Bellan, L. Comunian, M. Donegani, E.M. Eshraqi, M. Grespan, F. Jones, B. Laface, E. Levinsen, Y. Milas, N. Miyamoto, R. Neri, L. Noll, D. Pisent, A. Plostinar, D.C. Sosa, A.G. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-215-8 10.18429/JACoW-LINAC2022-TUPORI29 English 618-621 rfq electron LEBT extraction ion-source Contribution to a conference proceedings 2022 2022-09 https://doi.org/10.18429/JACoW-LINAC2022-TUPORI29 https://jacow.org/linac2022/papers/tupori29.pdf The mechanism of space charge compensation given by the residual gas ionization is a key factor for the emittance containment in the low energy beam transport (LEBT) lines of high intensity hadron injectors. A typical front end including a microwave Ion source, a LEBT and Radio Frequency Quadrupole (RFQ), is equipped with two repellers at each interface to prevent electrons from flowing back, to the source, or forward, to the RFQ. In this paper we will emphasize the importance of the ion Source and LEBT repellers on giving the appropriate boundary conditions for the space-charge compensation building-up mechanism. The theory and simulations are supported by experiments performed in the high intensity facility such as ESS and IFMIF/EVEDA.