Speaker
Description
The electronic density ne is a major parameter, both for real-time tokamak control and plasma physics. On the WEST tokamak, X-mode reflectometry provides post-treatment radial density profiles ne(r) with a centimeter precision[1]. The current reconstruction method initializes the profile using the signal amplitude jump at the edge plasma position and reconstructs the profile using a step-by-step algorithm[2] within a computational time of 10 to 20 ms per profile. A real-time measurement of the density profile would enable the control of density at the plasma edge, a key parameter for plasma stability, such as for maintaining the equilibrium of the Radiative X-Point configuration to optimize confinement time.
Real-time reflectometry measurement on WEST is being developed using the innovative Nectarine digitizer[3]. The data processing has been adapted to be performed in real-time. For the profile initialization, a new method was tested relying on the jump in the beating frequency signal, due to the wave reflected faster on the inner wall than on the plasma. In addition, a new method is proposed for the profile reconstruction, based on the time of flight instead of the phase is used[4]. Then, the data extraction is easier and less sensitive to noise and biases, enabling a faster reconstruction with a reduced number of radial positions.
The single profile reconstruction code is programmed in C language and runs in 2 ms, a duration comparable to the WEST control cycle time.
References
[1] Clairet, F., et al. "Fast sweeping reflectometry upgrade on Tore Supra." Rev. Scien. Inst. 81.10 (2010).
[2] Bottollier‐Curtet, H. "Microwave reflectometry with the extraordinary mode on tokamaks: Determination of the electron density profile of Petula‐B." Review of scientific instruments (1987)
[3] C. Bouchand, et al. “The data acquisition system of WEST’s New Thomson Scattering diagnostics” 24th IEEE Real Time Conference, 22–26 avr. 2024
[4] Sabot, R., This conference
