Relativistic Jets in the Accretion & Collimation Zone: New Challenges
  Enabled by New Instruments
  Jets are a ubiquitous part of the accretion process, seen in a wide variety
of objects ranging from active galaxies (AGN) to X-ray binary stars and even
newly formed stars. AGN jets are accelerated by the supermassive black hole of
their host galaxy by a coupling between the magnetic field and inflowing
material. They are the source for many exciting phenomena and can profoundly
influence the larger galaxy and surrounding cluster.
  This White Paper points out what advances can be achieved in the field by new
technologies, concentrating on the zone where jets are accelerated to
relativistic speeds and collimated. The ngVLA and new space VLBI missions will
give higher angular resolution, sensitivity and fidelity in the radio,
penetrating this zone for additional objects and allowing us to resolve
fundamental questions over the physics of jet acceleration and collimation.
Interferometry in other bands would allow us to probe directly flaring
components. We also emphasize the need for polarimetry, which is essential to
revealing the role and configuration of magnetic fields.
