Plasma behaviour at high β and high density in the Madison Symmetric Torus RFP

Wyman, Max; Chapman, B. E.; Ahn, J.-W.; Almagri, A. F.; Anderson, J. K.; Bonomo, F.; Brower, D. L.; Combs, S. K.; Craig, D.; Hartog, D. J. Den; Deng, B. H.; Ding, W. X.; Ebrahimi, F.; Ennis, D.A.; Fiksel, G.; Foust, C. R.; Franz, P.; Gangadhara, S.; Goetz, J. A.; O’Connell, R.; Oliva, S. P.; Prager, S. C.; Reusch, J.A.; Sarff, J. S.; Stephens, H.D.; Yates, T.

doi:10.1088/0029-5515/49/1/015003

Cited by 22 publications

(31 citation statements)

References 42 publications

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“…Some of the key parameters from these plasmas are shown in table 1. Recent work from the MST [15] and RFX-mod [34] experiments has demonstrated that the Greenwald density limit for tokamaks [35] applies to these two RFP devices as well. This limit on the line-averaged electron density = I φ /π a 2 , where I φ is the toroidal plasma current in megaamperes, a is the plasma minor radius in metres, and the density limit is in units of 10 20 m −3 .…”

Section: Improved Confinement At Higher Density and High Betamentioning

confidence: 99%

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Improved-confinement plasmas at high temperature and high beta in the MST RFP

Chapman¹,

Ahn²,

Almagri³

et al. 2009

Nucl. Fusion

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We have increased substantially the electron and ion temperatures, the electron density, and the total beta in plasmas with improved energy confinement in the Madison Symmetric Torus (MST). The improved confinement is achieved with a well-established current profile control technique for reduction of magnetic tearing and reconnection. A sustained ion temperature >1 keV is achieved with intensified reconnection-based ion heating followed immediately by current profile control. In the same plasmas, the electron temperature reaches 2 keV, and the electron thermal diffusivity drops to about 2 m 2 s −1. The global energy confinement time is 12 ms. This and the reported temperatures are the largest values yet achieved in the reversed-field pinch (RFP). These results were attained at a density ∼10 19 m −3. By combining pellet injection with current profile control, the density has been quadrupled, and total beta has nearly doubled to a record value of about 26%. The Mercier criterion is exceeded in the plasma core, and both pressure-driven interchange and pressure-driven tearing modes are calculated to be linearly unstable, yet energy confinement is still improved. Transient momentum injection with biased probes reveals that global momentum transport is reduced with current profile control. Magnetic reconnection events drive rapid momentum transport related to large Maxwell and Reynolds stresses. Ion heating during reconnection events occurs globally, locally, or not at all, depending on which tearing modes are involved in the reconnection. To potentially augment inductive current profile control, we are conducting initial tests of current drive with lower-hybrid and electron-Bernstein waves.

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Section: Improved Confinement At Higher Density and High Betamentioning

confidence: 99%

“…In other discharges with current profile control, we have quadrupled the plasma density with injection of deuterium pellets [14,15]. Core and edge fluctuations are reduced, energy confinement is improved and the ion temperature rises along with the electron temperature.…”

Section: Introductionmentioning

confidence: 99%

Improved-confinement plasmas at high temperature and high beta in the MST RFP

Chapman¹,

Ahn²,

Almagri³

et al. 2009

Nucl. Fusion

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“…Plasmas are created in an aluminum torus with a major radius of 1.5 m (R 0 ), a minor radius of 0.52 m (a), and a thickness of 0.05 m. 10,15,17 The torus acts as the vacuum vessel, the conducting shell and the toroidal field winding (single turn). Discharges can have plasma currents from 200 to 600 kA and electron densities on the order of $10 13 cm À3 .…”

Section: Apparatus and Experimentsmentioning

confidence: 99%

“…Discharges can have plasma currents from 200 to 600 kA and electron densities on the order of $10 13 cm À3 . 15 MST discharges are typically deuterium plasmas lasting $70 ms with ion energies up to 40 keV (using neutral beam injection, NBI). 12 To make measurements on MST, the CNPA needed to be upgraded and calibrated for deuterium with ion temperatures between 0.1 and 2 keV.…”

Section: Apparatus and Experimentsmentioning

confidence: 99%

Low energy ion distribution measurements in Madison Symmetric Torus plasmas

Titus

Mezonlin

Johnson³

2014

Physics of Plasmas

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Charge-exchange neutrals contain information about the contents of a plasma and can be detected as they escape confinement. The Florida A&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).

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“…This system was developed to provide a flexible means of plasma fueling on a wide variety of magnetic confinement devices, at relatively low costs for installation and operations. The original prototype was installed on the Madison Symmetric Torus (MST) in early 2002 [5,6] and has since been used extensively in plasma experiments [6,[7][8][9]. This injector type is ideally suited for the TJ-II application [10,11].…”

Section: Introductionmentioning

confidence: 99%

A new four-barrel pellet injection system for the TJ-II stellarator

Combs

Foust

McGill

et al. 2011

2011 IEEE/NPSS 24th Symposium on Fusion Engineering

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A new pellet injection system for the T J-II stellarator has been developed/constructed as part of a collaboration between the Oak Ridge National Laboratory (ORNL) and the Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT). ORNL is providing most of the injector hardware and instrumentation, the pellet diagnostics, and the pellet transport tubes; ClEM AT is responsible for the injector stand/interface to the stellarator, cryogenic refrigerator, vacuum pumps/ballast volumes, gas manifolds, remote operations, plasma diagnostics, and data acquisition. The pellet injector design is an upgraded version of that used for the ORNL injector installed on the Madison Symmetric Torus (MST). It is a four-barrel system equipped with a cryogenic refrigerator for in situ hydrogen pellet formation and a combined mechanical punch/propellant valve system for pellet acceleration (speeds -100 to 1000 m/s). On T J-II, it will be used as an active diagnostic and for fueling. To accommodate the plasma experiments planned for T J-II, pellet sizes significantly smaller than those typically used for the MST application are required. The system will initially be equipped with four different pellet sizes, with the gun barrel bores ranging between -0.5 to 1.0 mm. The new system is almost complete and is described briefly here, highlighting the new features added since the original MST injector was constructed. Also, the future installation on TJ-I1 is reviewed.

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Plasma behaviour at high β and high density in the Madison Symmetric Torus RFP

Cited by 22 publications

References 42 publications

Improved-confinement plasmas at high temperature and high beta in the MST RFP

Improved-confinement plasmas at high temperature and high beta in the MST RFP

Low energy ion distribution measurements in Madison Symmetric Torus plasmas

A new four-barrel pellet injection system for the TJ-II stellarator

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