Arrays of edge magnetic coils and statistical analysis techniques have been used to investigate the magnetic fluctuation structure in the HBTX-1A reversed field pinch. The superficially random fluctuations can in fact be attributed almost entirely to global modes with poloidal mode number m = 0 and 1, provided account is taken of toroidal distortion of the modes. A toroidal array of coils discloses a broad spectrum of toroidal mode numbers with peak at |n| ~ 10 and significant variation with time and frequency. Cross-correlation establishes that |n| ~ 10 corresponds to m = 1, a helical mode resonant inside the reversal surface, and also shows the presence of m = 0, n ~ 0. The time-scales of the fluctuation indicate that the instabilities are probably resistive in character, and the mode amplitudes are such that island overlap and magnetic field ergodization should occur. The energy confinement time due to stochastic transport, estimated from the measured fluctuations, is consistent with that observed experimentally.

https://iopscience.iop.org/article/10.1088/0029-5515/24/1/006/pdf

The structure of magnetic fluctuations in the HBTX-1A reversed field pinch

The paper summarizes the theoretical basis for the RFP and reviews the status of research in this field. The RFP is a relaxed state system well described by Taylor's theory which explains many observations. The RFP is of interest because its study will increase the understanding of toroidal confinement in general, which might lead to better reactor designs, and the RFP itself has potential as a reactor, for example the improved, high energy density, compact RFP reactor. In the last five or ten years, RFP research has expanded, with some 15-20 machines operating or under construction, and the plasma parameters have improved substantially, with a confinement time of 0.5-1 ms and temperatures approaching 1 keV; values of βθ ~ 5-15% are reached routinely. Following an overview of recent results, three key problems are discussed in more detail: (1) resistivity, edge physics and ion heating (the ions are heated by fluctuations which drive the RFP dynamo); (2) operation of the RFP with an (electrically) thin shell which permits the growth of new unstable modes which degrade the confinement; and (3) scaling. Over the current range of 0.5 MA, favourable scaling trends of temperature and confinement with current are identified, but experiments at much higher currents on the two mega-ampere machines – RFX at Padua and CPRF at Los Alamos – due to operate in the early 1990s, are needed. A brief account of the compact RFP reactor is given, followed by a summary with an indication of future trends.

The reversed field pinch

In the reversed-field pinch (RFP), the plasma is confined in an axisymmetric toroidal configuration by a combination of toroidal (B/sub phi/) and poloidal (Btheta/sub ) fields with B/theta /sub >> B/phi /sub outside the plasma and B/theta approx. = B/sub phi/ within the plasma. The essential property of the RFP equilibrium is that it is a near-minimum-energy relaxed state that the plasma finds naturally; the spontaneous generation of reversed toroidal field (dynamo process) is a consequence of this relaxation, and, if the plasma current is maintained, the field generation continues so that the configuration exists as a quasi steady state. Since such equilibria have little free energy to drive instabilities, the systems has good stability properties, and, theoretically, confinment at high beta is possible; the plasma current can be sufficiently high to allow the possibility of plasma ignition in deuterium-tritium by ohmic heating alone. Experimentally, values of poloidal beta typically 10% or more are usually observed, and conditions have been found in which the temperature is found to scale approximately linearly with the plasma current up to 0.5 MA; maximum temperatures of the order of 0.5 keV have been observed. This temperature scaling corresponds to a current dependence of themore » energy confinement time of I/sub phi//sup 3/2/. Ohmically heated RFP reactors are discussed with emphasis on improved designs with increased power density up to values comparable to those in fission systems.« less

The reversed-field pinch: From experiment to reactor

The ZT‐40M [Fusion Tech. 8, 1571 (1985)] reversed‐field pinch has been used to study magnetic flux perturbations during high‐θ [θ=Bθ(a)/〈Bφ〉>1.6] discharges. Asymmetric toroidal magnetic flux perturbations are found to be associated with magnetic flux emerging through the toroidal shell gap and with m=0 magnetic disturbances moving toroidally. Ramping current discharges, which are a special case of high‐θ operation, show the most robust self‐generation of toroidal flux. The electron density fluctuations on the inside major radius and associated m=1 and m=0 fluctuations seen on edge magnetic field probes provide a clearer picture of activity during a soft x‐ray sawtooth crash. During the sawtooth crash, significant magnetic energy is apparently converted into kinetic energy of the particles.

Asymmetric magnetic flux generation, m=1 activity, and edge phenomena on a reversed‐field pinch

Equations are proposed to describe the radial variation of the magnetic field and current density in a circular, cylindrical reversed field pinch (RFP). These equations are used to derive the electrical circuit parameters (inductance, resistance, and coupling coefficient) for a RFP discharge. The circuit parameters are used to evaluate the flux and energy consumption for various start‐up modes and for steady‐state operation using oscillating field current drive. The results are applied to the MST device [Bull. Am. Phys. Soc. 32, 1830 (1987)].

Electrical circuit modeling of reversed field pinches

Magnetic field fluctuations have been studied in the ETA-BETA II experiment as a function of density, time and radius The spectral analysis of the measured fluctuations has shown that the higher frequency portion of the spectrum (>50 kHz) is more sensitive to the density variation, whereas the lower frequency portion ( approximately 10 kHz) shows a radial profile which, especially at later times during the discharge, resembles the characteristic shape of MHD resistive modes Radial correlation lengths of several centimeters are found In general the amplitude of the fluctuations increases at lower densities and is larger toward the end of the discharge and in the outer plasma region These trends may be correlated with the typical variation of the streaming parameter However, the lower frequency fluctuations, in particular, can be interpreted as MHD instabilities which can produce large distortion of the magnetic surfaces leading to island formation and overlapping resulting in stochastic behaviour of the magnetic field lines in a relevant radial extent ( approximately=1 cm) of the outer plasma regions

Characteristics of the magnetic field fluctuations in the ETA-BETA II reversed field pinch experiment

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

V Antoni

Author Tools

Chat about Author

Papers

Characteristics of the magnetic field fluctuations in the ETA-BETA II reversed field pinch experiment