S. G. Lee

Imaging x-ray crystal spectrometer on EAST

A high-resolution imaging x-ray crystal spectrometer is described for implementation on the EAST tokamak to provide spatially and temporally resolved data on the ion temperature, electron temperature and poloidal plasma rotation. These data are derived from observations of the satellite spectra of helium-like argon, Ar XVII, which is the dominant charge state for electron temperatures in the range from 0.4 to 3.0 keV and which is accessible to EAST. Employing a novel design, which is based on the imaging properties of spherically bent crystals, the spectrometers will provide spectrally and spatially resolved images of the plasma for all experimental conditions, which include ohmically heated discharges as well as plasmas with rf and neutral-beam heating. The experimental setup and initial experimental results are presented.

Performance of the magnetic sensor and the integrator for the KSTAR magnetic diagnostics

Magnetic sensors and the integrator for the magnetic field measurement have been developed for the engineering design of the KSTAR magnetic diagnostics (MDs). The frequency characteristics of a magnetic sensor (for magnetic fluctuation measurement) is investigated from the measurement of the response function of the sensor and the analysis of the equivalent electronic circuit in the frequency range of 10 kHz –15 MHz. An analog integrator, which automatically compensates a drift, is fabricated and its performance test (connected with a magnetic sensor) is carried out under a rf environment. The experimental results from the performance test of the sensor and the analog integrator are presented.

The first experimental results from x-ray imaging crystal spectrometer for KSTAR

The x-ray imaging crystal spectrometer (XICS) for the Korea Superconducting Tokamak Advanced Research has been first applied for the experimental campaign in 2009. The XICS was designed to provide measurements of the profiles of the ion and electron temperatures from the heliumlike argon (Ar XVII) spectra. The basic functions of the XICS are properly working although some satellites lines are not well matched with the expected theoretical values. The initial experimental results from the XICS are briefly described.

Magnetic diagnostics for the first plasma operation in Korea Superconducting Tokamak Advanced Research

Magnetic diagnostics for the first plasma operation in the Korea Superconducting Tokamak Advanced Research device are described. The main discussion is the feasibility studies from the magnetic flux and field measurements utilizing the superconducting poloidal field coils before the first plasma generation.

Upgrades of imaging x-ray crystal spectrometers for high-resolution and high-temperature plasma diagnostics on EAST

Upgrade of the imaging X-ray crystal spectrometers continues in order to fulfill the high-performance diagnostics requirements on EAST. For the tangential spectrometer, a new large pixelated two-dimensional detector was deployed on tokamaks for time-resolved X-ray imaging. This vacuum-compatible detector has an area of 83.8 × 325.3 mm(2), a framing rate over 150 Hz, and water-cooling capability for long-pulse discharges. To effectively extend the temperature limit, a double-crystal assembly was designed to replace the previous single crystals for He-like argon line measurement. The tangential spectrometer employed two crystal slices attached to a common substrate and part of He- and H-like Ar spectra could be recorded on the same detector when crystals were chosen to have similar Bragg angles. This setup cannot only extend the measurable Te up to 10 keV in the core region, but also extend the spatial coverage since He-like argon ions will be present in the outer plasma region. Similarly, crystal slices for He-like iron and argon spectra were adopted on the poloidal spectrometer. Wavelength calibration for absolute rotation velocity measurement will be studied using cadmium characteristic L-shell X-ray lines excited by plasma radiation. A Cd foil is placed before the crystal and can be inserted and retracted for in situ wavelength calibration. The Geant4 code was used to estimate X-ray fluorescence yield and optimize the thickness of the foil.

Analog integrator for the Korea superconducting tokamak advanced research magnetic diagnostics.

An analog integrator, which automatically compensates an integrating drift, has been developed for the magnetic diagnostics in the Korea superconducting tokamak advanced research (KSTAR). The compensation of the drift is done by the analog to digital converter-register-digital to analog converter in the integrator. The integrator will be used in the equilibrium magnetic field measurements by using inductive magnetic sensors during a plasma discharge in the KSTAR machine. Two differential amplifiers are added to the signal path between each magnetic sensor and the integrator in order to improve the performance of the integrator because a long signal cable of 100 m will be used for the measurement in the KSTAR machine. In this work, the characteristics of the integrator with two differential amplifiers are experimentally investigated.

Development of advanced X-ray imaging crystal spectrometer utilizing a large area segmented proportional counter for KSTAR

An advanced x-ray imaging crystal spectrometer (XICS) for KSTAR tokamak has been developed by utilizing a segmented two dimensional (2D) position-sensitive multiwire proportional counter. The XICS for the KSTAR tokamak provides time-resolved measurements of the radial ion and electron temperature profiles, toroidal plasma rotation velocity, and ionization equilibrium. The segmented 2D detector with delay-line readout and supporting electronics has been adopted to improve the photon count rate capability. The current fabrication status of the XICS for the KSTAR tokamak and the first performance test results of the prototype segmented 2D detector are presented.

Data acquisition system for an advanced x-ray imaging crystal spectrometer using a segmented position-sensitive detector

A versatile time-to-digital converter based data acquisition system for a segmented position-sensitive detector has been developed. This data acquisition system was successfully demonstrated to a two-segment position-sensitive detector. The data acquisition system will be developed further to support multisegmented position-sensitive detector to improve the photon count rate capability of the advanced x-ray imaging crystal spectrometer system.

Diamagnetic loop for the first plasma in the KSTAR machine.

The diamagnetic loop (DL) is installed for the plasma diamagnetic measurement at the first plasma in the Korea superconducting tokamak advanced research (KSTAR) machine. Experimental results from the position measurement of the DL inside the KSTAR vacuum vessel and the vacuum flux measurement by using the DL for the evaluation of the geometrical data and the balance coefficient of the DL for the compensation of the vacuum flux in the diamagnetic measurement are described. In addition, a preliminary work of an instrument for a hardware compensation of the vacuum flux is presented.

Measurement of helium-like and hydrogen-like argon spectra using double-crystal X-ray spectrometers on EAST

A two-crystal assembly was deployed on the tangential X-ray crystal spectrometer to measure both helium-like and hydrogen-like spectra on EAST. High-quality helium-like and hydrogen-like spectra were observed simultaneously for the first time on one detector for a wide range of plasma parameters. Profiles of line-integrated core ion temperatures inferred from two spectra were consistent. Since tungsten was adopted as the upper divertor material, one tungsten line (W XLIV at 4.017 Å) on the short-wavelength side of the Lyman-α line (Lα1) was identified for typical USN discharges, which was diffracted by a He-like crystal (2d = 4.913 Å). Another possible Fe XXV line (1.85 Å) was observed to be located on the long-wavelength side of resonance line (w), which was diffracted from a H-like crystal (2d = 4.5622 Å) on the second order. Be-like argon lines were also observable that fill the detector space between the He-like and H-like spectra.