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Events During the Week of March 29th through April 5th, 2026
Sunday, March 29th, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar
Monday, March 30th, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar
Tuesday, March 31st, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar
Wednesday, April 1st, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar; Thesis Defense; Some statistical results in ion temperature gradient-driven turbulence theory; Time: 10:30 am - 12:30 pm; Place: Chamberlin 5310; Speaker: Augustus Azelis; Abstract: Understanding the nonlinear saturation of microturbulence remains a central problem in magnetically confined fusion plasmas. In ion temperature gradient (ITG) driven turbulence, saturation emerges from a complex interplay between linearly unstable drift waves, linearly stable eigenmodes, and nonlinearly generated zonal flows. This dissertation develops and applies weak turbulence closure theory to investigate these processes, with particular emphasis on eigenmode dynamics, nonlinear energy transfer, and the emergence of intermittent statistics. Analytical predictions are systematically compared with numerical simulations of a reduced fluid model for ITG turbulence.

A self-consistent weak turbulence closure is constructed for the second-order correlations governing energetic dynamics in a collisionless ITG fluid model. In the collisionless limit, the governing equations exhibit parity–time reversal symmetry, resulting in centrosymmetric correlation evolution operators. The resulting saturated states are characterized by equipartition of energy between stable and unstable eigenmodes at each wavenumber. These results highlight the central role of zonal-flow–catalyzed nonlinear energy transfer from unstable to stable modes and suggest a mechanism by which turbulent heat flux can vanish despite the presence of linear instability. Numerical simulations confirm the predictions of the closure theory.

A novel weak turbulence closure technique is then developed to calculate two-point, two-time correlation functions and power spectra in systems of instability-driven turbulence. Application of this framework to zonal flows yields a complex nonlinear decorrelation frequency that governs both oscillatory behavior and temporal decay of the two-time energy spectrum. The resulting power spectra demonstrate that nonlinear interactions strongly modify zonal flow dynamics, imparting wavenumber-dependent oscillation frequencies absent at the linear level.

Weak turbulence closure theory is further extended to fourth-order statistics to investigate the Dimits shift through the lens of intermittent turbulence. A new closure method is developed to compute the growth rate of a fourth-order cumulant associated with energy fluctuations. The resulting evolution equation predicts the development of intermittent, non-Gaussian statistics at large spatial scales below the nonlinear critical gradient, and their decay above it. These predictions are validated through comparisons with numerical simulations, including measurements of probability distribution functions, kurtosis, and entropy of the turbulent heat flux. The emergence and suppression of intermittency are traced to qualitative changes in nonlinear mode coupling between stable and unstable eigenmodes across the nonlinear threshold.

Overall, this work demonstrates that weak turbulence closure theory provides a unified framework for describing saturation, temporal correlations, and intermittency in ITG turbulence, and offers new insight into the dynamical mechanisms underlying zonal-flow–regulated transport and the Dimits regime.; Host: Paul W. Terry; Add this event to your calendar
Thursday, April 2nd, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar
Friday, April 3rd, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar; Preliminary Exam; Design of Magnetic Shielding for a Wide Field of View Sounding Rocket Instrument; Time: 1:30 pm - 3:30 pm; Place: Sterling B343; Speaker: Sophia Nowkak; Abstract: Diffuse hot gas near 10^6 K emits almost entirely in X-rays below 400 eV, creating a dense forest of emission lines. In order to disentangle the various elements and ionization states we require detectors with an energy resolution better than 2 eV FWHM. We are developing a new sounding rocket payload equipped with an array of high-resolution sensors. To get enough counts for a useful spectrum during the ~250s flight, the detector array will need >2.5^2 cm collecting area and ~1 steradian field of view (FOV).

Transition-edge sensors (TES) and their superconducting quantum interference device (SQUID) readouts are extremely sensitive to magnetic fields, and need to be well-shielded from changes in the ambient magnetic field. Primary magnetic field sources during flight are stray fields from the adiabatic demagnetization refrigerator (ADR) and the Earth’s magnetic field. Other TES-based space missions, like Athena and Micro-X, only have to accommodate the f-number of the converging beam from their telescope mirror, which X-ray reflection physics limits to ~f/4. They can therefore utilize long narrow cones of nested mu-metal and niobium in front of their detectors to improve shielding effectiveness. With our 1 sr direct FOV, this would necessitate impractically large and long shields. Using COMSOL Multiphysics, we explore a design which features a Nb superconducting mesh closing the front of the shield close to the detectors and enabling a much more compact shield.; Host: Dan McCammon; Add this event to your calendar
Saturday, April 4th, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar
Sunday, April 5th, 2026: Academic Calendar; Spring Recess; Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu; Add this event to your calendar

Events at Physics

Events During the Week of March 29th through April 5th, 2026