5-9 September 2016
Prague Congress Centre
Europe/Prague timezone

P1.052 Performance assessment of critical waveguide bends for the ITER in-vessel plasma position reflectometry systems

5 Sep 2016, 14:20
1h 40m
Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Foyer 2A (2nd floor), 3A (3rd floor)

Prague Congress Centre

5. května 65, Prague, Czech Republic
Board: 52
Poster D. Diagnostics, Data Acquisition and Remote Participation P1 Poster session

Speaker

Jorge Belo (Instituto de Plasmas e Fusão Nuclear)

Description

The Plasma Position Reflectometry (PPR) diagnostic will be used in ITER to measure the plasma position/shape in order to provide a reference for the magnetic diagnostics during very long (>1000s) pulse operation, where the position deduced from the magnetics is known to be subject to substantial error. It consists of five reflectometers distributed at four locations, known as gaps 3-6, operating in O-mode in the frequency range 15-75 GHz. The systems of gaps 4 and 6, which are considered here, are known as the PPR in-vessel systems, since its bi-static antenna system and feeding waveguides are installed inside the ITER vacuum vessel – for gap 4 the antennas are on the low-field side, for gap 6 on the high-field side. A critical issue in the design of these systems is the transmission line (TL) to/from the antennas since it uses oversized rectangular waveguides that, being welded to the vessel inner-shell must conform to an intricate path/geometry. This includes a 90º bend right behind the antennas, for both gaps 4 and 6, and a 120º bend just before entering the port extension, exclusively for gap 4. However, oversized bends can excite higher order modes and create resonances, which increase the transmission losses and could significantly affect the diagnostic’s ability to meet the measurement requirements. Hence, careful assessment of these components will be crucial to the diagnostic’s success. Here, the performance of the 90º and 120º bends is studied via numeric simulations and, in the case of the 90º bend, compared to laboratory measurements of a prototype which revealed an excellent performance, with overall losses around 0.5 dB and no resonances across the whole frequency range.

Co-authors

Antonio Silva (Instituto de Plasmas e Fusão Nuclear, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal) Jorge Belo (Instituto de Plasmas e Fusão Nuclear, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal) Paulo Quental (Instituto de Plasmas e Fusão Nuclear, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal) Paulo Varela (Instituto de Plasmas e Fusão Nuclear, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal)

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