  The Advanced Wakefield Experiment (AWAKE) at CERN relies on the seeded
Self-Modulation (SM) of a long relativistic proton bunch in plasma to
accelerate an externally injected MeV witness electron bunch to GeV energies.
During AWAKE Run 1 (2016-2018) and Run 2a (2021-2022), two seeding methods were
investigated experimentally: relativistic ionization front seeding and electron
bunch seeding. In the first one, a short laser pulse copropagates within the
proton bunch and ionizes the rubidium vapor, generating the plasma. In the
second, a short electron bunch propagates in plasma ahead of the proton bunch
and drives the seed wakefields. Both seeding methods will be further employed
during AWAKE Run 2b (2023-2024) to study their effect on the SM evolution in
the presence of a plasma density step. In this contribution, we will show the
main experimental results and discuss their impact for the future design of the
experiment, in particular for Run 2c (starting in 2028), where the plasma will
be split in two sections: one dedicated to SM of the proton bunch, and the
other to the electron acceleration process.
