RESUMO
The 30 keV lithium beam diagnostic on DIII-D is suitable to measure both the radial electron density and poloidal magnetic field profiles in the pedestal. The refurbished system features a new setup to measure the Doppler shift allowing accurate alignment of the spectral filters. The injector has been optimized to generate a stable lithium neutral beam with a current of I = 15-20 mA and a diameter of 1.9 ± 0.1 cm measured by beam imaging. The typical temporal resolution is Δt = 1-10 ms and the radial resolution of ΔR = 5 mm is given by the optical setup. A new analysis technique based on fast Fourier transform avoids systematic error contributions from the digital lock-in analysis and accounts intrinsically for background light correction. Latest upgrades and a detailed characterization of the system are presented. Proof-of-principle measurements of the poloidal magnetic field with a statistical error of typically 2% show a fair agreement with the predictions modeled with the Grad-Shafranov equilibrium solver EFIT within 4%.
RESUMO
Four collisional radiative models (CRMs) for reconstruction of the edge electron density profile from the measured Li I (2s-2p) emission profile of an accelerated lithium beam are compared using experimental data from DIII-D. It is shown for both L- and H-mode plasmas that edge density profiles reconstructed with the CRMs DDD2, ABSOLUT, [Sasaki et al. Rev. Sci. Instrum. 64, 1699 (1993)] and a new model developed at DIII-D agree in a density scan from n(e) (ped) = (2.0-6.5) × 10(19) m(-3) within 20%, 20%, <5%, and 40%, respectively, of the pedestal density measured with Thomson scattering. Profile shape and absolute density vary in a scan of the effective ion charge Z(eff) = 1-6 up to a factor of two but agree with Thomson data for Z(eff) = 1-2 within the error bars.
RESUMO
Radial profiles of electron temperature and density are measured at high spatial (â¼1 mm) and temporal (≥10 µs) resolution using a thermal supersonic helium jet. A highly accurate detection system is applied to well-developed collisional-radiative model codes to produce the profiles. Agreement between this measurement and an edge Thomson scattering measurement is found to be within the error bars (â²20%). The diagnostic is being used to give profiles near the ion cyclotron resonant heating antenna on TEXTOR to better understand RF coupling to the core.
RESUMO
A supersonic helium beam diagnostic, based on the line-ratio technique for high resolution electron density and temperature measurements in the plasma edge (r/a > 0.9) was designed, built, and optimised at TEXTOR (Torus Experiment for Technology Oriented Research). The supersonic injection system, based on the Campargue skimmer-nozzle concept, was developed and optimised in order to provide both a high neutral helium beam density of n(0) = 1.5 × 10(18) m(-3) and a low beam divergence of ±1° simultaneously, achieving a poloidal resolution of Δ(poloidal) = 9 mm. The setup utilises a newly developed dead volume free piezo valve for operation in a high magnetic field environment of up to 2 T with a maximum repetition rate of 80 Hz. Gas injections are realised for a duration of 120 ms at a repetition rate of 2 Hz (duty cycle 1/3). In combination with a high sensitivity detection system, consisting of three 32 multi-channel photomultipliers (PMTs), measurements of edge electron temperature and density with a radial resolution of Δ(radial) = 2 mm and a maximum temporal resolution of Δt ≃ 2 µs (470 kHz) are possible for the first time. The diagnostic setup at TEXTOR is presented. The newly developed injection system and its theoretical bases are discussed. The applicability of the stationary collisional-radiative model as basis of the line-ratio technique is shown. Finally, an example of a fluctuation analysis demonstrating the unique high temporal and spatial resolution capabilities of this new diagnostic is presented.
