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Recent ALMA observations have revealed that a large fraction ofprotoplanetary discs contain bright rings at (sub)millimeter wavelengths. Dusttrapping induced by pressure maxima in the gas disc is a popular explanationfor these rings. However, it is unclear whether such pressure bumps can survivefor evolutionary time-scales of the disc. In this work, we investigate analternative scenario, which involves only dust-gas interactions in a smooth gasdisc. We postulate that ALMA rings are a manifestation of a dense, clumpymid-plane that is actively forming planetesimals. The clumpy medium itselfhardly experiences radial drift, but clumps lose mass by disintegration andvertical transport and planetesimal formation. Starting from a seed ring, wenumerically solve the transport equations to investigate the ring's survival.In general, rings move outward, due to diffusion of the clump component.Without pressure support, rings leak material at rates $\sim$40$M_\oplus\,\mathrm{Myr}^{-1}$ and in order for rings to survive, they must feedfrom an external mass reservoir of pebbles. In the case where the pebble sizeis constant in the disk, a cycle between ring formation and dispersion emerges.Rings produce large quantities of planetesimals, which could be material forplanet formation and explain the massive budget inferred debris disc. Mockimages of ALMA observations compare well to the rings of Elias 24 and AS 209from DSHARP's sample.

Survival of ALMA Rings in the Absence of Pressure Maxima