The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited

The charged particle stopping power in a highly ionized and weakly to moderately coupled plasma has been calculated to leading and next-to-leading order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas behind this calculation, we use a Fokker-Planck equation derived by BPS to compute the electron-ion energy partitioning of a charged particle traversing a plasma. The motivation for this application is ignition for inertial confinement fusion -- more energy delivered to the ions means a better chance of ignition, and conversely. It is therefore important to calculate the fractional energy loss to electrons and ions as accurately as possible, as this could have implications for the Laser Megajoule (LMJ) facility in France and the National Ignition Facility (NIF) in the United States. The traditional method by which one calculates the electron-ion energy splitting of a charged particle traversing a plasma involves integrating the stopping power dE/dx. However, as the charged particle slows down and becomes thermalized into the background plasma, this method of calculating the electron-ion energy splitting breaks down. As a result, the method suffers a systematic error of order T/E0, where T is the plasma temperature and E0 is the initial energy of the charged particle. In the case of DT fusion, for example, this can lead to uncertainties as high as 10% or so. The formalism presented here is designed to account for the thermalization process, and in contrast, it provides results that are near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical Society meeting on plasma physic

Calculating the Charged Particle Stopping Power Exactly to Leading and Next-to-leading Order

I will discuss a new method for calculating transport quantities, such as the charged particle stopping power, in a weakly to moderately coupled plasma. This method, called dimensional continuation, lies within the framework of convergent kinetic equations, and it is powerful enough to allow for systematic perturbative expansions in the plasma coupling constant. In particular, it provides an exact evaluation of the stopping power to leading and next-to-leading order in the plasma coupling, with the systematic error being of cubic order. Consequently, the calculation is near-exact for a weakly coupled plasma, and quite accurate for a moderately coupled plasma. The leading order term in this expansion has been known since the classic work of Spitzer. In contrast, the next-to-leading order term has been calculated only recently by Brown, Preston, and Singleton (BPS), using the aforementioned method, to account for all short- and long-distance physics accurate to second order in the plasma coupling, including an exact treatment of the quantum-to-classical scattering transition. Preliminary numerical studies suggest that the BPS stopping power increases the ignition threshold, thereby having potential adverse implications for upcoming high energy density facilities. Since the key ideas behind the BPS calculation are possibly unfamiliar to plasma physicists, and the implications might be important, I will use this opportunity to explain the method in a pedagogical fashion.Comment: 4 pages, proceedings for the 5th International Conference on Inertial Fusion Science and Applications (IFSA-07), Kobe, Japan, 9-14 September 200

Charged Particle Motion in a Highly Ionized Plasma

A recently introduced method utilizing dimensional continuation is employed to compute the energy loss rate for a non-relativistic particle moving through a highly ionized plasma. No restriction is made on the charge, mass, or speed of this particle. It is, however, assumed that the plasma is not strongly coupled in the sense that the dimensionless plasma coupling parameter g=e^2\kappa_D/ 4\pi T is small, where \kappa_D is the Debye wave number of the plasma. To leading and next-to-leading order in this coupling, dE/dx is of the generic form g^2 \ln[C g^2]. The precise numerical coefficient out in front of the logarithm is well known. We compute the constant C under the logarithm exactly for arbitrary particle speeds. Our exact results differ from approximations given in the literature. The differences are in the range of 20% for cases relevant to inertial confinement fusion experiments. The same method is also employed to compute the rate of momentum loss for a projectile moving in a plasma, and the rate at which two plasmas at different temperatures come into thermal equilibrium. Again these calculations are done precisely to the order given above. The loss rates of energy and momentum uniquely define a Fokker-Planck equation that describes particle motion in the plasma. The coefficients determined in this way are thus well-defined, contain no arbitrary parameters or cutoffs, and are accurate to the order described. This Fokker-Planck equation describes the longitudinal straggling and the transverse diffusion of a beam of particles. It should be emphasized that our work does not involve a model, but rather it is a precisely defined evaluation of the leading terms in a well-defined perturbation theory.Comment: Comments: Published in Phys. Rep. 410/4 (2005) 237; RevTeX, 111 Pages, 17 Figures; Transcription error corrected in temperature equilibration rate (3.61) and (12.44) which replaces \gamma-2 by \gamma-

A TDM synchronization system for multiple access satellite communication

Time Division Multiple Access /TDMA/ system for satellite communication with ground station syste

Ascent from the lunar surface

Ascent from lunar surface problem with solution by variational calculu

Spectral Analysis of the Stromlo-APM Survey I. Spectral Properties of Galaxies

We analyze spectral properties of 1671 galaxies from the Stromlo-APM survey, selected to have 15 < b_J < 17.15 and having a mean redshift z = 0.05. This is a representative local sample of field galaxies, so the global properties of the galaxy population provide a comparative point for analysis of more distant surveys. We measure Halpha, Oii 3727, Sii 6716, 6731, Nii 6583 and Oi 6300 equivalent widths and the D_4000 break index. The 5A resolution spectra use an 8 arcsec slit, which typically covers 40-50% of the galaxy area. We find no evidence for systematic trends depending on the fraction of galaxy covered by the slit, and further analysis suggests that our spectra are representative of integrated galaxy spectra. We classify spectra according to their Halpha emission, which is closely related to massive star formation. Overall we find 61% of galaxies are Halpha emitters with rest-frame equivalent widths EW(Halpha) >= 2A. The emission-line galaxy (ELG) fraction is smaller than seen in the CFRS at z = 0.2 and is consistent with a rapid evolution of Halpha luminosity density. The ELG fraction, and EW(Halpha), increase at fainter absolute magnitudes, smaller projected area and smaller D_4000. In the local Universe, faint, small galaxies are dominated by star formation activity, while bright, large galaxies are more quiescent. This picture of the local Universe is quite different from the distant one, where bright galaxies appear to show rapidly-increasing activity back in time. (Abridged)Comment: 40 pages, 25 figures, MNRAS, in pres

Negotiating Change: An Analysis of the Origins of Ghana\u27s National Health Insurance Act

Given the neo-liberal ideologies of the majority party and global trends toward market-based approaches to social services, the passage of Ghana’s National Health Insurance Scheme, which provides coverage for all, seems anomalous. To answer the questions raised by this legislation, I analyze evidence from the government and consulting agencies. I find that a shift in international focus to allow social service reform combined with domestic electoral political influences. The scheme’s foundation of district mutual health organizations evolved from a USAID-funded consulting agency’s work, and may additionally reflect creative borrowing from the United States’ failed healthcare reforms of 1993

The National Board Certification Process: A Comparison of the Perceptions of National Board Certified Teachers and National Board Candidates in West Virginia

More than twenty years of research have been devoted to the National Board of Professional Teaching Standards (NBPTS) certification process, much of it focused on the effects of National Board certified teachers (NBCTs) on student achievement. Less attention has been paid to the effects of the process on teachersʼ skills and practices, while virtually no research has focused on teachers who attempted the process but did not succeed (NB Candidates). Using the NBPTS Five Core Propositions as a basis for survey items and open-ended questions, this mixed-methods study examined and compared the perceptions of West Virginia NBCTs and National Board Candidates (NB Candidates) from 2004-2009. Data indicated that NBCTs perceived the process as having great effect on their teaching practices in five areas: creating a positive learning environment, planning effective instruction, delivering effective instruction, assessing student learning, and belonging to a larger learning community. NB Candidates perceived the process as having moderate effects, at best, on those same practices. Neither group perceived any effect on their knowledge of subject matter. Results also indicated that while the pay raise associated with National Board certification was the primary motivation for both groups, teachers whose motivations included professional development or encouragement from friends and colleagues were slightly more likely to certify. Similarly, teachers who utilized a support group of friends and colleagues were more likely to certify, whereas those who utilized a RESA sponsored support group were less likely to certify. Support components such as deadlines, mentoring, feedback, collegiality, and help with directions were perceived as most important. Ancillary findings included higher certification rates for females in the population as well as higher certification rates for more experienced teachers