Principles and Challenges of Controlled Nuclear Fusion Presenter: Dr. Rajesh Miangi, event hosted by the American Nuclear Society at UMD. Occured Nov. 25, 2025, 7-8pm, over Zoom.
Following introductions, Dr. Miangi introduced us to a couple definitions. Nuclear fusion, he explained, is the process of combining small atoms into larger ones. He then walked through an example with hydrogen fusion (as seen in stars) and deuterium-tritium fusion. He also defined plasma to be a state of matter when atoms decompose into “a soup of ions and electrons” where electrons are free to move around between different ions. This is important because fusion requires atoms to be very energetic. Ions must be heated enough to overcome electric repulsion, so “we have to pass through a plasma state to reach temperatures suitable for fusion”. In fact, particles have to be about 200 million Kelvin. “Immense heat, immense energy,” he tells us. “You have to have some way to confine it. How do you maintain that?”
We can’t physically contain plasma; all of our current materials melt long before then. The main part of Dr. Miangi’s lecture was discussing gravitational, magnetic, and inertial confinement. He justifies our use of magnetic confinement – which confines plasma in the direction across the field – by comparing it to gravity as seen in the sun. He then explains that magnetic fields don’t “hold” particles like matter does, but instead guides its motion, so we can’t just make a simple tube because the plasma would go out. Along this line of reasoning, he justifies the torus shape we typically associate with fusion reactors. Finally, he discusses how we heat up plasma to those temperatures. After some discussion on resistive, wave, and ion beam heating, he took questions.
I found this talk pretty convincing. It’s not so much an argumentative presentation than an informative one, and the things he shared were largely basic information within the field. He cited information consistent with what I’ve learned in the past. One part that I wasn’t fully convinced by was why we used a torus; Dr. Miangi explained that any sphere would have a dead spot where plasma could leak, citing something called the “hairy ball theorem”. Informally, he asked us to imagine combing a coconut; it’s impossible to do so without forming a “cowlick”, a place where the hair sticks out.
This connection wasn’t fully clear to me, so I did some searching. This video I found explains it succinctly, giving a formal definition:
“Suppose V: S^2 -> T(S^2) is continuous. Then there exists a point p in S^2 such that V(p) = 0.”
From my understanding, this means that if we have a sphere (or something topologically equivalent to one) residing in 3D, and a vector field where the vector at any point on the surface is tangent to the surface, the vector at some point on the surface must be 0. Now that I have this image in my mind, it makes sense why this is relevant; if there’s no magnetic field at a certain point, then there’s nothing there to deflect plasma, so nothing’s stopping plasma from escaping there. On one hand, I’d say that this connection wasn’t clear in the original presentation; on the other hand, since Dr. Miangi was presenting to people of varied backgrounds, he couldn’t assume that we were comfortable with vector fields.
Another part that stuck out to me was his justification of using electromagnetic confinement over gravitational confinement. He showed us that the electromagnetic forces between two atoms was on the order of 10^26 times as strong as the gravitational ones between them, and that the mass of magnets used in the International Thermonuclear Experimental Reactor (ITER) is 10^22 times less than the minimum amount needed for fusion to occur in stars. I found this to be a strange piece of justification; from a purely intuitive point of view, no reasonable amount of deuterium or tritium we can gather will have enough gravity to hold itself together, let alone enough to sustain fusion. While I did enjoy the scale comparisons, it didn’t seem necessary to explain why we don’t use gravitational containment, although this feels like a nitpick.
All in all, I am fairly convinced by this talk. Some of it went over my head, but I’d argue it was because of my lack of background in fusion rather than a poor presentation. Everything presented was something I either know as a fact, or well-corroborated enough for me to treat as a fact.