Arjmand, S. Anania, M.P. Biagioni, A. Costa, G. Crincoli, L. Del Franco, M. Ferrario, M. Galletti, M. Giulietti, D. Lollo, V.L. Pellegrini, D. Pompili, R. Zigler, A. JACoW Publishing Geneva, Switzerland 2673-5490 978-3-95450-227-1 10.18429/JACoW-IPAC2022-WEPOST035 English 1776-1779 Contribution to a conference proceedings 2022 2022-07 https://doi.org/10.18429/JACoW-IPAC2022-WEPOST035 https://jacow.org/ipac2022/papers/wepost035.pdf The research concerns the study of the plasma sources for plasma-based accelerators (PBAs) at the SPARC_LAB test-facility (LNF-INFN). The interest in compact accelerators, overcoming the gigantism of the conventional radio-frequency (RF) accelerators, is growing in High Energy Physics. The plasma-based accelerating gradients can attain the GV/m scale. At the SPARC_LAB test-facility, a plasma device is under development. It consists of a capillary in which one or more inlets inject neutral gas (Hydrogen), ionized by a high-voltage (HV) discharge. Electron density has been measured as a function of time through the Stark broadening profiles of the Balmer line.