Magnetohydrodynamic mode identification from magnetic probe signals via a matched filter method

Abstract

A matched filter analysis has been developed to identify the amplitude and phase of magnetohydrodynamic modes in DIII-D tokamak plasmas using magnetic probe signals (δBp). As opposed to conventional Fourier spatial analysis of toroidally spaced probes, this analysis includes data from both toroidally and poloidally spaced magnetic probe arrays. Using additional probes both improves the statistics of the analysis and more importantly incorporates poloidal information into the mode analysis. The matched filter is a numeric filter that matches signals from the magnetic probes with numerically predicted signals for the mode. The numerical predictions are developed using EFIT equilibrium reconstruction data as input to the stability code GATO and the vacuum field code VACUUM. Changes is the plasma equilibrium that occur on the same time scale as the mode are taken into account by modeling simple matched filter vectors corresponding to changes in total plasma current, plus vertical and horizontal plasma shifts. The matched filter method works well when there is good understanding of a mode and good modeling of its structure. Matched filter analysis results for a fast growing ideal kink mode, where equilibrium change effects are minimal, show the effectiveness of this method. A slow growing resistive-wall mode (RWM) is also analyzed using the matched filter method. The method gives good results for identifying the amplitude and phase of the RWM but the simple equilibrium vectors are insufficient for complete elimination of equilibrium changes on this time scale. An analysis of the computational requirements of the scheme indicates that real-time application of the matched filter for RWM identification will be possible.

Radial Structure of Alfvén Eigenmodes in the DIII-D Tokamak through Electron-Cyclotron-Emission Measurements

“…For ITER, a similar ECE system is planned, and diagnostics capable of monitoring core Alfvénic activity beyond typical magnetic probes will be essential. These results suggest a reliable means for identifying internal AEs in ''real time'' by use of ECE measurements in present and future experiments, possibly in combination with ideal MHD calculations to form the basis for a matched-filter-type mode identification [23]. Additionally, this study shows that viewing geometry design in future ECE radiometers is critical in order to optimize resolution of AEs, paying particular attention to viewing beam-waist size compared to the expected poloidal wavelength of AEs.…”

DIII-D Integrated plasma control solutions for ITER and next-generation tokamaks

“…The mode amplitude estimate is calculated using the Far-Tech, Inc. matched filter derived from the vector magnetic diagnostic signals predicted by a linear MHD stability code [12]. The matched filter is thus completely physics-based, with no empirical data or experiment-specific adjustments.…”

Model-based Static and Dynamic Filter Application to Resistive Wall Mode Identification and Feedback Control in DIII-D

“…GATO [18]), in which the perturbed magnetic fields at the plasma surface are calculated. Then, the induced magnetic fields or currents on the magnetic sensors (or resistive wall) are calculated, assuming only vacuum exists between plasma surface and wall [13]. Then, the calculated signals become the basis vectors of the RWM mode pattern.…”

“…WelT1..10 45th IEEE CDC, San Diego, USA, Dec. [13][14][15]2006 The state-equation of the DIII-D/RWM system model is composed of a few circuit equations which can be described in terms of xp, xw, and x,. Here, the coil states (xc) are the feedback coil currents.…”