William Capecchi

Job Description

I received my PhD in physics from the University of Wisconsin-Madison in 2017. I tried working in industry for a couple years (Sr. Simulation Engineer at Donaldson Inc.), but ultimately found the work unfulfilling. Instead I wanted to apply my efforts to something much more ambitious and potentially impactful. Luckily I tried to transition back into fusion at an opportune time and am now a postdoc through the University of WI working on LTX-b at the Princeton Plasma Physics Lab (PPPL).

Research

Current: Similar to my PhD research, I’m working on fast-ion physics on LTX-b. A neutral beam was installed last year, and I’ve been working to bring it up to full operation. The current effort is how to improve the beam coupling with the plasma.

Past: My PhD research focused on identifying a pressure limit in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) plasma device. More specifically, a certain type of magnetic instability called a “bursting” mode was identified and thought to be related the population of high energy ions (“fast-ions”) injected via the neutral beam. At a certain fast-ion pressure threshold (or normalized to the magnetic field a beta threshold) the ions would non-linearly interact with the background magnetic field driving a perturbation unstable resulting in the loss of a large portion of the fast-ion population.

To measure this threshold I developed a collimated neutron detector, which by measuring the neutron emissivity across the plasma cross section allowed us to infer the fast-ion density and pressure profiles. This work involved extensive data modeling and analysis, but ultimately led to the first measurement of the fast-ion profile and bursting mode threshold, the first such measurement in an RFP.