Simultaneous projection and detection system of four different frequencies for microwave imaging reflectometry in Large Helical Device

A simultaneous projection/detection system of four different frequencies for microwave imaging reflectometry (MIR) was developed for three-dimensional observation of electron density fluctuations in the Large Helical Device (LHD). The microwave with four frequency components at 60.410, 61.808, 63.008, and 64.610 GHz is projected in a continuous-wave mode to illuminate the target LHD plasma. A two-dimensional horn-antenna mixer array (2D HMA) receives the reflected wave from the plasma as well as the wave from the local oscillator operating at 55.800 GHz. The first intermediate frequency (IF) signals at 4.610, 6.008, 7.208, and 8.810 GHz were confirmed to be obtained by downconversion of these microwaves using the 2D HMA. Each of these first IF components is filtered from each other and downconverted again for the superheterodyne detection. It was confirmed that both the amplitudes and the phases of the detected signals reflect the fluctuations in LHD plasmas.     

Electron cyclotron emission diagnostics on KSTAR tokamak

A new electron cyclotron emission (ECE) diagnostics system was installed for the Second Korea Superconducting Tokamak Advanced Research (KSTAR) campaign. The new ECE system consists of an ECE collecting optics system, an overmode circular corrugated waveguide system, and 48 channel heterodyne radiometer with the frequency range of 110-162 GHz. During the 2 T operation of the KSTAR tokamak, the electron temperatures as well as its radial profiles at the high field side were measured and sawtooth phenomena were also observed. We also discuss the effect of a window on in situ calibration.     

Intermediate frequency band digitized high dynamic range radiometer system for plasma diagnostics and real-time Tokamak control

An intermediate frequency (IF) band digitizing radiometer system in the 100-200 GHz frequency range has been developed for Tokamak diagnostics and control, and other fields of research which require a high flexibility in frequency resolution combined with a large bandwidth and the retrieval of the full wave information of the mm-wave signals under investigation. The system is based on directly digitizing the IF band after down conversion. The enabling technology consists of a fast multi-giga sample analog to digital converter that has recently become available. Field programmable gate arrays (FPGA) are implemented to accomplish versatile real-time data analysis. A prototype system has been developed and tested and its performance has been compared with conventional electron cyclotron emission (ECE) spectrometer systems. On the TEXTOR Tokamak a proof of principle shows that ECE, together with high power injected and scattered radiation, becomes amenable to measurement by this device. In particular, its capability to measure the phase of coherent signals in the spectrum offers important advantages in diagnostics and control. One case developed in detail employs the FPGA in real-time fast Fourier transform (FFT) and additional signal processing. The major benefit of such a FFT-based system is the real-time trade-off that can be made between frequency and time resolution. For ECE diagnostics this corresponds to a flexible spatial resolution in the plasma, with potential application in smart sensing of plasma instabilities such as the neoclassical tearing mode (NTM) and sawtooth instabilities. The flexible resolution would allow for the measurement of the full mode content of plasma instabilities contained within the system bandwidth.     

Measure of electron cyclotron emission at multiple angles in high T(e) plasmas of JET

The oblique electron cyclotron emission (ECE) diagnostic installed at JET allows simultaneous analysis of the ECE spectra along three lines of sight (with toroidal angles of 0°, ～ 10°, and ～ 20°) and two linear polarizations for each oblique line of sight. The diagnostic is capable of measuring EC emission over the band of 75–800 GHz with 5 ms time resolution and 7.5 GHz spectral resolution, and it is designed to investigate the features of ECE spectra related to electron distribution in the thermal velocity range. Instrumental accuracy was assessed using sources at different temperatures (77–900 K) and with plasma emission. ECE from high temperature plasmas and in the presence of fast ions has been compared to simulations performed with the modeling code SPECE, setting an upper limit to possible discrepancies from thermal emission.     

Relatively scaled ECE temperature profiles of KSTAR plasmas

A scheme to obtain relatively scaled profiles of electron cyclotron emission (ECE) temperature directly from uncalibrated raw radiometer data is proposed and has been tested for the 2009 campaign KSTAR plasmas. The proposed method utilizes a position controlled system to move the plasma adiabatically and compares ECE radiometer channels at the same relative radial positions assuming the profile consistency during the adiabatic change. This scaling method is an alternative solution when an absolute calibration is unreliable or too time consuming. The application to the two dimensional ECE imaging data, wherein calibration is extremely difficult, may also prove to be useful.     

Development of KSTAR ECE imaging system for measurement of temperature fluctuations and edge density fluctuations

The ECE imaging (ECEI) diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport [H. K. Park, N. C. Luhmann, Jr., A. J. H. Donne? et al., Phys. Rev. Lett. 96, 195003 (2006)]. An improved ECEI system capable of visualizing both high- and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfve?n eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.     

Computer simulation of adaptive optics for laser systems in atmospheric applications

Software for computer simulations of adaptive optics systems for atmospheric laser applications designed on the basis of advanced parallel programming techniques is developed. The adaptive optics system model includes the emitting aperture geometry and beam propagation path scenario, vertical profiles of atmospheric parameters, fast parallel split-step Fourier algorithm for solving wave diffraction and propagation equations, time-dependent models of “frozen” atmospheric turbulence with a wide range of scales, and models of the wavefront sensor and controlled deformable mirror. The hardware system for computer simulations is an off-the-shelf desktop with a 6-core 12-thread Intel® Core? i7-970 CPU at the maximum frequency of 3.5 GHz and an NVIDIA® GeForce GTX 580 graphic accelerator with 512 universal processors operating at 1.5 GHz. Results of simulations of adaptive imaging and laser beam shaping, aimed at estimating the efficiency of adaptive optics systems on atmospheric paths are presented.     

Millimeter-wave radiometer diagnostics of harmonic electron cyclotron emission in the Levitated Dipole Experiment

A 110/137 GHz radiometer pair with collimated antenna pattern is being used to diagnose optically thin harmonic electron cyclotron emission from hot electrons in LDX. Signal levels of 0.1-1 keV and 110/137 ratios of 2-4 stationary with ECRH power have been observed. The large plasma core magnetic field gradient causes all relevant harmonics to be simultaneously viewed over a angle(k,B) angular range of 0°-90° representing a unique geometry for interpretation of ECE in terms of hot electron temperature and density.     

A High-Speed Continuous Wave GPR

In this work an innovative high speed continuous wave stepped frequency GPR has been designed and implemented with the aim of overcoming the low speed issue of wide bandwidth CW-SF GPRs. It is based on a structure combining a Digital Direct Synthesizer (DDS), a Phase Lock Loop (PLL) and a quadrature modulator (I/Q Modulator). The radar is an L-S band GPR able to scan a 1 GHz bandwidth (1500–2500 MHz) with 200 steps in 10 ms. The system has been developed for automatic synthetic aperture radar (SAR) imaging of historical-artistic interest structures. Some system tests and laboratory tests on a realistic masonry setup were carried out in order to asses the performances of this system.     

Multipixel system for gigahertz frequency-domain optical imaging of finger joints

Frequency-domain optical imaging systems have shown great promise for characterizing blood oxygenation, hemodynamics, and other physiological parameters in human and animal tissues. However, most of the frequency domain systems presented so far operate with source modulation frequencies below 150 MHz. At these low frequencies, their ability to provide accurate data for small tissue geometries such as encountered in imaging of finger joints or rodents is limited. Here, we present a new system that can provide data up to 1 GHz using an intensity modulated charged coupled device camera. After data processing, the images show the two-dimensional distribution of amplitude and phase of the light modulation on the finger surface. The system performance was investigated and test measurements on optical tissue phantoms were taken to investigate whether higher frequencies yield better signal-to-noise ratios (SNRs). It could be shown that local changes in optical tissue properties, as they appear in the initial stages of rheumatoid arthritis in a finger joint, are detectable by simple image evaluation, with the range of modulation frequency around 500 MHz proving to yield the highest SNR.     

Detecting non-maxwellian electron velocity distributions at JET by high resolution Thomson scattering

The present work is motivated by a long standing discrepancy between the electron temperature measurements of Thomson scattering (TS) and electron cyclotron emission (ECE) diagnostics for plasmas with strong auxiliary heating observed at both JET and TFTR above 6–7 keV, where in some cases the ECE electron temperature measurements can be 15%–20% higher than the TS measurements. Recent analysis based on ECE results at JET has shown evidence of distortions to the Maxwellian electron velocity distribution and a correlation with the TS and ECE discrepancies has been suggested. In this paper, a technique to determine the presence of non-Maxwellian behavior using TS diagnostics is outlined. The difficulties and limitations of modern TS system designs to determine the electron velocity distribution are also discussed. It is demonstrated that small deviations such as those suggested by previous ECE analysis could be potentially detected, depending on the spectral layout of the TS polychromators. The spectral layout of the JET high resolution Thomson scattering system is such that it could be used to determine these deviations between 1 and 6 keV, and the results presented here indicate that no evidence of non-Maxwellian behavior is observed in this range. In this paper, a modification to the current polychromator design is proposed, allowing non-Maxwellian distortions to be detected up to at least 10 keV.     

Broadband dielectric microwave microscopy on micron length scales

We demonstrate that a near-field microwave microscope based on a transmission line resonator allows imaging in a substantially wide range of frequencies, so that the microscope properties approach those of a spatially resolved impedance analyzer. In the case of an electric probe, the broadband imaging can be used in a direct fashion to separate contributions from capacitive and resistive properties of a sample at length scales on the order of one micron. Using a microwave near-field microscope based on a transmission line resonator we imaged the local dielectric properties of a focused ion beam milled structure on a high-dielectric-constant Ba(0.6)Sr(0.4)TiO(3) thin film in the frequency range from 1.3 to 17.4 GHz. The electrostatic approximation breaks down already at frequencies above approximately 10 GHz for the probe geometry used, and a full-wave analysis is necessary to obtain qualitative information from the images.     

A near-field scanning microwave microscope for characterization of inhomogeneous photovoltaics

We present a near-field scanning microwave microscope (NSMM) that has been configured for imaging photovoltaic samples. Our system incorporates a Pt-Ir tip inserted into an open-ended coaxial cable to form a weakly coupled resonator, allowing the microwave reflection S(11) signal to be measured across a sample over a frequency range of 1 GHz - 5 GHz. A phase-tuning circuit increased impedance-measurement sensitivity by allowing for tuning of the S(11) minimum down to -78 dBm. A bias-T and preamplifier enabled simultaneous, non-contact measurement of the DC tip-sample current, and a tuning fork feedback system provided simultaneous topographic data. Light-free tuning fork feedback provided characterization of photovoltaic samples both in the dark and under illumination at 405 nm. NSMM measurements were obtained on an inhomogeneous, third-generation Cu(In,Ga)Se(2) (CIGS) sample. The S(11) and DC current features were found to spatially broaden around grain boundaries with the sample under illumination. The broadening is attributed to optically generated charge that becomes trapped and changes the local depletion of the grain boundaries, thereby modifying the local capacitance. Imaging provided by the NSMM offers a new RF methodology to resolve and characterize nanoscale electrical features in photovoltaic materials and devices.     

A broadband ferromagnetic resonance spectrometer to measure thin films up to 70 GHz

We report the development of a broadband ferromagnetic resonance (FMR) system operating in the frequency range from 10 MHz to 70 GHz using a closed-cycle He refrigeration system for measurements of thin films and micron/nano structures. The system is capable of carrying out measurements in frequency and field domain. Using two coplanar waveguides, it is capable of simultaneously measuring two samples in the out of plane and in plane FMR geometries. The system operates in the temperature range of 27-350 K and is sensitive to less than one atomic monolayer of a single crystal Fe film.     

High coherent bi-chromatic laser with gigahertz splitting produced by the high diffraction orders of acousto-optic modulator used for coherent population trapping experiments

To prepare the coherent population trapping (CPT) states with rubidium and cesium, the commonly used atoms in CPT studies, a coherent bi-chromatic light field with frequency difference of several GHz is a basic requirement. With a 200 MHz center frequency acousto-optic modulator (AOM), we have realized bi-chromatic laser fields with several GHz frequency splits through high diffraction orders. We have experimentally studied the coherence between two frequency components of a bi-chromatic laser beam, which is composed of ±6 orders with frequency split of 3 GHz diffracted from the same laser beam, and the measured residual phase noise is Δφ(2)<0.019 rad(2). The bi-chromatic laser fields were used to prepare CPT states with (85)Rb and (87)Rb atoms, and high contrast CPT signals were obtained. For CPT states preparation, our study result shows that it is a feasible approach to generate the bi-chromatic light field with larger frequency splits through high diffraction orders of AOM.     

对某城市越野车车外加速噪声的降噪试验研究

针对某城市越野车车外加速噪声超出欧标ECE R51-02的规定限值的状况,通过试验研究,综合运用噪声源识别方法,识别出进气系统噪声和动力总成系统噪声是造成车外加速噪声偏高的主要原因。根据噪声源的特性采取降噪措施,使被测车辆车外加速噪声下降了5.33dB(A),满足了ECE R51-02对该类车车外加速噪声限值的要求。     

Quasioptical design of integrated Doppler backscattering and correlation electron cyclotron emission systems on the DIII-D tokamak

The quasioptical design of a new integrated Doppler backscattering (DBS) and correlation electron cyclotron emission (CECE) system is presented. The design provides for simultaneous measurements of intermediate wavenumber density and long wavelength electron temperature turbulence behavior. The Doppler backscattering technique is sensitive to plasma turbulence flow and has been utilized to determine radial electric field, geodesic acoustic modes, zonal flows, and intermediate scale (k～1-6?cm(-1)) density turbulence. The correlation ECE system measures a second turbulent field, electron temperature fluctuations, and is sensitive to long poloidal wavelength (k≤1.8?cm(-1)). The integrated system utilizes a newly installed in-vessel focusing mirror that produces a beam waist diameter of 3.5-5 cm in the plasma depending on the frequency. A single antenna (i.e., monostatic operation) is used for both launch and receive. The DBS wavenumber is selected via an adjustable launch angle and variable probing frequency. Due to the unique system design both positive and negative wavenumbers can be obtained, with a range of low to intermediate wavenumbers possible (approximately -3 to 10?cm(-1)). A unique feature of the design is the ability to place the DBS and CECE measurements at the same radial and poloidal locations allowing for cross correlation studies (e.g., measurement of nT cross-phase).     

光电成像系统的性能优化

探讨了光学系统和阵列探测器构成的光电成像系统的整体性能和优化设计问题。针对阵列探测器的不断快速更新换代,研究了如何对光学系统进行改进以优化光电成像系统的性能。从采样成像系统的取样定理出发,研究了光电成像系统的传递函数特性,讨论了采样成像系统的相位平均传递函数,分析了光电成像系统的加工与使用误差对传递函数的影响。同时,给出了光电成像系统的信噪比计算公式。文中提出用于遥感观测的大型光电成像系统的光学系统传递函数的归一化空间频率等于0.5左右可与阵列探测器的奈奎斯特频率相匹配。结果显示,如此设计可在满足信噪比的同时使传递函数在奈奎斯特频率处达到0.1左右,分辨率达到奈奎斯特频率并且不产生频谱混叠效应。     

Efficiency characteristics of piezostack pump for linear actuators

A piezostack pump for linear actuators is presented and studied in terms of mechanical energy efficiency (MEE), energy conversion efficiency (ECE) and design method. MEE is defined as the ratio of the output mechanical energy to that converted from input electrical energy, and ECE is the ratio of output mechanical energy to input electrical energy. The analysis results show that both MEE and ECE decrease with the increase of stiffness of the chamber diaphragm (k_s), which is a function of the radius ratio (rigid disk radius to chamber radius). There is respective optimal external load (F_c) for them to achieve peak value for a given piezostack with blocked force (F_b) and stiffness (k_a). The optimal force ratio (F_c/F_b) is a constant of 0.5 for maximum MEE, and between 0.57 and 0.5 for maximum ECE. Considering the deflection of the pump chamber and dynamic response of the piezostack, the stiffness ratio (k_s/k_a) should be limited between 0.3 and 1, and the relative radius ratio is between 0.7 and 0.8. With the increase of the radius ratio in the range, the maximal MEE decreases from 0.38 to 0.25, and the peak ECE decreases from 0.20 to 0.14.     

Precisely tunable continuous-wave terahertz source with interferometric frequency control

We realized a tunable continuous-wave terahertz source with megahertz frequency resolution. The system is based on optical heterodyning of two near-infrared distributed feedback diode lasers, each laser being stabilized by electronic feedback from a low-finesse quadrature interferometer. The control loop permits precisely linear laser frequency scans over >1200 GHz, and a beat signal linewidth of 1 MHz at 80 ms time scale. Using GaAs photomixers and log-periodic antennae, we achieve a signal-to-noise ratio of the terahertz power of >70 dB at 100 GHz and 100 ms integration time, and still approximately 30 dB at 1 THz. As an example for high-resolution terahertz spectroscopy, we characterize the transmission properties of a subwavelength metal grating.