Progress on the ITER electron cyclotron heating and current drive upper launcher steering mirror control system

The ITER ECRH upper launcher (UL) uses a steering mechanism assembly (SMA) to steer the beams in the appropriate location for controlling magnetohydrodynamic (MHD) activity in the plasma (NTMs and sawtooth oscillations). Switching and modulation rotation cycles with an accuracy of 0.1° are requirements for Neoclassical Tearing Modes (NTMs) stabilisation in ITER. Two SMA prototypes have been manufactured. A test stand that reproduces the expected pneumatic configuration of the UL has been built to perform control tests on both SMA prototypes. The first SMA prototype has been tested, and tests on the second prototype are foreseen on the second half of the present year. An "off-the-shelf" commercial servo-valve with a PID controller has been used to control the pressure with good results for the switching cycle. These tests have shown that a more sophisticated control strategy will be needed to attain the desired accuracy for the modulation cycles, since the present controller presents a permanent tracking error for ramp commands.