In a nutshell the plasma would be made of an isotope of hydrogen atoms (deuterium and/or tritium) which is ionized meaning their electron is stripped and holds an electric charge (+). That is how the plasma is confined with magnets because it is composed of positively charged particles of hydrogen nuclei. These hydrogen isotopes used have 1 or 2 extra neutrons at their core. When two core/nuclei fuse to make helium, they will eject the neutrons which will escape the chamber in every direction since they have no electrical charge and are not confined in the magnetic field. Neutrons that are slowed down by heavy water, for example, will heat the media (and probably the reactor walls as well). At that point it becomes similar to a nuclear plant where neutrons are slowed down by a media that will soak up the heat.

It's a power generator [sciencealert.com]

Ad Astra... the 2019 movie?

@Lukian [adastrarocket.com]

@mek7730 ah! nope. This is a power generator mentioned above by @Rufus_Maximus.

it's the inner view of a fusion reactor. Ionize hydrogen is kept in a doughnut shape cloud around the center core using very powerful magnets in the middle and around the chamber. The plasma is heated to millions of degrees (hotter than the sun). I'm not sure but the fire fly like sparkles could be fusing particles that when controlled in larger amounts should be releasing more energy than required to run the machine: Cheap clean pure energy.

@Lukian wow! sweet and pretty.

@hankster my thoughts exactly

@Blindbird that's a damn good question right there

@Blindbird, @hankster The secret is the magnetic field. It holds the plasma in a doughnut while preventing it from touching the walls. This is a very complicated and complex piece of engineering technology.
This additional video will explains a little more how these things work although it is a different design.

@Lukian that is way out there Beyond sweet and pretty. it is freakishly complex. is it the cooling of the magnets that keeps them from melting? or does the magnetic field itself act as an insulator of sorts not allowing the heat to move?

@hankster the magnets require to be cooled at very low temperature to make them superconducting. The ionized gas, which is the plasma, is very hot (100 million degrees) but also low density on the edges which means it does not radiate heat outwards. If it does not touch the wall them no problem. Kinda like a fluorescent tube at home that works at 6500 Kelvin or 11,240F or 6000C. The tubes don't feel very hot if you touch them because the plasma is mostly kept hot in the middle. It's the advantage of plasma.

@Lukian but what we all want to know is, if it goes wrong will it be spectacular!?

Lol... probably not. It takes so many parameters to make it work that if something goes wrong it snuffs out.