Imaging Neutral Particle Analyzer (INPA) measurements of confined fast ions in DIII-D

Abstract

A: A novel imaging neutral particle analyzer (INPA) which provides energy-resolved radial profiles of confined fast ions on the DIII-D tokamak is discussed. The INPA measures chargeexchanged energetic neutrals by viewing an "active" neutral beam through a 1D pinhole camera with a rear collimating slit that defines the neutral particle collection sightlines. The incident neutrals are ionized by 10 nm thick carbon stripping foils and the local tokamak magnetic field acts as a magnetic spectrometer to disperse ions onto a phosphor scintillator. A fast (160 Hz) CCD camera provides 2D images of the escaping neutrals mapped to energy and radial position in the plasma. The INPA typically probes passing orbits with an energy resolution of ≈7.5 keV (E = 20 − 80 keV) and a spatial resolution that ranges from 4 cm half width at half max (HWHM) in the core to 3 cm at the plasma edge. The INPA clearly resolves fast ion transport in localized regions of phase space due to individual sawteeth and a replenishing before each event. Extension to proton and triton DD fusion product measurements in high-performance DIII-D plasmas is analyzed and simulations show peak signals which are 10 −6 lower than that from neutral beam ions for the same configuration. Possible modifications to increase fusion product signals are discussed along with upgrades to improve the overall diagnostic performance. K: Plasma diagnostics -charged-particle spectroscopy; Nuclear instruments and methods for hot plasma diagnostics 1Corresponding author.

Visualization of Fast Ion Phase-Space Flow Driven by Alfvén Instabilities

“…Transport by Alfvén eigenmodes (AE) is a particular concern. To address this, an imaging neutral particle analyzer (INPA) [9,10] was developed in the DIII-D tokamak. The first ever visualization of fast ion phase-space flow driven by AEs is reported here.…”

“…The INPASIM also finds that fast ions with the pitch v k =v from ∼0.77 to 0.84 can be collected by INPA, illustrated as the black band (v k refers to the fast ion velocity parallel to the magnetic field line). Note that the validation of the INPA system [9,10] and synthetic modeling [11] in a broad range of plasma parameters were systematically reported in Refs. [11,13].…”

“…6(a). This is because the neutral beam nearly tangential to the magnetic field line populates the magnetic axis region with a pitch of ∼0.68, outside of the INPA-interrogated pitch [10]. In contrast, the I SD HP in the highpower shot is significantly flattened along the streamline [red line in Fig.…”

Design and simulation of an Imaging Neutral Particle Analyzer for the ASDEX Upgrade tokamak

“…1 For this purpose, novel diagnostic techniques to measure the FI distribution in phase-space with Alfvénic temporal resolution are currently being developed. The Imaging Neutral Particle Analyser (INPA), already installed at the DIII-D tokamak 2,3 , which is able to measure the radial position and energy of the confined FI population with fast temporal response response, is one example among these novel diagnostics.…”

Design and simulation of an imaging neutral particle analyzer for the ASDEX Upgrade tokamak

“…1 For this purpose, novel diagnostic techniques to measure the FI distribution in phase space with Alfvénic temporal resolution are currently being developed. The Imaging Neutral Particle Analyzer (INPA), already installed at the DIII-D tokamak, 2,3 which is able to measure the radial position and energy of the confined FI population with a fast temporal response, is one example among these novel diagnostics.…”