Constraints of radiation loss on thermonuclear reactor designs based on burning p–11B in a dense plasma focus

A challenge in creating an aneutronic thermonuclear fusion reactor is the rapid loss of energy by bremsstrahlung emission, which can cool the plasma faster than fusion reactions can heat it. Recent studies proposing a reactor design based on burning p–11B in a dense plasma focus claim to overcome the radiation loss problem through novel physics mechanisms associated with strong magnetization of the plasma. The first is a quantum magnetic field effect, which is proposed to reduce the bremsstrahlung emission rate due to Landau quantization of the electron gyromotion. The other is a strong suppression of the electron–ion collision rate by the magnetic field, which allows the maintenance of an electron temperature that is much lower than the ion temperature. Here, each of these proposed effects is assessed using recent advances in the kinetic theory of strongly magnetized plasmas. It is shown that the quantum magnetic field effect is not relevant in the plasma parameter and magnetic field strength regimes of a dense plasma focus. It is also shown that the electron–ion temperature relaxation rate is not strongly suppressed by the magnetic field at these conditions. Inefficient energy deposition of fusion products is expected to exacerbate the issue of the cooling rate exceeding the heating rate. Furthermore, the rate of cyclotron radiation emission is expected to surpass bremsstrahlung emission at the proposed plasma conditions. Many of the arguments presented here also apply to other proposed reactor concepts based on burning p–11B.