3,984 research outputs found
Modeling heat transfer from quench protection heaters to superconducting cables in Nb3Sn magnets
We use a recently developed quench protection heater modeling tool for an
analysis of heater delays in superconducting high-field Nb3Sn accelerator
magnets. The results suggest that the calculated delays are consistent with
experimental data, and show how the heater delay depends on the main heater
design parameters.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet,
Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva,
Switzerlan
Cryogenic-coolant He4-superconductor dynamic and static interactions
A composite superconducting material (NbTi-Cu) was evaluated with emphasis on post quench solid cooling interaction regimes. The quasi-steady runs confirm the existence of a thermodynamic limiting thickness for insulating coatings. Two distinctly different post quench regimes of coated composites are shown to relate to the limiting thickness. Only one regime,, from quench onset to the peak value, revealed favorable coolant states, in particular in He2. Transient recovery shows favorable recovery times from this post quench regime (not drastically different from bare conductors) for both single coated specimens and a coated conductor bundle
Thermal to Nonthermal Energy Partition at the Early Rise Phase of Solar Flares
In some flares the thermal component appears much earlier than the nonthermal
component in X-ray range. Using sensitive microwave observations we revisit
this finding made by Battaglia et al. (2009) based on RHESSI data analysis. We
have found that nonthermal microwave emission produced by accelerated electrons
with energy of at least several hundred keV, appears as early as the thermal
soft X-ray emission indicative that the electron acceleration takes place at
the very early flare phase. The non-detection of the hard X-rays at that early
stage of the flares is, thus, an artifact of a limited RHESSI sensitivity. In
all considered events, the microwave emission intensity increases at the early
flare phase. We found that either thermal or nonthermal gyrosynchrotron
emission can dominate the low-frequency part of the microwave spectrum below
the spectral peak occurring at 3-10 GHz. In contrast, the high-frequency
optically thin part of the spectrum is always formed by the nonthermal,
accelerated electron component, whose power-law energy spectrum can extend up
to a few MeV at this early flare stage. This means that even though the total
number of accelerated electrons is small at this stage, their nonthermal
spectrum is fully developed. This implies that an acceleration process of
available seed particles is fully operational. While, creation of this seed
population (the process commonly called `injection' of the particles from the
thermal pool into acceleration) has a rather low efficiency at this stage,
although, the plasma heating efficiency is high. This imbalance between the
heating and acceleration (in favor of the heating) is difficult to reconcile
within most of available flare energization models. Being reminiscent of the
tradeoff between the Joule heating and runaway electron acceleration, it puts
additional constraints on the electron injection into the acceleration process.Comment: 11 pages, 12 figures, accepted for Ap
Cryogenic-coolant He-4-superconductor interaction
The thermodynamic and thermal interaction between a type 2 composite alloy and cryo-coolant He4 was studied with emphasis on post quench phenomena of formvar coated conductors. The latter were investigated using a heater simulation technique. Overall heat transfer coefficients were evaluated for the quench onset point. Heat flux densities were determined for phenomena of thermal switching between a peak and a recovery value. The study covered near saturated liquid, pressurized He4, both above and below the lambda transition, and above and below the thermodynamic critical pressure. In addition, friction coefficients for relative motion between formvar insulated conductors were determined
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The structural design for a "canted cosine-theta" Superconducting dipole coil and magnet structure-CCT
The Superconducting Magnet Group, at Lawrence Berkeley National Laboratory (LBNL), has been developing a canted cosine-theta (CCT) superconducting dipole coil as well as the coil's supporting magnet structure. This contribution reports on the progress in the development of the coil's winding mandrel and its fabrication options. A comprehensive study of the coil's Lorentz forces was performed to validate the winding mandrel's "stress interception" attributes. The design of the external structure and the application of the "Bladder & Key" technology is also discussed. Additionally, the application of these studies to a curved ion-therapy CCT dipole magnet is reported
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Towards Integrated Design and Modeling of High Field Accelerator Magnets
The next generation of superconducting accelerator magnets will most likely use a brittle conductor (such as Nb{sub 3}Sn), generate fields around 18 T, handle forces that are 3-4 times higher than in the present LHC dipoles, and store energy that starts to make accelerator magnets look like fusion magnets. To meet the challenge and reduce the complexity, magnet design will have to be more innovative and better integrated. The recent design of several high field superconducting magnets have now benefited from the integration between CAD (e.g. ProE), magnetic analysis tools (e.g. TOSCA) and structural analysis tools (e.g. ANSYS). Not only it is now possible to address complex issues such as stress in magnet ends, but the analysis can be better detailed an extended into new areas previously too difficult to address. Integrated thermal, electrical and structural analysis can be followed from assembly and cool-down through excitation and quench propagation. In this paper we report on the integrated design approach, discuss analysis results and point out areas of future interest
Nonlinearity-induced conformational instability and dynamics of biopolymers
We propose a simple phenomenological model for describing the conformational
dynamics of biopolymers via the nonlinearity-induced buckling and collapse
(i.e. coiling up) instabilities. Taking into account the coupling between the
internal and mechanical degrees of freedom of a semiflexible biopolymer chain,
we show that self-trapped internal excitations (such as amide-I vibrations in
proteins, base-pair vibrations in DNA, or polarons in proteins) may produce the
buckling and collapse instabilities of an initially straight chain. These
instabilities remain latent in a straight infinitely long chain, because the
bending of such a chain would require an infinite energy. However, they
manifest themselves as soon as we consider more realistic cases and take into
account a finite length of the chain. In this case the nonlinear localized
modes may act as drivers giving impetus to the conformational dynamics of
biopolymers. The buckling instability is responsible, in particular, for the
large-amplitude localized bending waves which accompany the nonlinear modes
propagating along the chain. In the case of the collapse instability, the chain
folds into a compact three-dimensional coil. The viscous damping of the aqueous
environment only slows down the folding of the chain, but does not stop it even
for a large damping. We find that these effects are only weakly affected by the
peculiarities of the interaction potentials, and thus they should be generic
for different models of semiflexible chains carrying nonlinear localized
excitations.Comment: 4 pages (RevTeX) with 5 figures (EPS
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