The design and performance of the ATLAS inner detector trigger for Run-2 LHC collisions at $\sqrt{s} = 13$ TeV

The Run-2 of the Large Hadron Collider presents challenging high rate conditions for data analysis and processing within the ATLAS trigger system. The ATLAS Inner Detector (ID) trigger implements the algorithms used for identification of tracks for all physics signatures within the ATLAS trigger. The ID trigger was updated and redesigned during the 2013-2015 long shutdown to meet the challenging conditions of Run-2. As well, for Run-2 a new pixel detector layer was added in very close proximity to the beam pipe, to enhance the ID Trigger performance. The redesigned ID trigger algorithms for Run-2 are described, illustrating the significant improvements gained by the new tracking strategies adopted to deal with the increased rate. The performance of the ID trigger in Run-2 is shown in terms of efficiency and resolution, using data collected from the 25 ns bunch spacing data collected in 2015. The ID trigger continues to show excellent performance, with efficiencies greater than 99%.