  We present studies for optimizing the next generation of ground-based imaging
atmospheric Cherenkov telescopes (IACTs). Results focus on mid-sized telescopes
(MSTs) for CTA, detecting very high energy gamma rays in the energy range from
a few hundred GeV to a few tens of TeV. We describe a novel, flexible detector
Monte Carlo package, FAST (FAst Simulation for imaging air cherenkov
Telescopes), that we use to simulate different array and telescope designs. The
simulation is somewhat simplified to allow for efficient exploration over a
large telescope design parameter space. We investigate a wide range of
telescope performance parameters including optical resolution, camera pixel
size, and light collection area. In order to ensure a comparison of the arrays
at their maximum sensitivity, we analyze the simulations with the most
sensitive techniques used in the field, such as maximum likelihood template
reconstruction and boosted decision trees for background rejection. Choosing
telescope design parameters representative of the proposed Davies-Cotton (DC)
and Schwarzchild-Couder (SC) MST designs, we compare the performance of the
arrays by examining the gamma-ray angular resolution and differential
point-source sensitivity. We further investigate the array performance under a
wide range of conditions, determining the impact of the number of telescopes,
telescope separation, night sky background, and geomagnetic field. We find a
30-40% improvement in the gamma-ray angular resolution at all energies when
comparing arrays with an equal number of SC and DC telescopes, significantly
enhancing point-source sensitivity in the MST energy range. We attribute the
increase in point-source sensitivity to the improved optical point-spread
function and smaller pixel size of the SC telescope design.
