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This Week at Physics

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Events During the Week of April 15th through April 22nd, 2018

Monday, April 16th, 2018

Plasma Physics (Physics/ECE/NE 922) Seminar
Unique Solutions to the Challenges of Microwave Coupling in Overdense Plasmas
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Dr. Stephanie J. Diem, Oak Ridge National Laboratory
Abstract: Overdense plasmas, where the electron plasma frequency exceeds the electron cyclotron frequency, prohibit the use of electron cyclotron (EC) heating and current drive methods often used to heat fusion-grade plasmas. The electrostatic electron Bernstein wave (EBW) can propagate in overdense plasmas and is readily absorbed and emitted near EC harmonics. Additionally, EBWs do not experience a density dependent cutoff. As such, EBWs may enable local electron temperature measurements and provide local heating and current drive. EBWs cannot propagate in vacuum but can couple to electromagnetic waves, so for these applications efficient coupling between the EBWs and electromagnetic waves outside the plasma is needed. Results of the first experimental verification of EBW collisional damping and its mitigation by evaporated lithium conditioning in overdense plasmas on the National Spherical Torus Experiment (NSTX) will be presented. Initial measurements of EBW emission, coupled from NSTX plasmas via double-mode conversion to O-mode waves, exhibited < 10% transmission efficiencies. Simulations show 80% of the EBW energy is dissipated by collisions in the edge plasma. Li conditioning reduced the edge collision frequency by a factor of 3 and increased the fundamental EBW transmission to 60%. Expanding upon this work, recent results of EBW heating in the Proto-MPEX linear device, which takes advantage of resonance Doppler-broadening, will be discussed. Calculations show that by utilizing the effects of Doppler broadening resonance absorption, power deposition near the centerline of the Proto-MPEX device is possible. Significant collisional damping with neutral particles, leading to edge absorption, is expected to occur due to high neutral pressure. Experiments were designed to minimize these effects and resulted in electron temperature increase by a factor of 4 during the injection of 28 GHz microwave power when the neutral pressure is reduced below 0.13 Pa (~1 mTorr.). The results discussed are a product of active collaboration between the code development groups, experimentalists and theorists that allow our field to bridge the gap between traditional theory/modeling and the experimental community.
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Tuesday, April 17th, 2018

Chaos & Complex Systems Seminar
Are modern psychological and social behavior investigators missing a boat developmental neuroscience could help them catch?
Time: 12:05 pm
Place: 4274 Chamberlin (Refreshments will be served)
Speaker: Bernard Z. Friedlander, Department of Psychology, University of Hartford
Abstract: Large bodies of research with people of all ages tend to confirm that children who perform better on tests of delayed gratification (DG) tend to do well in life, while those with limited capacities for DG as children do less well in the progress of their lives. This paper presents the possibility that DG and related behavioral realities represent critical processes in individual psychological development. These processes are open to new vectors of understanding based on new thinking about the autonomic nervous system and developmental neuroscience. New ways of thinking about old problems offer tantalizing possibilities for new research.
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Magnetic reconnection, a celestial phenomenon in the laboratory
Time: 1:20 pm
Place: 2241 Chamberlin Hall
Speaker: Jan Egedal, UW Madison Department of Physics
Host: Wesley Smith
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Wednesday, April 18th, 2018

No events scheduled

Thursday, April 19th, 2018

Atomic Physics Seminar
Ultracold Polyatomic Molecules via Laser Cooling – N Atoms Too Many
Time: 2:00 pm
Place: 5310 Chamberlin
Speaker: Prof. John Doyle , Harvard
Abstract: Triatomic molecules are deceptively simple. Even though there is only one additional atom compared to a diatomic molecule, this leads to non-trivial additional motional degrees of freedom and new associated quantum numbers. This, plus the larger density of states, realizes a quantum object whose complexity leads to new chemistry and physics research opportunities and concomitantly presents new challenges in molecular control. The science opportunities include the development of accurate and precise manipulation of chemical reactions and collisions in a qualitatively more complex species. But the reach of triatomics also includes dramatically improved, novel approaches to searches for physics beyond the Standard Model, and enhanced platforms for quantum computing using molecular tweezer arrays, both of which are aided by the low lying bending modes present in triatomic molecules. All of these research frontiers with triatomics, and their symmetric and asymmetric top brethren, either require or are greatly enhanced by chilling them to ultracold temperatures where they can be prepared in exquisitely well-defined internal and external motional states.



The recent experimental advances in direct laser cooling of diatomic molecules and triatomic molecules clearly indicates that full extension of laser tools - the creation of a magneto-optical trap (MOT) plus sub-Doppler cooling - to triatomic species should be possible. Recently in our laboratory we achieved a magneto-optical trap of diatomic molecules with CaF, sub-Doppler cooling to 40 µK, and loading of these molecules into an optical dipole trap. We also accomplished the first laser cooling and bichromatic force deflection of a polyatomic molecule, using SrOH. In addition, in 2016 we proposed the laser cooling of more complex polyatomic molecules using the methods we have now demonstrated. In particular, symmetric top molecules like CaOCH3 (and, possibly, related asymmetric top molecules) look extremely promising for direct laser cooling. The experimental prospects for a MOT of CaOH, YbOH, and CaOCH3 will be discussed.

Host: Saffman
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Astronomy Colloquium
"The Atomic to Molecular (HI-to-H2) Transition in Galaxy Star-Forming Regions"
Time: 3:30 pm
Place: 4421 Sterling Hall, Cookies and Coffee 3:30 PM, Talk begins at 4:00 PM
Speaker: Dr. Amiel Sternberg, Tel Aviv University, Max Planck Inst. for Extraterrestrial Physics, Germany, Flatiron Institute, Simons Foundation USA
Abstract: The atomic to molecular hydrogen (HI-to-H2) phase transition is of fundamental importance for star-formation and the emergence of chemical complexity in the interstellar medium of galaxies. I will present an overview, and discuss recent theoretical studies, numerical and analytic, of the HI-to-H2 transition in irradiated systems, with applications to the multi-scale behavior observed in star-forming galaxy disks from low- to high-redshift.
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Friday, April 20th, 2018

JIMFEST 2018
High energy density plasma simulations using ultracold neutral plasmas
Time: 1:00 pm
Place: 2241 Chamberlin Hall
Speaker: Scott Bergeson, Brigham Young University
Abstract: Strongly-coupled Coulomb systems are typically fluid-like plasmas characterized by the ratio of the nearest-neighbor electrical potential energy to the average kinetic energy. When this ratio is near unity, the plasmas are non-ideal and the foundational assumptions of plasma physics are no longer valid. Astronomical examples include the crusts of white dwarf stars, the interior of Jovian planets, and the dust belts of Saturn. Laboratory examples include laser-driven compression shocks, exploding wires, inertially confined plasmas, and, surprisingly, photo-ionized laser-cooled atoms. Transport properties in these widely disparate plasmas scale with the ratio of potential-to-kinetic energy (the Coulomb coupling parameter). Even systems that are widely disparate in temperature and density can be thermodynamically similar if this ratio is the same. I'll talk about our work in photo-ionized laser-cooled atoms, presenting progress in thermalization, transport, and equilibration.
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JIMFEST 2018
UW Laboratory Astrophysics
Time: 1:30 pm
Place: 2241 Chamberlin Hall
Speaker: Elizabeth DenHartog, University of Wisconsin-Madison
Abstract: In this talk I will describe the laboratory astrophysics program of the Jim Lawler group at the University of Wisconsin – Madison, focusing on the laboratory techniques and instruments used for the measurement of transition probabilities. Transition probabilities are determined from the combination of radiative lifetimes and branching fractions. Radiative lifetimes are measured using time-resolved laser-induced fluorescence on a slow atomic/ionic beam. This experiment has been extremely productive over the 3+ decades of its operation. The atomic beam source at the heart of this experiment was designed by Jim in the early 1980’s, and can produce a gas phase neutral and singly-ionized sample of any metal, and many non-metals. This source is a big reason for the success and productivity of this experiment. Branching fractions are measured in emission using Fourier transform or grating spectroscopy, or a combination thereof. Fourier Transform spectrometers have many advantages for branching fraction work, but have one major drawback. As with any interferometric device, the noise from all lines in the spectrum distribute evenly throughout the spectrum, making the measurement of very weak branches difficult to impossible. I will describe a more recent instrument of Jim’s design – the 3 meter echelle spectrograph – which is ideal for the measurement of the branching fractions of very weak spectral lines.
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JIMFEST 2018
Spectroscopic study of the 7p J=1/2 and 7p J=3/2 states in neutral cesium-133
Time: 2:00 pm
Place: 2241 Chamberlin Hall
Speaker: Maria-Teresa Herd, Mt. Holyoke College
Abstract: I will start with a few observations of connections between spectroscopy and other (seemingly unrelated) research topics, then focus on Doppler free spectroscopy on the 7p J=1/2 and 7p J=3/2 states in neutral cesium-133. A frequency doubled titanium sapphire laser stabilized to a temperature stabilized ultra-low expansion optical cavity was used to find the absolute frequencies for the centers of gravity of the two cesium states. These measurements are an improvement of a factor of 650 and 500 over previously reported measurements. The magnetic dipole and electric quadrupole constants were also measured and found to be consistent with previously published values.
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JIMFEST 2018
A Fresh Look at Abundances of Iron-group Elements in Very Metal-Poor Stars
Time: 2:45 pm
Place: 2241 Chamberlin Hall
Speaker: Chris Sneden, University of Texas, Austin
Abstract: Studies of very metal-poor stars have focused attention on the neutron-capture (Z > 30) elements, whose dramatic star-to-star variations give us insights to element production in extreme, explosive nucleosynthesis environments. Neglected in this fascinating exotic element concentration is that the Fe group (Z = 21-30) often have inadequate abundances to say much of anything useful to massive star evolution theorists. Major improvements are ongoing in treatment of radiative transfer and stellar atmosphere structure. But these modeling improvements will completely wasted if the basic atomic data cannot be trusted. Jim Lawler's Wisconsin atomic physics group is nearly completion of lab work on neutrals and first ions of nearly all of the Fe-group elements. This talk will describe them and show how they are being used to overturn prevailing notions of early synthesis of the most abundant heavy elements in our Galaxy.
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Physics Department Colloquium
The astrophysical r-process: what we are learning from gravitational waves, dwarf galaxies, and stellar archaeology
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Ian Roederer, University of Michigan, Ann Arbor
Abstract: Understanding the origin of the elements is one of the major challenges of modern astrophysics. The rapid neutron-capture process, or r-process, is one of the fundamental ways that stars produce the elements listed along the bottom two-thirds of the periodic table, but key aspects of the r-process are still poorly understood. I will describe three major advances in the last few years that have succeeded in confirming neutron star mergers as an important site of the r-process. These include the detection of freshly produced r-process material powering the kilonova associated with the merger of neutron stars detected via gravitational waves (GW170817), the detection of a dwarf galaxy where most of the stars are highly enhanced in r-process elements (Reticulum II), and advances in deriving abundances of previously-undetected r-process elements (Se, Te, Pt) in ultraviolet and optical spectra of metal-poor stars in the Milky Way halo field. I will describe future prospects that connect these three research directions and future rare isotope accelerators to associate specific physics with specific sites of the r-process. Finally, I will highlight the major impact of Jim Lawler's atomic spectroscopy group at Wisconsin in enabling these advances.
Host: Jim Lawler
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JIMFEST 2018
Measurements of branching fractions using Fourier transform and grating spectroscopy
Time: 5:00 pm
Place: 2241 Chamberlin Hall
Speaker: Gillian Nave, National Institute of Standards and Technology
Abstract: The measurement of lifetimes using laser-induced fluorescence at the University of Wisconsin-Madison has been one of the most productive experiments in the measurement of atomic spectroscopic data. The NIST bibliographic database on Atomic Transition Probabilities lists over 60 papers with Jim Lawler as an author or coauthor on lifetimes of neutral and singly-ionized elements ranging from carbon to mercury. The applications of these measurements range from astrophysics to lighting research. However, it is necessary to combine these lifetimes with branching fractions in order to obtain the atomic transition probabilities, and these branching fractions are now frequently the limiting factor in the accuracy of the measurements. I shall describe how the combination of measurements of branching fractions using Fourier transform spectroscopy at NIST with those of weak lines using the UW echelle spectrograph can improve the reliability of these measurements and provide the atomic data for weak lines that are challenging to measure using Fourier transform spectroscopy alone.
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JIMFEST 2018
Downstream hydrogen plasma cleaning for mass metrology at NIST
Time: 5:30 pm
Place: 2241 Chamberlin Hall
Speaker: Eric Benck, National Institute of Standards and Technology
Abstract: On International Metrology Day, May 20, 2019, the redefinition of the International System of Units (SI) is scheduled to be implemented. When this occurs the kilogram, the last remaining unit defined by a physical artifact, will be redefined to be based on a fundamental physical constant, the Planck constant. As a consequence, the NIST mise en pratique, a series of steps for the realization and dissemination of the revised definition of the kilogram, must be significantly modified. In particular, the mise en pratique will need to address for the first time the measurement and handling of masses in a vacuum. At NIST this will includes 5 major components: NIST-4 Kibble Balance, Magnetic Suspension Mass Comparator (MSMC), Mass-in-Vacuum Comparator, storage chambers, and mass transport vehicles (MTV). In addition to these components, there also is a need to develop new procedures to maintain and clean masses in vacuum. Over long periods of time masses can become coated with a carbon containing contamination layer, even while stored in a vacuum. A downstream hydrogen plasma source is being investigated as a means of gently removing these carbonaceous layers. Atomic hydrogen can react with carbon on the mass surface and convert it to volatile hydrocarbons which can then be pumped out of the system. Initial results demonstrating the etching of carbon coatings off a quartz crystal microbalance (QCM) in our downstream hydrogen plasma cleaner will be presented.
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Saturday, April 21st, 2018

JIMFEST 2018
Six Lines to Tell a Story
Time: 9:30 am
Place: 2241 Chamberlin Hall
Speaker: Michael Wood, University of St. Thomas
Abstract: In this talk, I will highlight a recently completed investigation into a challenge brought against our earlier work on vanadium. The discrepancy between six transition probabilities and its resolution touches on several aspects of transition probability research, the important contributions of our stellar collaborators, and future directions for study.
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JIMFEST 2018
TBD
Time: 10:00 am
Place: 2241 Chamberlin Hall
Speaker: Uwe Kortshagen, University of Minnesota
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JIMFEST 2018
How I Became a Non-Chemist
Time: 10:30 am
Place: 2241 Chamberlin Hall
Speaker: Ken Menningen, UW Stevens Point
Abstract: Some scientists direct their careers with laser focus to answer a small set of questions. Others wander around like a trapped photon. I will tell the story about how a plasma physicist ended up studying combustion chemistry, and how the student he trained learned about growing diamonds, thermophoresis, synchrotrons, radiation trapping, photoelectrochemical water splitting, and anticrepuscular rays.
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JIMFEST 2018
Studying interesting phenomena: GE and Jim Lawler
Time: 11:30 am
Place: 2241 Chamberlin Hall
Speaker: Tim Sommerer, GE Global Research
Abstract: The world is full of interesting and mysterious phenomena that can be made more understandable by applying the scientific method. This talk will focus on two examples: (i) what it means to do physics at a place like General Electric, and (ii) Jim Lawler. Observations will be reported, models will be proposed, and conclusions will be drawn.
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JIMFEST 2018
Gas Discharge Lamps – A Requiem
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Graeme Lister, Lighting Consultant
Abstract: Almost a century has passed since the introduction into the market of gas discharge lamps for general lighting in the form of fluorescent lamps, made possible by the discovery of phosphors able to convert ultra-violet (UV) light to visible light in 1924. The journey from the first fluorescent lamps to, efficient lamps producing high quality light was an exciting one for researchers, and much of the basic theory of gas discharge physics was developed by scientists during the early stages of gas discharge development. The trend for steady improvement continued through the end of last century, but the discovery of efficient blue light emitting Light Emitting Diodes (LEDs) in the 1990s provided a path for lamp efficacies undreamed of and unattainable by gas discharge sources. These “legacy” lamps will remain with us for many years, perhaps decades to come, but the overriding trend in the market is towards introduction of LEDs for most general lighting applications, due to the huge energy savings that will accompany them. There are certainly niche markets where LEDs have difficulty competing, but the general trend appears irreversible.
This talk will take an affectionate and nostalgic backward look at the gas discharge research for lighting to which I have devoted much of my career. Most of the successes I have had would not have been possible without the inspiration, insight and friendship of Jim Lawler. The number of papers we have published together bears testimony to this. The talk will describe a journey along the paths we trod to understand how gases produce light, the fundamental principles involved, the experiment performed and the means of interpreting the results. Topics include studies of the negative glow, the positive column, and an extended look at “electrodeless“ fluorescent lamps and the efforts made to understand their performance. More recent efforts to produce electrodeless metal halides will be discussed, and finally a view on applications of discharge lamps in the expanding market of lighting for plant growth.
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