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The effect of surface texturing on the friction of polyoxymethylene was investigated in terms of surface texturing density. Surface texture was machined using CNC machining. Five different surface texturing densities were machined and tested in a pin-on-disk sliding configuration. Bearing steel was used as a mating material on polyoxymethylene (POM). Sliding speed and nominal contact pressure were 0.1 m/s and 1.35 MPa, respectively. Sliding distance was 1 km, and the lubricant was SAE 5W-30 oil. The lowest coefficient of friction was obtained with a 10% texturing density, where the reduction in friction was about 50% of that of the non-textured POM.

Ferritic stainless steel, which has been used as material for decoration parts in automobile, is recently used as material for the exhaust system due to its good performance at high temperature. To improve the fuel efficiency and purify automotive exhaust gas, it is needed to increase the temperature of exhaust gas. However, it is frequently reported that the rising of the temperature of exhaust gas increases thermal stress at exhaust manifold, which results in thermal fatigue failure in welded joints. Therefore, in this study, effects of chemical composition of steel and welding parameters on thermal fatigue properties of synthetic heat affected zone in ferritic stainless steel have been investigated. It has been found that thermal fatigue life in heat affected zone is affected by bead shape of welded joint and amount of soluble Nb in steel. Especially, Nb-Ti added steel has higher thermal fatigue life in comparison to Nb added steel, which is attributed to difference of precipitation behavior in both steels.

A laser hybrid welding process in which a defocused laser beam is applied beside a gas metal arc weld (GMAW) pool to modify the bead shape was studied. The present paper aims to produce welds with improved toe geometry and better fatigue life than those made with GMAW alone and to apply a numerical simulation to help configure the hybrid process. First, stationary hybrid welds were made to validate weld bead shape predictions and to characterise the spreading of the arc weld deposit to the laser heated spot. Next, the travelling hybrid process was configured with the aid of simulations and fatigue test specimens were welded. Proper application of the laser heat input induced molten metal to spread to the laser heated area, increasing the fillet weld leg length. This produced a larger weld toe angle that decreased the stress concentration and increased the fatigue life of the welds relative to standard mean values.

The tribological behavior of polyphenylene sulfide (PPS) filled with molybdenum-concentrate (MC) deposit from Armenia was studied. The deposit MC was a complex mixture of compounds such as MoS 2 , SiO 2 , CuS, Al 2 O 3 , and others. Whereas MC as the filler in particulate form reduced the steady state wear rate of PPS, the optimum reduction in wear was found to occur with the addition of polytetrafluoroethylene (PTFE) along with PPS. The behavior of PPS composites made with MC and PTFE sliding against a steel counterface was investigated as a function of the MC and PTFE proportions, sliding speed, and counterface roughness. For this purpose, pin-on-disk configuration and the design of experiments approach utilizing Taguchi's orthogonal arrays were used. Of all the above factors, the change in MC proportion, while PTFE was also present, had the greatest effect on the reduction in wear rate. The variation of the coefficient of friction was found to be in the narrow range of 0.27–0.33. The lowest wear rate was found in the case of PPS + 17 vol.% MC + 10 vol.% PTFE composite sliding at 1.5 m/s against a counterface roughness of 0.1 μm Ra. Optical and scanning electron microscopy of the transfer films were performed for observation of the features such as coverage, thickness, topography, and bonding. Friction and wear results are discussed in terms of these observations.

The extensive design effort for KSTAR has been focused on two major aspects of the KSTAR project mission - steady-state-operation capability and advanced tokamak physics. The steady state aspect of the mission is reflected in the choice of superconducting magnets, provision of actively cooled in-vessel components, and long pulse current drive and heating systems. The advanced tokamak aspect of the mission is incorporated in the design features associated with flexible plasma shaping, double null divertor and passive stabilizers, internal control coils and a comprehensive set of diagnostics. Substantial progress in engineering has been made on superconducting magnets, the vacuum vessel, plasma facing components and power supplies. The new KSTAR experimental facility with cryogenic system and deionized water cooling and main power systems has been designed, and the construction work is under way for completion in 2004.

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.

For the first time, the DRAM device composed of 6F/sup 2/ open-bit-line memory cell with 80nm feature size is developed. Adopting 6F/sup 2/ scheme instead of customary 8F/sup 2/ scheme made it possible to reduce chip size by up to nearly 20%. However, converting the cell scheme to 6F/sup 2/ accompanies some difficulties such as decrease of the cell capacitance, and more compact core layout. To overcome this strict obstacles which are originally stemming from the conversion of cell scheme to 6F/sup 2/, TIT structure with AHO (AfO/AlO/AfO) is adopted for higher cell capacitance, and bar-type contact is adopted for adjusting to compact core layout. Moreover, to lower cell V/sub th/ so far as suitable for characteristic of low power operation, the novel concept, S-RCAT (sphere-shaped-recess-channel-array transistor) is introduced. It is the improved scheme of RCAT used in 8F/sup 2/ scheme. By adopting S-RCAT, V/sub th/ can be lowered, SW, DIBL are improved. Additionally, data retention time characteristic can be improved.

The technology innovation for extending the RCAT structure to the sub-70nm DRAM is presented. The new technology overcomes the problems induced by shrinkage of the RCAT structure and meets the requirements for the next generation DRAMs, such as high speed and low power performance. The technology roadmap down to the 50nm DRAM feature size of the RCAT development is presented.

For the first time, S-RCAT (sphere-shaped-recess-channel-array transistor) technology has been successfully developed in a 2Gb density DRAM with 70nm feature size. It is a modified structure of the RCAT (recess-channel-array transistor) and shows an excellent scalability of recessed-channel structure to sub-50nm feature size. The S-RCAT demonstrated superior characteristics in DIBL, subthreshold swing (SW), body effect, junction leakage current and data retention time, comparing to the RCAT structure, in this paper, S-RCAT is proved to be the most promising DRAM array transistor suitable for sub-50nm and mobile applications.

The initial objective of the KSTAR ECH system is to produce seed plasmas by irradiation of powerful millimeter waves for the main ohmic discharges. A specially designed gyrotron, manufactured by CPI, has specifications of 500 kW, 84 GHz, and 2- second pulse duration. It adopts the state-of-arts technologies of a diode gun, a depressed potential collector, an internal mode converter, and a diamond window. As a part of the final acceptance tests of the gyrotron, we constructed a test and including a test modulator to confirm its operating conditions. With short-pulses of 20 microseconds, we produced the output peak power of 500 kW at 84 GHz. The output power distribution is confirmed to be a Gaussian by IR images on targets. In this experimental study, we describe details of the gyrotron, the test stand, and experimental results.

Fully reliable lean-free stacked capacitor, with the meshes of the supporter made of Si/sub 3/N/sub 4/, has been successfully developed on 80nm COB DRAM application. This novel process terminates persistent problems caused by mechanical instability of storage node with high aspect ratio. With Mechanically Enhanced Storage node for virtually unlimited Height (MESH), the cell capacitance over 30fF/cell has been obtained by using conventional MIS dielectric with an equivalent 2.3nm oxide thickness. This inherently lean-free capacitor makes it possible extending the existing MIS dielectric technology to sub-70nm OCS (one cylindrical storage node) DRAMs.

For the first time, novel robust capacitor (Leaning exterminated Ring type Insulator - LERI) and new storage node (SN) contact process (Top Spacer Contact - TSC) are successfully developed with 82nm feature size. These novel processes drastically improved electrical characteristics such as cell capacitance, parasitic bit line capacitance and cell contact resistance, compared to a conventional process. The most pronounced effect using the LERI in COB structure is to greatly improve cell capacitance without twin bit failure. In addition, the TSC technology has an ability to remove a critical ArF lithography. By using the LERI and TSC processes in 82nm 512M DDR DRAM, the cell capacitance of 32fF/cell is achieved with Toxeq of 2.3nm and the parasitic bit line capacitance is reduced by 20%, resulted in great improvement of tRCD (1.5ns).

PLS 2-GeV Linac employs the E-3712 klystron tubes manufactured by the TOSHIBA as one of the pulsed high power microwave sources. The rated power of the tube is 80-MW at 4 /spl mu/s pulse width with 60 Hz pulse repetition rate. As a part of the main linac we have completed the installation of two units of the E-3712 klystron tubes and the matching 200-MW modulators together with the accompanying waveguide networks and the accelerating columns. Since all the components are exposed as a virgin to high power microwave, careful power conditioning procedures are underway. The rest of linac components installation is also underway. We present the performance characteristics of the E-3712 klystron tube measured with the water load. The result of the initial power conditioning operation for the waveguide network and the accelerating structures installed as a part of the PLS 2-GeV linac is also presented. >

The PLS linac has been injecting 2-GeV electron beams to the Pohang Light Source (PLS) storage ring since September 1994. PLS 2-GeV linac has 11 units of high-power pulsed klystron-modulator (K&M) system for the main RF sources for the beam acceleration. The klystron has rated output peak power of 80-MW at 4 /spl mu/sec pulse width with 120 pps, and the matching modulator has 200-MW peak output power. The total accumulated high voltage run time of the oldest unit has reached beyond 20000 hours and the sum of all the high voltage run time is approximately 180000 hours. In this paper, we review overall system performance of the high power K&M system together with the description of the K&M system. A special attention is paid on the analysis of all failures and troubles of the K&M system which affected the linac RF operations as well as beam injection operations for the period of 1994 to May 1996.

A C-band (5,712 MHz) RF system for an e+e- linear collider at 500 GeV center-of-mass energy requires total 4,080 units of 50 MW pulse klystrons and matching 111 MW peak-power modulators for two main linacs. An initial design value of the wall plug power for the entire RF system is 150 MW with 2.5 /spl mu/sec RF pulse width and 100 Hz pulse repetition rate. A detailed circuit analysis shows that it is possible to get the overall RF system efficiency of approximately 24%, or equivalent to 210 MW wall plug power. This includes 85% DC high voltage charging efficiency using compact inverter power supplies, and 70% pulse efficiency using 3.5 /spl mu/sec pulse length (ESW) with less than 1% flat top ripple, and auxiliary powers for thyratron heater, klystron heater, focusing magnet, pulse transformer reset, and etc.

The PLS, a 2-GeV dedicated electron synchrotron light source, has been in normal operation mode for users since September 1995. It consists of 2-GeV electron linear accelerator, which works as a full energy injector, and a storage ring. The linac is 150-m long and has 42 accelerating sections. The storage ring has a 12-cell TBA type lattice with 4 RF cavities. The construction of PLS was started in 1988, and the installation was completed in August 1994. From then until December 24, 1994, which we call the first commissioning phase, we succeeded in stacking the 2-GeV electrons up to 300-mA in the storage ring. After baking out the vacuum chamber, the second commissioning was performed from April to July 1995. In 1996, the user beam time reaches about 2,800 hours among 4,800 hours of the accelerator operation time. We present the current operational status of PLS in this paper.

The PLS 2-GeV linac employs 11 units of high-power pulsed klystrons (80-MW) as the main RF sources. The matching modulators of 200-MW (400-kV, 500-A) can provide a flat-top pulse width of 4.4 /spl mu/s with a maximum pulse repetition rate of 120-Hz at the full power level. For a good stability of electron beams, the pulse-to-pulse flat-top voltage variation of a modulator requires less than 0.5%. In order to achieve this goal, we stabilized high-voltage charging power supplies within 1% by a phase controlled SCR voltage regulator. In addition, we employed ac/dc feedback together with a resistive De-Q'ing system to achieve far less than 0.5% variation of the PFN charging voltage. This paper presents the main features of the klystron-modulator system and the characteristics of the pulsed high-power RF system performance during the beam injection operation for the Pohang Light Source commissioning.

The PLS 2-GeV electron linac at the Pohang Accelerator Laboratory (PAL) has been constructed as a full energy injector to the storage ring of the Pohang Light Source (PLS) project. The 150-m long linac uses 11 klystrons of 80-MW maximum output power driven by 200-MW modulators. There are 42 constant gradient acceleration sections and 6 quadrupole triplets. By December 10, 1993, we completed the linac installation with the beam analyzing station and the beam transport line to the beam dump of 30-m long. We completed the machine commissioning by June 30, 1994. Since September 1, 1994, it provides 2-GeV beams to the PLS storage ring for its commissioning, which is also completed by December 24, 1994 with 300-mA stored current. In this paper, we present the operational experience of the PLS 2-GeV linac.

4 Gb DRAM has been developed successfully using 0.11 /spl mu/m DRAM technology. Considering manufacturability, we have focused on developing patterning technology that makes 0.11 /spl mu/m design rules possible using KrF lithography. Also, novel DRAM technologies, which have a big influence on the future DRAM integration, are developed as follows:, using novel oxide (SOG) for the enhanced capability of gap-filling, borderless metal contact and stud processes, line-type storage node SAC, thin gate oxide, and CVD Al process for metal interconnections.

The S-band linear accelerator (linac), which was built to be the electron source and the front end of the Advanced Photon Source (APS) injector, is now also being used to support a low-energy undulator test line (LEUTL) to drive a free-electron laser (FEL). The APS linac system employs five units of pulsed high-power klystrons (35-MW class) as the main rf sources. The matching pulse modulators provide high-voltage pulses running at 280 kV and 300 A with 3.5-/spl mu/s pulse width and a nominal pulse repetition rate of 30 Hz. The system availability of the entire APS linac during the last run period of calendar year 2000 was estimated to be slightly over 95%. We present a discussion of the reliability and various fault statistics of the klystron-modulator system together with the key features of the system hardware.

The Pohang Accelerator Laboratory uses a 100-MeV electron linac for the pulsed neutron source as one of the long-term nuclear RD one for short pulse mode with the various repetitions between 2 ns and 100 ns and the other for long pulse mode with 1 /spl mu/s. The major beam parameters are as follows; the nominal beam energy is 100 MeV, the maximum beam power is 10 kW, and the beam current is varied from 300 mA to 5 A and depends on the pulse repetition. We constructed and tested a test-linac based on the existing equipment such as a SLAC-5045 klystron, two constant gradient accelerating sections, and thermionic RF-gun. We describe the characteristics of the test-linac and report the status of the pulsed neutron source facilities including a target system and time-off-flight paths.