Description
A series of experiments was conducted on the WEST tokamak to study particle transport using gas puff modulation [1,2] under varying LHCD power and density conditions. Leveraging long steady-state discharges (up to 40 s), a 5-point LHCD power scan (0-4 MW) and a 3-point density scan (1.8–2.7×1019 m-3 at ρ_pol~0.95) were completed. Real-time density control, operating at sufficiently low bandwidth, did not counteract the feed-forward gas modulation (1-5 Hz) and ensured steady conditions [3].
The newly commissioned mid-plane profile reflectometer [4,5] provided high-resolution density profiles (from ρ_pol≳0.35 to far SOL), capturing the amplitude and phase responses to the modulation. Operated in burst-mode, with up to 160,000 profiles per discharge, the reflectometer revealed subtle modulation up to ~1e17 m-3 and demonstrated excellent repeatability despite significant background fluctuations across 0.5-15 Hz. Line-averaged density measurements with interferometer complemented reflectometer measurements providing robust cross-validation.
Detailed analysis of these discharges is underway to interpret the observed trends and facilitate qualitative comparisons with modeling efforts using both HFPS-TGLF [6] and SOLEDGE [7], which explore similar parameter scans. Initial tentative modelling shows weak neutral penetration while significant inward (turbulent) particle pinch drives the density peaking.
[1] A. Salmi et al 2023 PPCF 65 055025 [2] T. Tala et al 2023 Nucl. Fusion 63 112012
[3] R. Pintelon and J. Schoukens. System identification: a frequency domain approach. John Wiley & Sons, 2012. [4] M. Carrard et al 2025 PPCF 67 075018 [5] A Jamann et al 2025 PPCF 67 085036 [6] M. Romanelli et al. Plasma and Fusion Research 9, 3403023, 2014 [7] H. Bufferand et al 2015 Nucl. Fusion 55 053025