The electromagnetic radiation emitted when charged particles are decelerated by the electric fields of ions in a fusion plasma, representing both a fundamental energy loss mechanism and a valuable diagnostic tool.
Bremsstrahlung (German for "braking radiation") is emitted whenever a charged particle is deflected by the Coulomb field of another charged particle. In a fusion plasma, the dominant process is electron–ion bremsstrahlung. The emitted photon spectrum is continuous, with most radiated power in the X-ray regime for plasmas at 10–30 keV.[1]
The Te1/2 dependence—weaker than the T2 scaling of fusion reaction rates—means that at sufficiently high temperature, fusion power outpaces bremsstrahlung losses. This crossover is essential to achieving net energy gain.[3]
Even a few percent of carbon (Z=6) or tungsten (Z=74) can raise Zeff substantially since the contribution scales as Z2. This is why impurity control via divertors is so critical.[1]
Bremsstrahlung is also a valuable diagnostic tool. X-ray continuum measurements provide direct determination of electron temperature, and visible bremsstrahlung is used to reconstruct Zeff profiles.[4]
At the optimal ignition temperature of ~15 keV, bremsstrahlung accounts for the single largest radiative loss in a clean D–T plasma. The requirement that alpha heating exceed bremsstrahlung (plus transport losses) provides one route to deriving the Lawson criterion.[3]