The Front Steering Launcher Design for the ITER ECRH Upper Port

The ECRH ITER upper port antenna's role is to stabilize the neoclassical tearing mode (NTM) on either the q = 2 or 3/2 rational flux surfaces, which requires a narrow current deposition profile (jCD) over a wide range along the resonance surfaces. The width of jCD should be equivalent to the marginal island width to fully stabilise the NTM. Two antenna concepts are under consideration for the upper port launcher: front steering (FS) and remote steering (RS). The FS launcher decouples the steering and focusing aspects using a two mirror system (one focusing and one steering), achieving a wider steering range and higher current density for NTM stabilisation than required by ITER, offering a threefold increase in NTM stabilization efficiency over the RS launcher. The improved physics performance has motivated the further design study of the FS launcher aiming toward a build to print launcher. The present design is compatible with >=2.0 MW CW operation and 8 beams per port plug. A frictionless backlashfree system is envisioned for the steering mechanism. An overview of the launcher design, the calculated physics performance and the possibility of using the upper port launcher for extended physics applications (beyond NTM stabilisation) are discussed.