A. Ouroua

Time-series analysis of nonstationary plasma fluctuations using wavelet transforms

A wavelet or time-scale approach to analyzing a single time series and two time series, in which the fluctuating quantities are statistically nonstationary, is presented. The time scale and scale “power spectra” are introduced and utilized to analyze transient potential fluctuations measured at the core of sawtoothing TEXT-U plasmas. The results show features that have not been previously observed using any Fourier techniques. In addition, the linear time-scale “coherence spectrum” is developed to quantify the degree of linear relationship between two nonstationary fluctuating quantities in the time-scale domain. Such a spectrum is also useful in tracking the time-varying phase difference. A numerical example is provided to demonstrate the efficacy of the time-scale spectra.

Measurement of neutral density profile in TEXT using a diagnostic neutral beam

We use a diagnostic neutral beam, a scanning neutral particle energy analyzer, and Hα measurements to estimate the neutral density profile from the edge to the center of the TEXT tokamak. The diagnostic neutral beam provides a spatially localized density of neutrals. The plasma neutral density is measured from the ratio of the signals seen with and without the beam. The Hα measurements provide neutral profiles in the edge region and the global particle confinement time τp. The shapes of the observed neutral energy spectra put a lower bound on the central neutral density. Results are compared with estimates of NUT and general agreement is found. Error estimates are given.

Electron cyclotron emission diagnostic for ITER

Electron temperature measurements and electron thermal transport inferences will be critical to the nonactive and deuterium phases of ITER operation and will take on added importance during the alpha heating phase. The diagnostic must meet stringent criteria on spatial coverage and spatial resolution during full field operation. During the early phases of operation, it must operate equally well at half field. The key to the diagnostic is the front end design. It consists of a quasioptical antenna and a pair of calibration sources. The radial resolution of the diagnostic is less than 0.06 m. The spatial coverage extends at least from the core to the separatrix with first harmonic O-mode being used for the core and second harmonic X-mode being used for the pedestal. The instrumentation used for the core measurement at full field can be used for detection at half field by changing the detected polarization. Intermediate fields are accessible. The electron cyclotron emission systems require in situ calibration, which is provided by a novel hot calibration source. The critical component for the hot calibration source, the emissive surface, has been successfully tested. A prototype hot calibration source has been designed, making use of extensive thermal and mechanical modeling.

Measurements of neutral density profiles on the TEXT tokamak

Neutral density profiles are measured in the outer third of the plasma of the TEXT tokamak in conjunction with ion temperature measurements using the far line wings of a Hα profile. The advantage of this technique is that it does not require a radial inversion of the data to obtain a measure of the local neutral density. The ion temperature profiles are compared with the results from a neutral particle analyzer, and the neutral profiles with the results of a numerical code which solves a system of coupled linear equations describing particle transport from a neutral source.

Design, Analysis, and Testing of a Hot Calibration Source for the ITER-ECE Diagnostic System

Abstract This paper describes the development of a prototype hot calibration source for the ITER-ECE diagnostic system. A resistive heating element encapsulated in an Inconel heating block was initially selected to heat a silicon carbide emitter to the required 700°C temperature. Radiative and direct contact heat transfer methods were considered and tested in a test prototype. The radiative heat transfer approach was selected and methods to improve the heater emissivity were investigated. Extended tests were conducted to verify long term heating performance, materials stability, and ITER vacuum compatibility. Design iterations guided by initial test results followed and alternative heater materials, heating elements, and heater design features were considered. Initial design, analysis, and test results are presented. Subsequent efforts to meet the full requirements of the hot calibration source are also presented.

Development of a new q‐diagnostic for TEXT

The vertically injected diagnostic neutral beam on TEXT provides a ripple trapped population of fast monoenergetic ions with a large v⊥ and small v∥. The neutrals formed in a second charge exchange collision of these fast ions leave the tokamak in a plane perpendicular to the local magnetic field. The direction of the B field can be accurately determined by locating this plane using a toroidal array of detectors looking for neutrals at the beam energy. This technique should allow full q‐profile measurement for all plasma conditions with a time resolution less than 1 ms, and angular resolution better than 0.1°. We describe a series of experiments to establish the proof of principle and present details of the design of a 40‐channel detector array for application on TEXT‐Upgrade.

Physics design of the in-vessel collection optics for the ITER electron cyclotron emission diagnostic.

Measurement of the electron cyclotron emission (ECE) is one of the primary diagnostics for electron temperature in ITER. In-vessel, in-vacuum, and quasi-optical antennas capture sufficient ECE to achieve large signal to noise with microsecond temporal resolution and high spatial resolution while maintaining polarization fidelity. Two similar systems are required. One views the plasma radially. The other is an oblique view. Both views can be used to measure the electron temperature, while the oblique is also sensitive to non-thermal distortion in the bulk electron distribution. The in-vacuum optics for both systems are subject to degradation as they have a direct view of the ITER plasma and will not be accessible for cleaning or replacement for extended periods. Blackbody radiation sources are provided for in situ calibration.