Prototype mitre bends of the ex-vessel waveguide system for the ITER upper launcher: Thermal hydraulic simulations and experiments with off-center mm-wave beams

On ITER, long pulse gyrotrons are required as a power source for electron cyclotron heating (ECH) and current drive (CD). The microwaves are guided from the gyrotrons, which are placed far from the Tokamak, into the plasma by transmission lines (TLs) and a launching antenna (launcher). Each of the four ECH Upper launchers features eight waveguide (WG) TLs, with at least 95% of the power from the gyrotrons coupled into in the main HE mode of the TLs. In the ex-vessel portion of the system between the port-plug closure plate and the isolation valve and diamond window, there are miter bends (MBs) that change the direction of the TL by reflecting the millimeter waves (mm-waves) using mirrors; the mirrors must handle 1.31 MW, 170 GHz, 3600 s pulses. Various MBs perform these reflections at an angle of 90 degrees, or nearly 100 degrees. As a result of the ohmic dissipation, an intensive peaked heat flux appears near the center of the MB mirror and thus, a dedicated cooling system is present to ensure the temperature control of the mirror and housing e.g. [1]. The power that is not found in the HE mode can cause the beam to be not perfectly centered, resulting in an off-centered heat flux on the mirror surface; as is the case for the experiments described here. This study presents new finite element modeling of such beams, created in CFX of ANSYS Workbench [2], compared to the experimental findings for pulses of 170 GHz, 0.5 MW and 240 s. Monitor points are placed in the same positions as TCs that have been fitted in the mirror close to the heated surface and direct comparison of the temperature values is performed. Through transient simulation the time constants are calculated and compared with those of the experiments

Thermo-mechanical analysis of an ITER ECH&CD Upper Launcher mirror

The Mirror one Lower (LM1) is part of the in-vessel quasi-optical beam propagation system for the ITER Electro Cyclotron (EC) Upper Launcher (UL), where eight beams are reflected through four mirrors during its passage to the plasma. The mirrors are grouped into two rows of four beams each and the mirror LM1 refers to a four mirror set. High power millimeter (mm) waves are generated by the gyrotrons and delivered to the in-vessel components via corrugated wave-guides. The design of the LM1 shall guarantee the optimal propagation of the beams during their transmission through the optical system taking into consideration 1) the shape of the reflecting surfaces, 2) loads coming from the beams themselves, the plasma and nuclear reactions as well as off-normal events and 3) the port plug space restrictions. This paper reports the Ohmic loss assessment at LM1 as function of frequency, surface roughness and resistivity using the most suitable material and the power input (1.31 MW at 170 GHz). It describes the design investigation of the cooling solutions for the normal scenario via computational fluid dynamic analyses, based on the ITER Primary Heat Transfer System (PHTS) cooling boundary conditions, needed to remove similar to 20 kW of power deposition on the mirror surface. Finite element analyses are performed to guide the design choices in an effort to minimize the maximum mirror surface temperature and thus diminishing the deformation of the reflecting surfaces. The conclusion of this study will provide a feasible design solution for the LM1 and Upper Mirror 1 (UM1)

Progress on the design and manufacturing of the mirrors for the ITER Electron Cyclotron Heating and Current Drive upper launcher

Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control the magneto-hydrodynamic (MHD) instabilities