Index of content:
Volume 80, Issue 2, February 2009
- NUCLEAR PHYSICS, FUSION AND PLASMAS
80(2009); http://dx.doi.org/10.1063/1.3077281View Description Hide Description
An ion cyclotron range of frequency system requires rf diagnostics for a rf-plasma coupling or for maintaining a correct operation. A detector based on a digital demodulation technique collects the rf amplitude and phase at the same time without errors from the imbalance inherent in an analog counterpart. The theory of such a detector was studied and implemented for the first campaign of the KSTAR tokamak. Experimental results of the rf and other diagnostics are presented and discussed.
80(2009); http://dx.doi.org/10.1063/1.3069290View Description Hide Description
A new, high-field side scanning probe has been added to Alcator C-Mod’s complement of edge diagnostics. The wall scanning probe is designed to provide all the benefits of a linear plunge, multielectrode scanning probe while working from the confined space of the inner tokamak wall. The drive mechanism is an embedded coil which produces a torque with the ambient toroidal magnetic field when energized, thus allowing the probe to plunge to different preprogramed depths at different times during a plasma discharge. The probe tip is designed for easy replacement and is presently configured to operate as a modified, high heat-flux “Gundestrup-type” probe with four tungsten electrodes. The probe has demonstrated the ability to obtain cross-field profiles for electron temperature, density, floating potential, and plasma flow information (parallel and perpendicular to ) up to a depth of a few millimiters inside the last-closed flux surface in standard C-Mod discharges. The tungsten-tipped probe has proved very robust and shows little or no damage though it routinely handles surface heat fluxes on the order of at peak insertion.
Localized measurement of short wavelength plasma fluctuations with the DIII-D phase contrast imaging diagnostic80(2009); http://dx.doi.org/10.1063/1.3065094View Description Hide Description
A novel rotating mask system has been designed and implemented on the DIII-D phase contrast imaging (PCI) diagnostic to produce the first spatially localized PCI measurements of a tokamakplasma. The localization technique makes use of the variation in the magnetic field component perpendicular to the viewing chord as a function of chord height. This new capability provides measurements in the range of , , and . This technique provides a spatial resolution of 10 cm at and can realistically provide measurements at a rate of 10 profiles/s. Calibration measurements show accurate characterization of the system transfer function making feasible a time dependent analysis that results in improved localization. Initial measurements show turbulence to peak near the plasma edge. This upgrade is part of a broader program to operate the DIII-D PCI at wave numbers up to to probe electron scale turbulence in the plasma core.
80(2009); http://dx.doi.org/10.1063/1.3082041View Description Hide Description
An energy analyzer device has been developed which utilizes a series of stacked foils and Rogowski current monitors to the measure time resolved current of an intense electron beam. The energy distribution of the electron beam is unfolded from measured current ratios using computer simulations. This device is particularly useful where electron beams are guided by external magnetic fields which may make other electron energy measurement techniques difficult. This technique was used to determine the energy distribution of a 550 keV, 95 kA electron beam as it propagates in the gas mixture of a high power KrF laser. The resulting energy distributions at various depths in the gas are in agreement with three-dimensional particle-in-cell simulations providing confidence in the measurement technique.
Radio-frequency electromagnetic field measurements for direct detection of electron Bernstein waves in a torus plasma80(2009); http://dx.doi.org/10.1063/1.3082047View Description Hide Description
To identify the mode-converted electron Bernstein wave(EBW) in a torus plasma directly, we have developed an interferometry system, in which a diagnosticmicrowave injected outside of the plasma column was directly detected with the probing antenna inserted into the plasma. In this work, plasma production and heating are achieved with , electron cyclotron heating (ECH), whereas diagnostics are carried out with a lower power separate frequency microwave. Three components, i.e., two electromagnetic (toroidal and poloidal directions) and an electrostatic (if refractive index is sufficiently higher than unity, it corresponds to radial component), of ECRF electric field are simultaneously measured with three probing antennas, which are inserted into plasma. Selectivities of each component signal were checked experimentally. Excitation antennas have quite high selectivity of direction of linear polarization. As probing antennas for detecting electromagnetic components, we employed a monopole antenna with a length of , and the separation of the poloidal (-wave) and toroidal (-wave) components of ECRF electric field could be available with this antenna. To detect EBW, which is an electrostatic wave, a small tip antenna was used. As the preliminary results, we detected signals that have three characteristics of EBW, i.e., short wavelength, backward propagation, and electrostatic.