Reduction in Neutral Beam Driven Current in a Tokamak by Tearing Modes

Forest, C.B.; Ferron, J. R.; Gianakon, T. A.; Harvey, R. W.; Heidbrink, W. W.; Hyatt, A.W.; Haye, R.J. La; Murakami, M.; Politzer, Peter; John, H.E. St.

doi:10.1103/physrevlett.79.427

Cited by 39 publications

(18 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Since any beam ion transport resulting from these fluctuations is not quantified, the result cannot be considered a strong argument for microturbulence-induced transport. Specifically, tearing modes are well known 115 to reduce NBCD. Additional analysis of these high-power shots is presented in other publications, 44,48 but still without quantifying the effects of coherent fluctuation activity.…”

Section: B Consideration Of Previous Resultsmentioning

confidence: 99%

Energetic ion transport by microturbulence is insignificant in tokamaks

et al. 2013

Self Cite

View full text Add to dashboard Cite

Energetic ion transport due to microturbulence is investigated in magnetohydrodynamic-quiescent plasmas by way of neutral beam injection in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. A range of on-axis and off-axis beam injection scenarios are employed to vary relevant parameters such as the character of the background microturbulence and the value of E b =T e , where E b is the energetic ion energy and T e the electron temperature. In all cases, it is found that any transport enhancement due to microturbulence is too small to observe experimentally. These transport effects are modeled using numerical and analytic expectations that calculate the energetic ion diffusivity due to microturbulence. It is determined that energetic ion transport due to coherent fluctuations (e.g., Alfvén eigenmodes) is a considerably larger effect and should therefore be considered more important for ITER. V C 2013 AIP Publishing LLC.

show abstract

Section: B Consideration Of Previous Resultsmentioning

confidence: 99%

Energetic ion transport by microturbulence is insignificant in tokamaks

et al. 2013

Self Cite

View full text Add to dashboard Cite

show abstract

“…7,8 As far as low-frequency ͑ / 2 Շ 20 kHz͒ MHD modes are concerned, for passing particles the formation of socalled drift islands can lead to particle losses, either because of orbit stochasticity due to the overlap of drift islands, 9,10 or because the drift islands intersect the plasma-facing components. 11 These mechanisms have been invoked as an explanation for the observed reduction of neutral-beam driven current in tokamaks 12 and for the losses of NBIgenerated fast passing ions recently observed at ASDEX Upgrade ͑AUG͒ tokamak. 11,13,14 In this paper, the focus is on the expulsion of energetic trapped particles due to low-frequency magnetohydrodynamic perturbations.…”

Section: Introductionmentioning

confidence: 99%

Observation and modeling of fast trapped ion losses due to neoclassical tearing modes

et al. 2008

View full text Add to dashboard Cite

Losses of trapped fast ions in the presence of low-frequency modes are observed in the ASDEX Upgrade tokamak ͓Fusion Science and Technology 44, 569 ͑2003͒, Special Issue on ASDEX Upgrade͔ during ion-cyclotron heated discharges by means of a new fast-ion-losses detector. The expulsion is explained in terms of the magnetic drift induced by the perturbation field when the ratio between the bounce frequency and the toroidal precession frequency equals the toroidal mode number.

show abstract

“…The confinement of fast ions is relatively insensitive to the stochastic field of the RFP. Despite the weak toroidal field and multiple resonant tearing modes which could diminish fast ion confinement, 36,37 fast ions are observed to slow classically and have a confinement time much larger than thermal particles. 26 The dearth of transport within the modestly stochastic magnetic field is understood to result from the decoupling of the fast ion orbits from the magnetic perturbations.…”

Section: Confinement Of Ions In the Rfpmentioning

confidence: 99%

Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma

et al. 2016

View full text Add to dashboard Cite

While reconnection-driven ion heating is common in laboratory and astrophysical plasmas, the underlying mechanisms for converting magnetic to kinetic energy remain not fully understood. Reversed field pinch discharges are often characterized by rapid ion heating during impulsive reconnection, generating an ion distribution with an enhanced bulk temperature, mainly perpendicular to magnetic field. In the Madison Symmetric Torus, a subset of discharges with the strongest reconnection events develop a very anisotropic, high energy tail parallel to magnetic field in addition to bulk perpendicular heating, which produces a fusion neutron flux orders of magnitude higher than that expected from a Maxwellian distribution. Here, we demonstrate that two factors in addition to a perpendicular bulk heating mechanism must be considered to explain this distribution. First, ion runaway can occur in the strong parallel-to-B electric field induced by a rapid equilibrium change triggered by reconnection-based relaxation; this effect is particularly strong on perpendicularly heated ions which experience a reduced frictional drag relative to bulk ions. Second, the confinement of ions varies dramatically as a function of velocity. Whereas thermal ions are governed by stochastic diffusion along tearing-altered field lines (and radial diffusion increases with parallel speed), sufficiently energetic ions are well confined, only weakly affected by a stochastic magnetic field. High energy ions traveling mainly in the direction of toroidal plasma current are nearly classically confined, while counter-propagating ions experience an intermediate confinement, greater than that of thermal ions but significantly less than classical expectations. The details of ion confinement tend to reinforce the asymmetric drive of the parallel electric field, resulting in a very asymmetric, anisotropic distribution.

show abstract

Reduction in Neutral Beam Driven Current in a Tokamak by Tearing Modes

Abstract: Profiles of noninductive current driven by neutral beam injection into a tokamak have been measured and compared with theory. The driven current can be less than the theoretical prediction ( by up to 80%) in the presence of islands driven by tearing modes. [S0031-9007(97)

Cited by 39 publications

References 19 publications

Energetic ion transport by microturbulence is insignificant in tokamaks

Energetic ion transport by microturbulence is insignificant in tokamaks

Observation and modeling of fast trapped ion losses due to neoclassical tearing modes

Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma

Contact Info

Product

Resources

About