24,357 research outputs found
The Diffraction Model and its Applicability for Wakefield Calculations
The operation of a Free Electron Laser (FEL) in the ultraviolet or in the
X-ray regime requires the acceleration of electron bunches with an rms length
of 25 to 50 micro meters. The wakefields generated by these sub picosecond
bunches extend into the frequency range well beyond the threshold for Cooper
pair breakup (about 750 GHz) in superconducting niobium at 2 K. It is shown,
that the superconducting cavities can indeed be operated with 25 micro meter
bunches without suffering a breakdown of superconductivity (quench), however at
the price of a reduced quality factor and an increased heat transfer to the
superfluid helium bath. This was first shown by wakefield calculations based on
the diffraction model. In the meantime a more conventional method of computing
wake fields in the time domain by numerical methods was developed and used for
the wakefield calculations. Both methods lead to comparable results: the
operation of TESLA with 25 micro meter bunches is possible but leads to an
additional heat load due to the higher order modes (HOMs). Therefore HOM
dampers for these high frequencies are under construction. These dampers are
located in the beam pipes between the 9-cell cavities. So it is of interest, if
there are trapped modes in the cavity due to closed photon orbits. In this
paper we investigate the existence of trapped modes and the distribution of
heat load over the surface of the TESLA cavity by numerical photon tracking.Comment: Linac2000 conference paper ID No. MOE0
Proton radii of 4,6,8He isotopes from high-precision nucleon-nucleon interactions
Recently, precision laser spectroscopy on 6He atoms determined accurately the
isotope shift between 4He and 6He and, consequently, the charge radius of 6He.
A similar experiment for 8He is under way. We have performed large-scale ab
initio calculations for 4,6,8He isotopes using high-precision nucleon-nucleon
(NN) interactions within the no-core shell model (NCSM) approach. With the
CD-Bonn 2000 NN potential we found point-proton root-mean-square (rms) radii of
4He and 6He 1.45(1) fm and 1.89(4), respectively, in agreement with experiment
and predict the 8He point proton rms radius to be 1.88(6) fm. At the same time,
our calculations show that the recently developed nonlocal INOY NN potential
gives binding energies closer to experiment, but underestimates the charge
radii.Comment: 5 pages, 9 figure
Characteristics of Separated Flow Regions Within Altitude Compensating Nozzles Final Report
Characteristics of separated flow regions within altitude compensating nozzle
Real-Time Operating System/360
RTOS has a cost savings advantage for real-time applications, such as those with random inputs requiring a flexible data routing facility, display systems simplified by a device independent interface language, and complex applications needing added storage protection and data queuing
A spectroscopic study of the cycling transition 4s[3/2]_2-4p[5/2]_3 at 811.8 nm in Ar-39: Hyperfine structure and isotope shift
Doppler-free saturated absorption spectroscopy is performed on an enriched
radioactive Ar-39 sample. The spectrum of the 3s^2 3p^5 4s [3/2]_2 - 3s^2 3p^5
4p [5/2]_3 cycling transition at 811.8 nm is recorded, and its isotope shift
between Ar-39 and Ar-40 is derived. The hyperfine coupling constants A and B
for both the 4s [3/2]_2 and 4p [5/2]_3 energy levels in Ar-39 are also
determined. The results partially disagree with a recently published
measurement of the same transition. Based on earlier measurements as well as
the current work, the isotope shift and hyperfine structure of the
corresponding transition in Ar-37 are also calculated. These spectroscopic data
are essential for the realization of laser trapping and cooling of Ar-37 and
Ar-39
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