A Partnership to Increase Access to Our Nation's Historical Records

The City of Philadelphia, Department of Records, in collaboration with the Free Library of Philadelphia has designed this collaborative project in an effort to link critical historical data collections from across the region, providing access to a broader scope of information to researchers, historians, genealogists, students, and other members of the public. To conduct this project, the partnership is seeking $108,882 over a two year period from this grant award (to be matched by$37,644 in City General Revenues). This project is designed to begin the process of collaboration between these two organizations with two of the library's most critical and historically significant digital collections--the Centennial Exhibition of 1876 Collection and the Historical Images of Philadelphia Collection. Through this project the partners will both integrate metadata and implement new user tools that will enhance end-user access

Creative art experience for elementary age blind children.

Thesis (Ed.M.)--Boston Universit

Effective Critical Electric Field for Runaway-Electron Generation

In this Letter we investigate factors that influence the effective critical electric field for runaway-electron generation in plasmas. We present numerical solutions of the kinetic equation and discuss the implications for the threshold electric field. We show that the effective electric field necessary for significant runaway-electron formation often is higher than previously calculated due to both (1) extremely strong dependence of primary generation on temperature, and (2) synchrotron radiation losses. We also address the effective critical field in the context of a transition from runaway growth to decay. We find agreement with recent experiments, but show that the observation of an elevated effective critical field can mainly be attributed to changes in the momentum-space distribution of runaways, and only to a lesser extent to a de facto change in the critical field.Comment: 5 pages, 4 figure

An advection-diffusion model for cross-field runaway electron transport in perturbed magnetic fields

Disruption-generated runaway electrons (RE) present an outstanding issue for ITER. The predictive computational studies of RE generation rely on orbit-averaged computations and, as such, they lack the effects from the magnetic field stochasticity. Since stochasiticity is naturally present in post-disruption plasma, and externally induced stochastization offers a prominent mechanism to mitigate RE avalanche, we present an advection-diffusion model that can be used to couple an orbit-following code to an orbit-averaged tool in order to capture the cross-field transport and to overcome the latter's limitation. The transport coefficients are evaluated via a Monte Carlo method. We show that the diffusion coefficient differs significantly from the well-known Rechester-Rosenbluth result. We also demonstrate the importance of including the advection: it has a two-fold role both in modelling transport barriers created by magnetic islands and in amplifying losses in regions where the islands are not present

Guiding-center transformation of the radiation-reaction force in a nonuniform magnetic field

In this paper, we present the guiding-center transformation of the radiation-reaction force of a classical point charge traveling in a nonuniform magnetic field. The transformation is valid as long as the gyroradius of the charged particles is much smaller than the magnetic field nonuniformity length scale, so that the guiding-center Lie-transform method is applicable. Elimination of the gyromotion time scale from the radiation-reaction force is obtained with the Poisson bracket formalism originally introduced by [A. J. Brizard, Phys. Plasmas 11 4429 (2004)], where it was used to eliminate the fast gyromotion from the Fokker-Planck collision operator. The formalism presented here is applicable to the motion of charged particles in planetary magnetic fields as well as in magnetic confinement fusion plasmas, where the corresponding so-called synchrotron radiation can be detected. Applications of the guiding-center radiation-reaction force include tracing of charged particle orbits in complex magnetic fields as well as kinetic description of plasma when the loss of energy and momentum due to radiation plays an important role, e.g., for runaway electron dynamics in tokamaks.Comment: 17 pages, submitted to Journal of Plasma Physic

Electron Bernstein wave current drive modeling in toroidal plasma confinement

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 333-340).The steady-state confinement of tokamak plasmas in a fusion reactor requires non-inductively driven toroidal currents. Radio frequency waves in the electron cyclotron (EC) range of frequencies can drive localized currents and are thus particularly attractive for control of the current profile. In the high-[beta] regimes of spherical tokamaks (ST) such as NSTX and MAST, heating and current drive (CD) by conventional electron cyclotron waves is not possible. However, electron Bernstein waves (EBW) have been proposed as an alternative for CD in these overdense devices. Given the important role predicted for CD by EBWs in high-[beta] STs, a detailed study of EBWCD must be undertaken. In this thesis a systematic analysis of EBWCD is provided. In particular, the characteristics of EBWs, the physics of resonant wave-particle interaction, and the CD mechanisms are investigated in detail. The CD efficiency and the current deposition profile are calculated using the numerical code DKE, which solve the drift-kinetic equation. Two scenarios for EBWCD are identified. The first scenario consists of approaching a harmonic of the EC resonance from a lower B-field region and drives current in the plasma core using the Fisch-Boozer mechanism.(cont.) The other scenario consists of approaching a harmonic of the EC resonance from a higher B-field region and drives current off-axis on the outboard side using the Ohkawa mechanism. Both schemes drive current in the toroidal direction opposite to the parallel wave vector. The EBWCI) efficiency is found to be higher than ECCD efficiency because the EBW power is deposited in the tail of the electron distribution function. The results of this thesis confirm the important role of EBWs for driving currents in high-[beta] plasmas. The analytical and numerical tools developed as part of this thesis can be used to design, predict, and analyze future EBWCD experiments. Among these tools is the kinetic solver DKE, which can be used for electron current drive calculations in toroidal plasmas for different types of radio-frequency waves, such as lower hybrid and electron cyclotron waves.by Joan Decker.Ph.D