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Spring 2009

Schedule Spring 2009

January 13, 2009
3:00 pm (Tuesday)

Dr. Hugh Montgomery
Jefferson Lab
The Structure of Matter: Nuclear Physics at Jefferson Laboratory

Understanding the internal structure of nuclei and nucleons is an important field of physics. Elucidation has come in large part as a result of using electromagnetic probes, in particular by the scattering of electrons and muons from the targets of interest. Jefferson Laboratory, where physicists are using powerful electron beams, is a world leader in this field. The speaker will discuss, and attempt to provide an accessible view of, this fascinating and exciting research.

January 20, 2009
3:00 pm (Tuesday)

Dr. Shyh-Yuan Lee
Indiana University

Design and construction of a compact Inverse Compton X-ray source

A low energy electron storage ring is designed to have many desirable properties, such as varying momentum compaction factor, damping partition numbers, favorable betatron tunes for multiturn accumulations, and excellent dynamic aperture. This storage ring can be used for debunching rf linac beams in one turn, for compression of linac pulses, and more importantly for a compact photon source based on inverse Compton scattering of laser beams. Accelerator physics studies relevant to future high energy accelerators, and coherent light source will be discussed.

January 27, 2009
3:00 pm (Tuesday)

Dr. Michael Syphers
Fermi National Accelerator Laboratory

Accelerating Charged Particles to High Energy -- past, present and future

Modern high-energy accelerators used for high energy physics research have relied upon the generation of electromagnetic fields oscillating at radio frequencies (RF) to provide kinetic energy to charged particles. In this talk we will review the history of RF accelerators and discuss some of the issues facing the advancement of accelerators of ever-increasing size and complexity. Existing energy-frontier accelerators using standard RF technology demand innovative upgrades to continue to meet the requirements of the user community. As the Large Hadron Collider finally nears completion in Europe, and an International Linear Collider community attempts to form, these facilities, too, are designing toward upgradeability. A short glimpse of the LHC, the ILC concept, and possible future acceleration techniques will be provided.

February 3, 2009
3:00 pm (Tuesday)

Dr. Scott Bergeson
Brigham Young University

Ultracold neutral plasmas and other things that don't go together

We often think of plasmas at high temperatures, like the Solar Corona (T=10,000K) or fusion plasmas (T=100,000,000K). But some plasmas exist at low temperatures, like the interstellar medium (T=2.7K). We make even colder plasmas(T=0.001K) using laser-cooled atoms. This system is far from equilibrium but relaxes on very short time scales.

In general, the plasma evolution can be predicted using a hydrodynamical model with a little atomic physics thrown in. And a number of unbelievably complicated experiments that were intended to find "new physics" ended with the resigned admission that the theory is right after all. But some recent data from our lab appears to lie outside the standard cold plasma model.

I will give an overview of this field, try to explain why it is interesting, and present a few unsolved puzzles from our lab.

February 10, 2009
3:00 pm (Tuesday)

Dr. John Gillaspy
National Institute of Standards and Technology

One Hundred Million Degrees on a Tabletop: Fusion Energy, Electron Beam Ion Traps, and the Science of Highly Charged Ions

The long term goal of harnessing the energy source of the stars (thermonuclear fusion) is being pursued by an international collaboration of unprecedented scale. Although the probability of success is uncertain, the potential payoff is great: a virtually inexhaustible supply of clean and safe energy for all nations. Currently under construction, the giant ITER fusion reactor has been called the most expensive science experiment ever undertaken on earth. When complete, it will produce temperatures much hotter than the core of the sun, and hopefully demonstrate an energy gain factor of 10. At the National Institute of Standards and Technology, we are carrying out spectroscopic studies of highly charged ions such as W46+, which are expected to be of use in the diagnostics of ITER. In order to perform these measurements, we use a small electron beam ion trap to produce ions at similar temperatures (but lower densities) than those anticipated in ITER. The study of the spectra of highly charged heavy elements is of interest for basic science as well, as it allows one to test ab-initio predictions of the electronic structure of atoms under conditions so extreme that the results sometimes seem bizarre. I will illustrate the latter by discussing recent results in which the "fine structure" splitting of the D-line in sodium-like ions is observed to become so large that it exceeds the mean value of the energy. In order to put the diagnostics work in context, I will review some general aspects of the global fusion energy effort

February 17, 2009
3:00 pm (Tuesday)

Dr. Jean Delayen
Thomas Jefferson National Accelerator Facility/ODU

"Accelerator Science? Why?"

Accelerator science is an often ill-defined and poorly understood area of scientific research that defies classification since it touches on many branches of science and technology from the highly theoretical to the very practical.
This talk will present a personal perspective on accelerator science, on the opportunities that it offers students to make significant contributions to science, and address some of the challenges facing society where accelerators could be part of the solution.

February 19, 2009
12:20 pm (Thursday)

Dr. Wayne D. Cornelius
Scientific Solutions

Electron Cooling Module for a Low-Energy Proton Storage Ring

The design of a cooling module for a low-energy proton storage ring will be described. The cooling module is comprised of an electron gun, an electron-proton beam merging segment, and the cooling interaction region. Particular emphasis will be placed on the design of the electron gun and electron beam diagnostic module.

March 3, 2009
3:00 pm (Tuesday)

Dr. Yongxiang Hu
NASA, Langley Research Center

Global observations of the atmosphere and ocean from lidar in space

Special Physics & OEAS Joint Colloquium

This talk will introduce recent scientific studies using the lidar measurements made from CALIPSO spacecraft. The focus of the talk includes simple physics of measurement concepts and preliminary results of:
1. global cloud climatology, such as cloud phase, cloud microphysics,...;
2. aerosol climatology using combined CALIPSO ocean surface return and AMSR-E sea surface wind;
3. Air-sea gas transfer velocity and global sea surface wind statistics at high spatial resolution (70 meter CALIPSO footprint);
4. ocean sub-surface particulate backscatter statistics.

March 17, 2009
3:00 pm (Tuesday)

Dr. Biswa Ganguly
Air Force Research Laboratory

Diode Laser Spectroscopic Measurements of Gas Temperature and Metastable Density in High Pressure Argon Pulsed Dielectric Barrier Discharges

The average gas temperature rise within an argon dielectric barrier discharge (DBD) operating from 100 to 500 Torr pressure has been measured by tunable diode laser absorption spectroscopy for short pulse excited, low duty cycle, discharge conditions, where the gas temperature rise is < 150 K from the ambient condition. Under these conditions, gas temperature cannot be obtained from Doppler width, since Voigt profile is dominated by the Lorentzian component. For measurements in these types of high pressure DBD, two novel temperature measurement techniques have been employed that takes advantage of the relatively strong argon nonresonant collision line broadening and collisional frequency shifts of argon transitions 1s3-2p2 and 1s5-2p7 which originate from the two metastable states. Since Lindholm-Foley theory gives only approximate values of collision induced line broadening and frequency shift, an in-situ calibration of argon nonresonant collision line broadening and collisional frequency shift coefficients have been employed to obtain accurate gas temperature measurements from red shift of the frequencies as well as line broadening of 1s3-2p2 and 1s5-2p7 transitions.

The applied voltage pulse rise time dependency of the both 1s3 and 1s5 argon metastable states production efficiency have been also quantified from the diode laser absorption spectroscopy.

March 24, 2009
3:00 pm (Tuesday)

Dr. Dorin Todor
Virginia Commonwealth University

Nine years later: my journey in Medical Physics

An overview of the Radiation Oncology department will be given with emphasis on the Medical Physics section, its research, clinical and educational activities. Given my own interests as clinical physicist I will further present the state of the art in the radiation treatment for breast, prostate and gynecological cancers.

March 31, 2009
3:00 pm (Tuesday)

Dr. Alex Gurevich
Florida State University

Ferro pnictides: a new family of high-temperature, high-field superconductors.

In 2008 the group of H. Hosono at Tokyo Institute of Technology discovered high-temperature superconductivity in an extensive family of ReOFeAs pnictides, which become superconducting upon substituting F for O. Within less than 3 months many other rarecearths ions Re had been tried, pushing the maximum critical temperature to Tc = 55 K in SmO0.85F0.15AsFe. The microscopic mechanism of superconductivity in pnictides is not yet understood, but even at this early stage it is already clear that several features definitely set them apart, not only from the conventional low-Tc superconductors but also from the high-Tc cuprates. Superconductivity in pnictides appears upon doping parent semimetal compounds, which undergo antiferromagnetic and structural transitions around 140K, well above Tc. However, a striking feature of the pnictides is that Cooper pairing occurs on the Fe-As planes, even though they contain the quintessential pair-breaking magnetic Fe2+ ions, which would usually strongly suppress traditional superconductivity (be it the s-wave low-Tc superconductivity in Nb-based compounds, or the d-wave high-Tc superconductivity in the cuprates). However, it is the Fe orbitals which form the disconnected pieces of the Fermi surface of the pnictides, so strong magnetic correlations and multiband effects in these materials appear to be inherently connected to their color superconductivity.
Recent measurements performed at NHMFL have shown that, in addition to their high critical temperatures, the pnictides exhibit extremely high upper critical magnetic fields > 100Tesla, which can find important applications in high-field magnets. Moreover, the pnictides appear to have an exponentially low RF surface resistance at low temperature, which could make them new contender materials for the next generation SRF cavities for particle accelerators. In this talk I will give an overview of superconducting and magnetic properties of oxypnictides and discuss different physical mechanisms, which control their unusual behavior under strong dc magnetic and RF fields.

April 28, 2009
3:00 pm (Tuesday)

Old Dominion University

Senior Thesis Presentations

"Photomultiplier Tube Magnetic Shielding Analysis for the CLAS12 Central Time of Flight Counter"
Mr. Brian Wieland

"Plasma Surface Modification of Bulk Copper"
Mr. Kevin Brannick

"Relationship Between Magnetic Flux Geometry and Levitation Properties of Field Cooled YBCO"
Mr. Michael Moore

"Electron Density Measurements In A Supersonic Flowing Discharge"
Mr. Patrick Laurin

"Characterization of a Plasmoid in the Afterglow of a Supersonic Flowing Discharge"
Mr. Shawn Miller