Installation of Bidirectional Lost Fast-Ion Probe in the Large Helical Device

A bidirectional scintillator-based lost fast-ion probe is installed to measure fast-ion losses induced by energetic-ion-driven magnetohydrodynamic (MHD) instabilities in the Large Helical Device (LHD). It has two set of an aperture assembly so as to measure losses of co-going fast-ions in both clockwise and counter-clockwise directions of the toroidal field. Each aperture assembly was designed to detect escaping energetic ions, whose pitch angle and gyroradius are respectively 30-70 degrees and 3-15 cm, and to block plasma stray light. The scintillator P11 (ZnS:Ag) was adopted because of its high luminosity toward high-energy particles.