2017 March 15 - April 24
2017 May 17 - June 29
2017 BTR deadline: 04/17/17
2017 October 11 - December 21
2017 Proposal deadline: 08/01/17
2017 BTR deadline: 09/10/17
Thursday, March 16, 2017, 1:00 pm (rescheduled from 3/15)
Dr. Henri Lee
Pohang Accelerator Lab, Korea
"Can we make reliable capillary optics?"
Abstract: CHESS is a leader in mono bounce capillary optic since CHESS has been developing it and its technology more than 10 years. CHESS capillaries mostly have rotationally symmetric ellipsoidal shape and this is suitable focusing optic for current CHESS beamlines to deliver x-ray beam into 10~50um spot size due to its large intercepted beam area.
As for CHESS-U and other 3rd Synchrotrons, both x-ray source size and emittance are getting smaller, a great leap in capillary technology is on demand to meet their purpose. Desirable capillaries should provide smaller focused beam size and/or extended x-ray energy regime To realize these properties, Micron-scale Controlled Capillary (MC2-cap1), Metal Coated Capillary (MC2-cap2), and both are inevitable.
The issue of MC2-cap1 is realizing a good capillary with high profile accuracy and overall straightness in micron scale. A process optimization for single pulling (making) process is surely possible but it is more like a master craftsman’s work. On the other hand, to realize this MC2-cap1 in general, multiple modification and measurement (figure) could be introduced to meet each parametric tolerance.
The aim of metal coated capillary, of MC2-cap2 is to extend available x-ray energy regime higher than 30keV or to enhance gain efficiency by increasing intercepted beam area. For these purposes, increasing critical energy of x-ray reflectivity is essential by proper thin layer coating. High-Z metal or its compound are desirable and Platinum can be a typical candidate.
In addition, I’ll briefly summarize my work in CHESS during my sabbatical and discuss possible collaborations.
Process concept of micron-scale modification by iterative thermal process.
Friday, March 3, 2017, 1:00 pm
Dr. Kelly Nygren
University of Illinois Urbana-Champaign
University of Wisconsin Madison
"Beneath the Fracture Surface: Directly observing the microstructure beneath striations to understand the role of hydrogen during fatigue crack growth in stainless steels"
Abstract: The presence of hydrogen in metals and alloys can lead to premature or catastrophic failure known as hydrogen embrittlement. While this phenomenon has been studied for over a century, the physical driving mechanisms for it are not fully understood, resulting in a paucity of functioning, physically based predictive models. Understanding the relationship between microstructure and macroscale properties is essential to illuminate the under-lying mechanisms, but remains a primary challenge in materials science. A multi-scale approach is one central way of addressing this problem. In this series of studies, the evolved microstructural state and subsequent fracture path following fatigue loading of SUS 304 and SUS 316L austenitic stainless steels is analyzed in the presence and absence of internal hydrogen (104 wppm). Single-edge notch specimens of uncharged and hydrogen-charged SUS 304 and SUS 316L were subjected to uniaxial fatigue tests performed at R = 0.1 and a frequency of 1 Hz. The fracture surface morphology was examined using scanning electron microscopy and electron transparency samples were extracted using focused ion beam machining from regions containing features of interest. The microstructure directly beneath these striations was assessed using conventional diffraction contrast imaging techniques as well as zone-axis scanning transmission electron microscopy imaging conditions.
The high hydrogen content led to a reduction in fatigue life for all samples. Direct observation of the microstructure beneath regions of interest can be treated as a series of evolving microstructural zones as a function of depth, relating to the microstructure occurring during fatigue crack growth. Beneath each striated surface, there exists a region of refined grains or rotations at the fracture surface, followed by a banded region superimposed on dense dislocation cells. The bands were martensitic laths and deformation twins in SUS 304 and SUS 316L, respectively. The impact of hydrogen is interpreted through differences in the development of these two microstructural regions, specifically in terms of the effect of hydrogen on the collective behavior of dislocations, deformation twinning, and the transition of fracture mode. Additional comments on current understanding of striation formation and fatigue crack advance will be made.
Friday, February 24, 2017, 1:00 pm
Associate Director, CHESS
"The CHESS-U upgrade project: why all the work?"
Abstract: Make no mistake: replacing a sixth of CESR and building six new x-ray beamlines in half-a-year or so will be one of the biggest challenges Wilson laboratory has ever undertaken. The primary reason to do this is to keep CHESS on the cutting-edge of providing unique x-ray research capabilities and enabling new types of scientific investigations. At the completion of CHESS-U in 2018, CHESS will be the premier synchrotron source in the US for x-ray microscopy and time-resolved studies in the 20-100 keV regime with the speed, sensitivity, and versatility to push R&D frontiers. This talk will try to explain the future scientific needs our research community envisions, as well as how those needs are shaping the scope of the project.
Friday, February 10, 2017, 1:00 pm
"CBETA: A new type of accelerator and the world’s first multi-turn SRF-ERL with FFAG return loop"
Abstract: At Wilson lab, a new type of particle accelerator is being constructed that opens the door to the production of medium energy (a few hundred MeV) and high current (a few times ten mA) electron beam of very high power. This presentation will cover the accelerator's design, its beam dynamics, the status of construction, plans for its completion, and applications of this new kind of accelerator.