This Week at Physics

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Events During the Week of January 29th through February 5th, 2012

Monday, January 30th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
Fusion Cuisine: Mingling Inertial and Magnetic Fusion Concepts in High Energy Density Plasma Physics
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Dr. Kirk Flippo, Los Alamos National Laboratory
Abstract: High Energy Density Laboratory Plasma (HEDLP) science is one of the few areas in physics where the US, compared to the rest of the world, has a significant lead. In general, HEDLP has great breadth encompassing high energy density hydrodynamics, radiation-dominated dynamics and material properties, magnetized high energy density plasma physics, nonlinear optics of plasmas, relativistic high energy density plasma physics and warm dense matter physics. Specific to fusion this entails Inertial Confinement Fusion (ICF) and several alternative concepts known collectively as Magnetized Target Fusion (MTF) or Magneto-Inertial Fusion (MIF). MIF concepts are basically a mixture of Magnetic Confinement Fusion and ICF, where the ICF fuel can now be less dense and compressed less due to the insulating effects of the applied magnetic field. A very brief history of the Controlled Thermonuclear Research program at Los Alamos is presented to illustrate how the more modern concepts for fusion came about, and how our recent work in laser-accelerated electrons and ions is poised to further bring about important changes and additions to these concepts. Our work has focused on a small subset of HEDLP, namely ultra-high intensity laser matter interactions, which have been producing high energy particles for over 10 years, and now the technology is reaching a maturity where the physics can be controlled and applied to the aforementioned problems, as well as a host of others from hadron cancer therapy to illicit nuclear material detection. These interactions create Megagauss magnetic fields and Megaamp current beams of MeV kinetic energy. The extremes (temperatures, pressures and field strengths) of the field have led some to brand it the X-games of physics. In all seriousness, eXtreme hype aside, HEDLP science has a bright future, with the potential to be the next technological and economic driver of the 21st century.
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Tuesday, January 31st, 2012

Chaos & Complex Systems Seminar
3D and beyond: Multidimensional imaging of cell based processes
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Kevin W. Eliceiri, UW Departments of Biomedical Engineering and Molecular Biology Director, Laboratory for Optical and Computational Instrumentation (LOCI)
Abstract: Revolutionary advances in biological and biomedical imaging over the last twenty years have brought about the development of improved methods for non-invasively imaging dynamic biological processes. Of particular significance have been optical (photonic) techniques that have allowed for the visualization and manipulation of molecular and cellular structures within living tissue with minimal perturbation. The efforts of the multidisciplinary UW-Madison Laboratory for Optical and Computational Instrumentation (LOCI), to develop optical and computational approaches for biological and biomedical studies will be presented. These efforts include signal processing approaches for multidimensional image analysis, image informatics, nonlinear optical and intrinsic fluorescence studies, optical histopathology, and approaches for deep imaging of biological tissue.
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Recent Discoveries in Neutrino Physics
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Karsten Heeger, University of Wisconsin Department of Physics
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Theory Seminar (High Energy/Cosmology)
Title to be announced
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Matt Reece, Harvard University
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Wednesday, February 1st, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
Ambipolar ion acceleration from plasma expansion through a magnetic nozzle and near-term spacecraft propulsion applications
Time: 12:00 pm
Place: 2241 Chamberlin
Speaker: Dr. Benjamin Longmier, University of Houston
Abstract: The helicon plasma stage in the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine was used to characterize an axial plasma potential profile within an expanding magnetic nozzle region of the laboratory based device. The ion acceleration mechanism is identified as an ambipolar electric field produced by an electron pressure gradient, resulting in a local axial ion speed of Mach 4 downstream of the magnetic nozzle. A 20 eV argon ion kinetic energy was measured in the helicon source, which had a peak magnetic field strength of 0.17 T. The helicon plasma source was operated with 25 mg s−1 argon propellant and 30kW of RF power. The maximum measured values of plasma density and electron temperature within the exhaust plume were 1e20 m−3 and 9 eV, respectively. The measured plasma density is nearly an order of magnitude larger than previously reported steady-state helicon plasma sources. The exhaust plume also exhibits a 95% to 100% ionization fraction. The thickness of the potential structure was found to be 1e4 to 1e5 Debye lengths depending on the local electron temperature in the magnetic nozzle, many orders of magnitude larger than previously reported laboratory double layer structures. The background plasma density and neutral argon pressure were 1e15 m−3 and 2e−5 Torr, respectively, in a 150m^3 vacuum chamber during operation of the helicon plasma source. The agreement between the measured plasma potential and plasma potential that was calculated from an ambipolar ion acceleration analysis over the bulk of the axial distance where the potential drop was located is a strong confirmation of the ambipolar acceleration process. Future propulsion applications using ambipolar ion acceleration will be discussed.
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Thursday, February 2nd, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Recent Results from the COUPP Dark Matter Search
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Andrew Sonnenschein, Fermilab
Abstract: Bubble chambers have emerged as promising detectors for Weakly Interacting Massive dark matter Particles (WIMPs). A very high degree of background discrimination can be achieved by tuning the thermodynamic parameters to avoid nucleation by electron recoils, while maintaining low nuclear-recoil thresholds. Nuclear recoils from WIMPs can be discriminated from alpha particle induced events by analysis of the acoustic pulses produced by the expanding bubbles. The COUPP collaboration operated a 4-kg CF3I bubble chamber at SNOLAB in 2010-2011 and is in the process of commissioning a 60-kg chamber. Initial data from SNOLAB demonstrate reduced alpha backgrounds and greatly improved sensitivity to WIMPs.
Host: Karsten Heeger
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Astronomy Colloquium
A (Re) Introduction to the Milky Way (AAS Reprise)
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Bob Benjamin, UW Whitewater
Abstract: If your picture of the Milky Way is that it consists of a bulge, disk, and halo, you might want to attend this talk. I will review the many recent advances in understanding the global structure of our Galaxy, with a principal emphasis on the disk and inner galaxy. Radio parallaxes to maser sources, extinction distances to dark clouds, and large-scale near and mid-infrared mapping of red clump giants now allow us to map out different components (star formation, gas, and old stars) of the Galaxy without the serious issues that plagued earlier efforts. I will review some of the recent discoveries and directions for future work as I did at a plenary session at the American Astronomical Society meeting in Austin this January. After 60 years of effort, I'd say we're about 50% done mapping the Milky Way.

But as a special only-in-Wisconsin add-on, I will also show an interesting (and in retrospect, totally predictable) discovery I made while preparing for this talk, as well as showing some evidence that indicates the resurgence in Galactic structure may yet hit some rocky roads ahead.
Host: Astronomy Dept
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Friday, February 3rd, 2012

Atomic Physics Seminar
Atomic dipole traps formed in the diffraction pattern of a circular aperture for use in neutral atom quantum computing
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Katharina Gillen, California Polytechnic State University
Abstract: The quantum computing community is making evermore progress towards constructing a fully functional quantum computer. However, none of the many approaches in the different fields of physics have succeeded to date. In the neutral atom quantum computing approach, which uses atoms trapped by light fields as quantum bits (qubits), many of the requirements for a quantum computer (initialization, readout, single-qubit gates) can be met with well-established spectroscopic techniques. The recent accomplishment of two-qubit gates with neutral atoms leaves only one unattained criterion for a quantum computer: The ability to create an addressable array of many qubits.

We will present computational results on a possible solution to this problem. The diffraction pattern formed by laser light incident on a circular aperture exhibits localized bright and dark spots that can be used as atomic dipole traps. An array of such apertures results in a two-dimensional array of dipole traps that can be individually addressed with a laser beam from the third dimension. By exploiting the polarization dependence of these traps, we can also bring traps together and apart to facilitate the performance of two-qubit gates, thus creating a potential candidate for a scalable quantum memory for a neutral atom quantum computer.
Host: Saffman
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Physics Department Colloquium
Beyond the Standard Model: The Particle Physics Frontier
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Michael Ramsey-Musolf, University of Wisconsin-Madison
Abstract: The quest to explain nature's fundamental interactions and how they shaped the evolution of the universe is one of the most compelling in modern science. The standard model of particle physics provides a partial explanation, but we know that it must be part of a larger, more complete framework. Experiments hoping to uncover what lies beyond the standard model are being carried out at three frontiers: the high energy frontier, involving facilities such as the Large Hadron Collider; the astrophysical frontier; and the intensity frontier.

In this talk, I review the motivation for searching for physics beyond the standard model. I then discuss how studies at the three frontiers may help solve one of the key problems not solvable in the standard model: the origin of matter.
Host: Department
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