Plasma start up simulations with DYON code for FIRST

A spherical tokamak, FIRST, is currently under construction in Taiwan to study high-beta physics. Establishing a robust plasma start-up scenario is a key priority before initiating experimental operations. However, due to geometric and engineering constraints, plasma initiation via ohmic heating (OH) is more challenging in spherical tokamaks. To investigate viable start-up pathways, we employ the DYON code to simulate prefill gas breakdown, plasma current evolution, and burn-through dynamics. The simulations are coordinated with the machine design and construction timeline. We present results for various background magnetic field strengths and scenarios with electron cyclotron heating (ECH) pre-ionization. These simulations reveal the temporal evolution of plasma volume, electron density, and temperature, illustrating how transport parameters affect the transition to flux surface formation. The findings provide guidance for defining an experimental start-up scenario for FIRST.