Qiang, J. Hwang, K. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-WEPOB29 English 964-966 WEPOB29 ion electron cavity cathode space-charge Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-WEPOB29 https://jacow.org/napac2016/papers/wepob29.pdf Dark current from unwanted electrons in photoinjector can present significant danger to the accelerator operation by causing damage to photocathode and power deposition onto conducting wall. In this paper, we present numerical models of dark current generation from the field emission and from the electron impact ionization of the residual gas that were recently developed in the IMPACT-T code. We also report on the application of above numerical model to an LCLS-II like photoinjector.