Weisen, H.Alberti, S.Berry, S.Behn, R.Blanchard, P.Bosshard, P.Buhlmann, F.Chavan, R.Coda, S.Deschenaux, C.Dutch, M. J.Duval, B. P.Fasel, D.Favre, A.Franke, S.Furno, I.Goodman, T.Henderson, M.Hofmann, F.Hogge, J. P.Isoz, P. F.Joye, B.Lister, J. B.Llobet, X.Magnin, J. C.Mandrin, P.Marletaz, B.Marmillod, P.Martin, Y.Mayor, J. M.Moret, J. M.Nieswand, C.Paris, P.Perez, A.Pietrzyk, Z. A.Piffl, V.Pitts, R. A.Pochelon, A.Razumova, K.Reimerdes, H.Refke, A.Rommers, J.Roy, I.Sauter, O.Suttrop, W.van Toledo, W.Tonetti, G.Tran, M. Q.Troyon, F.Vyas, P.Ward, D. J.2008-04-162008-04-162008-04-16199710.1088/0741-3335/39/12B/011https://infoscience.epfl.ch/handle/20.500.14299/21408WOS:000071677500011The TCV tokamak (B-T < 1.5 T, R approximate to 0.88 m, a < 0.25 m) has produced a wide variety of plasma configurations, both diverted and limited, with elongations kappa(a), ranging from 0.9 to 2.58, triangularities delta(a) from -0.7 to 1 as well as discharges with nearly rectangular cross sections. Plasma currents of 1 MA have been obtained in elongated discharges (kappa(a) approximate to 2.3). Ohmic discharges with delta(a) < 0 have smaller sawteeth and higher levels of MHD mode activity than plasmas with delta(a) > 0. The main change in MHD behaviour when elongation is increased beyond two is an increase in the relative importance of modes with m, n < 1 and a reduction of sawtooth amplitudes. Confinement is strongly dependent on plasma shape. In ohmic limiter L-modes energy confinement times improve typically by a factor of two as the plasma triangularity is reduced from 0.5 to 0 at constant q(a). There is also an improvement of confinement as the elongation is increased. In most discharges the changes in confinement are explained by a combination of geometrical effects and power degradation. A global factor of merit H-s (shape enhancement factor) has been introduced to quantify the effect of Bur surface geometry. The introduction of H-s into well known confinement scaling expressions such as Neo-Alcator and Rebut-Lallia-Watkins scaling leads to improved descriptions of the effect of shape for a given confinement mode. In some cases with kappa(a) greater than or equal to 1.7 limited ohmic L-modes undergo a slow transition to a confinement regime with an energy confinement improved by a factor of up to 1.5 and higher particle confinement. First experiments to study the effect of shape in ECRH at a frequency of 83 GHz (second harmonic) have been undertaken with 500 kW of additional power.ITERtext::journal::journal article::research article