The purpose of this paper is to introduce a systematic method of designing a beam-type vibration absorber that attenuates vibration at multiple frequencies. This vibration absorber is a non-uniform beam with natural frequencies intentionally designed to coincide with or close to the frequencies of excitation, e.g. the rotating speed of a rotary machine and its harmonic orders. Therefore it can reduce the vibration response due to rotor eccentric, rotor shaft bending, mechanical looseness, etc. The thickness profile of the non-uniform beam can be determined systematically using the impedance technique proposed in this paper. A design is given to demonstrate the methodology and the result is experimentally validated.

A novel method for shifting the natural frequencies of a structure to specific values using structural patches is introduced. When a host structure is bonded with multiple structural patches, its natural frequencies can be shifted to the desired values by tuning the patch thickness and the patch location on the host structure. These parameters can be analytically determined using the methodology proposed in this paper The time consuming process produced using the traditional optimal search method is thereby avoided. The results show that multiple natural frequencies can be changed simultaneously to the desired values. The number of natural frequencies shifted requires using the same number of structural patch pairs. Several examples using this technique are demonstrated and the results are experimentally validated.

The purpose of this paper is to introduce a systematic method of designing a vibration absorber that affects vibration attenuation at multiple frequencies. This vibration absorber is a nonprismatic beam with natural frequencies intentionally designed to coincide with the frequencies of excitation, e.g., the rotating speed of a rotary machine and its harmonic orders. Therefore, it can reduce the vibration response due to rotor eccentric, rotor shaft bending, mechanical looseness, etc. The thickness profile of the nonprismatic beam can be approximated discretely by a large amount of block masses. Each block mass behaves as an elastic structure member, and its thickness can be determined systematically using the impedance technique proposed in this paper. A design is given to demonstrate the methodology, and the result is experimentally validated.

An impedance-based system modeling technique has been developed to determine the output forces of multiple piezoelectric (PZT) patch actuators on an active structure to produce a known vibration response. In the analysis of the dynamic response of a structure driven by multiple PZT patches, the proposed model includes not only the dynamic interactions between the PZT patch and the host structure but also the impedance couplings among PZT patches. Therefore this approach can apply to a structure with multiple PZT actuators. Furthermore, the bending stiffness and the thickness of a PZT patch that are proved to be important as increases of excitation frequency are included in the proposed impedance model. Examples are given to demonstrate how to synthesize a known vibration response and how to suppress vibration response at an arbitrary location on structures using this technique.

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.

In the Levitated Dipole Experiment (LDX), a hot plasma is formed about a levitating superconducting dipole magnet in the center of a 5 m diameter vacuum vessel. The levitated magnet is suspended magnetically during an eight hour experimental run, then lowered and recooled overnight. The floating F-coil magnet consists of a layer-wound magnet with 4 sections, designed to wrap flux lines closely about the outside of the levitated cryostat. The conductor is a niobium-tin Rutherford cable, with enough stabilizer to permit passive quench protection. Lead strips are used as thermal capacitors to slow coil heating. An optimized system of bumpers and cold-mass supports reduces heat leak into the helium vessel. Airbags catch the floating coil on quenches and faults, preventing collision with the vacuum vessel.

The KSTAR (Korea Superconducting Tokamak Advanced Research) project is the major effort of the Korean National Fusion Program to design, construct, and operate a steady-state-capable superconducting tokamak. The project is led by Korea Basic Science Institute and shared by national laboratories, universities, and industry along with international collaboration. It is in the conceptual design phase and aims for the first plasma by mid 2002. The key design features of KSTAR are: major radius 1.8 m, minor radius 0.5 m, toroidal field 3.5 T, plasma current 2 MA, and flexible plasma shaping (elongation 2.0; triangularity 0.8; double-null poloidal divertor). Both the toroidal and the poloidal field magnets are superconducting coils. The device is configured to be initially capable of 20 s pulse operation and then to be upgraded for operation up to 300 s with non-inductive current drive. The auxiliary heating and current drive system consists of neutral beam, ICRF, lower hybrid, and ECRF. Deuterium operation is planned with a full radiation shielding.

The LDX Experiment, presently being designed and built at MIT, requires a superconducting coil that can be floated within a large vacuum chamber. The 90 cm diameter, 1.2 MA, Nb3Sn floating coil utilizes a novel cryostat design. The > 400 kg coil will float for up to 8 hours, centered within a 5 m diameter, 3 m tall vacuum chamber. When levitated from above, the coil is unstable only to vertical motion. A digital control system will be used for feedback control of the vertical position and damping of horizontal, tilt and rotational motions. A simple diagnostic set is being developed to measure plasma equilibria, profiles, and instabilities. Equilibrium reconstruction from flux loops and hall probes will yield information on hot electron β and stored energy. A x-ray energy analyzer, xuv array, and reflectometer will measure hot electron profile parameters. Edge probes, magnetics and the xuv array will diagnose hot electron interchange instabilities driven by supercritical gradients. During thermal plasma operation, ion profiles will be measured using a charge exchange analyzer and secondary electron detector array.

The Korean Superconducting Tokamak Advanced Research (KSTAR) at the Korea Basic Science Institute in Taejon will be the first Tokamak with an advanced all superconducting magnet system, including toroidal field (TF), poloidal field (PF),and field error correction (FEC) coils. The conductors are all cable-in-conduit (CICC) superconductors with a single conduit similar to those in the International Thermonuclear Experimental Reactor (ITER)

Dual-stripe MR heads with linear density capability of 200 KBPI and track density capability of 11000 TPI have been manufactured. The write head, with a 15 turn coil and a gap length of 0.3 /spl mu/m, is made of conventionally plated Permalloy for both the leading and trailing poles. The thickness and track width of the trailing pole are 3.5 and 2.1 /spl mu/m, respectively. The MR elements have a 1.4 /spl mu/m track width, 1.1 /spl mu/m stripe height and a 17.5 nm thickness. The shield-to-shield separation is 0.18 /spl mu/m. The two MR elements are mutually biased and patterned-exchange domain stabilized. Recording tests were performed on a thin-film disk with a coercivity of about 3000 Oe and an M/sub r/t of 0.75 memu/cm/sup 2/. The read-back amplitude is as large as 1.02 mV(p-p), and the 50% roll-off density is as high as 160 kfci. Error rate test with a PRML channel at a data rate of 105 Mbits/s showed that a low on track error rate of 10/sup -10/ and an off-track capability of more than 15% of the track pitch could be easily achieved at a linear density of 200 KBPI and a track density of 11000 TPI.

Control of the poloidal field (PF) in the Tokamak Physics Experiment (TPX) is critical to achieving its mission of advanced tokamak research. Extensive examination of the plasma equilibrium; plasma start-up; plasma position, shape, and current control; and plasma shape reconstruction have been performed as part of the design process. This paper reports the progress in this area. The PF coils have been designed to produce a wide range of plasmas. plasma start-up can be achieved for multiple conditions. Fast plasma position control coils inside the vacuum vessel are used for short timescale control of the plasma vertical and radial position. Shape and total plasma-current control are provided by the PF coils over a slower timescale. A new algorithm for shape control of a few critical plasma boundary points is described and used in simulations using the Tokamak Simulation Code. Fast magnetostatic reconstruction of the plasma shape is examined to determine the impact of measurement locations and their quality.

Ce- and Th-doped Nd 2 CuO 4+ y superconducting and related compounds were systematically synthesized and characterized. An X-ray diffraction analysis of the variation of lattice dimensions of the Nd 2- x M x CuO 4+ y compounds revealed that Ce had an average ionic radius of 0.998 Å and an effective valence of +3.84, significantly different from those of the formal Ce 3+ and Ce 4+ ions. An iodometric titration analysis detected excess oxygen above the nominal value of 4 in both the Ce- and Th-doped materials. The analysis also showed that the average [Cu-O] p charge reversed from positive to negative as x increased, and reached a negative maximum x =0.15 where superconductivity appeared. Using effective valences of +3.84 for Ce and +4 for Th ions, the values of p were found to be -0.067 and -0.048 for the 21 K Nd 1.85 Ce 0.15 CuO 4.030 and the 15 K Nd 1.85 Th 0.15 CuO 4.048 electron superconductors, respectively.