Engineering topics
Huang, X
Publications and source records attributed to Huang, X.
Electron and Hole Spin Relaxation in InAs Quantum Dots and Quasi-2D Structure
Temperature dependence of hole and electron spin relaxation times in both InAs quantum dots (QDs) and quasi-two-dimensional (2D) monolayers has been investigated experimentally using time-resolved photoluminescence (TRPL). The results show that hole spin relaxation time is long enough to be comparable with that of electrons in the quasi-2D InAs structure, but is one order of magnitude smaller than the electron spin relaxation time in QDs structure. It is shown that both hole and electron spin relaxation times decrease monotonically with increasing temperature for InAs QDs, but show non-monotonic temperature-dependent behavior for the quasi-2D structure. Different spin relaxation mechanisms responsible for spin relaxation in the two structures have been discussed.
Bunch Length and Impedance Measurements at SPEAR3
Streak camera measurements were made at SPEAR3 to characterize longitudinal coupling impedance. For the nominal optics, data was taken at three rf voltages and a single-bunch current range of 0-20mA. Both bunchcentroid phase shift and bunch lengthening were recorded to extract values for resistive and reactive impedance. An (R+L) and a Q=1 model were then back-substituted into the Haissinski equation and compared with raw profile data. In the short bunch (low-{alpha}) mode, distribution 'bursting' was observed.
Ideas for a Future PEP-X Light Source
SLAC is developing a long-range plan to transfer the evolving scientific programs at SSRL from the SPEAR3 light source to a much higher performing synchrotron source -- PEP-X -- a new storage ring that would occupy the existing PEP-II tunnel and support two experimental halls, each containing 16 x-ray beam lines. Operating at 4.5 GeV and 1.5 A with a horizontal emittance of 0.14 nm-rad, reached using 90 m of damping wigglers, PEP-X would have an order of magnitude higher average brightness and flux in the 1-{angstrom} x-ray range than any existing or planned future storage ring sources. Higher brightness in the soft x-ray regime might be reached with partial lasing in long undulators, and high peak brightness could be reached with seeded FEL emission. The status of preliminary studies of PEP-X is presented.
Lattice Modeling and Calibration with Turn-by-Turn Orbit Data
A new method that explores turn-by-turn BPM data to calibrate lattice models of accelerators is proposed. The turn-by-turn phase space coordinates at one location of the ring are first established using data from two BPMs separated by a simple section with a known transfer matrix, such as a drift space. The phase space coordinates are then tracked with the model to predict positions at other BPMs, which can be compared to measurements. The model is adjusted to minimize the difference between the measured and predicted orbit data. BPM gains and rolls are included as fitting variables. This technique can be applied to either the entire or a section of the ring. We have tested the method experimentally on a part of the SPEAR3 ring.
LauePt, a graphical-user-interface program for simulating and analyzing white-beam x-ray diffraction Laue patterns.
LauePt is a robust and extremely easy-to-use Windows application for accurately simulating, indexing and analyzing white-beam X-ray diffraction Laue patterns of any crystals under arbitrary diffraction geometry. This program has a user-friendly graphic interface and can be conveniently used by nonspecialists with little X-ray diffraction or crystallography knowledge. Its wide range of applications include (1) determination of single-crystal orientation with the Laue method, (2) white-beam topography, (3) white-beam microdiffraction, (4) X-ray studies of twinning, domains and heterostructures, (5) verification or determination of crystal structures from white-beam diffraction, and (6) teaching of X-ray crystallography.