For a comprehensive list of publications, please see my Google Scholars page.

Pegasus-III Experiment

Diem is the Principal Investigator of a new DOE funded facility called the Pegasus-III Experiment at the University of Wisconsin-Madison. The Pegasus-III Experiment is a new magnetic confinement experiment that began operations in July 2023. This experiment seeks to develop new and innovative ways to start up future fusion power plants without using a central magnetic to initiate the plasma. The device replaces large central electromagnets with small plasma injectors (that look like lightsabers!) to startup the experiment and seeks to develop models to predict performance in large-scale, fusion power plant like devices. For more information, journal articles and presentations, please see the Pegasus-III website.

The Just Fusion Collaborative is a new, interdisciplinary group that seeks to understand the intersection of society, the environment, economics and fusion energy technology while engaging communities early in the design process. More information to come soon!

Electron Bernstein Wave Heating and Current Drive for High Density Plasmas

Diem received her Ph.D. in Plasma Physics from Princeton University while doing her dissertation research at the National Spherical Torus Experiment (NSTX), at the Princeton Plasma Physics Laboratory. Diem’s dissertation research, “Investigation of EBW Thermal Emission and Mode-Conversion Physics in the National Spherical Torus Experiment”, resulted in the first experimental observation of EBW collisional damping and she developed a method to mitigate these effects via lithium evaporation. She has led experimental research and modeling efforts in establishing electron Bernstein wave heating on the linear plasma devices, Proto-MPEX, at the Oak Ridge National Laboratory, collaborated with several devices around the world including MAST in the UK and is establishing a new radio frequency wave heating system on the Pegasus-III Experiment at the University of Wisconsin-Madison.

Previous Research on Understanding and Controlling Edge Instabilities in Plasmas

Mitigation of Edge-Localized-Modes, ELMs, is critical for the success of ITER and other future burning plasma devices. Several methods of ELM mitigation are being explored such as: gas puffing to inject fuel or impurities in the plasma edge to control the plasma pedestal density, 3D magnetic perturbations to create an edge stochastic layer increasing the transport to lower the pedestal pressure gradient, lithium granule injections, etc. One method of reducing the negative effects on materials and plasma confinement from large ELMs is to induce high frequency, small ELMs, thus reducing transient heat pulses to the diverter to manageable levels. This method is known as ELM pacing.

ELM pacing has been shown to reduce transient heat pulses to the diverter by inducing high frequency, small ELMs. Studies have predicted that ITER requires a frequency enhancement > 30 times the natural ELM frequency. One approach to ELM pacing is to inject small pellets of fuel or impurities into the edge of the plasmas, which can trigger an ELM at a rate exceeding the natural ELM frequency. For this work, Diem ran 2D and 3D M3D-C1 models of ELM pellet pacing experiments in the DIII-D tokamak.