350 research outputs found
Polymer Release out of a Spherical Vesicle through a Pore
Translocation of a polymer out of curved surface or membrane is studied via
mean first passage time approach. Membrane curvature gives rise to a constraint
on polymer conformation, which effectively drives the polymer to the outside of
membrane where the available volume of polymer conformational fluctuation is
larger. Considering a polymer release out of spherical vesicle, polymer
translocation time is changed to the scaling behavior for
, from for , where is the polymer contour
length and , are vesicle radius and polymer radius of gyration
respectively. Also the polymer capture into a spherical budd is studied and
possible apparatus for easy capture is suggested.Comment: 14 pages RevTeX, 6 postscript figures, published in Phys. Rev. E 57,
730 (1998
Tangential soft x-ray camera for Large Helical Device
A tangentially viewing soft x-ray camera system is to be installed on the Large Helical Device (LHD). This camera system is aimed at exploring both detailed structures of the magnetic surfaces of the LHD plasma and helical islands induced either due to magnetic field errors or MHD instabilities. The frequency range this system is capable of exploring is 0<v<2?kHz; this range can be extended, if the space resolution or the viewing area were reduced
High-speed tangentially viewing soft x-ray camera to study magnetohydrodynamic fluctuations in toroidally confined plasmas (invited)
A high-speed tangentially viewing soft x-ray camera system has been developed and installed on the large helical device (LHD) using a video camera with a maximum framing rate of 13.5 kHz. Low-frequency activities, for example, structures with toroidal/poloidal mode number n/m = 1/2, are directly detected with this system
Steady state RF current drive based upon the relativistic Fokker-Planck equation with quasilinear diffusion
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Determination of the electron velocity distribution from the soft and hard x-ray emission during lower-hybrid current drive on PLT
During lower-hybrid heating in low-density-tokamak discharges, a nonMaxwellian tail of high-energy electrons is formed. This tail carries the plasma current. Utilizing the fact that relativistic electrons emit bremsstrahlung predominantly in the forward direction, we investigate the shape of the electron distribution by measuring the dependence of the x-ray emission on the angle between the magnetic field and the line of sight. The experimental data indicate that the distribution function is predominantly peaked in the forward direction, although a small fraction of the electrons is in the backward cone. The energy dependence of the x-ray spectra is consistent with that of a velocity distribution which has a plateau extending out to several hundred kiloelectron volts. Radial profiles show that the hot electrons are located in the central plasma region and form a high-conductivity plasma with the current profile frozen in. The slope of the spectrum depends on the rf power and on the phasing of the waveguide grill, but not on the externally applied plasma voltage. Relaxation oscillations occur shortly after switching the rf off. They also appear during the rf for low rf power and at the high-density limit of the lower-hybrid current drive. The x-ray spectra confirm that parallel energy is transferred to perpendicular energy during the instability, suggesting an instability due to the anomalous Doppler effect
High-speed tangentially viewing soft x-ray camera to study magnetohydrodynamic fluctuations in toroidally confined plasmas (invited)
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Design studies for ITER x-ray diagnostics
Concepts for adapting conventional tokamak x-ray diagnostics to the harsh radiation environment of ITER include use of grazing-incidence (GI) x-ray mirrors or man-made Bragg multilayer (ML) elements to remove the x-ray beam from the neutron beam, or use of bundles of glass-capillary x-ray ``light pipes`` embedded in radiation shields to reduce the neutron/gamma-ray fluxes onto the detectors while maintaining usable x-ray throughput. The x-ray optical element with the broadest bandwidth and highest throughput, the GI mirror, can provide adequate lateral deflection (10 cm for a deflected-path length of 8 m) at x-ray energies up to 12, 22, or 30 keV for one, two, or three deflections, respectively. This element can be used with the broad band, high intensity x-ray imaging system (XIS), the pulseheight analysis (PHA) survey spectrometer, or the high resolution Johann x-ray crystal spectrometer (XCS), which is used for ion-temperature measurement. The ML mirrors can isolate the detector from the neutron beam with a single deflection for energies up to 50 keV, but have much narrower bandwidth and lower x-ray power throughput than do the GI mirrors; they are unsuitable for use with the XIS or PHA, but they could be used with the XCS; in particular, these deflectors could be used between ITER and the biological shield to avoid direct plasma neutron streaming through the biological shield. Graded-d ML mirrors have good reflectivity from 20 to 70 keV, but still at grazing angles (<3 mrad). The efficiency at 70 keV for double reflection (10 percent), as required for adequate separation of the x-ray and neutron beams, is high enough for PHA requirements, but not for the XIS. Further optimization may be possible
Multipole (E1, M1, E2, M2, E3, M3) transition wavelengths and rates between 3l5l' excited and ground states in nickel-like ions
A relativistic many-body method is developed to calculate energy and
transition rates for multipole transitions in many-electron ions. This method
is based on relativistic many-body perturbation theory (RMBPT), agrees with
MCDF calculations in lowest-order, includes all second-order correlation
corrections and includes corrections from negative energy states. Reduced
matrix elements, oscillator strengths, and transition rates are calculated for
electric-multipole (dipole (E1), quadrupole (E2), and octupole (E3)) and
magnetic-multipole (dipole (M1), quadrupole (M2), and octupole (M3))
transitions between 3l5l' excited and ground states in Ni-like ions with
nuclear charges ranging from Z = 30 to 100. The calculations start from a
1s22s22p63s23p63d10} Dirac-Fock potential. First-order perturbation theory is
used to obtain intermediate-coupling coefficients, and second-order RMBPT is
used to determine the matrix elements. A detailed discussion of the various
contributions to the dipole matrix elements and energy levels is given for
nickellike tungsten (Z = 74). The contributions from negative-energy states are
included in the second-order E1, M1, E2 M2, E3, and M3 matrix elements. The
resulting transition energies and transition rates are compared with
experimental values and with results from other recent calculations. These
atomic data are important in modeling of M-shell radiation spectra of heavy
ions generated in electron beam ion trap experiments and in M-shell diagnostics
of plasmas.Comment: 21 pages, 8 figures, 11 table
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