| New
Monochromator Design for F2 MAD Experiments
|
-
The optics for the F2 station have been re-designed to be
optimized for work in the fast growing field of MAD crystallography. A
new monochromator, along with a new collimating white beam mirror located
upstream on F-line, will provide many advantages for MAD experiments at
F2.
-
The upstream mirror will reduce heat load by two-thirds and
increase the energy resolution at the MAD experiment to its source-size
limit. Even though Si (111) will remain the work-horse monochromator, a
set of Si (220) crystals is being planned which, when used with the upstream
collimating mirror, will provide an energy resolution at the core-hole
life-time limit for the K-edges of selenium and other elements.
-
The new single-rotation-stage monochromator is able to change
wavelengths quickly and reliably. Two separate angle-segment stages, one
for each crystal, are used to fine tune the second-crystal translation
tilt so that a fixed-exit beam can be maintained throughout the useable
energy range of 6-18 keV.
-
The reduction of high-energyphotons by the upstream mirror
and the new separated vacuum chambers for each optical element in the F-cave
area will greatly reduce energy drifts due to secondary heating sources
and thermal cross-talks between the optical components.
|
| High-Heat-Load
Management for Wiggler Beamlines & Optics
|
-
White-beam mirrors: Given the
recent successful operation of a water-cooled white-beam glid-cop mirror
at A2 wiggler station, we are planning to install similar Rh-coated glid-cop
mirrors for all F, G, and A wiggler beamlines. These 1m-long mirrors (or
a possible multilayer for A1) located upstream of the monochromators will
substantially reduce the heat loads on the monochromator crystals, by a
factor of about three. Together with the new lower-critical-energy G/A-line
wiggler, these power-filters will allow more manageable designs of high-heat-load
monochromators using conventional water-cooling.
-
Beam stops: Both A- and F-wiggler
beam stops have been completely redesigned and rebuilt so that these crucial
devices can be safely operated at high CESR currents of 500 mA. A water-cooled
5-deg horizontal V-shape copper block serves as the main heat absorber
for each beam stop. Similar cooling designs have been implemented in other
critical beam-line components such as beam position monitors and apertures.
-
Beryllium windows: A graphite-filter/beryllium-window
design has been implemented in the A-line and the F-line vacuum window
sections. This design employs a 0.25-0.5 mm thick highly-oriented pyrolitic
graphite (HOPG) as a prefilter to reduce the heat load on the first vacuum
beryllium window. Unlike most graphite filter designs in other synchrotron
sources that rely entirely on radiative cooling, the HOPG filter in this
design is brazed onto a water-cooled copper flange which substantially
lowers its maximum temperature and prolongs its operational lifetime.
-
Monochromators: Significant
improvements to the high-heat-load monochromators have been made at the
high-resolution wiggler stations such as F2. Due to the large beam-footprint
and the high total power of the wigglers, our effort has been focused on
internally-water-cooled silicon monochromators with optimized coolant channels.
One of such designs, involving a set of mini-cooling-channels, a high-flow-rate
water supply-return manifold, and an innovative high-temperature metal-diffusion
bond by Karl Smolenski, has been successfully operated at F2 station for
the past three years. The metal-diffusion bond proves to be the crucial
step in the design, since it needs to provide a water-tight radiation-resistant
seal that does not strain the silicon crystal. The test result shows an
almost linear response in x-ray throughput versus CESR current and the
total flux delivered to the station is an order-of-magnitude higher than
the old externally-cooled designs.
|
Recent
Publications
on High-Heat-Load Engineering & Optics
Development
|
-
Qun Shen, C. Henderson, M. Keeffe, M. Marston, K.D. Finkelstein,
and B.W. Batterman, "Design of beam line components for high power wiggler
beam line at CHESS", Nucl. Instrum. Meth. A 347, 609 (1994).
-
P. Doing, J. White, and Qun Shen, "A high power and high
flux x-ray wiggler station at CHESS", Nucl. Instrum. Meth. A 347,
73 (1994).
-
K.W. Smolenski, C. Conolly, P. Doing, B. Kiang, and Qun Shen,
"Bonding techniques for the fabrication of internally cooled x-ray monochromators",
SPIE
Proceedings 2856, 246 (1996).
-
K.W. Smolenski, Qun Shen, and Park Doing, "Improved internally
water-cooled monochromators for a high-power wiggler beam line at CHESS",
SPIE
Proceedings, 3151, 181-187 (1997).
-
Qun Shen, K.W. Smolenski, and E. Fontes, "Design of graphite
power-filters and beryllium windows at wiggler beam lines at CHESS", SPIE
Proceedings, 3151, 116-122 (1997).
-
K.W. Smolenski, Qun Shen, and P. Doing, "Silver bonded, internally
water-cooled monochromators for CHESS wiggler beamlines", AIP Conference
Proceedings 417, 66-70 (1997).
-
Qun Shen, "New monochromator upgrades at CHESS", Synch.
Rad. News, vol.10, no.3, pp.38-39 (1997).
-
K.W. Smolenski, R.L. Headrick, A.M. Khounsary, C. Liu, A.T.
Macrander, and Q. Shen, "Water-cooled multilayer optics for a wiggler beam
line", SPIE Proceedings 3448, 27 (1998).
-
P. Doing, S. Kycia, and Q. Shen, "Mosaic monochromator applications
at CHESS", SPIE Proceedings 3448, 32 (1998).
-
Stefan Kycia, Karl W. Smolenski, R. Headrick, and Qun Shen,
"Multilayer design for wiggler beam line at CHESS", AIP Conference Proceedings,
in press (1999).
|
