Fast-ion Dα measurements of the fast-ion distribution (invited)

The fast-ion Dα (FIDA) diagnostic is an application of charge-exchange recombination spectroscopy. Fast ions that neutralize in an injected neutral beam emit Balmer-α light with a large Doppler shift. The spectral shift is exploited to distinguish the FIDA emission from other bright sources of Dα light. Background subtraction is the main technical challenge. A spectroscopic diagnostic typically achieves temporal, energy, and transverse spatial resolution of ～1?ms, ～10?keV, and ～2?cm, respectively. Installations that use narrow-band filters achieve high spatial and temporal resolution at the expense of spectral information. For high temporal resolution, the bandpass-filtered light goes directly to a photomultiplier, allowing detection of ～50?kHz oscillations in FIDA signal. For two-dimensional spatial profiles, the bandpass-filtered light goes to a charge-coupled device camera; detailed images of fast-ion redistribution at instabilities are obtained. Qualitative and quantitative models relate the measured FIDA signals to the fast-ion distribution function. The first quantitative comparisons between theory and experiment found excellent agreement in beam-heated magnetohydrodynamics (MHD)-quiescent plasmas. FIDA diagnostics are now in operation at magnetic-fusion facilities worldwide. They are used to study fast-ion acceleration by ion cyclotron heating, to detect fast-ion transport by MHD modes and microturbulence, and to study fast-ion driven instabilities.     

Masking a CCD camera allows multichord charge exchange spectroscopy measurements at high speed on the DIII-D tokamak

Charge exchange spectroscopy is one of the standard plasma diagnostic techniques used in tokamak research to determine ion temperature, rotation speed, particle density, and radial electric field. Configuring a charge coupled device (CCD) camera to serve as a detector in such a system requires a trade-off between the competing desires to detect light from as many independent spatial views as possible while still obtaining the best possible time resolution. High time resolution is essential, for example, for studying transient phenomena such as edge localized modes. By installing a mask in front of a camera with a 1024 × 1024 pixel CCD chip, we are able to acquire spectra from eight separate views while still achieving a minimum time resolution of 0.2 ms. The mask separates the light from the eight spectra, preventing spatial and temporal cross talk. A key part of the design was devising a compact translation stage which attaches to the front of the camera and allows adjustment of the position of the mask openings relative to the CCD surface. The stage is thin enough to fit into the restricted space between the CCD camera and the spectrometer endplate.     

Scintillator-based diagnostic for fast ion loss measurements on DIII-D

A new scintillator-based fast ion loss detector has been installed on DIII-D with the time response (>100?kHz) needed to study energetic ion losses induced by Alfve?n eigenmodes and other MHD instabilities. Based on the design used on ASDEX Upgrade, the diagnostic measures the pitch angle and gyroradius of ion losses based on the position of the ions striking the two-dimensional scintillator. For fast time response measurements, a beam splitter and fiberoptics couple a portion of the scintillator light to a photomultiplier. Reverse orbit following techniques trace the lost ions to their possible origin within the plasma. Initial DIII-D results showing prompt losses and energetic ion loss due to MHD instabilities are discussed.     

Measurement of the D alpha spectrum produced by fast ions in DIII-D

Fast ions are produced by neutral beam injection and ion cyclotron heating in toroidal magnetic fusion devices. As deuterium fast ions orbit around the device and pass through a neutral beam, some deuterons neutralize and emit D(alpha) light. For a favorable viewing geometry, the emission is Doppler shifted away from other bright interfering signals. In the 2005 campaign, we built a two channel charge-coupled device based diagnostic to measure the fast-ion velocity distribution and spatial profile under a wide variety of operating conditions. Fast-ion data are acquired with a time resolution of approximately 1 ms, spatial resolution of approximately 5 cm, and energy resolution of approximately 10 keV. Background subtraction and fitting techniques eliminate various contaminants in the spectrum. Neutral particle and neutron diagnostics corroborate the D(alpha) measurement. Examples of fast-ion slowing down and pitch angle scattering in quiescent plasma and fast-ion acceleration by high harmonic ion cyclotron heating are presented.     

A tangentially viewing fast ion D-alpha diagnostic for NSTX

A second fast ion D-alpha (FIDA) installation is planned at NSTX to complement the present perpendicular viewing FIDA diagnostics. Following the present diagnostic scheme, the new diagnostic will consist of two instruments: a spectroscopic diagnostic that measures fast ion spectra and profiles at 16 radial points with 5-10 ms resolution and a system that uses a band pass filter and photomultiplier to measure changes in FIDA light with 50 kHz sampling rate. The new pair of FIDA instruments will view the heating beams tangentially. The viewing geometry minimizes spectral contamination by beam emission or edge sources of background emission. The improved velocity-space resolution will provide detailed information about neutral-beam current drive and about fast ion acceleration and transport by injected radio frequency waves and plasma instabilities.     

Development of two-grating spectrometer for the charge exchange spectroscopy system on KSTAR

The charge exchange spectroscopy (CES) system on Korea Superconducting Tokamak Advanced Research (KSTAR) was installed last year and had been applied to measure the C VI ion temperature and rotation velocity profiles. The ion temperature and rotation velocity profiles had been estimated from the C VI 5290.5 ? (n = 8-7) charge-exchange spectrum signal measured by a Czerny-Turner type spectrometer and a thinned back-illuminated charge coupled device (CCD) camera. However, the Czerny-Turner type spectrometer used for the KSTAR CES system showed so low signal to noise ratio for KSTAR plasmas in the 2010 experimental campaign that the time resolution of the CES system had been limited to 100 ms due to the increased exposure time of the attached CCD camera. Then, new two-grating spectrometer had been developed in order to improve the time resolution of the CES system. The spectrometer consists of two gratings (1200 g/mm and 1800 g/mm each) with additive configuration, concave mirrors (f = 50 cm), and a cylindrical lens (f = 50 cm). The time resolution of the CES system increases by a factor of 2-4 with the two-grating spectrometer. The C VI ion temperature and rotation velocity profiles obtained by the two-grating spectrometer are compared to those by Czerny-Turner type spectrometer in this paper.     

高分辨宽光谱微型拉曼光谱仪的设计

为了同时满足光谱分辨率、光谱范围、探测器(CCD)上光谱信号覆盖区域要求,提出一种基于Czerny-Turner(CT)结构拉曼光谱仪的综合设计方法,通过Zemax软件采用逐步手动调节光栅倾斜,自动优化聚焦镜、柱面镜以及CCD间倾角和距离的方式,设计出全波段光谱分辨率优于4cm-1,光谱波数范围为80~3 967cm~(-1),光学结构尺寸为90mm×130mm×40mm的微型拉曼光谱仪。     

SAR光学处理器输出图像的实时处理装置

合成孔径雷达获得的图像是一种准全息图像。它通过光学相关器转换成可见光图像信息。本论文研究的内容是把这种光图像信息,在通用的监视器上实时显示的转换装置。它由光学系统、线阵CCD像机和帧存储实时显示系统三个部分组成。光学相关器输出的光图像信号通过光学系统成像在线阵CCD像敏元上,并转换成电信号,通过帧存储实时显示系统按照电视体制输出,在监视器上实时显示。图像的各种显示方式由单片机控制。     

A fast beam switch for controlling the intensity in electron energy loss spectrometry

The fast deflection system described in this paper is suitable for controlling the intensity reaching the detector of a magnetic sector electron spectrometer mounted below an analytical transmission electron microscope. Amongst other things, this allows the low loss region of the spectrum to be recorded with the same electron probe conditions used to record core losses, something that is essential for high spatial resolution studies. The plate assembly restricts the width of the electron distribution reaching the viewing screen to a strip approximately 17 mm wide in the direction approximately normal to the dispersion direction of the spectrometer. The resulting deflection has no detectable effect on the FWHM of the zero-loss peak for exposure times as short as 1 micros. At incident energies up to 300 keV, positioning the deflection plates in the 35 mm camera port above the viewing chamber allows voltages of < +/- 3 kV to deflect the electrons out of the spectrometer and beyond the edge of the annular detector. When the deflection is switched on, the electrons are deflected out of the spectrometer in < 40 ns and when the deflection is switched off, the electrons return to within 10 microm of the undeflected position within 100 ns. Thus, even at an exposure time of 30 micros, the smallest time likely to be used in practice with a GATAN 666 spectrometer, < 1% of the signal in the spectrum is from electrons whose scattering conditions differ from those in the undeflected position. The performance of the deflection system is such that it will also be suitable for use with the new and much faster GATAN ENFINA spectrometer system. At incident energies up to 200 keV and possibly up to 300 keV, deflection voltages of +/- 3 kV are sufficient to deflect the electrons off a 1 k x 1 k charge coupled device (CCD) camera placed below the photographic camera. Thus the deflection system can be used as a very fast, non-mechanical shutter for such a CCD camera.     

Design and performance of the collective Thomson scattering receiver at ASDEX Upgrade

Here we present the design of the fast-ion collective Thomson scattering receiver for millimeter wave radiation installed at ASDEX Upgrade, a tokamak for fusion plasma experiments. The receiver can detect spectral power densities of a few eV against the electron cyclotron emission background on the order of 100 eV under presence of gyrotron stray radiation that is several orders of magnitude stronger than the signal to be detected. The receiver down converts the frequencies of scattered radiation (100-110 GHz) to intermediate frequencies (IF) (4.5-14.5 GHz) by heterodyning. The IF signal is divided into 50 IF channels tightly spaced in frequency space. The channels are terminated by square-law detector diodes that convert the signal power into DC voltages. We present measurements of the transmission characteristics and performance of the main receiver components operating at mm-wave frequencies (notch, bandpass, and lowpass filters, a voltage-controlled variable attenuator, and an isolator), the down-converter unit, and the IF components (amplifiers, bandpass filters, and detector diodes). Furthermore, we determine the performance of the receiver as a unit through spectral response measurements and find reasonable agreement with the expectation based on the individual component measurements.     

Thomson scattering diagnostic upgrade on DIII-D

The DIII-D Thomson scattering system has been upgraded. A new data acquisition hardware was installed, adding the capacity for additional spatial channels and longer acquisition times for temperature and density measurements. Detector modules were replaced with faster transimpedance circuitry, increasing the signal-to-noise ratio by a factor of 2. This allows for future expansion to the edge system. A second phase upgrade scheduled for 2010-2011 includes the installation of four 1 J/pulse Nd:YAG lasers at 50 Hz repetition rate. This paper presents the first completed phase of the upgrade and performance comparison between the original system and the upgraded system. The plan for the second phase is also presented.     

Modeling the response of a fast ion loss detector using orbit tracing techniques in a neutral beam prompt-loss study on the DIII-D tokamak

A numerical model describing the expected measurements of neutral beam prompt-losses by a newly commissioned fast ion loss detector (FILD) in DIII-D is presented. This model incorporates the well understood neutral beam deposition profiles from all eight DIII-D beamlines to construct a prompt-loss source distribution. The full range of detectable ion orbit phase space available to the FILD is used to calculate ion trajectories that overlap with neutral beam injection footprints. Weight functions are applied to account for the level of overlap between these detectable orbits and the spatial and velocity (pitch) properties of ionized beam neutrals. An experimental comparison is performed by firing each neutral beam individually in the presence of a ramping plasma current. Fast ion losses determined from the model are in agreement with measured losses.     

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS)

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, Phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.     

CCD数字像元的合并方法及其应用

星载差分吸收光谱仪中的科学级帧转移型电荷耦合器件(CCD)通常使用四行像元合并(4-Binning)方法提升载荷的信噪比,但该方法仅能工作在目标光强较弱的环境。为使载荷适应目标光线较强的环境,设计了数字像元合并方法(4-AVR)来提升载荷的探测能力。考虑相对常规的4-Binning方法,4-AVR方法会产生CCD信号衰减现象,故对这一现象进行了理论分析,得到由于CCD读出速率导致的信号衰减系数为0.699。在实验室搭建了测试装置,验证了上述结果,结果表明,4-AVR方法下获取的CCD像素值相对于4-Binning方法获取的像素值的衰减系数为0.698,从而证实了理论分析的正确性。实验显示,使用这一系数可完成对4-AVR方式下获取的像素值的校正,从而实现两种方法的无差别化。将校正方法作为载荷一级数据处理的一部分,进行了大气痕量气体的反演测试。结果表明数字像元合并方法可保证大气痕量气体的反演精度,进一步验证了数字像元合并方法的可靠性。     

An optical spectrometer for a confocal scanning laser microscope

An optical spectrometer for the visible range has been developed for the confocal scanning laser microscope (CSLM) Phoibos 1000. The spectrometer records information from a single point or a user-defined region within the microscope specimen. A prism disperses the spectral components of the recorded light over a linear CCD photodiode array with 256 elements. A regulated cooling unit cools the diode array, thereby reducing the detector dark current to a level, which allows integration times of up to 60 s. The spectral resolving power, λ/Δλ, ranges from 400 at λ = 375 nm to 100 at λ = 700 nm. Since the entrance aperture of the spectrometer has the same diameter as the detector aperture of the CSLM, the three-dimensional spatial resolution for spectrometer readings is equivalent to that of conventional confocal scanning, that is, down to 0.2 μm lateral and 0.8 μm axial resolution with an N.A.=1.3 objective.     

A light-emitting diode monitoring system of the PHOS photon spectrometer in the ALICE experiment on the large hadron collider

A light-emitting diode (LED) monitoring system of the PHOS photon spectrometer in the ALICE experiment on the CERN large hadron collider is described. The spectrometer includes three modules in the form of 64 × 56 matrices consisting of plumbum tungstate (PWO) crystals. As test light signal sources, Kingbright L934SCC superbright green light-emitting diodes with an individual instrumental regulation of light flash intensities in each channel of the spectrometer are used. The system ensures adjustment and monitoring of the electronics at the stage of preparing for the physical trigger of the PHOS modules and is intended to perform special test measurements with the spectrometer without using high-energy particles. In addition, in the course of the experiment, it allows one to promptly monitor each channel of the spectrometer and keep track of temperature variations of the light yield of the PWO crystals. In this case, the long-term relative channel monitoring stability is ensured at a 1.2 × 10⁻³ level.     

Design and application of wireless signal strength measurement system on the near-ground

The wireless communication system’s performance is greatly constrained by the wireless channel characteristics,especially in some specific environment.Therefore,signal transmission will be greatly impacted even if not in a complicated topography.Testing results show that it is hardly to characterize the radio propagation properties for the antenna installed on the ground.In order to ensure a successful communication,the radio frequency(RF)wireless signal intensity monitor system was designed.We can get the wireless link transmission loss through measuring signal strength from received node.The test shows that the near-ground wireless signal propagation characteristics still can be characterized by the log distance propagation loss model.These results will conduce to studying the transmission characteristic of Near-Earth wireless signals and will predict the coverage of the earth’s surface wireless sensor network.     

便携式光谱仪的CCD智能检测器设计

光谱仪是一种重要的检测仪器,CCD光谱仪正朝着小型化甚至微型化的方向发展。针对便携式光谱仪的特点及要求提出一种光谱仪CCD智能检测器设计方案,它结合了单片机智能化控制的特点和CPLD时序准确、可编程的优点。并且该检测器集成了USB数据接口,可通过计算机软件进行光谱采集,并能实时控制积分时间,实现了光谱仪CCD检测器的小型化、智能化和集成化。     

A synthetic diagnostic for the evaluation of new microwave imaging reflectometry diagnostics for DIII-D and KSTAR

The first microwave imaging reflectometry (MIR) system for characterization of fluctuating plasma density has been implemented for the TEXTOR tokamak [H. Park et al., Rev. Sci. Instrum. 75, 3787 (2004)]; an improved MIR system will be installed on DIII-D and KSTAR. The central issue remains in preserving phase information by addressing antenna coupling between the reflection layer and the detector array in the presence of plasma turbulence. A synthetic diagnostic making use of coupled full-wave diffractive codes has been developed in geometries and applied to a variety of optical arrangements. The effectiveness of each scheme is quantitatively compared with respect to the fluctuation levels accessible in the simulation.     

平板式光谱仪的结构设计

光谱仪的平板化,可以扩大仪器使用范围。本文主要研究一种基于CCD的平板式光谱仪的结构设计。使用合适的光纤、光栅、反射镜和CCD,通过理论计算,引入聚焦反射和分光,将色散光投射到CCD,简化结构。不同于传统的垂直光电隔离式设计,采用平面光电隔离式设计,使光谱仪厚度明显减小,光电分离式设计进一步提高了仪器应用的灵活性。