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Title: Low energy ion distribution measurements in Madison Symmetric Torus plasmas

Abstract

Charge-exchange neutrals contain information about the contents of a plasma and can be detected as they escape confinement. The Florida A and M University compact neutral particle analyzer (CNPA), used to measure the contents of neutral particle flux, has been reconfigured, calibrated, and installed on the Madison Symmetric Torus (MST) for high temperature deuterium plasmas. The energy range of the CNPA has been extended to cover 0.34–5.2 keV through an upgrade of the 25 detection channels. The CNPA has been used on all types of MST plasmas at a rate of 20 kHz throughout the entire discharge (∼70 ms). Plasma parameter scans show that the ion distribution is most dependent on the plasma current. Magnetic reconnection events throughout these scans produce stronger poloidal electric fields, stronger global magnetic modes, and larger changes in magnetic energy all of which heavily influence the non-Maxwellian part of the ion distribution (the fast ion tail)

Authors:
;  [1];  [2]
  1. Florida A and M University, Tallahassee, Florida 32310 (United States)
  2. Pyramid Plasmas LLC, Lawrenceville, Georgia 30043 (United States)
Publication Date:
OSTI Identifier:
22299972
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 6; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHARGE EXCHANGE; DEUTERIUM; ELECTRIC CURRENTS; KEV RANGE 01-10; KHZ RANGE 01-100; NEUTRAL PARTICLE ANALYZERS; PLASMA; PLASMA CONFINEMENT

Citation Formats

Titus, J. B., E-mail: jtitus@cepast.famu.edu, Mezonlin, E. D., and Johnson, J. A. Low energy ion distribution measurements in Madison Symmetric Torus plasmas. United States: N. p., 2014. Web. doi:10.1063/1.4883645.
Titus, J. B., E-mail: jtitus@cepast.famu.edu, Mezonlin, E. D., & Johnson, J. A. Low energy ion distribution measurements in Madison Symmetric Torus plasmas. United States. doi:10.1063/1.4883645.
Titus, J. B., E-mail: jtitus@cepast.famu.edu, Mezonlin, E. D., and Johnson, J. A. 2014. "Low energy ion distribution measurements in Madison Symmetric Torus plasmas". United States. doi:10.1063/1.4883645.
@article{osti_22299972,
title = {Low energy ion distribution measurements in Madison Symmetric Torus plasmas},
author = {Titus, J. B., E-mail: jtitus@cepast.famu.edu and Mezonlin, E. D. and Johnson, J. A.},
abstractNote = {Charge-exchange neutrals contain information about the contents of a plasma and can be detected as they escape confinement. The Florida A and M University compact neutral particle analyzer (CNPA), used to measure the contents of neutral particle flux, has been reconfigured, calibrated, and installed on the Madison Symmetric Torus (MST) for high temperature deuterium plasmas. The energy range of the CNPA has been extended to cover 0.34–5.2 keV through an upgrade of the 25 detection channels. The CNPA has been used on all types of MST plasmas at a rate of 20 kHz throughout the entire discharge (∼70 ms). Plasma parameter scans show that the ion distribution is most dependent on the plasma current. Magnetic reconnection events throughout these scans produce stronger poloidal electric fields, stronger global magnetic modes, and larger changes in magnetic energy all of which heavily influence the non-Maxwellian part of the ion distribution (the fast ion tail)},
doi = {10.1063/1.4883645},
journal = {Physics of Plasmas},
number = 6,
volume = 21,
place = {United States},
year = 2014,
month = 6
}
  • Two types of fast bolometers are described for the plasma energy transport study in the Madison symmetric torus plasma confinement device. Both types use pyrocrystals of LiTaO[sub 3] or LiNbO[sub 3] as the sensors. One type is used for measurements of the radiated heat losses and is situated at the vacuum shell inner surface. Another type is insertable in the plasma and measures the plasma particle heat flux. The frequency response of the bolometers is measured to be in the 150--200 kHz range. The range of the measured power fluxes is 0.1 W/cm[sup 2]--10 kW/cm[sup 2] and can be adjustedmore » by changing the size of the entrance aperture. The lower limit is determined by the amplifier noise and the frequency bandwidth, the higher limit by destruction of the bolometer sensor.« less
  • Charge exchange recombination spectroscopy measurements of impurity ion temperature (T{sub i}) and velocity (v{sub i}) on the Madison Symmetric Torus present a unique challenge due to two coupled effects: low temperature--typically 300-500 eV, though up to 2 keV in high current plasmas--and a dominant contribution from background, i.e., non charge exchange driven, emission. For low T{sub i}, the background emission line shape is significantly asymmetric as a result of spin-orbit coupling effects. Accurate modeling of both the background and beam emission is therefore required to obtain precise values for local ion parameters. A model has been developed to provide robustmore » simulation of the experimental measurements with {approx}10 {mu}s temporal resolution using atomic data obtained from the Atomic Data and Analysis Structure database. Measurements are made using C VI emission at 343.4 nm, with background and beam emissions obtained simultaneously using two fiber bundles with slightly displaced lines of sight. Emission from O VI contributes substantially to the background signal, and is included in the modeling. A complete description of the model will be presented, along with results for T{sub i} measurements during magnetic reconnection.« less
  • The impurity ion temperature evolution has been measured during three types of impulsive reconnection events in the Madison Symmetric Torus reversed field pinch. During an edge reconnection event, the drop in stored magnetic energy is small and ion heating is observed to be limited to the outer half of the plasma. Conversely, during a global reconnection event the drop in stored magnetic energy is large, and significant heating is observed at all radii. For both kinds of events, the drop in magnetic energy is sufficient to explain the increase in ion thermal energy. However, not all types of reconnection leadmore » to ion heating. During a core reconnection event, both the stored magnetic energy and impurity ion temperature remain constant. The results suggest that a drop in magnetic energy is required for ions to be heated during reconnection, and that when this occurs heating is localized near the reconnection layer.« less
  • In this paper measurements of momentum and current transport caused by current driven tearing instability are reported. The measurements are done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] in a regime with repetitive bursts of tearing instability causing magnetic field reconnection. It is established that the plasma parallel momentum profile flattens during these reconnection events: The flow decreases in the core and increases at the edge. The momentum relaxation phenomenon is similar in nature to the well established relaxationmore » of the parallel electrical current and could be a general feature of self-organized systems. The measured fluctuation-induced Maxwell and Reynolds stresses, which govern the dynamics of plasma flow, are large and almost balance each other such that their difference is approximately equal to the rate of change of plasma momentum. The Hall dynamo, which is directly related to the Maxwell stress, drives the parallel current profile relaxation at resonant surfaces at the reconnection events. These results qualitatively agree with analytical calculations and numerical simulations. It is plausible that current-driven instabilities can be responsible for momentum transport in other laboratory and astrophysical plasmas.« less