8,204 research outputs found
Micromegas TPC studies at high magnetic fields using the charge dispersion signal
The International Linear Collider (ILC) Time Projection Chamber (TPC)
transverse space-point resolution goal is 100 microns for all tracks including
stiff 90 degree tracks with the full 2 meter drift. A Micro Pattern Gas
Detector (MPGD) readout TPC can achieve the target resolution with existing
techniques using 1 mm or narrower pads at the expense of increased detector
cost and complexity. The new MPGD readout technique of charge dispersion can
achieve good resolution without resorting to narrow pads. This has been
demonstrated previously for 2 mm x 6 mm pads with GEMs and Micromegas in cosmic
ray tests and in a KEK beam test in a 1 Tesla magnet. We have recently tested a
Micromegas-TPC using the charge dispersion readout concept in a high field
super-conducting magnet at DESY. The measured Micromegas gain was found to be
constant within 0.5% for magnetic fields up to 5 Tesla. With the strong
suppression of transverse diffusion at high magnetic fields, we measure a flat
50 micron resolution at 5 Tesla over the full 15 cm drift length of our
prototype TPC.Comment: 7 pages, 3 figure
(2+1) resonant enhanced multiphoton ionization of H_2 via the E, F^(1)ÎŁ^+_g state
In this paper, we report the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2+1) REMPI of H_2 via the E, F^(1)ÎŁ^+_g state, and compare these with the experimental data of Anderson et al. [Chem. Phys. Lett. 105, 22 (1984)]. These results show that the observed nonâFranckâCondon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydbergâvalence mixing in the resonant intermediate state
Electric field Induced Patterns in Soft Visco-elastic films: From Long Waves of Viscous Liquids to Short Waves of Elastic Solids
We show that the electric field driven surface instability of visco-elastic
films has two distinct regimes: (1) The visco-elastic films behaving like a
liquid display long wavelengths governed by applied voltage and surface
tension, independent of its elastic storage and viscous loss moduli, and (2)
the films behaving like a solid require a threshold voltage for the instability
whose wavelength always scales as ~ 4 x film thickness, independent of its
surface tension, applied voltage, loss and storage moduli. Wavelength in a
narrow transition zone between these regimes depends on the storage modulus.Comment: Accepted for Publication in Physical Review Letter
Circular dichroism in photoelectron angular distributions from twoâcolor (1+1) REMPI of NO
A detailed experimental and theoretical study of dichroic effects in photoelectron angular distributions is reported for (1+1), twoâcolor REMPI of NO via the A^â2ÎŁ^+, v=0 state. Optically aligned A state rotational levels are probed through ionization by circularly polarized light. Resultant photoelectron angular distributions exhibit significant leftâright asymmetry, the phase and magnitude of which are shown to be related to the curvature of the excited state M_J distribution. Theoretical calculations involving a full ab initio treatment of the ionization dynamics result in circularly dichroic angular distribution (CDAD) parameters in good agreement with those derived experimentally. Additional effects including hyperfine depolarization and coherence are also discussed in relation to the observed CDAD data
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