29th Symposium on Fusion Technology (SOFT 2016)

P2.037 Advances in technology and high power performance of the ECH system on DIII-D

6 Sep 2016, 14:20

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 37

Poster B. Plasma Heating and Current Drive P2 Poster session

Speaker

Mirela Cengher (General Atomics)

Description

The gyrotron complex on DIII-D has been updated and comprises six gyrotrons installed and routinely operating reliably for injection of up to 3.6 MW into the plasma. The operational maximum of 5 s pulse length for the six gyrotrons allows up to 18 MJ total energy to be injected into the plasma. Recent system upgrades include faster launcher mirror scans and control by the plasma control system, a new 117.5 GHz operating frequency, and new 4-port power monitors. The eight sets of real time steerable mirrors that are installed on DIII-D inject the rf power from the tokamak low field side. The mirrors control the ECH deposition location. The real time steering feature with feedback is now routinely used for neoclassical tearing mode (NTM) experiments. The launched rf can be directed over ±20º from perpendicular toroidally, or steered poloidally over 40º in 200 ms. The transmission efficiency in the six operating 31.75 mm diameter corrugated waveguide lines is better than -1.1 dB. The measured HE1,1 mode content is over 85% for all the lines. Two grooved mirrors installed in miter bends are used for launching the arbitrary elliptical polarization required for different plasma configurations. The transmission line was upgraded with new rf power monitors at the last miter bend before the tokamak, which can measure wave polarization and mode content. Rf power reflected from the plasma is also monitored, and, together with visible light detectors, can give indication of low absorption in the plasma. A new design depressed collector gyrotron in the 1.5 MW class, operating at 117.5 GHz, is expected to be installed during 2016. Plans call for an expansion of the ECH system to ten gyrotrons including the new 1.5 MW gyrotrons operating at 117.5 GHz, providing up to 9.5 MW injected power.