Synchrotron radiation losses in ETRs

In next-generation Engineering Test Reactors (ETRs), one major objective is envisioned to be a long-pulse or steady-state burn using noninductive current drive. At the high temperatures needed for efficient current drive, synchrotron radiation could represent a large power loss, especially if wall reflectivity (R) is very low. Many INTOR-class ETR designs (FER, NET, OTR, TIBER, etc.) call for carbon-covered surfaces for which wall reflectivity is uncertain. Global radiation losses are estimated for these devices using empirical expressions by Trubnikov (and others). Various operating scenarios are evaluated under the assumption that the plasma performance is limited by either the density limit (typical of the ignition phase) or the beta limit (typical of the current drive phase). For a case with ≥90% wall reflectivity, synchrotron radiation is not a significant contribution to the overall energy balance (the ratio of synchrotron to alpha power is less than 10-20%, even at -- 30 keV) and thus should not adversely alter performance in these devices. In extreme cases with 0% wall reflectivity, the ratio of synchrotron radiation to alpha power may approach 30-60% (depending on the device and limiting operating scenario), adversely affecting the performance characteristics