Physics Analysis of the ITER ECRH & ECCD Upper Launcher Design for NTM Stabilisation-Final Report on deliverables for EFDA Task TW5-TPHE-ECHULA

In this Report the main results of the physics analysis carried out by the beam tracing code GRAY under the Task TW5-TPHE ECHULA are reviewed. The main goal of the physics analysis has been to evaluate the performance of the two launcher designs, both in terms of the required steering range and of the figure of merit for NTMs stabilisation (miNTM=JECCD/Jbs), for (2,1) and (3,2) modes for three reference ITER scenarios: inductive scenario 2, hybrid scenario 3a, low q scenario 5. In Del. (f).2.1 the dogleg 6 beams variant of the RS Launcher has been analyzed. Both the two sets of beams for two slightly different designs of this variant led to low values of ?NTM for all reference cases, except for q=2 of reference Scenario 2, the only case where the physics goal miNTM >=1.2 has been met. The main physical reason is that the RF beams, that are astigmatic, are very divergent in the quasi-poloidal direction, leading to large spot sizes at relevant surfaces and, as a consequence, to broad current profiles. In Del. (f).3.2 two circular beams, representative of Upper and Lower rows, have been used in the calculation of performances of FS Launcher. The beam parameters have been given by CRPP, for an intermediate design first and then for the final design. The FS launcher uses a front steering mirror that provides optimum focusing and the possibility for a wide steering range. In particular, the beams taken into account for the calculation are convergent up to close the q=2 surface of reference Scenario 2 and then slightly divergent, leading to quite small spot sizes at all relevant surfaces. Quite good figures of merit have been obtained for all reference Scenarios: miNTM >=2 for all (2,1) modes and miNTM >=1.8 for all (3,2) modes. In Del. (f).6 the capabilities to drive efficient and well localized co-current for a range of relevant surfaces in ELMy-H mode ITER plasmas at low magnetic fields have been explored, up to half field with respect to the reference magnetic field. The low-field ITER scenarios have been obtained by scaling the kinetic profiles of the inductive reference scenario 2, under the following constraints: i) q95=const, ii) Betapol=const, iii) ni*=const. The calculations that have been performed have shown that: -for magnetic fields in the range 4.8 T <= B <= 5.3 T, the upper launcher, by injecting from its present location and with the design value of the toroidal angle (Beta =20 degree) 20 MW of power as O-mode first harmonic, may drive efficient current density to stabilize NTM over all the radial locations of rational q surfaces (3/2 and 2/1) pointed out from the analysis of many equilibria; -for magnetic fields in the range 4.3 T <= B < 4.8 T, the accessibility to innermost surfaces is lost, unless the toroidal injection angle is increased up to values Beta ~26 degrees - 280; -between about 4.3 T and 3 T the upper launcher is not usable for a fixed frequency source =170 Ghz, because first harmonic is out and second harmonic is still on the low field side with respect to the launcher location; -below 2.9 T up to ~2.2 T, efficient current density may be driven if second harmonic X-mode is used.