27,639 research outputs found
Remarks on Form Factor Bounds
Improved model independent upper bounds on the weak transition form factors
are derived using inclusive sum rules. Comparison of the new bounds with the
old ones is made for the form factors h_{A_1} and h_V in B -> D* decays.Comment: 8 pages, 2 figures, title changed and typos corrected for journal
publicatio
Anomalies in Universal Intensity Scaling in Ultrarelativistic Laser-Plasma Interactions
Laser light incident on targets at intensities such that the electron
dynamics is ultrarelativistic gives rise to a harmonic power spectrum extending
to high orders and characterized by a relatively slow decay with the harmonic
number m that follows a power law dependence, m^{-p}. Relativistic similarity
theory predicts a universal value for p = 8/3 up to some cut-off m = m*. The
results presented in this work suggest that under conditions in which plasma
effects contribute to the emission spectrum, the extent of this contribution
may invalidate the concept of universal decay. We report a decay with harmonic
number in the ultrarelativistic range characterised by an index 5/3 < p < 7/3,
significantly weaker than that predicted by the similarity model.Comment: 5 pages, 4 figure
Raman gain against a background of non-thermal ion fluctuations in a plasma
A complex stimulated Raman scattering event against a background of non-thermal ion acoustic waves in an inhomogeneous plasma is described. We obtain analytic forms for the Raman gain due to a five-wave interaction consisting of conventional three-wave Raman scattering followed by the decay of the Raman Langmuir wave into a second Langmuir wave (or a second scattered light wave) and an ion acoustic wave. Very modest levels of ion waves produce a. significant effect on Raman convective gain. A combination of plasma inhomogeneity and suprathermal ion fluctuations may offer a means for the control of Raman gain
Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands
Electron beam wire tomography in the H-1NF heliac enables high resolution mapping of vacuum flux surfaces with minimal disruption of the plasma operations schedule. Recent experimental results have proven this technique to be a highly accurate and high resolution method for mapping vacuum magnetic islands. Islands of width as small as delta approximately 8 mm have been measured, providing estimates of the internal rotational transform of the island. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, enables systematic exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping technique significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields. This article presents recent experimental results and associated techniques.with support from
the Australian Research Council Grant No. DP0344361
- …