A fast exhaust-gas analyzer for the ITER divertor

This paper presents a first demonstration of an rf-excited optical gas analyzer (RF-OGA) designed to quantitatively measure minority species inside the neutralization region of the ITER divertor. The sensor head, which creates its own plasma excitation and plasma light emission, is designed to operate in a strong magnetic field and the rf coupling leads to strong light emission. It also allows for operation at low voltages, avoiding radiation-enhanced breakdowns expected when high voltages are present in the ITER environment. Furthermore, the preferred sensor head features full isolation of the metal rf electrodes from the induced plasma. This ¿electrodeless¿ operation will permit long operation without frequent maintenance. First tests of the RF-OGA in a strong (~2T) magnetic field show a mostly linear response of the HeI-6678 A¿ line emission to the He concentration that would produce a He measurement error of ±2%.