352 research outputs found
A new beam emission polarimetry diagnostic for measuring the magnetic field line angle at the plasma edge of ASDEX Upgrade
A new edge beam emission polarimetry diagnostic dedicated to the measurement of the magnetic
field line angle has been installed on the ASDEX Upgrade tokamak. The new diagnostic relies on the
motional Stark e
ff
ect and is based on the simultaneous measurement of the polarization direction of
the linearly polarized
π
(parallel to the electric field) and
σ
(perpendicular to the electric field) lines of
the Balmer line D
α
. The technical properties of the system are described. The calibration procedures
are discussed and first measurements are presentedEuropean Union (EUROfusion 633053)European Union (EUROfusion Grant WP14-FRF-IPP)Ministerio de Economía y Competitividad (Grant No. FJCI-201422139
Assessment of the current density evolution during an ELM cycle using beam emission polarimetry at ASDEX Upgrade
EUROfusion Consortium 63305
Two-Loop Diagrammatics in a Self-Dual Background
Diagrammatic rules are developed for simplifying two-loop QED diagrams with
propagators in a constant self-dual background field. This diagrammatic
analysis, using dimensional regularization, is used to explain how the fully
renormalized two-loop Euler-Heisenberg effective Lagrangian for QED in a
self-dual background field is naturally expressed in terms of one-loop
diagrams. The connection between the two-loop and one-loop vacuum diagrams in a
background field parallels a corresponding connection for free vacuum diagrams,
without a background field, which can be derived by simple algebraic
manipulations. It also mirrors similar behavior recently found for two-loop
amplitudes in N=4 SUSY Yang-Mills theory.Comment: 16 pp, Latex, Axodra
The role of radial electric field and neoclassical transport in the establishment and sustainment of the edge transport barrier in the ASDEX Upgrade tokamak
EUROfusion Consortium 63305
Do Instantons Like a Colorful Background?
We investigate chiral symmetry breaking and color symmetry breaking in QCD.
The effective potential of the corresponding scalar condensates is discussed in
the presence of non-perturbative contributions from the semiclassical
one-instanton sector. We concentrate on a color singlet scalar background which
can describe chiral condensation, as well as a color octet scalar background
which can generate mass for the gluons. Whereas a non-vanishing singlet chiral
field is favored by the instantons, we have found no indication for a
preference of color octet backgrounds.Comment: 25 pages, 7 figure
Pressure and interaction measure of the gluon plasma
We explore the thermodynamics of the gluon plasma in SU(3) Yang-Mills theory
emerging from the non-trivial spatial dynamics of valence gluons. The lattice
data suggest that these gluons interact with each other linearly at large
spatial separations. At high temperatures, valence gluons should reproduce the
pressure of the non-interacting Stefan-Boltzmann plasma along with the leading
perturbative correction. These properties of valence gluons can be modeled in
terms of the integral over their trajectories. We calculate such a world-line
integral analytically and obtain the pressure and the interaction measure
of the gluon plasma. Additionally, we account for the
contributions of stochastic background fields to these thermodynamic
quantities. The results turn out to be in a good agreement with the
corresponding lattice data. In particular, the lattice-simulated peak of the
interaction measure near the deconfinement critical temperature is reproduced.Comment: 20 pages, 5 figures. Final version. To appear in Nucl. Phys.
The QCD Phase Diagram at Nonzero Temperature, Baryon and Isospin Chemical Potentials in Random Matrix Theory
We introduce a random matrix model with the symmetries of QCD at finite
temperature and chemical potentials for baryon number and isospin. We analyze
the phase diagram of this model in the chemical potential plane for different
temperatures and quark masses. We find a rich phase structure with five
different phases separated by both first and second order lines. The phases are
characterized by the pion condensate and the chiral condensate for each of the
flavors. In agreement with lattice simulations, we find that in the phase with
zero pion condensate the critical temperature depends in the same way on the
baryon number chemical potential and on the isospin chemical potential. At
nonzero quark mass, we remarkably find that the critical end point at nonzero
temperature and baryon chemical potential is split in two by an arbitrarily
small isospin chemical potential. As a consequence, there are two crossovers
that separate the hadronic phase from the quark-gluon plasma phase at high
temperature. Detailed analytical results are obtained at zero temperature and
in the chiral limit.Comment: 13 pages, 5 figures, REVTeX
The Higher Derivative Expansion of the Effective Action by the String Inspired Method. Part II
We apply the string inspired worldline formalism to the calculation of the
higher derivative expansion of one-loop effective actions in non-Abelian gauge
theory. For this purpose, we have completely computerized the method, using the
symbolic manipulation programs FORM, PERL and M. Explicit results are given to
sixth order in the inverse mass expansion, reduced to a minimal basis of
invariants specifically adapted to the method. Detailed comparisons are made
with other gauge-invariant algorithms for calculating the same expansion. This
includes an explicit check of all coefficients up to fifth order.Comment: 37 pages, LaTeX, 3 figures, typos corrected, to appear in Ann. Phys.
(N.Y.
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