The Korea Superconducting Tokamak Advanced Research (KSTAR) project is the major effort of the national fusion programme of the Republic of Korea. Its aim is to develop a steady state capable advanced superconducting tokamak to establish a scientific and technological basis for an attractive fusion reactor. The major parameters of the tokamak are: major radius 1.8 m, minor radius 0.5 m, toroidal field 3.5 T and plasma current 2 MA, with a strongly shaped plasma cross-section and double null divertor. The initial pulse length provided by the poloidal magnet system is 20 s, but the pulse length can be increased to 300 s through non-inductive current drive. The plasma heating and current drive system consists of neutral beams, ion cyclotron waves, lower hybrid waves and electron cyclotron waves for flexible profile control in advanced tokamak operating modes. A comprehensive set of diagnostics is planned for plasma control, performance evaluation and physics understanding. The project has completed its conceptual design and moved to the engineering design and construction phase. The target date for the first plasma is 2002.

A reliable and reproducible surface-enhanced Raman scattering (SERS) measurement utilizing Au nanoparticle-encapsulated hydrogels as a substrate has been demonstrated. A hydrogel matrix was adopted to: (i) take advantage of its excellent water uptake capacity for facile access of an analyte into the substrate and (ii) securely hold Au nanoparticles. Silica-coated Au (Au@SiO(2)) nanoparticles were initially prepared and uniquely used as an initiator as well as a cross-linker for the polymerization of acrylic acid to synthesize Au nanoparticle-encapsulated hydrogels. Then, the outer silica layer of the Au nanoparticles in the hydrogel was etched out using hydrofluoric acid (HF) to make it possible for an analyte to approach the surface of the Au nanoparticles for generation of the SERS signal. In parallel, locally occurring SERS signals over the hydrogel were integrated using a wide area illumination scheme capable of covering a large area to improve quantitative representation of analyte concentration. To evaluate reproducibility of the proposed method, 6 independent hydrogels were prepared every two months over one year and then Raman spectra of 2-naphthalenethiol (2-NAT) captured hydrogels were collected. The resulting SERS intensities of 2-NAT acquired at each concentration were reproducible and clearly increased according to the elevation of 2-NAT concentration.

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The rotordynamic characteristics of a micro power system supported by air foil bearings were investigated. Stability analysis was performed by a finite element method with the predicted dynamic coefficients of the foil bearings. A preliminary test rig was developed to simulate the operating characteristics of the micro power system. It consisted of a rotor supported by two air foil journal bearings and two air foil thrust bearings, and an impulse driven turbine. The foil journal bearings had a diameter of 7 mm and a length of 7 mm (L/D = 1). The test rig was operated stably under various situations and speeded up to 300 000 rpm. The main portion of the rotor response was synchronous and the amplitude of synchronous vibration was about 5–20 µm. Further, theoretical and experimental results for the unbalance response were compared. From this study, we showed the possibility of stable performance for the micro power system supported by air foil bearings.

Microturbomachinery implements gas bearings in compact units of enhanced mechanical reliability. Gas bearings, however, have little damping and wear quickly during transient rub events. Flexure pivot tilting pad bearings offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability; and when modified for hydrostatic pressurization, demonstrate superior rotordynamic performance over other bearing types. External pressurization stiffens gas bearings thus increasing system critical speeds, albeit reducing system damping. Most importantly, measurements demonstrate that external pressurization is not needed for rotor supercritical speed operation. In practice, the supply pressure could be shut off at high rotor speeds with substantial gains in efficiency. This paper introduces a simple strategy, employing an inexpensive air pressure regulator to control the supply pressure into the hybrid bearings, to reduce or even eliminate high amplitudes of rotor motion while crossing the system critical speeds. Rotor speed coast-down tests with the pressure controller demonstrate the effectiveness of the proposed approach. A simple on-off supply pressure control, i.e., a sudden increase in pressure while approaching a critical speed, is the best since it changes abruptly the bearing stiffness coefficients and moves the system critical speed to a higher speed. A rotordynamic analysis integrating predicted bearing force coefficients forwards critical speeds in agreement with the test results. Predicted rotor responses for the controlled supply conditions show an excellent correlation with measured data. The experiments validate the predictive tools and demonstrate the controllable rotordynamic characteristics of flexure pivot hybrid gas bearings.