Visible light tomography of MHD eigenmodes in the H-1NF stellarator using magnetic coordinates

Haskey, S. R.; Blackwell, Boyd; Seiwald, Bernhard; Howard, J.

doi:10.1088/0029-5515/54/8/083031

Cited by 8 publications

(17 citation statements)

References 32 publications

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“…Linear growth rate scans are also complemented with global kinetic calculations from EUTERPE in Fig. (13). These qualitatively confirm the findings from the LGRO study, and demonstrate that the inclusion of finite Larmor radius effects can reduce the growth rate by a factor of three, but do not affect marginal stability.…”

Section: Discussionsupporting

confidence: 80%

Global Alfvén eigenmodes in the H-1 heliac

Hole

Blackwell

Bowden

et al. 2017

Plasma Phys. Control. Fusion

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Abstract. Recent upgrades in H-1 power supplies have enabled the operation of the H-1 experiment at higher heating powers than previously attainable. A heating power scan in mixed hydrogen/helium plasmas reveals a change in mode activity with increasing heating power. At low power (< 50 kW) modes with beta-induced Alfvén eigenmode (BAE) frequency scaling are observed. At higher power modes consistent with an analysis of nonconventional Global Alfvén Eigenmodes (GAEs) are observed, the subject of this work. We have computed the mode continuum, and identified GAE structures using the ideal MHD solver CKA and the gyrokinetic code EUTERPE. An analytic model for ICRH-heated minority ions is used to estimate the fast ion temperature from the hydrogen species. Linear growth rate scans using a local flux surface stability calculation, LGRO, are performed. These studies demonstrate growth from circulating particles whose speed is significantly less than the Alfvén speed, and are resonant with the mode through harmonics of the Fourier decomposition of the strongly-shaped heliac magnetic field. They reveal drive is possible with a small (n f /n 0 < 0.2) hot energetic tail of the hydrogen species, for which T f ast > 300 eV. Local linear growth rate scans are also complemented with global calculations from CKA and EUTERPE. These qualitatively confirm the findings from the LGRO study, and show that the inclusion of finite Larmor radius effects can reduce the growth rate by a factor of three, but do not affect marginal stability. Finally, a study of damping of the global mode with the thermal plasma is conducted, computing continuum, and the damping arising from finite Larmor radius and parallel electric fields (via resistivity). We find that continuum damping is of order 0.1% for the configuration studied. A similar calculation in the cylindrical plasma model produces a frequency 35% higher and a damping 30% of the three dimensional result: this confirms the importance of strong magnetic shaping to the frequency and damping. The inclusion of resistivity lifts the damping to γ/ω = −0.189. Such large damping is consistent with experimental observations that in absence of drive the mode decays rapidly (∼ 0.1 ms).

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Section: Discussionsupporting

confidence: 80%

Global Alfvén eigenmodes in the H-1 heliac

Hole

Blackwell

Bowden

et al. 2017

Plasma Phys. Control. Fusion

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“…In earlier work in tokamak physics, standing modes have been reconstructed from observed data using the standard least-squares method [2]. Here, we instead adopt a Bayesian approach to model-parameter estimation.…”

Section: Bayesian Inferencementioning

confidence: 99%

“…Bayes theorem is a fundamental result of probability theory which in our context can be written as P(I|D) = P(D|I)P(I) P(D) , (2) where: P(I), called the prior, is a probability distribution representing our underlying knowledge about the state of the currents; P(D|I), called the likelihood function, describes the probability of a particular measurement given the state and our knowledge of measurement errors; P(D), called the marginal probability, quantifies our belief that we will observe a particular piece of data in the case where we know as little as possible about the state. Note that we will usually ignore the marginal likelihood in what follows because in our context it is just a normalising constant which can be restored when needed.…”

Section: Bayesian Inferencementioning

confidence: 99%

A Bayesian formulation for perturbed current tomography in tokamaks

Bohlsen,

Hole

2023

Plasma Phys. Control. Fusion

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An initial investigation into the application of Bayesian inference to the reconstruction of the spatial distribution of current perturbations in tokamaks from diagnostic signals is presented. Previous work in Bayesian equilibrium current tomography is extended to the case of a complex phasor representation of harmonically time varying current distributions. A forward function to predict the response of magnetic diagnostics is constructed using only electrodynamics and not reduced models of ideal MHD. The extension of this forward function to incorporate a fully kinetic model of the plasma state is suggested. The response of soft x-ray diagnostics, and the Motional Stark Effect diagnostic to the current perturbations are also predicted and the integration of all diagnostics into a single estimate of the current perturbation is proposed. Simulations with synthetic diagnostics in simple geometry demonstrate that the perturbed current distribution can be reconstructed subject to prior assumptions regarding solution smoothness.

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“…Computed tomography is a promising approach for measuring the entire structure and the disparate scale of plasma fluctuations 12 . Tomography has been already used as plasma diagnostics to cylindrical and toroidal devices 13 – 25 , although the past and existing tomography applications have never detected the plasma fluctuations in sufficient temporal scales. Specifically, 2-D tomography has been constructed in the plasma assembly for nonlinear turbulence analysis (PANTA) device 26 .…”

Section: Introductionmentioning

confidence: 99%

The first observation of 4D tomography measurement of plasma structures and fluctuations

Moon

Yamasaki

Nagashima

et al. 2021

Sci Rep

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A tomography system is installed as one of the diagnostics of new age to examine the three-dimensional characteristics of structure and dynamics including fluctuations of a linear magnetized helicon plasma. The system is composed of three sets of tomography components located at different axial positions. Each tomography component can measure the two-dimensional emission profile over the entire cross-section of plasma at different axial positions in a sufficient temporal scale to detect the fluctuations. The four-dimensional measurement including time and space successfully obtains the following three results that have never been found without three-dimensional measurement: (1) in the production phase, the plasma front propagates from the antenna toward the end plate with an ion acoustic velocity. (2) In the steady state, the plasma emission profile is inhomogeneous, and decreases along the axial direction in the presence of the azimuthal asymmetry. Furthermore, (3) in the steady state, the fluctuations should originate from a particular axial position located downward from the helicon antenna.

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Visible light tomography of MHD eigenmodes in the H-1NF stellarator using magnetic coordinates

Cited by 8 publications

References 32 publications

Global Alfvén eigenmodes in the H-1 heliac

Global Alfvén eigenmodes in the H-1 heliac

A Bayesian formulation for perturbed current tomography in tokamaks

The first observation of 4D tomography measurement of plasma structures and fluctuations

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