H-mode accessibility in ohmic discharges on RFX-mod

RFX-mod is a toroidal device originally designed as a reversed field pinch, presently operated also as a tokamak. The RFX-mod is performing shaped discharges, both in Double Null and Single Null configuration [1], [2]. The next target of the experimental activity is the H-mod access in Single Null configuration. This contribution will deal with development of the diagnostic methods for the L-H transition detection and computation of the key quantity for the L-H transition: the heat flux crossing the separatrix carried by particles (Psep). The results of experiments on L-H transition that will be carried out during the spring 2015 will be presented as well. One of the quantities important for L-H transition detection is the poloidal beta. In the frame of this contribution, the development of two independent methods to measure this quantity will be presented. The first of the methods is based on the diamagnetic measurement and surface integrals computation, the other one described in [3] relies purely on the surface integral computation. The two methods yield consistent results. The second part of the contribution will focus on the computation of Psep especially during the transition phases of the discharge (current ramp-up and ramp-down phase, shaping phase). During these phases, the Psep can be increased [4] and can exceed the power needed for the L-H transition. The calculation will be used to support the activity on the discharge optimization to maximize the Psep and eventually to achieve the H-mod. References: [1] O. Kudlacek et al, EPS 2014 Berlin, P5.062 [2] G. Marchiori et al, EPS 2014 Berlin, P5.040 [3] L.L. Lao et al, Nuclear Fusion 1985 Vol. 25 1421-1436 [4] J. Havlicek et al, Global Power Balance in the COMPASS tokamak, WDS 2014