Four Separate Dimensionless Collisionality Scans in various JET Scenarios

Particle transport in tokamaks has received much less attention than electron and ion heat transport channels. It is still often not treated self-consistently in transport modelling and predictions for future tokamaks. As a consequence, particle transport and fuelling remain one of the major open questions in understanding the ITER physics [1]. The shape of the density profile has a significant influence on fusion performance and impurity transport. Particle transport has been extensively studied by performing several dimensionally matched collisionality scans in various plasma scenarios in JET. Gas puff modulation technique has been developed with high quality time-dependent density profile measurements to determine particle transport coefficients on JET [2]. The local electron density response to the gas injection was measured Thomson scattering diagnostics close to the midplane. Modulation amplitudes below 0.3-0.5% at mid-radius are reliably measured thus allowing minimal plasma disturbance and the possibility to use data from multiple harmonics. The gas puff modulation was performed with a gas valve at the top of the machine at 3Hz frequency using rectangular waveform, the rate varying from 0 to 6x1022 s-1 at 30% duty cycle. 2. Dimensionless