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A two-dimensional scanning probe instrument has been developed to survey spatial plasma characteristics in our electrodeless plasma acceleration schemes. In particular, diagnostics of plasma parameters, e.g., plasma density, temperature, velocity, and excited magnetic field, are essential for elucidating physical phenomena since we have been concentrating on next generation plasma propulsion methods, e.g., Rotating Magnetic Field plasma acceleration method, by characterizing the plasma performance. Moreover, in order to estimate the thrust performance in our experimental scheme, we have also mounted a thrust stand, which has a target type, on this movable instrument, and scanned the axial profile of the thrust performance in the presence of the external magnetic field generated by using permanent magnets, so as to investigate the plasma captured in a stand area, considering the divergent field lines in the downstream region of a generation antenna. In this paper, we will introduce the novel measurement instrument and describe how to measure these parameters. [ABSTRACT FROM AUTHOR]

Tokamak fusion test reactor (TFTR) probes are designed to study the interaction of the plasma with material surfaces such as the wall and limiters, and to study the transport of particles and energy between the core and edge. Present probe heads have evolved from prototypes in Princeton large toms (PLT), poloidal divertor experiment (PDX [Princeton BETA experiment (PBX)], and the initial phase of TFTR operation. The newest heads are capable of making several simultaneous measurements and include Langmuir probes, heat flux probes, magnetic coils, rotating calorimeter fast ion probes, and sample exposure specimens. This paper describes these probe heads and presents some of the data they and their prototypes have acquired. The paper emphasizes measurement of transient plasma effects such as fast ion loss during auxiliary heating, the evolution of the edge plasma during heating, compression, and free expansion, and fluctuations in the edge plasma. [ABSTRACT FROM AUTHOR]

One of the main diagnostic tools for measuring electron density profiles and the characteristics of long wavelength turbulent wave structures in fusion plasmas is beam emission spectroscopy (BES). The increasing number of BES systems necessitated an accurate and comprehensive simulation of BES diagnostics, which in turn motivated the development of the Rate Equations for Neutral Alkali-beam TEchnique (RENATE) simulation code that is the topic of this paper. RENATE is a modular, fully three-dimensional code incorporating all key features of BES systems from the atomic physics to the observation, including an advanced modeling of the optics. Thus RENATE can be used both in the interpretation of measured signals and the development of new BES systems. The most important components of the code have been successfully benchmarked against other simulation codes. The primary results have been validated against experimental data from the KSTAR tokamak. [ABSTRACT FROM AUTHOR]

Images of plasma from a fast-framing camera are the most intuitive and reliable data to understand the status of tokamak plasmas. Generation, movement, size variation, and disruptions of plasmas can be clearly observed from these images. However, it is not a simple task to obtain the exact positions and sizes of plasmas using these images because measured two-dimensional images inevitably lose the three-dimensional position information of their targets. In this paper, the exact positions and sizes of plasmas have been calculated from tangentially viewed images using the toroidal symmetry of the plasma in the Korea Superconducting Tokamak Advanced Research (KSTAR) device. The positions and sizes of the plasmas have been manually determined with displayed cursors on images and automatically determined using a correlation factor with calculated virtual plasma images as well. These two results correspond well with each other. The estimated positions have also been compared with those obtained from magnetic diagnostics analysis. [ABSTRACT FROM AUTHOR]

On the Tore Supra tokamak, the ten-channel far infrared interferometer consists of a double color (119 and 195 μm) system with two detectors for each channel to measure the plasma density. The phase measurement is obtained by combining a 100 kHz shifted reference beam with the probing beam that has crossed the plasma. The achieved precision—a few percent of a fringe—is very good compared with the expected variations due to plasma, which are on the order of several fringes. However, the counting of the fringe variations can be affected when the signal is perturbed by electromagnetic interferences or when it deviates in the presence of strong plasma refraction changes occurring during ICRH breakdowns, pellet injections, or disruptions. This induces a strong decrease in the reliability of the measurement, which is an important concern when the diagnostic is used for density control. We describe in this paper the renewing of the electronics that has been achieved to reduce and correct the number of the so-called fringe jumps. A new zero crossing method for phase measurement is used, together with a field programable gate array semiconductor integration, to measure the phase and activate the algorithm of corrections every 10 μs. Comparisons between a numerical oscilloscope analysis and the corrected acquired data in the case of laboratory amplitude modulation tests and in the case of real plasma perturbations are also discussed. [ABSTRACT FROM AUTHOR]

Gas, fluid, or solid Cherenkov-type detectors have been widely used in high-energy physics for determination of parameters of charged particles, which are moving with relativistic velocities. This paper presents experimental results on the detection of runaway electrons using Cherenkov-type detectors in the ISTTOK tokamak discharges. Such detectors have been specially designed for measurements of energetic electrons in tokamak plasma. The technique based on the use of the Cherenkov-type detectors has enabled the detection of energetic electrons (energies higher than 80 keV) and determination of their spatial and temporal parameters in the ISTTOK discharges. Obtained experimental data were found in adequate agreement to the results of numerical modeling of the runaway electron generation in ISTTOK. [ABSTRACT FROM AUTHOR]

In tokamak experiments, equilibrium reconstruction codes are used to calculate the location of the last closed flux surface, to map diagnostic information, and to derive important properties like current density and safety factor. At JET, the equilibrium code EFIT is automatically executed after each discharge. For speed and robustness, intershot EFIT is based on magnetic probe measurements only. As a consequence, the intershot profiles of the safety factor can be wrong for a variety of plasma scenarios. Internal diagnostic information, the pitch angle as measured with the motional stark effect, Faraday rotation angles, as well as pressure profile information can increase the accuracy of the EFIT equilibrium. In this paper, the accuracy of the internal diagnostics at JET and their impact on the EFIT results are discussed in detail. The influence of control parameters like the form of the test functions for ff′ and p′ on the equilibrium is investigated. The qmin from this analysis agrees with information from magnetohydrodynamics analysis (e.g., Alfvén cascades and sawtooth analysis) to within 10%–15%. [ABSTRACT FROM AUTHOR]

To monitor the global formation of the initial plasma and damage to the internal structures of the vacuum vessel, an in-vessel visible inspection system has been installed and operated on the Korean superconducting tokamak advanced research (KSTAR) device. It consists of four inspection illuminators and two visible/H-alpha TV cameras. Each illuminator uses four 150 W metal-halide lamps with separate lamp controllers, and programmable progressive scan charge-coupled device cameras with 1004×1004 resolution at 48 frames/s and a resolution of 640×480 at 210 frames/s are used to capture images. In order to provide vessel inspection capability under any operation condition, the lamps and cameras are fully controlled from the main control room and protected by shutters from deposits during plasma operation. In this paper, we describe the design and operation results of the visible inspection system with the images of the KSTAR Ohmic discharges during the first plasma campaign. [ABSTRACT FROM AUTHOR]

An 80-channel soft x-ray tomography system has been constructed for diagnosing the RTP (Rijnhuizen Tokamak Project) tokamak plasma. Five pinhole cameras, each with arrays of 16 detectors are distributed more or less homogeneously around a po1oidal plasma cross section. The cameras are positioned close to the plasma edge to enable viewing angles which could not be reached otherwise. The system can be used for making tomographic reconstructions of the soft x-ray emissivity with a relatively high poloidal mode number (up to both components of m=4), which is an improvement with respect to other plasma tomography systems presented in literature. The temporal resolution of the system is 5 µs. Apart from a description of the hardware and geometrical layout Of the system, the paper will focus on two important issues, namely the calibration of the detectors and the positioning of the cameras in the vacuum vessel of the tokamak. A dedicated x-ray source has been designed for the relative calibration of the detectors of each individual camera. Misalignment causes several artifacts in tomographic reconstructions obtained with multicamera systems. Therefore, two new methods are proposed which make use of the plasma itself for improving the knowledge about the positions of the cameras. [ABSTRACT FROM AUTHOR]

The boundary plasma of the Alcator C tokamak exhibits poloidal asymmetries in plasma parameters. In order to investigate this phenomenon, an array of 80 closely spaced Langmuir probes has been built to directly sample this plasma region. This specially developed, densely packed probe array (DENSEPACK) is unique in that it provides a simultaneous, timedependent, two-dimensional mapping (minor radius r, poloidal angle θ) of plasma density, electron temperature, and floating potential over nearly the full 360° poloidal extent of the boundary plasma in this circular cross-section tokamak. The construction and operation of the DENSEPACK probe array, as welt as support hardware and software systems needed to handle the large volume of data generated by this array, are described in this paper. [ABSTRACT FROM AUTHOR]

It now appears feasible to deposit positrons (e[sup +]) in a tokamak plasma by injecting bursts of neutral positronium atoms (e[sup +]e[sup -]), which are then ionized by the plasma. The annihilation time of these positrons in the plasma is long compared with typical particle containment times. Thus the subsequent transport of the positrons can be studied by monitoring the time dependence of the annihilation, gamma radiation produced when the positrons strike a limiter. This paper discusses the design of such an experiment, the kinds of data which can be obtained, and the physics questions which this experiment might address. This diagnostic technique could also be useful in studying transport in other magnetic confinement devices such as reversed-field pinches and magnetic mirrors. [ABSTRACT FROM AUTHOR]

Support vector machines (SVM) are machine learning tools originally developed in the field of artificial intelligence to perform both classification and regression. In this paper, we show how SVM can be used to determine the most relevant quantities to characterize the confinement transition from low to high confinement regimes in tokamak plasmas. A set of 27 signals is used as starting point. The signals are discarded one by one until an optimal number of relevant waveforms is reached, which is the best tradeoff between keeping a limited number of quantities and not loosing essential information. The method has been applied to a database of 749 JET discharges and an additional database of 150 JET discharges has been used to test the results obtained. [ABSTRACT FROM AUTHOR]

With the implementation of alternating discharges (ac) at the ISTTOK tokamak, the typical duration of the discharges increased from 35 to 250 ms. This time increase created the need for a real-time electron density measurement in order to control the plasma fueling. The diagnostic chosen for the real-time calculation was the microwave interferometer. The ISTTOK microwave interferometer is a heterodyne system with quadrature detection and a probing frequency of 100 GHz (λ0=3 mm). In this paper, a low-cost approach for real-time diagnostic using a digital signal programable intelligent computer embedded system is presented, which allows the measurement of the phase with a 1% fringe accuracy in less than 6 μs. The system increases its accuracy by digitally correcting the offsets of the input signals and making use of a judicious lookup table optimized to improve the nonlinear behavior of the transfer curve. The electron density is determined at a rate of 82 kHz (limited by the analog to digital converter), and the data are transmitted for each millisecond although this last parameter could be much lower (around 12 μs—each value calculated is transmitted). In the future, this same system is expected to control plasma actuators, such as the piezoelectric valve of the hydrogen injection system responsible for the plasma fueling. [ABSTRACT FROM AUTHOR]

This paper presents a feasibility study for a motional Stark effect (MSE) [F. M. Levinton et al., Phys. Rev. Lett. 63, 2060 (1989)] diagnostic on the TCV tokamak. A numerical simulation code has been used to identify the optimal port arrangement and geometrical layout. It predicts the expected measurement accuracy for a range of typical plasma scenarios. With the existing neutral beam injector (NBI) and a detection system based on current day technology, it should be possible to determine the safety factor with an accuracy of the order of 5%. A vertically injected beam through the plasma center would allow one to measure plasmas which are centered above the midplane, a common occurrence in connection with electron cyclotron resonance heating and electron cyclotron current drive experiments. In this case a new and ideally more powerful NBI would be required. [ABSTRACT FROM AUTHOR]

This paper presents the description and operational characteristics of an emissive electrode (EE) used in edge biasing experiments on small tokamak ISTTOK. The EE consists of a lanthanum hexaboride (LaB6) electron emitter heated by a tungsten filament. The emissive characteristics of EE have been investigated both in a simple vacuum diode configuration on test facility and in the plasma of tokamak. Emissive currents up to 20 A have been observed during negative bias in plasma accompanied by a strong modification of the electric field. The EE proved to be a valuable tool on the control of the plasma electric field, allowing a detailed investigation of its importance in plasma confinement. [ABSTRACT FROM AUTHOR]

This paper describes a technique for measuring magnetic fluctuations using a heavy ion beam probe (HIBP) and presents the results of the first experiment to measure locally the internal magnetic structure of MHD modes in a hot, tokamak plasma. In these experiments on the TEXT tokamak, the toroidal position of the HIBP beam at the detector is used to measure the toroidal component of the magnetic vector potential fluctuations, Ã[sub φ], at a localized position in the plasma. In an axisymmetric system a purely local measurement is possible. However, the detection method employed and the asymmetries in the tokamak introduce path effects. The importance of the path effects is estimated through numerical simulations of the experiment, and it is found that in this experiment the path effects are small throughout much of the plasma. In addition, toroidal asymmetries reduce the signal amplitude, but do not greatly distort the radial profile. The accuracy of the numerical simulations and detection technique is tested in a plasma with a known Ã[sub φ], with agreement obtained to within 5%. [ABSTRACT FROM AUTHOR]

Fluctuations with a dominant poloidal structure involving the intact displacement of the center of the discharge play a significant role in tokamak discharges. A technique for the deductive analysis of their structures, which involve multiple harmonics due to the multipole moments, is desired. This paper describes (1) a method for the inversion of line integral data from a single view of a rotating plasma based on a harmonic decomposition of the poloidal structure, and (2) some techniques for determining critical parameters by inspection. A simulation program generates sample data based on the assumption ora slowly evolving plasma with a displaced central hot spot and a plateau near the radius of the "q = 1" surface. The sample data are decomposed into time windows to permit reconstruction of the profiles every few rotations. Results of the reconstructions are compared to the source data. Applicability of the techniques to experimental tokamak data is discussed. [ABSTRACT FROM AUTHOR]

The designs of single transmission grating based extreme ultraviolet (XUV) and vacuum ultraviolet (VUV) imaging spectrometers can be adapted to build an imaging radiometer for simultaneous measurement of both spectral ranges. This paper describes the design of such an imaging radiometer with dual transmission gratings. The radiometer will have an XUV coverage of 20-200 Å with a ∼10 Å resolution and a VUV coverage of 200-2000 Å with a ∼50 Å resolution. The radiometer is designed to have a spatial view of 16°, with a 0.33° resolution and a time resolution of ∼10 ms. The applications for such a radiometer include spatially resolved impurity monitoring and electron temperature measurements in the tokamak edge and the divertor. As a proof of principle, the single grating instruments were used to diagnose a low temperature reflex discharge and the relevant data is also included in this paper. [ABSTRACT FROM AUTHOR]

The numerous applications of cw collective Thomson scattering in fusion plasmas are greatly enhanced by the addition of a multichannel capability. This permits the determination of the dispersive properties (ω vs k) of waves on a single tokamak discharge. This paper describes the development, calibration, and application of such systems in the far-infrared spectral region. The measurement of the wave dispersion of externally excited ion Bernstein waves leads to the determination of ion temperature in a tokamak plasma. In addition, the study of naturally occurring microturbulence has produced a series of unique observations which has both motivated theoretical effort and clarified the role of density fluctuations in anomalous transport. [ABSTRACT FROM AUTHOR]

This paper describes the design and operation of a new tungsten (W) injection system for impurity transport experiments in the Tore Supra tokamak. The system is mounted on a reciprocating manipulator and injects a controlled amount of gaseous tungsten hexacarbonyl, W(CO)6 at arbitrary depth in the scrape-off layer, using an inertially activated valve. Injected W(CO)6 is dissociated in the plasma, forming a radially localized plume of W atoms. The injector does not require an external gas feed and can perform a large number of injections from an on-board reservoir of W(CO)6. Some examples of W injections in Tore Supra are included, demonstrating successful operation and discussing some technical issues of the injector prototype. [ABSTRACT FROM AUTHOR]

A beam emission spectroscopy (BES) system based on direct imaging avalanche photodiode (APD) camera has been designed for Korea Superconducting Tokamak Advanced Research (KSTAR) and a trial system has been constructed and installed for evaluating feasibility of the design. The system contains two cameras, one is an APD camera for BES measurement and another is a fast visible camera for position calibration. Two pneumatically actuated mirrors were positioned at front and rear of lens optics. The front mirror can switch the measurement between edge and core region of plasma and the rear mirror can switch between the APD and the visible camera. All systems worked properly and the measured photon flux was reasonable as expected from the simulation. While the measurement data from the trial system were limited, it revealed some interesting characteristics of KSTAR plasma suggesting future research works with fully installed BES system. The analysis result and the development plan will be presented in this paper. [ABSTRACT FROM AUTHOR]

The preconceptual design phase of the Tokamak Fusion Core Experiment (TFCX) and Phase IIA of the International Tokamak Reactor (INTOR) workshop have included reassessment of the plasma diagnostic requirements for the large rf heated, neutron-generating plasmas in these devices. The three principal components of the work have been (i) to reassess the present level of diagnostic capability, (ii) to identify the diagnostics required for measurement before and during the burn phases of the two devices and (iii) to define a program of research and development activities of new or upgraded diagnostics. Both devices are expected to start operation in the early 1990's; it is, therefore, necessary to set up development programs on U.S. tokamaks to evaluate fusion product measurements, and to establish capability of reliable, radiation-hardened instruments. The adequacy of the operational information available with very limited access through the shielding and structure of the tokamaks also must be determined. This paper describes the present plans for these programs. [ABSTRACT FROM AUTHOR]