Effect of Vacuum-Chamber Wall Gassing on the Evolution of an ECR Discharge in a Magnetic Trap

We study the evolution of the ECR discharge sustained in a simple mirror magnetic trap by a powerful millimeter-wave radiation. Specific features of the discharge behavior are determined by the intense gassing of the vacuum chamber walls affected by a plasma that flows out of the trap. A model of the discharge dynamics is proposed. Solutions with explosive plasma-density increase were found and analyzed, and qualitative agreement between the model and experimental results was obtained.     

Measurement of Heating Rates in a Microscopic Surface-Electrode Ion Trap

We report measurement of heating rates of ~(40)Ca~+ ions confined in our home-made microscopic surface-electrode trap by a Doppler recooling method. The ions are trapped with approximately 800 μm above the surface, and are subjected to heating due to various noises in the trap. There are 3-5 ions involved to measure the heating rates precisely and efficiently. We show the heating rates in variance with the number and the position of the ions as well as the radio-frequency power, which are helpful for understanding the trap imperfection.     

Megawatt Gyrotrons for ECR Heating and Current-Drive Systems in Controlled-Fusion Facilities

We discuss the results and main trends in developing megawatt gyrotrons used as microwave sources for electron-cyclotron wave systems in controlled-fusion facilities. Such systems require gyrotrons with power no less than 1 MW operable during a time of about 1000 s in the frequency range 110–170 GHz. We also highlight the main design principles of such gyrotrons and the most striking aspects and prospects of their development in the last years.     

Subharmonics and aperiodicity in hysteresis loops

We show that it is possible to have hysteretic behavior for magnets that does not form simple closed loops in steady state, but cycles multiple times before returning to its initial state. We show this by studying the low temperature dynamics of the 3D Edwards-Anderson spin glass. The specific multiple varies from system to system and is often quite large and increases with system size. The last result suggests that the magnetization could be aperiodic in the large system limit for some realizations of randomness. It should be possible to observe this phenomenon experimentally.     

Three-Dimensional Compensation for Minimizing Heating of the Ion in Surface-Electrode Trap

The trapped ions confined in a surface-electrode trap(SET) could be free from rf heating if they stay at the rf potential null of the potential well.We report our effort to compensate three-dimensionally for the micromotion of a single ⁴⁰Ca⁺ ion near the rf potential null,which largely suppresses the ion’s heating and thus helps to achieve the cooling of the ion down to 3.4 mK,which is very close to the Doppler limit.This is the prerequosite of the sideband cooling in our S...     

Propagation and Absorption of ECR Waves in a Low Temperature Toroidal Plasma of Small Size and Magnetic Field

The propagation and absorption of ECR waves in a tokamak plasma with small size and low values of the electron temperature and the toroidal magnetic field is studied numerically. The cold plasma dispersion equation is solved and ray tracing calculations are performed to find the accessibility conditions and the optimal angle of wave launching for maximal ECR absorption. Absorption coefficients are computed in the high density approximation.     

Observation of Localized Electron Cyclotron Resonance Heating in a Magnetic Mirror

A right-hand circularly polarized (RHCP) electron cyclotron wave is launched along the axis of a steady-state magnetically confined plasma column. Detailed measurements of the spatial variation of electron temperature, density, plasma potential, and wave amplitude about the resonance zone are presented. In particular, data are presented where the temperature increase due to electron cyclotron resonance heating (ECRH) is strongly localized near the resonance position. A numerical wave heating model has been developed for electrons in a magnetic mirror and is found to be in qualitative agreement with observations.     

2D-Electron Heating in Electric and Magnetic Crossed Fields

2D-electron heating in a potential well of a single n-(AlAs) _x (GaAs)_1–x /i-GaAs (x = 0.28) heterojunction is studied for the cases of a classical (weak) magnetic field B and constant and pulsed electric fields at fixed temperatures 77 and 4.2 K. It is shown that the heating of two-dimensional electrons is similar to that of the bulk ones. The magnetic field cools electrons, and this is manifested in the shifts of the characteristic critical electric fields E _{c 1} and E _{c 2} and in the regions of nonlinearity of voltage-current characteristics. The dependence of the effective electron temperature on the electric field T _e(E)_B is determined.     

Lower Hybrid Heating of an Electron-Cyclotron-Resonance Plasma in a Canted Magnetic Mirror

Plasma heating at the lower hybrid resonance was studied experimentally in a canted magnetic mirror in order to determine the effects of magnetic field curvature on heating efficiency. Heating occurred mainly on what would be the "outside" of an equivalent torus, peaking near the hybrid resonant layer. The best conditions for heating were seen to be a relatively flat density profile of magnitude slightly below that where hybrid resonance would be expected. The density profile was seen to move "outward" as cant angle was increased, while the hybrid layers were seen to move oppositely, toward what would be the inside of the torus. No significant deleterious effects on the efficiency of the lower hybrid resonant heating (LHRH) were observed as the canting was changed.     

Low-Energy Collective Excitation of Bose-Einstein Condensates in an Anisotropic Magnetic Trap

We experimentally investigate the collective excitation of 87Rb Bose-Einstein condensates confined in a cigarshaped magnetic trap （QUIC trap）. Using a method of magnetic perturbation, the center-of-mass oscillation of the condensate is excited, so that the radial trapping frequency of the QUIC trap can be precisely determined. A high-order excitation, characterized by a fast shape oscillation, also occurs simultaneously, with a noticeable damping in the oscillation amplitude compared with the oscillation of the center of mass. The measured oscillation frequencies, associated with these two low-energy excitation modes, agree well with theoretical predictions based on the Gross-Pitaevskii equation.     

Energy Confinement Dynamics and Soft X-Ray Spectra in Experiments on ECR Plasma Heating in the L-2M Stellarator at Heating Powers to 1 MW

Bulletin of the Lebedev Physics Institute - The shape of soft X-ray spectra and energy confinement dynamics is studied in experiments on central ECR heating with a power to 1 MW using the L-2M...     

Perception of Pitch and Roughness in Vocal Signals with Subharmonics

Pitch and roughness were rated according to the extent of amplitude modulation (AM) and frequency modulation (FM) of a subharmonic [fundamental frequency (F0)/2]. The objective was to determine the identification boundaries for pitch and roughness and to discover how both kinds of modulation affect these boundaries. Another objective was to judge the reliability between subjects when identifying subharmonic-related pitch and roughness. Three procedures were used: ABX comparisons, method of adjustment, and rating of roughness. Results indicated that the crossover point to the lower pitch (associated with the subharmonic) occurred between 10% and 30% modulation, depending on modulation type and F0. Subjects demonstrated highly variable perceptions of pitch and roughness, with poor intersubject reliability.     

Production of Rubidium Bose-Einstein Condensate in an Optically Plugged Magnetic Quadrupole Trap

We experimentally produce the rubidium Bose-Einstein condensate in an optically plugged magnetic quadrupole trap.A far blue-detuned focused laser beam with a wavelength of 532 nm is plugged in the center of the magnetic quadrupole trap to increase the number of trapped atoms and to suppress the heating.An rf evaporative cooling in the magneto-optical hybrid trap is applied to decrease the atom temperature into degeneracy.The atom number of the condensate is 1.2(0.4)× 10~5 and the temperature is below 100 nK.We also study characteristic behaviors of the condensate,such as phase space density,condensate fraction and anisotropic expansion.     

Features and Limiting Characteristics of the Heating of a Substance by a Laser-Accelerated Fast Electron Beam

The features of plasma formation in a substance heated by a laser-accelerated fast electron beam have been studied. These features are related to the ratio of the heating rate to the rate of energy loss because of radiation processes and electronic thermal conductivity, which are governed by the dependence of the energy of the heating beam particles on the beam intensity, which is characteristic of laser-driven electron acceleration. It has been shown that energy losses increase with the beam intensity and significantly limit the maximum temperature of the formed plasma. The possibility of generating an intense γ-radiation pulse of a nonnuclear origin because of the bremsstrahlung of laser-accelerated electrons has been discussed.