Density profile peaking in JET H-mode plasmas: experiments versus linear gyrokinetic predictions

As an independent complement to previous studies (Weisen et al 2005 Nucl. Fusion 45 L1–4, Weisen et al 2006 Plasma Phys. Control. Fusion 48 A457–66, Angioni et al 2007 Nucl. Fusion 47 1326–35), density peaking in the JET tokamak was investigated on the dataset, comprising virtually all H-mode experiments performed in 2006–2007. Unlike previous studies, this work focuses on low collisionality data as most representative of reactor conditions. The study confirms that collisionality is the most important parameter governing density peaking in H-mode, followed by the NBI particle flux and/or the Ti/Te temperature ratio. For the first time in JET a modest, albeit significant dependence of peaking on internal inductance, or magnetic shear is seen. The experimental behaviour is compared with an extensive database of linear gyrokinetic calculations using the GS2 code. The predictions from GS2 simulations based on the highest linear growth rate mode are in good agreement with experimental observations. They are also corroborated by initial results from the non-linear code GYRO. PACS numbers: 52.55.Fa, 52.65.Tt, 52.25.Fi (Some figures in this article are in colour only in the electronic version)