60 research outputs found
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Beam Fields in an Integrated Cavity, Coupler and Window Configuration
In a multi-bunch high current storage ring, beam generated fields couple strongly into the RF cavity coupler structure when beam arrival times are in resonance with cavity fields. In this study the integrated effect of beam fields over several thousand RF periods is simulated for the complete cavity, coupler, window and waveguide system of the PEP-II B-factory storage ring collider. We show that the beam generated fields at frequencies corresponding to several bunch spacings for this case gives rise to high field strength near the ceramic window which could limit the performance of future high current storage rings such as PEP-X or Super B-factories
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BPM Breakdown Potential in the PEP-II B-factory Storage Ring Collider
High current B-Factory BPM designs incorporate a button type electrode which introduces a small gap between the button and the beam chamber. For achievable currents and bunch lengths, simulations indicate that electric potentials can be induced in this gap which are comparable to the breakdown voltage. This study characterizes beam induced voltages in the existing PEP-II storage ring collider BPM as a function of bunch length and beam current
Steam Turbine Efficiency Improvement Application And Conversion
LecturePg. 25-38This paper presents some recent technical innovations to improve mechanical drive steam turbine efficiency and presents a case study of a recent retrofit application of these features to a compressor driver. Various external and internal factors for consideration of the balance of plant efficiency gains are discussed. Descriptions of the turbine steam path improvements, testing, and results of the steam turbine conversion are also presented
Ultrafast manipulation of mirror domain walls in a charge density wave
Domain walls (DWs) are singularities in an ordered medium that often host
exotic phenomena such as charge ordering, insulator-metal transition, or
superconductivity. The ability to locally write and erase DWs is highly
desirable, as it allows one to design material functionality by patterning DWs
in specific configurations. We demonstrate such capability at room temperature
in a charge density wave (CDW), a macroscopic condensate of electrons and
phonons, in ultrathin 1T-TaS. A single femtosecond light pulse is shown to
locally inject or remove mirror DWs in the CDW condensate, with probabilities
tunable by pulse energy and temperature. Using time-resolved electron
diffraction, we are able to simultaneously track anti-synchronized CDW
amplitude oscillations from both the lattice and the condensate, where
photo-injected DWs lead to a red-shifted frequency. Our demonstration of
reversible DW manipulation may pave new ways for engineering correlated
material systems with light
Investigating dissociation pathways of nitrobenzene via mega-electron-volt ultrafast electron diffraction
As the simplest nitroaromatic compound, nitrobenzene is an interesting model
system to explore the rich photochemistry of nitroaromatic compounds. Previous
measurements of nitrobenzene's photochemical dynamics have probed structural
and electronic properties, which, at times, paint a convoluted and sometimes
contradictory description of the photochemical landscape. A sub-picosecond
structural probe can complement previous electronic measurements and aid in
determining the photochemical dynamics with less ambiguity. We investigate the
ultrafast dynamics of nitrobenzene triggered by photoexcitation at 267 nm
employing megaelectronvolt ultrafast electron diffraction with femtosecond time
resolution. We measure the first 5 ps of dynamics and, by comparing our
measured results to simulation, we unambiguously distinguish the lowest singlet
and triplet electronic states. We observe ground state recovery within 160 +/-
60 fs through internal conversions and without signal corresponding to
photofragmentation. Our lack of dissociation signal within the first 5 ps
indicates that previously observed photofragmenation reactions take place in
the vibrationally "hot" ground state on timescales considerably beyond 5 ps.Comment: 5 pages, 3 figures, and 1 tabl
Bayesian inferencing and deterministic anisotropy for the retrieval of the molecular geometry in gas-phase diffraction experiments
Currently, our general approach to retrieve the molecular geometry from
ultrafast gas-phase diffraction heavily relies on complex geometric simulations
to make conclusive interpretations. In this manuscript, we develop a broadly
applicable ultrafast gas-phase diffraction method that approximates the
molecular frame geometry distribution using Bayesian
Inferencing. This method does not require complex molecular dynamics simulation
and can identify the unique molecular structure. We demonstrate this method's
viability by retrieving the ground state geometry distribution
for both simulated stretched NO and measured ground
state NO. Due to our statistical interpretation, we retrieve a
coordinate-space resolution on the order of 100~fm, depending on signal
quality, an improvement of order 100 compared to commonly used Fourier
transform based methods. By directly measuring the width of
, this is generally only accessible through simulation,
we open ultrafast gas-phase diffraction capabilities to measurements beyond
current analysis approaches. Our method also leverages deterministic ensemble
anisotropy; this provides an explicit dependence on the molecular frame angles.
This method's ability to retrieve the unique molecular structure with high
resolution, and without complex simulations, provides the potential to
effectively turn gas-phase ultrafast diffraction into a discovery oriented
technique, one that probes systems that are prohibitively difficult to
simulate.Comment: 16 pages, 8 figures, 2 tables. Please find the analysis code and
templates for new molecules at https://github.com/khegazy/BIG
Diffractive Imaging of Coherent Nuclear Motion in Isolated Molecules
Observing the motion of the nuclear wave packets during a molecular reaction, in both space and time, is crucial for understanding and controlling the outcome of photoinduced chemical reactions. We have imaged the motion of a vibrational wave packet in isolated iodine molecules using ultrafast electron diffraction with relativistic electrons. The time-varying interatomic distance was measured with a precision 0.07 Ã… and temporal resolution of 230 fs full width at half maximum. The method is not only sensitive to the position but also the shape of the nuclear wave packet
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