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From the recent data analysis of the longitudinal feedback system and the streak camera, we have found a longitudinal relaxation beam oscillation whose frequency is a multiple of 36 Hz. When the relaxation oscillation is generated, horizontally oscillating wide beams are observed at the diagnostic beamline, and the beam lifetime is fluctuated. The strength of the longitudinal coupled bunch mode instabilities is also modulated sinusoidally. We have described the observed longitudinal relaxation oscillation in the Pohang Light Source storage ring.

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.

In the Pohang Light Source (PLS) storage ring, we have occasionally experienced the abnormal spontaneous beam. lifetime reduction and strong longitudinal damping. Due to the abnormal beam lifetime reduction, available beam time is reduced substantially. From the recent data analysis of the PLS longitudinal feedback system (LFS) and the streak camera, we have found that the abnormal phenomena can be generated by the RF noise via the dipole mode parametric resonance of the RF phase modulation. We describe the observation of the dipole mode parametric resonance driven by the RF noise and compare it with a simulation result in the PLS storage ring.

A compact standing-wave linac has been designed using S-band microwaves for medical and industrial applications. It uses a bi-periodic structure with constant impedance. It consists of a buncher section with three-cells and on-axis coupled cavities with nine-cells. The total length is 740.0 mm including the electron gun. Using SUPERFISH, HFSS and PARMELA codes, it is capable to deliver 4.5 MeV electron beams with pulsed microwaves of 4.8 MW at 2,856 MHz. In this paper, we present the detailed design studies on a compact S-band standing-wave linac.

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 single bunch collective effects such as the bunch lengthening due to the potential well distortion and the microwave instability which also increases the energy spread, the transverse head-tail instability, and the transverse strong head-tail instability are investigated in the Pohang Light Source storage ring. The threshold current and the Chao-Gareyte scaling factor of the bunch lengthening, the longitudinal broadband impedance, and the transverse impedance have been measured and compared with the ZAP code results.

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.

A new technique of real-value representation in inversion-recovery (IR) imaging by use of a phase-correction method is proposed. In this scheme, negative magnetizations at the beginning of the inversion point (T1 approximately equal to 0) are correctly represented as negative values rather than positive. By use of this new scheme, a consistent IR image set as a function of several inversion times (T1) can be obtained. The latter, i.e., consistent image set which represents the real value of T1 weighted images at several inversion times is important in the search for tumors and abnormalities since the inversion time (T1) in the pulse sequence strongly affects T1 contrast.

Multislice imaging techniques effectively applicable to inversion-recovery (IR) imaging are developed and applied to human imaging. These new multislice IR imaging sequences employ the time-multiplexing (TM) technique conventionally used in the slice-by-slice saturation-recovery (SR) imaging. Two new time-multiplexed multislice (TMM) IR imaging sequences are proposed and some of the experimental results obtained with the methods are presented.© 1985 Academic Press,Inc.

A quadrature multiplexed pulse sequence to double the data information in a given acquisition time is proposed for NMR tomography. This technique takes advantage of the Hermitian property of the Fourier transform operation in NMR imaging. The proposed technique uses two rf pulses with 90 degrees phase difference simultaneously applied for the excitation of the spins in two different slices. The method results in truly simultaneous data acquisition coming from two different anatomical slices which can be separated into the real and imaginary parts of the image domain. This technique, therefore, also allows us either to reduce the experiment time by half or double the number of slices in the same examination time, depending on the applied imaging scheme. As a preliminary study, simultaneous dual-slice imaging of a human head using a conventional single-slice imaging scheme was performed.