33 research outputs found
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PBFA Z: A 20-MA z-pinch driver for plasma radiation sources
Sandia National Laboratories is completing a major modification to the PBFA-II facility. PBFA Z will be a z-pinch driver capable of delivering up to 20 MA to a z-pinch load. It optimizes the electrical coupling to the implosion energy of z pinches at implosion velocities of {approximately} 40 cm/{mu}s. Design constraints resulted in an accelerator with a 0.12-{Omega} impedance, a 10.25-nH inductance, and a 120-ns pulse width. The design required new water transmission lines, insulator stack, and vacuum power feeds. Current is delivered to the z-pinch load through four, self-magnetically-insulated vacuum transmission lines and a double post-hole convolute. A variety of design codes are used to model the power flow. These predict a peak current of 20 MA to a z-pinch load having a 2-cm length, a 2-cm radius, and a 15--mg mass, coupling 1.5 MJ into kinetic energy. We present 2-D Rad-Hydro calculations showing MJ x-ray outputs from tungsten wire-array z pinches
Charged vortices in superfluid systems with pairing of spatially separated carriers
It is shown that in a magnetic field the vortices in superfluid electron-hole
systems carry a real electrical charge. The charge value depends on the
relation between the magnetic length and the Bohr radiuses of electrons and
holes. In double layer systems at equal electron and hole filling factors in
the case of the electron and hole Bohr radiuses much larger than the magnetic
length the vortex charge is equal to the universal value (electron charge times
the filling factor).Comment: 4 page
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Water-line design and performance of Z
A new set of bi-plate transmission lines have been designed and installed in the water-section of PBFA-II for the Z-pinch experiments. Thirty-six aluminum flat-plate transmission lines submerged in a water dielectric deliver a timed electrical pulse from coaxial tube sections to a ring stack section. Each of the lines are electrically isolated from each other by transit-time effects. The water-lines are configured radially at four vertical levels. Each level has nine sets of bi-plates, with a transition section that is unique to that level. Mechanically, the bi-plate sections are designed to carry both static and dynamic loads. Electrically, the lines are designed to transport electrical pulses that average 200 nanoseconds with peak voltage of 2.5 to 3.0 MV. The peak fields exceed 200kV/cm. All line sections are a series of chromate coated aluminum plates, broken down into short, light weight sections. The design of the plates was meticulously developed using the Electro code for voltage break down, and NISA for mechanical analysis. Electrical losses associated with impedance mismatching and voltage breakdown were carefully reviewed. Changes in the bi-plate gap, surface shapes and electrical path discontinuities (mechanical joints) were precisely calculated to achieve maximum electrical performance and reliability. Several iterations of surface shapes and line gaps were reviewed to achieve the most desirable characteristics possible. Additional criteria required that minimal time and effort be required to remove and install the water-lines. Special hardware was developed to help meet this requirement
Electromagnetic characteristics of bilayer quantum Hall systems in the presence of interlayer coherence and tunneling
The electromagnetic characteristics of bilayer quantum Hall systems in the
presence of interlayer coherence and tunneling are studied by means of a
pseudospin-texture effective theory and an algebraic framework of the
single-mode approximation, with emphasis on clarifying the nature of the
low-lying neutral collective mode responsible for interlayer tunneling
phenomena. A long-wavelength effective theory, consisting of the collective
mode as well as the cyclotron modes, is constructed. It is seen explicitly from
the electromagnetic response that gauge invariance is kept exact, this
implying, in particular, the absence of the Meissner effect in bilayer systems.
Special emphasis is placed on exploring the advantage of looking into quantum
Hall systems through their response; in particular, subtleties inherent to the
standard Chern-Simons theories are critically examined.Comment: 9 pages, Revtex, to appear in Phys. Rev.
Noncommutative Geometry, Extended W(infty) Algebra and Grassmannian Solitons in Multicomponent Quantum Hall Systems
Noncommutative geometry governs the physics of quantum Hall (QH) effects. We
introduce the Weyl ordering of the second quantized density operator to explore
the dynamics of electrons in the lowest Landau level. We analyze QH systems
made of -component electrons at the integer filling factor .
The basic algebra is the SU(N)-extended W. A specific feature is
that noncommutative geometry leads to a spontaneous development of SU(N)
quantum coherence by generating the exchange Coulomb interaction. The effective
Hamiltonian is the Grassmannian sigma model, and the dynamical field
is the Grassmannian field, describing complex Goldstone
modes and one kind of topological solitons (Grassmannian solitons).Comment: 15 pages (no figures
Broken-Symmetry States in Quantum Hall Superlattices
We argue that broken-symmetry states with either spatially diagonal or
spatially off-diagonal order are likely in the quantum Hall regime, for clean
multiple quantum well (MQW) systems with small layer separations. We find that
for MQW systems, unlike bilayers, charge order tends to be favored over
spontaneous interlayer coherence. We estimate the size of the interlayer
tunneling amplitude needed to stabilize superlattice Bloch minibands by
comparing the variational energies of interlayer-coherent superlattice miniband
states with those of states with charge order and states with no broken
symmetries. We predict that when coherent miniband ground states are stable,
strong interlayer electronic correlations will strongly enhance the
growth-direction tunneling conductance and promote the possibility of Bloch
oscillations.Comment: 9 pages LaTeX, 4 figures EPS, to be published in PR
Fractional vortices on grain boundaries --- the case for broken time reversal symmetry in high temperature superconductors
We discuss the problem of broken time reversal symmetry near grain boundaries
in a d-wave superconductor based on a Ginzburg-Landau theory. It is shown that
such a state can lead to fractional vortices on the grain boundary. Both
analytical and numerical results show the structure of this type of state.Comment: 9 pages, RevTeX, 5 postscript figures include
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Titanium K-Shell X-Ray Production from High Velocity Wire Arrays Implosions on the 20-MA Z Accelerator
The advent of the 20-MA Z accelerator [R.B. Spielman, C. Deeney, G.A. Chandler, et al., Phys. Plasmas 5, 2105, (1997)] has enabled implosions of large diameter, high-wire-number arrays of titanium to begin testing Z-pinch K-shell scaling theories. The 2-cm long titanium arrays, which were mounted on a 40-mm diameter, produced between 75{+-}15 to 125{+-}20 kJ of K-shell x-rays. Mass scans indicate that, as predicted, higher velocity implosions in the series produced higher x-ray yields. Spectroscopic analyses indicate that these high velocity implosions achieved peak electron temperatures from 2.7{+-}0.1 to 3.2{+-}0.2 keV and obtained a K-shell emission mass participation of up to 12%
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Composite wire plasma formation and evolution
The detailed understanding of the formation and evolution of plasma from rapidly heated metallic wires is a long-standing challenge in the field of plasma physics and in exploding wire engineering. This physical process is made even more complicated if the wire material is composed of a number of individual layers. The authors have successfully developed both optical and x-ray backlighting diagnostics. In particular, the x-ray backlighting technique has demonstrated the capability for quantitative determination of the plasma density over a wide range of densities. This diagnostic capability shows that the process of plasma formation is composed of two separate phases: first, current is passed through a cold wire and the wire is heated ohmically, and, second, the heated wire evolves gases that break down and forms a low-density plasma surrounding the wire