The behaviour of fast ions in tokamak experiments

Heidbrink, W.W.; Sadler, G.

doi:10.1088/0029-5515/35/2/514

Cited by 27 publications

(31 citation statements)

References 66 publications

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“…Velocityspace tomography is less developed [13,33,34] but could be particularly useful in studies of selective ejection or redistribution in velocity space. Several types of modes affect ions in only part of velocity space, for example sawteeth [35][36][37][38], Alfvén eigenmodes [6,[39][40][41][42][43] and neoclassical tearing modes [4,5]. Turbulent transport of fast ions also depends on the ion energy [44][45][46][47].…”

Section: Introductionmentioning

confidence: 99%

Combination of fast-ion diagnostics in velocity-space tomographies

et al. 2013

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Fast-ion D α (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fastion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods.

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Section: Introductionmentioning

confidence: 99%

Combination of fast-ion diagnostics in velocity-space tomographies

et al. 2013

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“…The deleterious effect of low (m, n) MHD modes on fast-ion confinement is well documented experimentally [3]. Discharge #49113 shows no detectable coherent MHD activity on the magnetic diagnostics; discharge #73457 has an edge Alfvén quasi-coherent mode at ∼200 kHz [21], but no low frequency coherent MHD activity.…”

Section: Discussionmentioning

confidence: 86%

“…This is attributed to finite gyro-radii effects and particle drifts [1,2]. However, the presence of strong MHD activity or large deviations in the magnetic field symmetry can cause substantial fast-ion losses [3]. For example, in DIII-D plasmas with strong Alfvén eigenmodes, up to 70% of the beam ions were lost from the plasma [4], while in JET, when the field ripple was increased from 1% to 12.5%, the confinement of 1 MeV tritons fell by 30-60% [5].…”

Section: Introductionmentioning

confidence: 99%

“…As a simplification, the transport is often quantified with an effective zero-dimensional diffusion coefficient D f [3]. Justification for such a treatment can be found in the fact that most of the fusion reactions take place near the plasma centre, where the confinement is the best, and where most of the plasma energy and neutron production are concentrated.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for spatially variable beam ion diffusion in TFTR

Ruskov¹,

Heidbrink²,

McCune³

et al. 1996

Plasma Phys. Control. Fusion

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Abstract. We present evidence that the fast-ion diffusion coefficient changes across the TFTR plasma column. Two MHD quiescent discharges are analysed: a high power D-T plasma heated with 21 MW of deuterium and tritium beams, and an ohmic plasma into which a 10 MW, 20 ms deuterium beam pulse was injected. The localized charge-exchange measurements in the ohmic plasma, and the neutron flux measurements in the D-T plasma are compared with predictions from the 1 1 2 D transport simulation code TRANSP. We have modified the code to allow modelling with arbitrary fast-ion diffusion profiles D f (r). Significant improvement in the agreement between measurement and simulation is obtained with a D f (r) profile that has low values in the inner half of the plasma column (D f < 0.05 m 2 s −1 ) and then rises rapidly towards the plasma periphery. This suggests a common underlying mechanism of enhanced beam ion transport in the two discharges, such as stochastic ripple diffusion.

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“…In particular, fast fusion-born alpha particles in next-step burning fusion devices must be well confined, both to maintain fusionrelevant temperatures through transfer of their kinetic energy to the background plasma, and to reduce their otherwise deleterious impact on the plasma-facing components. Fast ions can furthermore both drive and interact with a range of common plasma instabilities [1][2][3][4][5][6][7][8] and may thus have an important impact on the overall stability and performance of the plasma. Accurate characterization and detailed understanding of the behaviour of fast-ion populations in tokamak plasmas are thus important for attempts to optimize plasma heating, current drive, and overall fusion performance, and ultimately to achieve stable burning conditions in a future fusion power plant.…”

Section: Introductionmentioning

confidence: 99%

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

Rasmussen

Nielsen

Stejner

et al. 2015

Plasma Phys. Control. Fusion

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Abstract. Internally consistent characterization of the properties of the fastion distribution from multiple diagnostics is a prerequisite for obtaining a full understanding of fast-ion behavior in tokamak plasmas. Here we benchmark several absolutely-calibrated core fast-ion diagnostics at ASDEX Upgrade by comparing fastion measurements from collective Thomson scattering, fast-ion D α spectroscopy, and neutron rate detectors with numerical predictions from the TRANSP/NUBEAM transport code. We also study the sensitivity of the theoretical predictions to uncertainties in the plasma kinetic profiles. We find that theory and measurements generally agree within these uncertainties for all three diagnostics during heating phases with either one or two neutral beam injection sources. This suggests that the measurements can be described by the same model assuming classical slowing down of fast ions. Since the three diagnostics in the adopted configurations probe partially overlapping regions in fast-ion velocity space, this is also consistent with good internal agreement among the measurements themselves. Hence, our results support the feasibility of combining multiple diagnostics at ASDEX Upgrade to reconstruct the fast-ion distribution function in 2D velocity space.

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The behaviour of fast ions in tokamak experiments

Cited by 27 publications

References 66 publications

Combination of fast-ion diagnostics in velocity-space tomographies

Combination of fast-ion diagnostics in velocity-space tomographies

Evidence for spatially variable beam ion diffusion in TFTR

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

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