  The tidal disruption and subsequent accretion of a star by a supermassive
black hole can be used as a laboratory to study the physics of relativistic
jets. The ngVLA is the only planned instrument that can both discover and
characterize a large number of these short-lived radio sources. In particular
the high-frequency capabilities of the ngVLA enable this important leap
forward. Multi-frequency radio follow-up observations (3 - 100 GHz) of tidal
disruption events found in optical or X-ray surveys will provide a measurement
of the jet efficiency as a function of black hole spin, thus enabling a direct
test of the prediction that relativistic jets require high spin. Hundreds of
tidal disruption jets will be discovered in a blind ngVLA survey for radio
transients. By including VLBI observations with the ngVLA Long Baseline Array,
we can resolve some of these sources, obtaining a robust measurement of the jet
launch date and the magnetic field strength. From the thermal emission of the
tidal disruption flare we can measure the accretion rate at this launch date,
thus providing another unique opportunity to identify the conditions that lead
to jet production.
