Ion Heat Pulse Propagation Experiments in W7-X Operational Phase 2.2 and 2.3

Clamping of ion temperature (T_i) profiles in electron-cyclotron resonant heated (ECRH) plasmas in the W7-X stellarator limits plasma performance and is found across magnetic configurations [1]. Power balance studies in ECRH step down in combination with local GENE runs show ion channel turbulent transport is likely dominated by ion temperature gradient (ITG) turbulence. To further characterize the turbulence transport properties, ion heat pulse propagation studies were performed using neutral beam injection (NBI) modulation experiments in W7-X to measure T_i profile stiffness. In the last operational phases, experiments over a configuration scan of mirror ratio and during advanced heating scenarios utilizing density peaking were conducted. The T_i and carbon density measured by a fast charge exchange spectrometer operating at 1 kHz, in addition to measurements of density by Thomson and interferometry and electron temperature (T_e) by electron cyclotron emission (ECE) diagnostic in combination with ECRH modulation [2], allow measurements of particle, electron, and ion transport channels during modulation. Here we present results from these experiments and subsequent results of modelling efforts of the NBI as a source in the measured transport channels and of the resulting heat pulses.