses (LNCMI) develops different types of coils suited to specific experiments. We present some recent developments on magnet design. Several coils are dedicated to experiments in large scale facilities in France and Switzerland. A 30 T split-pair coil for X-rays diffraction and one 40 T coil for plasma physics at the LULI, two 30 T coils with axial access (one with an conical bore) for X-ray diffraction and absorption experiments. A 40 T wide angle conical access solenoid with a high duty-cycle for neutron scattering at the ILL is being constructed. For use at the installation in Toulouse we have developed, apart from our standard 60 and 70 T coils, several special coils: a coil with a long optical path with 30 T transverse magnetic field and a 90 T long pulse dual coil system.     

Designing highly homogenous superconducting magnets by computer

A method was developed to calculate the magnetic field of superconducting magnets with a computer, type ODRA 1304. This programme calculates the magnetic field of every individual layer of the coil at any point in space, and sums them. By this process it is possible to build magnets with better homogeneity, than 10^?6cm^?1. It guarantees two kinds of methods for realizing high homogeneity by overwinding the ends of the solenoid: both discreet coils of corrections and corrections of different continuous shape. The numerical results for the three experimentally examined magnets (cylindrical solenoid, Helmholtz's coil and corrected solenoid) are in close agreement with the theory.     

Plasma diagnostics and heating in fusion programs and the possible role of free electron lasers

In the research on controlled thermonuclear fusion there is a wide utilization of electromagnetic (EM) sources with regard to both plasma diagnostics and plasma heating. In this paper the analysis is focused on the applications to magnetic fusion lines, principally on tokamaks. Concerning the diagnostics, scattering of EM waves, which has the widest and most various applications of EM sources, is reviewed. The physical principles of Thomson and resonance fluorescence scattering are illustrated and the requirements of EM sources are outlined. Finally the most urgent needs are reported indicating possible and useful developments of FELs. Heating is then discussed and the three principal frequency ranges are indicated. The present and future principal projects of magnetic fusion are reported together with their EM power requirements and wave frequencies for plasma heating. It is suggested that a possible application of FELs is in the field of electron cyclotron heating.     

Dependence of the a-Si:H defect density of states on the magnetic field profile of an electron cyclotron resonance microwave plasma

The magnetic field profile of an electron cyclotron resonance microwave plasma was systematically altered to determine subsequent effects on a-Si:H film quality. The mobility gap deep density N_D deposition rate and light-to-dark conductivity were determined for the a-Si:H films. By variation of the magnetic field profile N_D could be altered by more than an order of magnitude, from 1 × 10¹⁶ to 1 × 10¹⁷ cm⁻³ at 0.7 mTorr and 1 × 10¹⁶ to 5 × 10¹⁷ cm⁻³ at 5 mTorr as determined by junction capacitance techniques. Two deposition regimes were found to occur for the conditions of this study. Highly divergent magnetic fields resulted in poor quality a-Si:H, while for magnetic field profiles defining a more highly confined plasma, the a-Si:H was of device quality and relatively independent of the magnetic field configuration. The data is interpreted as a consequence of silane depletion for highly divergent magnetic field profiles.     

磁场辅助等离子体增强化学气相沉积

本文根据螺线管线圈内部磁场的分布规律，以及磁场对等离子体内部电子的作用原理，设计了磁场辅助的等离子体增强化学气相沉积（PECVD）系统，并且研究了在PECVD系统中获得均匀磁场的方法。而后，以SiH4和N2为反应气体，在低气压下沉积了SiN薄膜。测量了SiN薄膜的沉积速率，折射率，表面形貌等参数。验证了磁场分布的均匀性，分析了磁场在等离子体增强化学气相沉积系统中的作用。     

Coil geometry models for power loss analysis and hybrid inductive link for wireless power transfer applications

This paper presents a hybrid inductive link for Wireless Power Transfer (WPT) applications. Achieving better power transfer efficiency over a relatively wider distance across coils is the prime objective in most of the WPT systems, but often suffers from power loss in the near field area of inductively coupled coils. One of the reasons for this power loss is the pattern of the magnetic field produced by the source coil used in the WPT system. Mostly the nature of magnetic field produced by the source coil is distributed radially over the coil, in which the produced magnetic field is not fully utilized. Achieving better efficiency and load current by reducing power loss is the main driving force of this work. One of the viable methods to reduce the power loss is by increasing the field intensity thereby redirecting the flux lines flow to be directional. With this aim, three coils such as solenoid, spiral and conical are designed and simulated to determine the magnetic field strength using Finite Element Method. The conical coil produces the highest self-inductance of 8.63 µH and a field strength of 1.542 Wb with the coil thickness of 3.20 mm. Then, WPT system is demonstrated with the inclusion of Maximum Power Point Tracking algorithm for improving efficiency. The schematic of flux generation of both in the transmitter and receiver sections are demonstrated and analyzed graphically. The efficiency of both simulation and experimental measurements are matched well with similar progression. The effect of parameters (angle, distance, and load resistance) on the efficiency is explored. The outcomes conclude that the inductive coupling has achieved 73% (average case) power transfer wirelessly over a distance of 5 cm with an input voltage of 5 V and 5 MHz frequency.     

Magnetopolarons on the surface of helium films

The energy spectrum of the surface electrons on liquid helium films in the presence of a perpendicular applied magnetic field is determined in different approaches within second order perturbation theory. The influence of the electron-ripplon interaction on the Landau levels are studied for arbitrary strength of the magnetic field and several values of the coupling constant. Current theories of the polaron ground-state and cyclotron resonance are compared to the exact weak-coupling results obtained. We found a shift down in the cyclotron resonance frequency due to polaron effects.     

Eighth order solenoids

Eighth order solenoids for producing honogeneous magnetic fields were computed. One such solenoid, designed to contain a polarized ³He target, was built and tested. Compared to usual Helmholtz-type coils of similar size and efficiency the new arrangement can secure a high degree of homogeneity over a volume 15–60 times larger.     

The effect of external cusp magnetic field on Ar ICP characteristics

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.     

Cyclotron resonance maser operating in a nonresonant electron bunching regime

A new scheme of the cyclotron resonance maser (CRM) based on the phenomenon of electron bunching in a nonresonant wave field is proposed. In this scheme, the electron-wave interaction space is divided into two regions due to magnetic field profiling. In the first (input) region, the magnetic field is such that the working traveling wave is relatively far from the resonance with electrons. It is established that, under certain conditions, the motion of electrons in a nonresonant wave field is accompanied by their effective bunching without significant changes in the energy. In the second (output) region, the magnetic field is close to the resonance and the bunched electron beam effectively radiates at the working wave frequency. Thus, the regular electrodynamic system features an electron-wave interaction of the klystron type with spatially separated processes of the electron bunching and wave emission. The proposed scheme can be used for increasing the efficiency of CRMs with various configurations. It is especially advantageous in CRMs with frequency multiplication, where the electron bunching in a low-frequency nonresonant wave field is accompanied by wave emission at a multiple frequency.     

Design, development and experiment of a 1.5 T MgB2 superconducting test magnet

Superconducting magnets using MgB₂ tapes are potentially applicable in many areas, such as medical magnetic resonance imaging and fault current limiting. Under conduction cooling environments, the magnets can work at 15-20 K. In this work, a solenoid structured magnet with ∅ 100 mm bore is designed, built and tested. The maximum field at its center is up to 1.5 T. The field homogeneity, the thermal stability and the quench characteristics in the magnet are also investigated.