UMD Plasma Seminar

Plasma Physics Seminar

Fall 2025 Schedule

September 3rd, Wed. 3:30PM ERF 1207, Large Conference Room	Open
September 10th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
September 17th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
September 24th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
October 1st, Wed. 3:30PM ERF 1207, Large Conference Room	Open
October 8th, Wed. 3:30PM ERF 1207, Large Conference Room	Ida Ekmark, Chalmers University Optimization of runaway electron mitigation by massive material injection in ITER and SPARC During tokamak disruptions, strong electric fields can arise which are sufficient to cause electron runaway, whereby electrons are accelerated continuously. In future large-current tokamaks, such as ITER and SPARC, significant runaway electron generation is expected, due to the runaway generation being exponentially sensitive to the pre-disruption plasma current. Should the beam of runaway electrons come in contact with the tokamak wall, its energy can be almost instantly deposited deep into the wall. During disruptions, high heat loads can also arise from heat being transported into the wall when the magnetic surfaces are broken up during the thermal quench. Additionally, if the current decay is too fast or too slow, electromechanical forces caused by eddy or halo currents can cause forces and torques on the tokamak structure. While all of these unwanted aspects of a disruption can individually be addressed by massive material injection, they pose conflicting requirements on the injected material quantity and composition. In this talk, we investigate disruptions mitigated with combined deuterium and noble gas injection in ITER and SPARC. We use multi-objective Bayesian optimization of the densities of the injected material, taking into account limits on the maximum runaway current, the transported fraction of the heat loss, and the current quench time. Regions in the injected material density space corresponding to successful mitigation are found for both machines when optimizing pure deuterium plasma scenarios. When optimizing deuterium-tritium plasma scenarios, on the other hand, simultaneous mitigation of runaway current, transported heat loss and electromechanical forces appear more challenging for ITER than for SPARC.
October 15th, Wed. 3:30PM ERF 1207, Large Conference Room	Sophia Sanchez-Maes, University of Maryland 3D Particle-in-Cell Simulations of Reconnection-Driven Particle Acceleration and Their Implications for Sagittarius A Flares The brightest X-ray flares from Sagittarius A* (Sgr A) reveal extreme episodes of particle acceleration. Explaining observed spectra requires electrons accelerated to Lorentz factors in the range of hundreds of thousands to millions, which is beyond what traditional approaches have demonstrated in this context. Magnetic reconnection offers a compelling mechanism, capable of efficiently accelerating particles to high energies. However, two-dimensional (2D) particle-in-cell (PIC) simulations have intrinsic limitations: particle motion is confined within plasmoids, restricting energy gain. Acceleration in 2D reconnection typically saturates near the plasma magnetization limit, falling short of the energies required to explain the brightest X-ray flares. In contrast, 3D reconnection introduces additional degrees of freedom, allowing particles to escape plasmoids and enhancing acceleration efficiency. To connect reconnection physics with observed Sgr A flare spectra, we perform 3D PIC simulations spanning a range of magnetic guide field strengths (Bg/B0), and investigate the resulting particle acceleration and synchrotron spectra. We find that the guide field plays an important role: a strong guide field limits particle energies and softens the spectrum, while a weak or absent guide field in 3D produces overly hard power-law slopes. Intermediate guide field strengths yield particle distributions more consistent with those observed during X-ray flares from Sgr A. These initial results suggest that reconnection-mediated acceleration can plausibly power the IR and X-ray variability observed near the Galactic Center's supermassive black hole. The strength of the guide magnetic field may further regulate whether flare emission extends into the X-ray, consistent with the fact that all Sgr A X-ray flares have IR counterparts, but not all IR flares produce observed X-rays.
October 22nd, Wed. 3:30PM ERF 1207, Large Conference Room	Yi-Min Huang, Goddard Space Flight Center
October 29th, Wed. 3:30PM ERF 1207, Large Conference Room	Will Fox, University of Maryland
November 5th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
November 12th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
November 19th, Wed. 3:30PM ERF 1207, Large Conference Room	APS DPP meeting
November 26th, Wed. 3:30PM ERF 1207, Large Conference Room	Thanksgiving Recess
December 3rd, Wed. 3:30PM ERF 1207, Large Conference Room	Emily Lichko, Naval Research Laboratory
December 10th, Wed. 3:30PM ERF 1207, Large Conference Room	Open

Contact Information: Marc Swisdak or Ian Abel