Fusion is a vast field requiring many different skills! You can be working on the nuclear physics of the fusion reactions themselves, understanding the ways that we can use various confinement methods to control a plasma, discover more about plasma instabilities and look at ways to be making measurements or simulating these environments. You could also be thinking about and helping design the materials that will surround the fusion 'furnace'! Depending on the approach to fusion there could be many many neutrons produced that pass out through the walls of the reactor, and neutrons don't go quietly- they can end up interacting with the materials and produce changes that could end up damaging our walls. The plasma is also incredibly hot, so you need a material capable of withstanding such temperatures!
As you get further out from the fuel you need to consider how the heat from the reactions is captured and converted to power. If you are using deuterium and tritium as your fuel source (the easiest fuel to make fusion happen with) then you need to be also breeding and harvesting your tritium from a surrounding' 'blanket' region.
For all of these tasks we need physicists, engineers, scientists, policy makers and educators on board. The fusion space is growing rapidly and there are many opportunities to get involved. If you are interested in internships I would recommend you checkout the website here: https://usfusionenergy.org/opportunities
If you are interested in research in universities then reach out to professors. You will find just because someone doesn't explicitly list they are working on research in fusion they may still have overlapping interests or expertise that will very much be applicable to a fusion power plant as well!
The heart of my research is understanding the plasma physics processes governing the fusion events. It also turns out that 99% of the visible universe is made of plasma and so not only do I get the chance to research fusion energy, I can also provide new knowledge about various phenomena throughout our universe! So look out for those 'laboratory astrophysics' plasma physics folk- there are even more overlapping interests.
At UC Berkeley we are fortunate to be located down the road from the Lawrence Livermore National Laboratory, the home of the National Ignition Facility (https://lasers.llnl.gov/about/what-is-nif). There are many opportunities for students to get involved in internships across the various national labs in the USA, both during the summers as well as during semesters or as post-baccalaureate positions so check them out! It's a great way to get introduced to the broad range of fields working on fusion!
https://lasers.llnl.gov/about/careers
https://science.osti.gov/wdts/suli
https://www.sandia.gov/careers/careers/students-and-postdocs/internships-co-ops/