Fast-Particle-Driven Alfvénic Modes in a Reversed Field Pinch

Koliner, J. J.; Forest, C. B.; Sarff, J. S.; Anderson, J. K.; Liu, D.; Nornberg, M. D.; Waksman, J.; Lin, L.; Brower, D. L.; Ding, W. X.; Spong, D. A.

doi:10.1103/physrevlett.109.115003

Cited by 17 publications

(29 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previously, it was shown that the n ¼ 4 frequency linearly depends on the Alfv en velocity but also remains well below the calculated n ¼ 4 TAE gap at 200-300 kHz. 13 In addition, earlier studies also revealed strong three-wave coupling among the n ¼ 5, n ¼ À1, and n ¼ 4 modes. The possibility that the n ¼ À1 mode is nonlinearly generated was speculated.…”

Section: Resultsmentioning

confidence: 92%

“…4). Previous frequency-scaling studies revealed that the n ¼ 5 mode frequency shows some dependence on the beam ion velocity but weak dependence on the Alfv en velocity, 13 suggesting a non-eigenmode identity. To better examine the temporal dynamics, Fig.…”

Section: Resultsmentioning

confidence: 98%

“…13 In the H-beam cases, switching from D-plasma to H-plasma increases t A0 by 42%, while the n ¼ 5 frequency only increases by 18% (from 65 kHz to 77 kHz). Similar weak dependence of the n ¼ 5 frequency on t A0 is observed in the Dbeam cases.…”

Section: A H-beam Into D-plasma (H To D) a H-beam Into H-plasma (H Tmentioning

confidence: 95%

“…IV A) with Eq. (13) show that q H f i % 0:215 is required to meet wave-particle resonance condition for the m ¼ 1, n ¼ 5 mode at the measured frequency. As q H f i is reduced below 0:215, the resonance condition for the m ¼ 1, n ¼ 5 mode is violated.…”

Section: Dependence On Safety Factormentioning

confidence: 97%

“…12 The first observation of the EP-instabilities in a RFP excited with a clear fast-ion source is from the Madison Symmetric Torus (MST) device where fast ions are generated by a 1 MW neutral beam injector. 13 Internal structure of the excited instabilities is measured with a combined interferometry-polarimetry diagnostic, including first direct observation of internal magnetic fluctuations associated with EP instabilities. 14 The density fluctuations exhibit dynamically evolving, inboard-outboard asymmetric spatial pattern.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

et al. 2014

Self Cite

View full text Add to dashboard Cite

Multiple bursty energetic-particle (EP) driven modes with fishbone-like structure are observed during 1 MW tangential neutral-beam injection in a reversed field pinch (RFP) device. The distinguishing features of the RFP, including large magnetic shear (tending to add stability) and weak toroidal magnetic field (leading to stronger drive), provide a complementary environment to tokamak and stellarator configurations for exploring basic understanding of EP instabilities. Detailed measurements of the EP mode characteristics and temporal-spatial dynamics reveal their influence on fast ion transport. Density fluctuations exhibit a dynamically evolving, inboardoutboard asymmetric spatial structure that peaks in the core where fast ions reside. The measured mode frequencies are close to the computed shear Alfv en frequency, a feature consistent with continuum modes destabilized by strong drive. The frequency pattern of the dominant mode depends on the fast-ion species. Multiple frequencies occur with deuterium fast ions compared to single frequency for hydrogen fast ions. Furthermore, as the safety factor (q) decreases, the toroidal mode number of the dominant EP mode transits from n ¼ 5 to n ¼ 6 while retaining the same poloidal mode number m ¼ 1. The transition occurs when the m ¼ 1, n ¼ 5 wave-particle resonance condition cannot be satisfied as the fast-ion safety factor (q fi ) decreases. The fast-ion temporal dynamics, measured by a neutral particle analyzer, resemble a classical predator-prey relaxation oscillation. It contains a slow-growth phase arising from the beam fueling followed by a rapid drop when the EP modes peak, indicating that the fluctuation-induced transport maintains a stiff fast-ion density profile. The inferred transport rate is strongly enhanced with the onset of multiple EP modes. V C 2014 AIP Publishing LLC. [http://dx.

show abstract

Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 98%

Section: A H-beam Into D-plasma (H To D) a H-beam Into H-plasma (H Tmentioning

confidence: 95%

Section: Dependence On Safety Factormentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

et al. 2014

Self Cite

View full text Add to dashboard Cite

show abstract

Measurement of energetic-particle-driven core magnetic fluctuations and induced fast-ion transport

et al. 2013

Self Cite

View full text Add to dashboard Cite

Internal fluctuations arising from energetic-particle-driven instabilities, including both density and radial magnetic field, are measured in a reversed-field-pinch plasma. The fluctuations peak near the core where fast ions reside and shift outward along the major radius as the instability transits from the n ¼ 5 to n ¼ 4 mode. During this transition, strong nonlinear three-wave interaction among multiple modes accompanied by enhanced fast-ion transport is observed. V

show abstract

Fast ion confinement and stability in a neutral beam injected reversed field pinch

et al. 2013

Self Cite

View full text Add to dashboard Cite

The behavior of energetic ions is fundamentally important in the study of fusion plasmas. While well-studied in tokamak, spherical torus, and stellarator plasmas, relatively little is known in reversed field pinch plasmas about the dynamics of fast ions and the effects they cause as a large population. These studies are now underway in the Madison Symmetric Torus with an intense 25 keV, 1 MW hydrogen neutral beam injector (NBI). Measurements of the time-resolved fast ion distribution via a high energy neutral particle analyzer, as well as beam-target neutron flux (when NBI fuel is doped with 3-5% D 2 ) both demonstrate that at low concentration the fast ion population is consistent with classical slowing of the fast ions, negligible cross-field transport, and charge exchange as the dominant ion loss mechanism. A significant population of fast ions develops; simulations predict a super-Alfv enic ion density of up to 25% of the electron density with both a significant velocity space gradient and a sharp radial density gradient. There are several effects on the background plasma including enhanced toroidal rotation, electron heating, and an altered current density profile. The abundant fast particles affect the plasma stability. Fast ions at the island of the core-most resonant tearing mode have a stabilizing effect, and up to 60% reduction in the magnetic fluctuation amplitude is observed during NBI. The sharp reduction in amplitude, however, has little effect on the underlying magnetic island structure. Simultaneously, beam driven instabilities are observed as repetitive $50 ls bursts which coincide with fast particle redistribution; data indicate a saturated core fast ion density well below purely classical predictions. V C 2013 AIP Publishing LLC [http://dx. INTRODUCTIONThe envisioned burning plasma experiment, regardless of magnetic concept, relies on sufficient confinement of the charged fusion product for plasma self heating. As such, the confinement of fast ions and their impact on the bulk plasma are crucial issues.A tremendous body of work demonstrates that fast ions in a tokamak plasma (born from fusion reactions, ICRF, or NBI) are generally well confined and thermalize via classical Coulomb collisions. However, a sufficiently intense fast ion population can excite collective instabilities that can lead to resonant fast ion transport. 1 A new body of work on the effects of a large fast ion population in the reversed field pinch (RFP) configuration has recently been opened. Despite the RFP's weak toroidal field and multiple resonant tearing modes which could diminish fast ion confinement, 2,3 NBI-born fast ions in low concentration are observed to slow classically and have a confinement time much larger than thermal particles. 4 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. The ions are routinely confined for up to a classical slowing time. 5 In this work, we investigate the effect of...

show abstract

Fast-Particle-Driven Alfvénic Modes in a Reversed Field Pinch

Cited by 17 publications

References 25 publications

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

Measurement of energetic-particle-driven core magnetic fluctuations and induced fast-ion transport

Fast ion confinement and stability in a neutral beam injected reversed field pinch

Contact Info

Product

Resources

About