KT—5C托卡马克离子温度及其涨落的实验研究

在ＫＴ－５Ｃ托卡马克上成功建立了一套静电离子探针诊断系统，测量了ＫＴ－５Ｃ托卡马克从芯部到边缘的离了温度及其涨落，实验结果表明，在边缘等离子体离子温度高于电子温度，在芯部二者趋于一致。在我们的实验条件下，离子温度和电子温度的相对涨落量基本一致，而且都是电子密度相对涨落量大小的５０％。     

Noise temperature distribution of superconducting hot electron bolometer mixers

We report on the investigation of optimal bias region of a wide-band superconducting hot electron bolometer(HEB)mixer in terms of noise temperature performance for multi-pixel heterodyne receiver application in the 5-meter Dome A Terahertz Explorer(DATE5) telescope. By evaluating the double sideband(DSB) receiver noise temperature(Trec) across a wide frequency range from 0.2 THz to 1.34 THz and with a large number of bias points, a broad optimal bias region has been observed, illustrating a good bias applicability for multipixel application since the performance of the HEB mixer is uniquely determined by each bias point. The noise temperature of the HEB mixer has been analyzed by calibrating the noise contribution of all RF components, whose transmissions have been measured by a time-domain spectroscopy. The corrected noise temperature distribution shows a frequency independence relation. The dependence of the optimal bias region on the bath temperature of the HEB mixer has also been investigated, the bath temperature has limited effect on the lowest receiver noise temperature until 7 K, however the optimal bias region deteriorates obviously with increasing bath temperature.     

Channel temperature determination of multifinger AlGaN/GaN high electron mobility transistor using micro-Raman technique

Self-heating in multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of AlGaN/GaN HEMT is estimated from the calibration curve of passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1 ℃ is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.     

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在HL-2A装置的电子回旋辐射(ECE)外差测量中,为实现电子温度剖面分布的绝对测量,采用双温度法和磁场扫描法分别对扫频和多道ECE测量系统进行了标定,获得了各道间的相对标定系数,并利用等离子体中心道Thomson散射测量的电子温度对ECE测量系统进行了绝对标定。结果表明,这两种方法都能实现可靠的标定,并对两者的优劣进行了比较和讨论。     

Channel temperature determination of a multifinger AlGaN/GaN high electron mobility transistor using a micro-Raman technique

Self-heating in a multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of the AlGaN/GaN HEMT is estimated from the calibration curve of a passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1°C is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.     

低混杂波高N‖分量对EAST等离子体电流驱动的影响

EAST等离子体高约束模运行条件下，在等离子体边缘区域观测到明显的等离子体电流带.在EAST托卡马克装置非圆截面平衡位形下，使用射线追踪方法研究低混杂波高平行折射率N_‖分量对电流驱动的影响.结果表明：当-8≤N_‖≤-6时，平行折射率分量能够在小半径（0.7 < r/a < 1）区域驱动kA量级的等离子体电流.对于具有台基区、等离子体边缘温度更高的电子温度剖面，驱动电流的位置r/a>0.9.低混杂波朗道阻尼的理论分析与数值模拟结果一致.另外，高N_‖低混杂波在等离子体边缘的功率沉积和电流驱动与电子温度分布和发射谱分布相关.     

Ion Temperature Measurement in the Edge Region of SINP Tokamak by a Retarding Field Analyser

Based on the principle of retarding field analyser an ion energy analyser has been developed for the measurement of ion temperature in the edge plasma region of the SINP tokamak. This has been used to determine the dependence of the ion temperature on the safety factor q in the normal q region (q=2 to 4), plasma current, plasma electron temperature and also the Spitzer resistivity.     

Phonon and electron transport in aluminum thin film: Influence of film thickness on electron and lattice temperatures

Influence of film thickness on non-equilibrium energy transport in the aluminum thin film is examined. The solutions of Boltzmann equation and the modified two-equation model are presented to predict electron and phonon temperatures in the film for various film thicknesses. It is found that electron and phonon temperatures predicted from the Boltzmann equation differ from the solution of two-equation model in the film for small film thickness. As the film thickness increases, this difference becomes negligibly small. Two-equation model predicts higher electron and phonon temperatures than those obtained from the solutions of the Boltzmann equation in the vicinity of the high temperature edge. This becomes opposite in the region of the low temperature edge.     

Application of Emissive Probes for Plasma Potential Measurements in Fusion Devices

In experimental fusion devices, up to now, only cold probes were used to determine the plasma potential in the s crape‐ o ff l ayer (SOL), and their floating potential was assumed to be proportional to the plasma potential. However, drifting electrons or beams shift the current‐voltage characteristic of a cold probe by a voltage, which corresponds to the mean kinetic energy of the drifting electrons. This problem can be avoided by the use of electron emissive probes, since an electron emission current is independent of electron drifts in the surrounding plasma. In addition emissive probes are insensitive to electron temperature fluctuations in the plasma. We have used an arrangement of three emissive probes in the edge plasma region of ISTTOK (Instituto Superior Técnico tokamak) at Lisbon. The probes have been mounted in such a way that the tips are positioned on the same poloidal meridian but on different minor radii in the SOL. With this arrangement, the plasma potential has been measured in the edge region of the ISTTOK, and first results are presented in this contribution.     

8mm波段外差时序多色仪实验

诊断托卡马克及其他磁约束聚变装置等离子体电子温度分布的有效手段之一是测量其电子迴旋辐射谱。现在世界上各聚变实验室为此所使用的谱仪有两大类:一类是时序谱仪,其中有扫频外差接收机和各种扫描干涉仪(如法-玻干涉仪,迈克尔逊干涉仪等);另一类是多色仪(如光栅光谱仪)。谱仪的频率范围一般在毫米波和亚毫米波段。对时序谱仪的要求除具有一定的频带宽度和接收灵敏度外,最主要的是扫描速率(指完成一幅给定谱宽的测量所需的时间T_t)。目前以返波管为本振的扫频外差接收机扫描速率最高。如60—90GHz扫频仪,T_t=1—10ms。各种扫描干涉仪则由于采用机械扫描,速率较低。     

消除载流子分布的不均匀性的影响准确测量深中心俘获载流子的截面

Zylbersztejn指出在空间电荷区边界层中,由于势垒的存在而引起的载流子分布的不均匀性,对测量深中心对载流子的俘获截面的不良影响,并且提出一种消除这种影响的方法。可惜的是,他的方法只适用于在能级相当深的情况下,测量低温时载流子的俘获截面。本文在详细分析结电容瞬态动力过程的基础上,提出一种消除载流子分布不均匀(包括边界层中载流子分布不均匀和体内浅施主或浅受主浓度不均匀)的影响,准确测量俘获截面的方法,不受测量温度及样品中的能级情况的严重限制。这对于研究俘获截面与温度的关系以及进而研究俘获动力学机制是很 关键词：     

Kondo effect in a quantum antidot

We report Kondo-like behavior in a quantum antidot (a submicron depleted region in a two-dimensional electron gas) in the quantum-Hall regime. When both spins of the lowest Landau level are present all around the antidot, the resonances between extended edge states via antidot bound states show an abnormal feature in alternate Coulomb-blockaded regions. The feature becomes suppressed when the temperature or source-drain bias is raised as for Kondo resonances in quantum dots. Although the exact mechanism is unknown, Kondo-like correlated tunneling may arise from a Skyrmion-type edge reconstruction. This observation demonstrates the generality of the Kondo phenomenon.     

The inelastic electron tunneling spectroscopy of edge-modified graphene nanoribbon-based molecular devices

The inelastic electron tunneling spectroscopy(IETS) of four edge-modified finite-size grapheme nanoribbon(GNR)-based molecular devices has been studied by using the density functional theory and Green's function method. The effects of atomic structures and connection types on inelastic transport properties of the junctions have been studied. The IETS is sensitive to the electrode connection types and modification types. Comparing with the pure hydrogen edge passivation systems, we conclude that the IETS for the lower energy region increases obviously when using donor–acceptor functional groups as the edge modification types of the central scattering area. When using donor–acceptor as the electrode connection groups, the intensity of IETS increases several orders of magnitude than that of the pure ones. The effects of temperature on the inelastic electron tunneling spectroscopy also have been discussed. The IETS curves show significant fine structures at lower temperatures. With the increasing of temperature, peak broadening covers many fine structures of the IETS curves.The changes of IETS in the low-frequency region are caused by the introduction of the donor–acceptor groups and the population distribution of thermal particles. The effect of Fermi distribution on the tunneling current is persistent.     

A fluid model of the current-voltage characteristics of an electron emitting electrode immersed in a two electron temperature plasma

The current voltage characteristics of a negatively biased electron emitting electrode immersed in a two-electron temperature plasma are analyzed by a simple one dimensional fluid model. Based on the assumption that the electron density in the pre-sheath region obeys the Boltzmann law the Bohm criterion is derived in the form of a transcendental equation for the Mach number, which can have up to 3 solutions. According to these solutions the ion velocity at the sheath edge can be determined either by the hot or by the cool electron temperature. When it is determined by the cool electron temperature and the hot electron temperature is high enough the critical electron emission current from the collector can have a very pronounced local maximum and a minimum when regarded as a function of the electrode potential. Because of that the current voltage characteristics of the electrode may exhibit up to 3 different floating potentials. This result is in good agreement with the experimental observations reported in [J. Appl. Phys. 63, 5674 (1988)].     

Analyses of edge plasma characteristics in HL-2A

The edge plasma characteristics are studied by both a movable array of Mach/Reynolds stress/Langmuir 10-probes in the boundary region and the fixed flush probe arrays on the 4 divertor neutralization plates at the same toroidal cross-section in the HL-2A tokamak. The dependence of the Reynolds stress on poloidal flow in the edge plasma is analysed. The result indicates that the sheared poloidal flow in tokamak plasma can be induced by the radial gradient of Reynolds stress. In the divertor experiments of HL-2A, the profiles of the electron temperature, density and floating potential on divertor plates are measured by the flush probe arrays. The edge electron temperature in divertor configuration is higher than that in limiter configuration. The temperature asymmetry between outer and inner target plates is observed. The result of magnetic surface reconstructed from 18 Mirnov coils signals is presented. Both the particle recycling and the impurity flux in the bulk plasma during divertor discharges are discussed. Neutral gas pressure in divertor chamber, measured by fast ionization gauge during divertor discharge, is given.     

Heterodyne detection for Fiber Bragg Grating sensors

In this paper, we present a Fiber-Bragg-Grating-based temperature sensor. The technique employs heterodyne detection using two Fiber Bragg Gratings. One of the gratings is used as a reference (local oscillator) and the second as a sensing arm. This sensor uses a Folded Mach-Zehnder interferometer. As the temperature changes, the Bragg wavelength of the FBG shifts. The heterodyne detection is used to detect the frequency difference between the reference and sensing signals that is caused by the temperature change. The dynamic range and sensitivity of the sensor were analyzed and presented.     

Laser cutting of sharp edge: Thermal stress analysis

Laser cutting of sharp edge and thermal stress development in the cutting section is examined. The finite element method is used to predict temperature and stress fields while the X-ray diffraction (XRD) technique is used to measure the residual stress around the cut edges. A mild steel sheet with 5 mm thickness is used in the simulations and the experiment. The morphological and metallurgical changes around the edges are examined using the optical microscopy and scanning electron microscopy (SEM). It is found that temperature remains high at the sharp edge when the laser beam is located in this region. This, in turn, lowers the cooling rate and reduces von Mises stress in this region. The magnitude of the residual stress is about 90 MPa at the sharp corner while the maximum von Mises stress is in the order of 280 MPa, which occurs away from sharp corner. In addition, the residual stress predicted agrees with the experimental data.     

Heterodyne mixing of laser fields for temporal gating of high-order harmonic generation

The concept of heterodyne mixing of laser fields is theoretically applied to the process of high-harmonic generation to enhance and modulate the kinetic energy of the active electron on subcycle time scales. A very small amount of intensity in the heterodyne field creates a significant modification of the electron kinetic energy, due to its amplification by the strong fundamental field in the kinetic-energy term, in which the heterodyne mixing occurs. Quantum calculations are carried out to verify the predictions of the classical results, demonstrating very good qualitative and quantitative agreement. Applications of the heterodyne-mixing concept are the extension of the harmonic cutoff to higher photon energies and the temporal gating of attosecond pulse production.     

Nonlinear simulations of peeling-ballooning modes with anomalous electron viscosity and their role in edge localized mode crashes

A minimum set of equations based on the peeling-ballooning (P-B) model with nonideal physics effects (diamagnetic drift, E×B drift, resistivity, and anomalous electron viscosity) is found to simulate pedestal collapse when using the new BOUT++ simulation code, developed in part from the original fluid edge code BOUT. Nonlinear simulations of P-B modes demonstrate that the P-B modes trigger magnetic reconnection, which leads to the pedestal collapse. With the addition of a model of the anomalous electron viscosity under the assumption that the electron viscosity is comparable to the anomalous electron thermal diffusivity, it is found from simulations using a realistic high-Lundquist number that the pedestal collapse is limited to the edge region and the edge localized mode (ELM) size is about 5%-10% of the pedestal stored energy. This is consistent with many observations of large ELMs.     

Remote sensing with infra-red heterodyne radiometers

The narrow spectral bandwidth capability of heterodyne radiometers can be utilized to construct highly selective pollutant sensing instruments. The infra-red spectral region is favourable due to the availability of pollutant absorption lines and the wavelength dependence of heterodyne sensitivity. We review the types of sensing systems which can make use of heterodyne techniques, including comments about the type of lasers which can serve as local oscillators. Sensitivity calculations of passive heterodyne radiometers to NO, CO₂, and SO₂ are then presented. Our concluding discussion involves the use of a heterodyne receiver in an active NO sensing system which is based on infra-red fluorescence.