9,090 research outputs found
LHC Symposium 2003: Summary Talk
This summary talk reviews the LHC 2003 Symposium, focusing on expectations as
we prepare to leap over the current energy frontier into new territory. We may
learn from what happened in the two most recent examples of leaping into new
energy territory. Quite different scenarios appeared in those two cases. In
addition, we review the status of the machine and experiments as reported at
the Symposium. Finally, I suggest an attitude which may be most appropriate as
we look forward to the opportunities anticipated for the first data from the
LHC.Comment: Summary Talk: LHC Symposium, May 1-3, 2003, Fermilab, Batavia, IL US
Calibration of the high-frequency magnetic fluctuation diagnostic in plasma devices
The increasing reservoirs of energetic particles which drive high-frequency modes, together with advances in the understanding of magnetohydrodynamics, have led to a need for higher-frequency (50 kHz to >20MHz) measurements of magnetic field fluctuations in magnetic fusion devices such as tokamaks. This article uses transmission line equations to derive the voltage response of a Mirnov coil at the digitizer end of a transmission line of length ℓ. It is shown that, depending on the terminations of the line, resonances can occur even for ℓ/λ⪡1, with λ the wavelength of a fluctuation in the transmission line. A lumped-circuit model based on the approach of Heeter et al. [R. F. Heeter, A. F. Fasoli, S. Ali-Arshad, and J. M. Moret. Rev. Sci. Instrum.71, 4092 (2000)] is extended to enable the inclusion simultaneously of both serial resistance and parallel conductance elements. As originally proposed by Heeter et al. the lumped-circuit model offers the advantage of remote calibration; this may be of particular value when upgrading existing systems to operate at frequencies above the original design specification. It is formally shown that the transmission line equations for the transfer function and measured impedance reduce to those of the lumped circuit model of Heeter et al. under specific conditions. The result extends the use of the lumped-circuit model of Heeter et al., which can be used to extract the transfer function from measurement of the impedance, beyond the case of an open-circuit termination. Although the numerical procedure does exhibit some problems associated with non-uniqueness, it provides a simple calibration method for systems that are not well defined. Using typical parameters for a high-frequency Mirnov coil installed on the Joint European Torus (JET) tokamak, the lumped-circuit approximation agrees with the steady-state transmission line model to within 0.015° in phase and 22% in amplitude for frequencies up to 1 MHz. A matched termination, though eliminating line resonances and reducing the length of time for the system to reach steady state, is inappropriate for the JET-type coils which exhibit significant temperature-dependent resistance. Finally, for fluctuations of finite duration, a method of computing the discrepancy due to the simplifying assumption of Fourier-stationary conditions is described.This work was funded jointly by the United Kingdom
Engineering and Physical Sciences Research Council and by EURATOM
Observation of quantum spin noise in a 1D light-atoms quantum interface
We observe collective quantum spin states of an ensemble of atoms in a
one-dimensional light-atom interface. Strings of hundreds of cesium atoms
trapped in the evanescent fiel of a tapered nanofiber are prepared in a
coherent spin state, a superposition of the two clock states. A weak quantum
nondemolition measurement of one projection of the collective spin is performed
using a detuned probe dispersively coupled to the collective atomic observable,
followed by a strong destructive measurement of the same spin projection. For
the coherent spin state we achieve the value of the quantum projection noise 40
dB above the detection noise, well above the 3 dB required for reconstruction
of the negative Wigner function of nonclassical states. We analyze the effects
of strong spatial inhomogeneity inherent to atoms trapped and probed by the
evanescent waves. We furthermore study temporal dynamics of quantum
fluctuations relevant for measurement-induced spin squeezing and assess the
impact of thermal atomic motion. This work paves the road towards observation
of spin squeezed and entangled states and many-body interactions in 1D spin
ensembles
Evidence cross-validation and Bayesian inference of MAST plasma equilibria
In this paper, current profiles for plasma discharges on the Mega-Ampere
Spherical Tokamak (MAST) are directly calculated from pickup coil, flux loop
and Motional-Stark Effect (MSE) observations via methods based in the
statistical theory of Bayesian analysis. By representing toroidal plasma
current as a series of axisymmetric current beams with rectangular
cross-section and inferring the current for each one of these beams,
flux-surface geometry and q-profiles are subsequently calculated by elementary
application of Biot-Savart's law. The use of this plasma model in the context
of Bayesian analysis was pioneered by Svensson and Werner on the Joint-European
Tokamak (JET) [J. Svensson and A. Werner. Current tomography for axisymmetric
plasmas. Plasma Physics and Controlled Fusion, 50(8):085002, 2008]. In
this framework, linear forward models are used to generate diagnostic
predictions, and the probability distribution for the currents in the
collection of plasma beams was subsequently calculated directly via application
of Bayes' formula. In this work, we introduce a new diagnostic technique to
identify and remove outlier observations associated with diagnostics falling
out of calibration or suffering from an unidentified malfunction. These
modifications enable good agreement between Bayesian inference of the last
closed flux-surface (LCFS) with other corroborating data, such as such as that
from force balance considerations using EFIT++ [L. Appel et al., Proc. 33rd EPS
Conf., Rome, Italy, 2006]. In addition, this analysis also yields errors on the
plasma current profile and flux-surface geometry, as well as directly
predicting the Shafranov shift of the plasma core.This work was jointly funded by the Australian Government
through International Science Linkages Grant No.
CG130047, the Australian National University, the United
Kingdom Engineering and Physical Sciences Research
Council under Grant No. EP/G003955, and by the European
Communities under the contract of Association between EURATOM and CCFE
Spin squeezing of atomic ensembles by multi-colour quantum non-demolition measurements
We analyze the creation of spin squeezed atomic ensembles by simultaneous
dispersive interactions with several optical frequencies. A judicious choice of
optical parameters enables optimization of an interferometric detection scheme
that suppresses inhomogeneous light shifts and keeps the interferometer
operating in a balanced mode that minimizes technical noise. We show that when
the atoms interact with two-frequency light tuned to cycling transitions the
degree of spin squeezing scales as where is the
resonant optical depth of the ensemble. In real alkali atoms there are loss
channels and the scaling may be closer to Nevertheless
the use of two-frequencies provides a significant improvement in the degree of
squeezing attainable as we show by quantitative analysis of non-resonant
probing on the Cs D1 line. Two alternative configurations are analyzed: a
Mach-Zehnder interferometer that uses spatial interference, and an interaction
with multi-frequency amplitude modulated light that does not require a spatial
interferometer.Comment: 7 figure
Review of Heavy-Quark Production at Fixed-Target Experiments
An increasingly large amount of quality fixed-target data on heavy-quark production at fixed-target energies is appearing. This data can provide information across a range of physics topics. The topics vary from investigations of QCD predictions to the understanding of the structure of hadrons. Recent results on neutrino, photon, and hadron production of charm and beauty will be reviewed in this context. The greatest insight will come from combining multiple measurements as they relate to the physics topics, and by ensuring that the parameters used in models are consistent with all the measurements. We have not yet really entered the time when this has been done for fixed-target measurements
Teacher Training for the Implementation of the Incredible Years at GFW Elementary School
The purpose of this research project was to determine whether training the Early Childhood Special Education (ECSE) teachers, paraprofessionals, and staff would increase the social and emotional literacy of the children as well as the staff in the ECSE classroom . The four areas of training & research consisted of: 1. Increasing staff’s positive attention, encouragement and praise while working as a team in the ECSE classroom; 2. Using incentives for the purpose of promoting positive attention in the classroom; 3. Using more proactive teaching techniques for the purpose of preventing behavior problems in the classroom, and 4. Increasing staff’s proficiency in teaching social skills, problem-solving skills, and anger management skills. The staff trainings served as a prerequisite for the successful implementation of the Incredible Years (IY) Child Training Program called the Dina Dinosaur Social Skills and Problem Solving curriculum. This curriculum will be fully implemented in the ECSE classroom beginning in the fall, 2010. Focus groups and grounded theory methodology were utilized to collect and analyze the data
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