The Magnetic Diagnostics for SPARC

Although SPARC will be groundbreaking in many ways, its magnetic diagnostics (MAGX) are rather conventional, albeit with several key features driven by SPARC’s unique conditions. Nearly all sensors will be located on the interior walls of the vacuum chamber, and therefore baking and D-T operation necessitate the use of mineral-insulated cable for the sensors and leads. The lack of in-vessel maintenance opportunities after initial operation warrants careful attention to redundancy and elimination of failure modes. For this reason MAGX will have electrical joints only at the vacuum feedthroughs, and feedthrough prototyping will include exhaustive testing for reliability. The high heat loads and disruption forces on first wall components require extensive structural supports, severely limiting the spaces in which MAGX sensors and leads can be located. As a consequence, nearly all flux measurements will use saddle flux loops in lieu of full toroidal loops, and there will be no in-vessel plasma current Rogowski sensors. SPARC plasmas will be ~30 s long (10 s flattop), so conventional analog integration of the inductive signals is suitable. Details of sensor layout and prototyping will be discussed. (See also Myers et al in this session.)