Overview of DIII-D off-axis neutral beam project

Murphy, Christopher J.; Abrahim, M.; Anderson, P.M.; Chiu, H.K.; Grunloh, H.J.; Hansink, M.; Holtrop, K.L.; Rao, Hong; Kellman, A.G.; Kellman, D.H.; Mauzey, P.S.; Noraky, S.; Pawley, C. J.; Rauch, J.; Scoville, J.T.; Zeeland, M. A. Van; Yip, H.H.; Wood, R.; Murakami, M.; Park, J.M.; Heidbrink, W. W.

doi:10.1109/sofe.2011.6052323

Cited by 6 publications

(5 citation statements)

References 2 publications

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“…The DIII-D tokamak is equipped with eight neutral-beam sources housed in four beamlines. A hydraulic lift can elevate one of the beamlines to steer the beam vertically [11]. When the beamline is elevated, the pair of sources in this beamline aim through a midplane port to a point below the centre in the plasma.…”

Section: Introductionmentioning

confidence: 99%

The effect of the fast-ion profile on Alfvén eigenmode stability

et al. 2013

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Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfvén eigenmodes (RSAE) and toroidal Alfvén eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇β f in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on-and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a 'critical-gradient' model of fast-ion transport.

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Section: Introductionmentioning

confidence: 99%

The effect of the fast-ion profile on Alfvén eigenmode stability

et al. 2013

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“…Each ion source accelerator grid is focused in the vertical direction at 10 m in front of the grid, while purely diverging in the horizontal plane. This is referred to as normal focus ion source in [23]. Streams of neutral particles launched in a Monte-Carlo algorithm with 0.008 73 rad horizontal divergence and 0.0227 rad vertical divergence produces a far-field diverging beam that agrees with imaging measurements [29].…”

Section: Neutral Beam Geometry In Nubeammentioning

confidence: 92%

“…In 2010-2011 the 150 • beamline was upgraded to enable tiltable off-axis injection with a maximum beamline angle of 16.3 • downward with respect to the vessel midplane, in the nominal co-current direction [23]. The initial assessment of the power delivered by the tilted beam indicated that less power was produced than expected [24], and subsequent study revealed additional losses and heating of internal beamline components [25,26].…”

Section: Neutral Beam Geometry and Imagingmentioning

confidence: 99%

“…Changing the direction of injection can be done in one calendar week, requiring a clean (nitrogen) vent of the vessel to rotate the beamline and reinstall the vacuum seals. For the co/counter off-axis neutral beam (CCOANB) upgrade, each ion source has been modified to achieve a stronger vertical focus by increasing the tilt angle that each of four ion source plates makes toward the beam centerline in a manner similar to [23]. The full width of the ion source plates has been kept constant in order to retain full power.…”

Section: Neutral Beam Geometry and Imagingmentioning

confidence: 99%

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Testing the DIII-D co/counter off-axis neutral beam injected power and ability to balance injected torque

Grierson¹,

Zeeland²,

Scoville³

et al. 2021

Nucl. Fusion

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DIII-D has undergone a major upgrade and successfully injected high power off-axis neutral beams (∼ 4 MW) in both co-current and counter-current directions. This capability of high power co/counter steerable off-axis neutral beams on a major tokamak opens a unique parameter space of broad pressure and current profiles for high beta steady-state advanced tokamak (AT) scenarios, while retaining the ability to balance the injected torque for low rotation studies. This co/counter off-axis neutral beam capability is being used to validate physics-based energetic particle and thermal transport models for designing next-step facilities based on the steady-state AT approach. This paper reports on the critical evaluation of the transmitted power and energetic ion population produced by this heating and current drive system, which is assessed through visible imaging, neutron measurements and rotation profile measurements at balanced torque. Minimal losses of neutral beam power have been achieved by optimizing the strongly focused ion sources required to pass through the aperture. Tilting of the ion source has been guided by fast visible imaging and resulted in neutral beam injection along the design centerline with empirical characterization of each beam's divergence derived from the imaging data and used in the NUBEAM description of the beam injection. Through exclusive power injection of each neutral beam into MHD quiescent plasmas across a range of neutral beam voltage, perveance and plasma current we conclude that a modest reduction (∼ 10%-15%) of transmitted power compared to on-axis, standard focus has been incurred. We report corrections that more accurately represent the injected power. Good ability to balance the neutral beam torque has been demonstrated by injecting the new off-axis counter injecting beam against the existing off-axis co-injected beam in 2.0 T, 1.0 MA, MHD quiescent L-mode plasmas. The torque balance studies verify the ability to operate with balanced injection, which is critical for achieving low torque and low rotation operation for physics studies and in ITER demonstration discharges.

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“…Previously, all eight sources injected into the tokamak at the midplane of the vacuum vessel. Prior to the 2011 experimental campaign, a massive hydraulic lift was installed beneath one of the beamlines to allow vertical steering [6]. When the beamline is elevated, the pair of sources in this beamline inject neutrals through the midplane port and below the midplane in the plasma.…”

Section: Introductionmentioning

confidence: 99%

Initial measurements of the DIII-D off-axis neutral beams

et al. 2012

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Two of the eight neutral-beam sources on the DIII-D tokamak were modified to allow injection below the midplane. To validate off-axis beam performance, the various beams are injected sequentially into low-power plasmas that are optimized for accurate neutron, neutral-particle, fast-ion D-alpha and fast-ion pressure measurements. As expected, the fast-ion profile is broader with off-axis injection than with on-axis injection. The driven toroidal rotation also broadens with off-axis injection and the central fast-ion density is several times smaller. The number of trapped ions in the core depends sensitively on the pitch of the magnetic field lines. Comparisons with classical predictions agree with the measurements for some diagnostics but are discrepant for others.

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Overview of DIII-D off-axis neutral beam project

Abstract: Abstract-DIII-D has four neutral beam lines (NB). Each of these beam lines has two ion sources, each of which injects up to

Cited by 6 publications

References 2 publications

The effect of the fast-ion profile on Alfvén eigenmode stability

The effect of the fast-ion profile on Alfvén eigenmode stability

Testing the DIII-D co/counter off-axis neutral beam injected power and ability to balance injected torque

Initial measurements of the DIII-D off-axis neutral beams

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