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In the Large helical device, a change of energetic particle mode is observedas He concentration is varied in ion-ITB type experiments, having constantelectron density and input heating power but with a clear increase of centralion temperature in He rich discharges. This activity consists of bursty, butdamped energetic interchange modes (EICs, X Du et al., Phys. Rev. Lett. 114p.155003 (2015)), whose occurrence rate is dramatically lower in the He-richdischarges. Mechanisms are discussed for the changes in drive and damping ofthe modes with He concentration. These EIC bursts consist of marked changes inthe radial electric field, which is derived from the phase velocity ofturbulence measured with the 2D phase contrast imaging (PCI) system. Similarbursts are detected in edge fast ion diagnostics. Ion thermal transport bygyro-Bohm scaling is recognised as a contribution to the change in iontemperature, though fast ion losses by these EIC modes may also contribute tothe ion temperature dependence on He concentration, most particularlycontrolling the height of an "edge-pedestal" in the $T_{i}$ profile. Thesteady-state level of fast ions is shown to be larger in Helium rich dischargeson the basis of a compact neutral particle analyser (CNPA), and the fast-ioncomponent of the diamagnetic stored energy. These events also have an influenceon turbulence and transport. The large velocity shear induced produced duringthese events transiently improves confinement and suppresses turbulence, andhas a larger net effect when bursts are more frequent in Hydrogen discharges.This exactly offsets the increased gyro-Bohm related turbulence drive inHydrogen which results in the same time-averaged turbulence level in Hydrogenas in Helium.

Role of Helium-Hydrogen ratio on energetic interchange mode behaviour and its effect on ion temperature and micro-turbulence in LHD