The Iranian Light Source Facility (ILSF) is 3+ generation synchrotron radiaition facility with the 400 mA beam current and 3 GeV of beam energy. The circumference of the storage ring is 528 meters. The current study is designing the vacuum system of ILSF storage ring. The design uses the stainless-steel vacuum chambers with a continuing keyhole profile all around the storage ring. The NEG cartridge and Ion pumps which are installed in the antechamber will pump all the vacuum sectors. Using Molflow and Synrad simulations proved that the machine could reach an average pressure of 1 nTorr after the commissioning phase, which could guarantee a vacuum life time of about 13 hours. The general layout of the vacuum system and the construction steps for the vacuum chambers is also be elaborated on in this study. Several discrete photon absorbers which are designed in three types will absorb all the synchrotron radiations. For the heat load study, a simulation with Synrad is performed to calculate the power distribution on the absorber surfaces. Then the result is used to calculate the stress and strain on the absorbers by Finite Element Analysis (FEA). As the next step in the study, the resistive wall impedance of the vacuum chamber is calculated by using CST. Also a detailed design for the RF shileds for bellows and gate valves is done and the vauum impedance of these components is simulated by CST. Then the TMCI and Head-Tail instabilities is studied in the present of impedences by using the analytical formula. The results of the study include the thresholde current for these instabilities.
