Radio frequency measurements of energetic-particle-driven emission using the ion cyclotron emission diagnostic on the DIII-D tokamak

Abstract

The Ion Cyclotron Emission (ICE) diagnostic on the DIII-D tokamak consists of two outboard midplane systems. In the first system, straps of an ion cyclotron range of frequencies antenna are configured as receiving antennas. For the second system, dedicated magnetic probes incorporated into the outer wall of carbon tiles have recently been restored. These systems collected a large set of radio frequency measurements in the 2015-2018 experimental campaigns by digitizing signals at 200 MSamples/sec for ∼5 seconds per discharge. Each shot typically yields 32 GB of data; techniques for successful handling and analysis of this challengingly large dataset are discussed. The raw voltage fluctuations (<0.2 V and <1 mW) are analyzed in frequency space via fast Fourier transforms. Signals can be analyzed between 1-200 MHz with appropriate filtering and aliasing; this frequency range is limited by DC breaks used to provide 5 kV DC isolation. Three types of high-frequency emission driven by energetic particles have so far been observed using this diagnostic: Compressional Alfvén Eigenmodes with f < 10 MHz, ICE from 5-100 MHz, and whistler waves with f > 100 MHz. ICE occurs at harmonics of the ion cyclotron frequency, enabling the frequency to be mapped to lab space via EFIT equilibrium reconstructions.

Characteristics of tongue-shaped deformations in hydrogen and deuterium plasmas in the Large Helical Device

“…A positive value of the displacement is equal to an outward shift of the plasma while a negative value is equal to an inward shift. Peak values of the normalised output of the high frequency RF probe of 880MHz are used as a trigger of the timing of the tongue event, as peaked high frequency radiation indicates loss of energetic ions at the plasma edge [15,16]. The start of relative time, τ = 0ms, is set to the moment of the RF peaks attain their highest value.…”

Fast wave interferometer for ion density measurement on DIII-D

“…The other is the combination of loop antennas at the same toroidal angle of 242 deg, similar to that described by Watson [7]. These antennas are currently shared with ion cyclotron emission measurement [13,14], and the details of receiver…”

“…antennas used for the FWI are described in past papers [7,13,14]. Since the wave propagates perpendicular to the magnetic field, antenna configurations at the same toroidal angle allows use of eq.…”

Origin of ion cyclotron emission at the proton cyclotron frequency from the core of deuterium plasmas in the ASDEX-Upgrade tokamak

“…Strongly suprathermal radiation known as ion cyclotron emisison (ICE) is widely observed in magnetic confinement fusion (MCF) plasmas [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. Its intensity is typically orders of magnitude greater than that of black-body radiation from thermal ions, and its spectral peak frequencies correspond to multiple cyclotron harmonics of one or more energetic ion species at a specific radial location.…”

“…Most of the early ICE observations were localised to the outer midplane edge region of the MCF plasmas [1,2,3,4,5,6,7,11,19,20], but recently ICE has also been detected from the core plasmas of ASDEX-Upgrade [8,9,10] and DIII-D [12,13,14]. Figure 5a of Ref.…”