Events at Physics |
Events During the Week of November 8th through November 14th, 2015
Monday, November 9th, 2015
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma/ Effect of Resonant Magnetic Perturbations on 3D equilibria in the MST RFP
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Physics Bldg
- Speaker: Jay Anderson/Stefano Munaretto, UW Madison, Plasma Physics
- Abstract: Jay Anderson:
Non-collisional heating and energization of ions is a powerful process in
reversed-field pinch (RFP) plasmas and in many astrophysical settings.
Tearing activity in the RFP (including linearly and nonlinearly driven modes
which span the plasma column) saturates through dynamo-like feedback on
the current density profile, rapidly releasing magnetic energy and inducing
a strong impulsive, parallel-to-B electric field as poloidal magnetic flux is
converted to toroidal flux. The global reconnection leads to strong ion heating
with a known anisotropy in temperature (T_perp > T_{||}), suggestive of a
perpendicular bulk heating mechanism.
In the subset of strongest reconnection events, multiple mechanisms combine to
create a most interesting ion distribution. Runaway of the reduced-friction naturally heated ions generates an asymmetric ion tail with E_{||} >> E_perp. The tail is reinforced by a confinement asymmetry, where runaway ions approach the limit of classical cross-field transport despite magnetic stochasticity from the broad spectrum of tearing modes. Confinement is lower in other regions of the
v_perp/v_{||} plane and reduces to Rechester-Rosenbluth-like transport experienced by thermal particles.
Stefano Munaretto:
The orientation of 3D, stellarator-like equilibria in the MST RFP can now be controlled with application of an m = 1 RMP. This has led to greatly improved diagnosis, revealing enhancements in both the central electron temperature and density. Coupled to a recent advance in the V3FIT code, reconstructions of the 3D equilibria have also been dramatically improved. The RMP also inhibits the generation of high-energy > 20 keV electrons that is otherwise common with the 3D state. This state occurs when the normally broad spectrum of core-resonant m = 1 tearing modes condenses, with the innermost resonant mode growing to large amplitude, reaching ~ 8% of the axisymmetric field strength. This occurs in plasmas of sufficiently large Lundquist number ~ IpTe^3/2, and the duration of the state is maximized with zero applied Bt (infinite toroidal beta). As the dominant mode grows, eddy current in MST's conducting shell slows the mode's rotation. This leads to locking of the 3D structure, but with an orientation that varies randomly shot to shot, making diagnosis difficult. An m = 1 RMP can now be applied with an array of saddle coils at the vertical insulated cut in the shell. With an amplitude br/B ~ 10% and a tailored temporal waveform, the RMP can force the 3D structure into any desired orientation relative to MST's diagnostics. A recent advance in V3FIT allows calculation of the substantial helical image current flowing in MST's shell, which has in turn allowed self-consistent utilization of both external and internal (Faraday rotation) measurements of the magnetic field. The ORBIT code predicts reduced stochasticity and improved confinement of high-energy electrons within the 3D structure. The suppression of these electrons by the m = 1 RMP may reflect a change to the central magnetic topology. The generation of these electrons is unaffected by non-resonant perturbations, such as m = 3. - Host: Plasma Physics
Tuesday, November 10th, 2015
- Astronomy Colloquium
- Colloquium at Noon
- Cosmic Ray Transport in MHD Turbulence
- Time: 12:00 pm - 1:00 pm
- Place: 4421 Sterling Hall, NOON TALK
- Speaker: Huirong Yan, Max-Planck Institute
- Abstract: Recent advances in MHD turbulence call for revisions in the paradigm of cosmic ray transport. I would like to clarify some outstanding issues related to particle transport in realistic turbulent astrophysical environments. We have carried out both analytical and numerical studies aiming at a theory-justified picture of the acceleration and transport processes based on the numerically confirmed modern theory of MHD turbulence. I shall address the issue of the transport of CRs, both parallel and perpendicular to the magnetic field and show that demonstrate that cosmic ray transport is medium dependent since compressible fast modes dominate the interactions. I shall also address the issue of perpendicular to the magnetic field and show that cosmic ray cross field transport is diffusive on large scales and super diffusive on scales less than the injection scale of turbulence. Implications for Galactic cosmic ray propagation and shock acceleration will be presented. Last but not least, the CR transport in molecular clouds shall be briefly discussed.
- Host: Prof Alex Lazarian
- Chaos & Complex Systems Seminar
- Will Darwin become a casualty of the Cambrian Explosion?
- Time: 12:05 pm - 1:00 pm
- Place: 4274 Chamberlin (refreshments will be served)
- Speaker: Jim Blair, Milton and Edgewood College
- Abstract: * Darwin and Neo-Darwinism<br>
* Anomalies and Paradigm Shifts<br>
* What Natural Selection does not Explain<br>
* Mendel, the Big Bang and the Cambrian Explosion<br>
- Host: Sprott
- Theory Seminar (High Energy/Cosmology)
- The Weak Gravity Conjecture: Variants and Inflationary Implications
- Time: 3:30 pm - 4:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Tom Rudelius, Harvard University
- Abstract: Although the landscape of effective theories constructed in string theory is enormous, the "swampland" of effective theories that do not admit a UV completion with gravity appears to be even larger. The weak gravity conjecture is a family of conjectures that attempt to delineate the swampland from the landscape. In this talk, we will explore this family of conjectures, and we will see that they have important implications for inflationary model building.
- Host: Pablo Soler
Wednesday, November 11th, 2015
- Department Meeting
- CANCELLED
- Time: 12:15 pm
- Place: 5310 Chamberlin Hall
- R. G. Herb Condensed Matter Seminar
- Electrically controlled qubits in silicon
- Time: 2:00 pm
- Place: 4274 Chamberlin Hall
- Speaker: Thaddeus Ladd, HRL Laboratories
- Abstract: Quantum information processing aims to leverage the properties of quantum mechanics to manipulate information in ways that are not otherwise possible. This would enable, for example, quantum computers that could solve certain problems exponentially faster than a conventional supercomputer. One promising approach for building such a machine is to use gated silicon quantum dots. In the approach taken at HRL Laboratories, individual electrons are trapped in a gated potential well at the barrier of a Si/SiGe heterostructure. Spins on these electrons are compelling candidates for qubits due to their long coherence time, all-electrical control, and compatibility with conventional fabrication techniques. In this talk I will discuss the recent demonstration of all-electrical control of silicon-based qubits made from triple quantum dots in isotopically purified material, including methods to mitigate charge noise. The results indicate a strong future for silicon-based quantum technology.
- Host: Coppersmith
Thursday, November 12th, 2015
- R. G. Herb Condensed Matter Seminar
- Topological Quantum Matter
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Yong Chen , Purdue University
- Abstract: Topological quantum matter (TQM), where topological order or topological invariants are used to distinguish different phases of matter, has emerged as a major paradigm in condensed matter physics in recent years. TQMs feature topological bulk-boundary correspondences, where some nontrivial topologically-protected boundary modes are guaranteed to emerge due to the topologically nontrivial states in the bulk of the system. The first example of TQM is the well-known quantum Hall (QH) effect of two-dimensional electrons in a perpendicular magnetic field, where the bulk is insulating due to energy gaps from Landau level formation, and topological conduction free of backscattering occurs via chiral edge states, giving rise to quantized Hall conductance in units of e2/h that is now used as a quantum metrology to help define “ohm” or the even Planck constant itself. The list of TQMs has dramatically expanded in the past decade to now include new states of matter such as topological insulators (TI), which can be a generalization of the QH states to three dimensions and zero magnetic field due to the presence of strong spin orbit coupling (SOC), giving rise to a gapped insulator in the bulk and conducting spin-helical Dirac fermions on the surface promising for spintronics and other applications; topological semimetals, which realize 3D Dirac or Weyl fermions that can exhibit a condensed matter version of the “chiral anomaly”; topological superconductors, which could host quasiparticle analogues of “majorana fermions” potentially useful as qubits for “topological” quantum computation. While so far mostly studied for electronic systems, it is also possible to engineer “synthetic” gauge fields or SOC that may help realize analogous or new kinds of TQMs for photons or neutral atoms. This talk will overview some of the key physics and promised device applications, and describe efforts in my group to make, improve and characterize TQMs --- a particular focus in the past few years has been to realize truly intrinsic TIs that demonstrate salient signatures of “topological” transport, such as a thickness independent conductance in thin films, “half-integer” Dirac fermion QH effects and helical spin polarized current characteristic of topological surface states (TSS), and a “half-integer” Aharonov-Bohm effect when such TSS are confined in a (cylindrical) curved space. Such TIs could also be used as a starting point to make topological semimetals and superconductors.
- Host: McDermott
- Astronomy Colloquium
- The Kepler Cluster Study: Planets and Gyrochronology
- Time: 3:30 pm - 5:00 am
- Place: 4421 Sterling Hall, Talk starts at 3:45 PM
- Speaker: Soren Miebom, Harvard CfA
- Abstract: The precise time-domain observations from NASA's Kepler mission have lead to a breakthrough in the search for exoplanets in star clusters and have begun a new era in the study of stellar rotation. The Kepler Cluster Study (KeCS) was implemented as part of the Kepler mission to search for transiting exoplanets in open star clusters and to study the dependencies of stellar rotation on the most fundamental stellar properties - age and mass. In this talk I will motivate the two primary goals of KeCS, present
our latest results, and discuss some of their implications for our
understanding of the formation and evolution of planetary systemsin star clusters, the angular momentum evolution of Sun-like stars, and for developing a new technique to determine stellar ages - gyrochronology. - Host: Professor Robert Mathieu
- Careers for Physicists
- What can you do with a degree in physics?
- Time: 3:30 pm - 4:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Dr. Johannes Loschnigg
- Abstract: Dr. Loschnigg was a Senior Policy Analyst at the White House Office of Science and Technology Policy (OSTP) in Washington DC from 2009 to 2013. As a member of OSTP's Environment and Energy Division, he was responsible for the development of federal policy for renewable energy, climate change, aerospace, and earth satellite observations. Prior to that, Dr. Loschnigg was the Staff Director for the Subcommittee on Space and Aeronautics of the Committee on Science in the U.S. House of Representatives, overseeing NASA and U.S. civil space programs. Dr. Loschnigg first came to the U.S. Congress in 2002 as a congressional science and technology policy fellow for the American Association for the Advancement of Science (AAAS), working for U.S. Senator Joseph Lieberman of Connecticut. While in the Senate he directed the development of legislation relating to innovation, broadband wireless communication, nanotechnology, defense research, and climate change policy. Between 1998 and 2002, Dr. Loschnigg was affiliated with the University of Hawaii, initially as post-doctoral fellow and later as a faculty research scientist in atmospheric and oceanic sciences, where he concentrated on coupled ocean-atmosphere modeling and impacts of climate variability on disease and human health. <br><br><br>
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Dr. Loschnigg has also been a Senior Advisor for the Administrator at NASA Headquarters in Washington DC, consultant for the National Academy of Sciences, scientific assistant at the NASA Ames Research Center in California and the Department of Physics at the University of Freiburg in Germany. Dr. Loschnigg holds BA degrees in both physics and international relations from the University of Wisconsin-Madison, and MS and PhD degrees in astrophysical, planetary and atmospheric sciences from the University of Colorado at Boulder. He currently is a consultant providing strategic advice for organizations and companies in areas such as energy, aerospace, and climate change. - Host: McCammon
- Graduate Introductory Seminar
- Condensed Matter Physics
- Time: 4:30 pm - 5:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Coppersmith, Eriksson, Joynt, Levchenko, McDermott, Onellion, Rzchowski, Vavilov, Winokur
Friday, November 13th, 2015
- Physics Department Colloquium
- SRC Tantalus Historic Site Reception
- Time: 2:45 pm - 3:15 pm
- Place: 5294 Chamberlin (Faculty Lounge)
- Speaker: N/A, N/A
- Abstract: Reception in the J.H. Van Vleck Physics Faculty Lounge with APS representatives, Physics Faculty, and interested parties.
- Host: Huber, Himpsel, Karle
- Physics Department Colloquium
- Dedication of SRC Tantalus as a Historic Site
- Time: 3:30 pm - 4:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Dr. Sam Aronson, APS President
- Abstract: - Opening remarks, Physics Department Chair<br>
- APS President, Sam Aronson, introduces the plaque<br>
- Marsha Mailick, Vice Chancellor of Research and Graduate Education<br>
- Dr. Katharine Gebbie, invites both representatives to the signing of the ledger of historic sites - Host: Albrecht Karle
- Physics Department Colloquium
- Scientific advances at Tantalus, world's first dedicated synchrotron radiation facility, and beyond
- Time: 4:00 pm - 5:00 pm
- Place: 2241 Chamberlin Hall (Coffee & Cookies at 3:15pm)
- Speaker: Tai Chiang with intro by David Lynch (Iowa State), University of Illinois at Urbana-Champaign
- Abstract: Tantalus, a 240 MeV electron storage ring, began operation in 1968 as the world's first dedicated synchrotron radiation user facility. This revolutionary idea of using synchrotron radiation for broad support of science and technology proved a resounding success, and it subsequently led to worldwide development of ever more powerful light sources for R&D. The main areas of research at Tantalus covered atomic and molecular spectroscopy, optical properties of solids, and electron spectroscopy (photoemission). Many of the early experiments were "the first," focusing on source and detector development, technical refinement, and exploration using the newly available tunable VUV and soft x-ray radiation. Major breakthroughs encompassed high-resolution gas phase measurements, band structure determination of solids, core level spectroscopy, surface chemistry, photoelectron diffraction, many-body excitations, etc. In this talk, I will review some key ideas and developments at Tantalus that paved the way for modern research in a variety of novel materials and systems. I will also make a few comments about the successor of Tantalus, the 1 GeV storage ring Aladdin, which began in 1986 and ended operation in 2014, where applications of synchrotron radiation including the IR spectral range covered diverse topics including superconductors, strongly correlated materials, graphenes, ultrasmooth thin films and epitaxial stacks, topological insulators, bio and medical systems, geological samples, historical and artistic artifacts, and extraterrestrial specimens. I will end with a brief perspective on the future of research using light source facilities.
- Host: Himpsel, Huber, Karle
Saturday, November 14th, 2015
- Atomic Physics Seminar
- Midwest Cold Atom Workshop (MCAW)
- Time: 8:00 am - 7:00 am
- Place: 2241 Chamberlin Hall
- Speaker: various, various
- Abstract: <a href="http://www.physics.wisc.edu/mcaw2015/">http://www.physics.wisc.edu/mcaw2015/</a>
- Host: Yavuz