89 research outputs found
Graphite triple point and solidus-liquidus interface experimentally determined up to 1000 atmospheres
Experimental determination of graphite triple point and liquid-solid interfac
Film boiling of mercury droplets
Vaporization times of mercury droplets in Leidenfrost film boiling on a flat horizontal plate are measured in an air atmosphere. Extreme care was used to prevent large amplitude droplet vibrations and surface wetting; therefore, these data can be compared to film boiling theory. Diffusion from the upper surface of the drop appears as a dominant mode of mass transfer from the drop. A closed-form analytical film boiling theory is developed to account for the diffusive evaporation. Reasonable agreement between data and theory is seen
Effect of ice contamination of liquid-nitrogen drops in film boiling
Previously reported vaporization time data of liquid nitrogen drops in film boiling on a flat plate are about 30 percent shorter than predicted from standard laminar film boiling theory. This theory, however, had been found to successfully correlate the data for conventional fluids such as water, ethanol, benzene, or carbon tetrachloride. Experimental evidence that some of the discrepancy for cryogenic fluids results from ice contamination due to condensation is presented. The data indicate a fairly linear decrease in droplet evaporation time with the diameter of the ice crystal residue. After correcting the raw data for ice contamination along with convection, a comparison of theory with experiment shows good agreement
A generalized correlation of vaporization times of drops in film boiling on a flat plate
Vaporization time correlations for drops in leidenfrost state of film boiling on flat plat
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Design and construction of a high charge and high current 1 - 1/2 cell L-band RF photocathode gun
The Argonne Wakefield Accelerator has been successfully commissioned and used for conducting wakefield experiments in dielectric loaded structures and plasmas. Although the initial wakefield experiments were successful, higher drive beam quality would substantially improve the wakefield accelerating gradients. In this paper we present a new 1-1/2 cell L-band photocathode RF gun design. This gun will produce 10-100 nC beam with 2-5 ps rms pulse length and normalized emittance less than 100 mm mrad. The final gun design and numerical simulations of the beam dynamics are presented
Observation of Enhanced Transformer Ratio in Collinear Wakefield Acceleration
One approach to future high energy particle accelerators is based on the
wakefield principle: a leading high-charge drive bunch is used to excite fields
in an accelerating structure or plasma that in turn accelerates a trailing
low-charge witness bunch. The transformer ratio R is defined as the ratio of
the maximum energy gain of the witness bunch to the maximum energy loss of the
drive bunch. In general, for configurations in which the two beams traverse the
accelerator along the same trajectory (collinear wakefield acceleration). A
number of techniques have been proposed to overcome the transformer ratio
limitation. We report here the first experimental study of the ramped bunch
train (RBT) technique in which a dielectric loaded waveguide was used as the
accelerating structure. A single drive bunch was replaced by two bunches with
charge ratio of 1:2.5 and a separation of 10.5 wavelengths of the fundamental
mode. An average measured transformer ratio enhancement by a factor of 1.31
over the single drive bunch case was obtained in this experiment.Comment: 14 pages, 4 figs, accepted by Phys Rev Let
Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection
We report on measurements of 11-18 cm wavelength radio emission from
interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield
Accelerator. The electrons were observed both in a configuration where they
produced primarily transition radiation from an aluminum foil, and in a
configuration designed for the electrons to produce Cherenkov radiation in a
silica sand target. Our aim was to emulate the large electron excess expected
to develop during an electromagnetic cascade initiated by an ultra high-energy
particle. Such charge asymmetries are predicted to produce strong coherent
radio pulses, which are the basis for several experiments to detect high-energy
neutrinos from the showers they induce in Antarctic ice and in the lunar
regolith. We detected coherent emission which we attribute both to transition
and possibly Cherenkov radiation at different levels depending on the
experimental conditions. We discuss implications for experiments relying on
radio emission for detection of electromagnetic cascades produced by ultra
high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR
Experimental Observation of Energy Modulation in Electron Beams Passing Through Terahertz Dielectric Wakefield Structures
We report observation of a strong wakefield induced energy modulation in an
energy-chirped electron bunch passing through a dielectric-lined waveguide.
This modulation can be effectively converted into a spatial modulation forming
micro-bunches with a periodicity of 0.5 - 1 picosecond, hence capable of
driving coherent THz radiation. The experimental results agree well with
theoretical predictions.Comment: v3. Reviewers' suggestions incorporated. Accepted by PR
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