29th Symposium on Fusion Technology (SOFT 2016)

O5B.2 Radio-frequency design of a lower hybrid slotted waveguide antenna

8 Sep 2016, 17:00

20m

Meeting Hall I 1st floor (Prague Congress Centre)

Board: 2

Oral B. Plasma Heating and Current Drive O5B

Speaker

Walid Helou (CEA)

Description

This paper presents the Radio-Frequency (RF) design of a new type of slow-wave Lower Hybrid Current Drive (LHCD) launcher, based on the Slotted Waveguide Antenna (SWA) concept, which is particularly attractive for the use in future magnetic fusion reactors. When compared to conventional LHCD slow-wave launchers, SWA are less obstructive, allow an “off-port” extension of the launcher and are particularly convenient for wave-injection from non-equatorial ports, which can be beneficial for the current drive efficiency. It also allows launching the waves into the plasma at low power density. There is no apparent restriction to combine SWA with the inherently load-resilient multi-junctions, or to adapt them with the ITER-relevant passive-active concepts. A low power prototype of a Slotted Waveguide Antenna has been designed for the COMPASS tokamak at IPP-Prague. The RF design of this low power prototype is based on hybrid electromagnetic calculations, combining Finite-Element-Method (FEM), Mode Matching (MM) and RF network computations. FEM calculations are performed using ANSYS Electronics Desktop ® for characterizing the waveguide vacuum components, while ALOHA [1], which is based on MM calculations, is used for computing the coupling of radiating slots into the magnetized plasma. Contrary to the simulations of conventional grill launchers, the scattering matrices for both vacuum and plasma sides include higher order modes in the SWA case. The SIDON [2] network solver is then used to combine the Generalized Scattering Matrices (GSM) resulting from FEM and MM calculations. The paper presents in addition the design of the array feeding circuit, combining waveguide and low power coaxial technology. [1] J. Hillairet, et al, Nucl. Fusion 50 (2010) 125010. [2] W. Helou, et al., Proc. 21^stst Topical Conf. on RF Power in Plasmas, AIP Conf. Proc. 1689 (2015) 070004.