The particles are confined by powerful magnetic field lines around which they spiral in tight helical paths. Also, the pressure of the plasma is low; it exists in what is essentially a very good vacuum. Recent K-Star literature gives the peak density as about 7x1019 particles per cubic meter, which sounds like a lot until you realize that the density of air at normal atmospheric pressure is about 2.6x1025 particles per cubic meter.
Thus, the density of the 100-million-degree plasma is roughly one-millionth of that of the air we breathe. In other words, there isn't much of it there.
A gas at 100 million degrees does radiate some pretty high-energy photons, hard X-rays, actually close to gamma rays in their energy content. Those pose the real danger, along with neutrons generated by any nuclear fusion events that occur.
thank you