Characterisation of electron density fluctuations in TCV H-mode pedestals with a Short Pulse Reflectometer

The Short-Pulse Reflectometer (SPR) on the TCV tokamak probes plasmas with V-band pulses of approximately 1 ns duration at a pulse repetition rate up to 50 MHz. This provides a density profile measurement with spatial resolution of around 3 mm in the typical TCV H-mode pedestal [1]. A 2-D scan in shaping and fuelling was performed exploring both the quasi-continuous exhaust (QCE) [2] and Type-I ELM H-mode regimes to exploit the SPR capabilities. This study demonstrates the first comprehensive and high-fidelity SPR density profile measurements on the TCV tokamak, highlighting the analytical challenges, solutions, and ongoing improvements.



SPR density profiles measured simultaneous to Thomson Scattering profiles were found to agree within experimental uncertainty throughout L-H transitions and both Type-I and QCE ELM cycles. Observations will be reported on pedestal dynamics, including some density transport studies, fluctuation spectra and analysis of pedestal reformation during the differing ELM cycles. Comparisons will be made with Doppler-Backscattering, Gas Puff Imaging and Thermal Helium Beam diagnostics.



[1] P A Molina Cabrera et al 2021 Plasma Phys. Control. Fusion 63 085019

[2] B. Labit et al 2019 Nucl. Fusion 59 086020