The isotope effect on the L mode density limit in JET hydrogen, deuterium and tritium divertor plasmas

The first systematic study on the mass dependence of the L mode density lim it is reported for JET hydrogen, deuterium and tritium divertor plasmas. Th e density limit, defined as the density at the onset of the X point MARFE, is found to scale inversely with the ion mass in vertical target configurat ions, while no isotope effect is found in horizontal target configurations. Two dimensional numerical simulations reproduce the observed mass dependen ce in vertical target discharges. The experiments indicate a coupling betwe en the mass and the power dependence of the L mode density limit. The exper imental results are compared with analytic models, which suggest that the i on-neutral transverse collisionality plays a role in the density limit.