K. A. Connor

Heavy ion beam probe energy analyzer for measurements of plasma potential fluctuations

The operation of a Proca and Green type 30° parallel plate electrostatic energy analyzer is modeled in a new manner that permits high‐resolution heavy ion beam probe measurements of fluctuating plasma potential. Systematic calibration procedures permit detection of potential changes smaller than 0.01% of the probing beam energy at frequencies up to a megahertz. Most recent applications of beam probes have made use of this new capability.

Elmo Bumpy Torus heavy ion probe

A diagnostic system based on the heavy ion beam probe technique has been developed for the Elmo Bumpy Torus. A variety of singly charged alkali metal ions have been used in the probing beam; detection of multiply charged reaction products allows a continuous spatially resolved monitor of the plasma space potential. Typical spatial resolution is 1 cm−3; time resolution is on the order of 1 s. The potential measurement is direct and properly referenced to the plasma ground. An investigation into possible sources of error in the measurement points to the conclusion that the uncertainty is an order of magnitude less than the experimentally measured potentials.

Internal magnetic and electrostatic fluctuation measurements of magnetohydrodynamic modes in the Texas Experimental Tokamak (TEXT)

A heavy ion‐beam probe has been used to make the first internal measurements of magnetic fluctuations in a hot tokamak. The magnetic vector potential fluctuation, Aφs, is measured during magnetohydrodynamic (MHD) activity and is in reasonable agreement with the prediction of a three‐dimensional, resistive, compressible, nonlinear MHD code. Associated density and potential fluctuation measurements and magnetic island widths are also presented.

A studio format for innovative pedagogy in circuits and electronics

This paper describes a new approach to two undergraduate courses in circuits and electronics whereby lecture, recitation, computer, and laboratory activities are combined in a single studio facility. The revised format encourages students to learn by doing, not just listening, and it provides new opportunities for innovative pedagody using interactive multimedia to enhance student understanding of difficult concepts. Rensselaer has offered both courses in parallel pilot studio and traditional formats in the past academic year. The results of standard testing show no statistically significant differences. Nevertheless, the studio format appears to offer significant improvement in student motivation as evidenced by end-of-semester comments and a near perfect rate of attendance. The studio format also allows the instructor to quickly assess the effectiveness of a particular presentation and to provide optimum assistance to students with different learning styles and capabilities.

Zonal flow measurements using a heavy ion beam probe

Zonal flows are of keen interest in efforts to understand transport in magnetically confined plasma. Of the well-developed diagnostics, the heavy ion beam probe, HIBP, is most suited to measure the radial electric field, Er, associated with the flows in present medium to large devices. This paper discusses why the HIBP is capable of measuring Er and how to design a HIBP to optimize zonal flow measurements. The TEXT HIBP is used as an example of a typical system. The NSTX spherical torus is used in a design study for future work with emphasis on zonal flow measurements. The key diagnostic considerations are (1) sample volume size, (2) sample volume orientation, and (3) the ability to rapidly scan the sample volume in the radial direction. The measurement of principal interest here is Er but there is additional information in a nonlinear analysis of the fluctuations.

Time domain finite element analysis of high power microwave aperture antennas

A high power microwave device with complicated structure is analyzed in the time domain using the finite element scheme which utilizes triangular elements. The convergence property is investigated and comparisons between conventional methods are shown. Results are also compared with frequency domain analysis. >

Ballooning characteristics in density fluctuations observed with the 2 MeV heavy ion beam probe on the TEXT-U tokamak

Heavy ion beam probe measurements of the interior of the TEXT-U tokamak plasma have been used to discover a density fluctuation spectrum that exhibits poloidal asymmetry with ballooning characteristics. The asymmetry was eliminated at the smallest radii during the electron cyclotron heating phase, which has a flatter density profile and a higher electron temperature

Recent advances in heavy ion beam probe diagnostics (invited)

Heavy ion beam probes (HIBPs) have proven to be a unique tool for measuring fluctuations and particle transport in tokamaks. They have been used to measure fluctuations in density, electric potential, and magnetic vector potential. The density and potential fluctuation measurements have determined the particle flux due to electrostatic turbulence in the TEXT and ISX‐B tokamaks. In these measurements, the frequency spectra (0–500 kHz) of the phase between density and potential, the wave numbers of the fluctuations, and the fluctuation level are obtained. Three topics are discussed in this paper. We present measurements of magnetic fluctuations during MHD activity using the TEXT HIBP. Analysis of these measurements indicates that the diagnostic is primarily sensitive to the local value of Aφ in the sample volume unless the local Aφ is small. In addition, we discuss instrumental effects associated with wave number measurements. We will discuss the effects of sample volume size on the wave number measurements...

Sweep system design for a heavy ion beam probe on Madison Symmetric Torus

The sweep system for the heavy ion beam probe on the Madison Symmetric Torus (MST) is described. The two components of the system are the primary sweep optics and secondary collimation plates. Key issues in the sweep system design are the small entrance and exit ports available on MST, the significant toroidal beam motion induced by the strong poloidal magnetic field, and the excessive current loading due to plasma and ultraviolet (UV). The design accommodates these issues using a crossover sweep plate design in two dimensions for the primary beam as well as two dimensional sweeping on the secondary beam. The primary beam sweep design results in a sweep range of ±20° in one direction and ±5° in the perpendicular direction. The secondary beam sweep design results in entrance angles to the energy analyzer of <3° in radial and ∼0° in toroidal directions. The procedure for calculating sweep performance including fringe fields, a system for active trajectory control, and initial experiments on plasma and UV lo...

A heavy ion beam probe for the Madison Symmetric Torus

A heavy ion beam probe (HIBP) is being developed for application on the Madison Symmetric Torus (MST). It will be used to make measurements of the plasma space potential Φ(r), fluctuations in potential Φ(r), the electron density ne(r), fluctuating electron density ne(r), and radial electric field Er(r) from the core to the edge region of the plasma in MST. While information on these quantities can and has been obtained with probes inserted in the surface region, none of the above measurements have been made in the core of a hot reversed field pinch. Measurements of Φ(r), Er(r), and ne(r) have been well established in previous HIBP systems on tokamaks such as Impurities Studies Experiment, Texas Experimental Tokamak (TEXT), and TEXT Upgrade, stellarators such as Advanced Toroidal Facility and Compact Helical System and Bumpy Tori such as Elmo Bumpy Torus and Nagoya Bumpy Torus. Less well developed in terms of HIBP measurements are equilibrium and fluctuating magnetic fields. Because the confining field on...