  Particle physicists at the Large Hadron Collider investigate the properties
of matter at subatomic length scales by colliding together bunches of
high-energy protons and observing the decay products of the collisions. ATLAS
is one of two general-purpose detectors that reconstruct the interactions and,
as part of a wide range of physics goals, measure the production of Higgs
bosons and searches for exotic new phenomena including supersymmetry, extra
dimensions of spacetime, and dark matter. Selecting the interesting collision
events using hardware- and software-based triggers is a major challenge that
will become more difficult as the luminosity increases in future data. The
ATLAS Fast TracKer (FTK) is a custom electronics system that performs fast
hardware-based tracking of charged particles for use in trigger decisions. In
2018, two FTK "Slices" covering portions of the ATLAS detector were installed
and commissioned using proton-proton collisions, to prepare for physics
data-taking in Run 3. The FTK track-finding and track-fitting strategies and
the tracking performance for the FTK Slices are presented. Strategies for
coping with changing beamspot and other conditions in future data are
discussed. A strategy for triggering on displaced tracks from long-lived
particles is also presented.
