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.

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.

The first plasma with target values of the plasma current and the pulse duration was finally achieved on June 13, 2008 in the Korea Superconducting Tokamak Advanced Research (KSTAR). The diagnostic systems played an important role in achieving successful first plasma operation for the KSTAR tokamak. The employed plasma diagnostic systems for the KSTAR first plasma including the magnetic diagnostics, millimeter-wave interferometer, inspection illuminator, H(alpha), visible spectrometer, filterscope, and electron cyclotron emission (ECE) radiometer have provided the main plasma parameters, which are essential for the plasma generation, control, and physics understanding. Improvements to the first diagnostic systems and additional diagnostics including an x-ray imaging crystal spectrometer, reflectometer, ECE radiometer, resistive bolometer, and soft x-ray array are scheduled to be added for the next KSTAR experimental campaign in 2009.

Ten modules of the integrator system of the initial magnetic diagnostics for the first plasma operation have been simultaneously tested in the Korea superconducting tokamak advanced research device by measuring the magnetic flux density from various magnetic diagnostics sensors when a small current was applied to the superconducting poloidal field coils. The measured drifts from the integrators show between 1x10(-6) and 1x10(-5) Wb/s. The results from the field tests before the first plasma generation are described.

For the measurement of the magnetic field distribution with high spatial resolution and high accuracy, the magnetic field sensing probe must be non-magnetic, but the MFM probe and sub-millimeter-meter size Hall probe use a ferromagnetic tip and block, respectively, to increase the sensitivity. To overcome this drawback, we developed a micro-size search coil magnetometer which consists of a single turn search coil, Terfenol-D actuator, scanning system, and control software. To reduce the noise generated by the stray ac magnetic field of the actuator driving coil, we employed an even function λ-H magnetostriction curve and lock-in technique. Using the developed magnetometer, we were able to measure the magnetic field distribution with a magnetic field resolution of 1 mT and spatial resolution of 0.1 mm × 0.2 mm at a coil vibration frequency of 1.8 kHz.