Measurement of a 2D fast-ion velocity distribution function by tomographic inversion of fast-ion D-alpha spectra

Salewski, M.; Geiger, B.; Jacobsen, A. S.; García-Muñoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S. K.; Rasmussen, Jesper; Stejner, M.; Tardini, G.; Weiland, M.

doi:10.1088/0029-5515/54/2/023005

Cited by 71 publications

(103 citation statements)

References 81 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The GCV method tends to regularize less than the L-curve method ( figure 4(b)) and roughly produces a regularization level as was sometimes judiciously selected [11,24,27]. The full energy beam injection peak (60 keV) does not appear but there is a clear ridge of large phase-space densities between the expected locations of the beam injection peaks.…”

Section: Standard Inversions and The Choice Of The Regularization Parmentioning

confidence: 99%

High-definition velocity-space tomography of fast-ion dynamics

et al. 2016

Self Cite

View full text Add to dashboard Cite

Velocity-space tomography of the fast-ion distribution function in a fusion plasma is usually a photon-starved tomography method due to limited optical access and signal-to-noise ratio of fast-ion D α (FIDA) spectroscopy as well as the strive for high-resolution images. In highdefinition tomography, prior information makes up for this lack of data. We restrict the target velocity space through the measured absence of FIDA light, impose phase-space densities to be non-negative, and encode the known geometry of neutral beam injection (NBI) sources. We further use a numerical simulation as prior information to reconstruct where in velocity space the measurements and the simulation disagree. This alternative approach is demonstrated for four-view as well as for two-view FIDA measurements. The high-definition tomography tools allow us to study fast ions in sawtoothing plasmas and the formation of NBI peaks at full, half and one-third energy by time-resolved tomographic movies.

show abstract

Section: Standard Inversions and The Choice Of The Regularization Parmentioning

confidence: 99%

High-definition velocity-space tomography of fast-ion dynamics

et al. 2016

Self Cite

View full text Add to dashboard Cite

show abstract

“…Good agreement is found for AUG#30382 at 2.5s where the remaining discrepancy can be explained by the absence of a source term (NBI fueling) in EBdyna. The FIDA diagnostic can further be used as a tomographic system ( [26], [27]) aimed at resolving the velocity space of fast Deuterium in the experiment [7]. The tomographic inversion of the FIDA measurements allows us to calculate the redistribution of fast particles resolved in velocity space.…”

Section: Fast Ions Deuterium-alpha (Fida) Spectroscopic Measurementsmentioning

confidence: 99%

Numerical and experimental study of the redistribution of energetic and impurity ions by sawteeth in ASDEX Upgrade

et al. 2016

Self Cite

View full text Add to dashboard Cite

Abstract. In the non-linear phase of a sawtooth, the complete reconnection of field lines around the q = 1 flux surface often occurs resulting in a radial displacement of the plasma core. A complete time-dependent electromagnetic model of this type of reconnection has been developed and implemented in the EBdyna go code. This contribution aims at studying the behaviour of ions, both impurity and fast particles, in the pattern of reconnecting field lines during sawtoothing plasma experiments in the ASDEX Upgrade tokamak by using the newly developed numerical framework. The simulation of full reconnection with tungsten impurity that include the centrifugal force are achieved and recover the Soft X-Ray (SXR) measurements. Based on this full-reconnection description of the sawtooth, a simple tool dedicated to estimate the duration of the reconnection is introduced. This work then studies the redistribution of fast ions during several experimentally observed sawteeth. In some cases of sawteeth at ASDEX Upgrade, full reconnection is not always observed or expected so the code gives an upper estimate of the actual experimental redistribution. The results of detailed simulations of the crashes are compared with measurements from various diagnostics such as Collective Thomson Scattering (CTS) and Fast-Ion DAlpha (FIDA) spectroscopy, including FIDA tomography. A convincing qualitative agreement is found in different parts of velocity space.

show abstract

“…For a more detailed analysis that includes all accessible wavelength ranges and viewing geometries, a tomographic inversion has been applied that is based on a truncated singular value decomposition as in previous work [34,35,36]. In this method the forward model to calculate FIDA spectra is formulated in the form of a matrix larger values for positive pitches than for negative pitches, explained by the co-current NBI injection geometry.…”

Section: Sawtooth-induced Fast-ion Transportmentioning

confidence: 99%

Fast-ion transport and neutral beam current drive in ASDEX upgrade

Geiger¹,

Weiland²,

Jacobsen³

et al. 2015

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

Abstract.The neutral beam current drive efficiency has been investigated in the ASDEX Upgrade tokamak by replacing on-axis neutral beams with tangential off-axis beams.A clear modification of the radial fast-ion profiles is observed with a fast-ion Dalpha diagnostic that measures centrally peaked profiles during on-axis injection and outwards shifted profiles during off-axis injection. Due to this change of the fast-ion population, a clear modification of the plasma current profile is predicted but not observed by a motional Stark effect diagnostic.The fast-ion transport caused by MHD activity has been studied in low collisionality discharges that exhibit strong (1,1) modes. In particular due to sawtooth crashes, significant radial redistribution of co-rotating fast-ions is observed which can very well be described by the Kadomtsev model. In addition, first tomographic reconstructions of the central 2D fast-ion velocity space in the presence of sawtooth crashes allow the investigation of the pitch dependence of the mode-imposed redistribution: A stronger redistribution of mainly co-rotating fast ions is observed than of those with smaller pitch values.

show abstract

Measurement of a 2D fast-ion velocity distribution function by tomographic inversion of fast-ion D-alpha spectra

Cited by 71 publications

References 81 publications

High-definition velocity-space tomography of fast-ion dynamics

High-definition velocity-space tomography of fast-ion dynamics

Numerical and experimental study of the redistribution of energetic and impurity ions by sawteeth in ASDEX Upgrade

Fast-ion transport and neutral beam current drive in ASDEX upgrade

Contact Info

Product

Resources

About