Browsing by Author "Lee, A. P."

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Driver linac design for a femtosecond head-on inverse Compton scattering X-ray source
(2011-05-01)
Huang, N. Y.
;
Lau, W. K.
;
Liang, C. C.
;
Lee, A. P.
;
Cheng, W. C.
The feasibility of generating an ultra-short relativistic electron beam with a thermionic cathode rf gun driver linac for a femtosecond head-on inverse Compton scattering (ICS) X-ray source has been examined by space charge tracking throughout the entire beamline, from the cathode to the interaction point. It has been determined that GHz-repetition-rate electron pulses as short as 49 fs can be produced by compressing the energy-chirped beam from a 2998-MHz, 1.5-cell rf gun with an alpha magnet and an rf linac operating at the injection phase near the zero crossing. These electron pulses, with a 42-pC bunch charge, are accelerated to 27 MeV with an S-band traveling-wave constant-gradient linac structure for the ICS in an interaction chamber located downstream. The driver linac design that allows the operation of an ultra-short ICS X-ray source at a 0.7-angstrom wavelength, with a peak photon flux of 9.08 x 10(17) photons/s, is presented in this paper. (C) 2010 Elsevier B.V. All rights reserved.
Liquid crystal alignment on the a-C : H films by Ar plasma ion immersion
(2007-07-31)
Chang, S. J.
;
Wu, K. Y.
;
Yang, Y. H.
;
Hwang, J.
;
Wu, Hsin-Ying
A plasma ion immersion treatment has been developed to enhance the liquid crystal (LC) alignment on the hydrogenated amorphous carbon (a-C:H) layer in an inductively coupled plasma (ICP) chamber. No LC alignment was observed for the a-C:H layer tilted at an angle of 0 degrees during the bombardment with plasma ions. The LC alignment occurs for the a-C:H layer tilted at an angle of 30 degrees or 60 degrees. Their pretilt angles (similar to 1.4 degrees) are approximately the same. The azimuthal anchoring strength is 1.98 x 10(-6) J/m(2) at a tilted angle of 30 degrees and 1.14 x 10(-4) J/m(2) at a tilted angle of 60 degrees. The mechanism for the LC alignment is attributed to the oblique incidence of ions within the matrix sheath of non-uniform thickness near the a-C: H surface under a negative pulse bias. The matrix sheath of non-uniform thickness is confirmed by the plasma density distribution in the ICP chamber and the X-ray photoemission spectra across the a-C:H layer. (C) 2007 Elsevier B.V. All rights reserved.