The invention comprises a negative ion beam source vacuum method and apparatus used as part of an ion beam injection system, which is used in conjunction with multi-axis charged particle or proton beam radiation therapy of cancerous tumors. The negative ion beam source contains a vacuum chamber isolated by a vacuum barrier from the vacuum tube of the synchrotron. The negative ion beam source vacuum system preferably includes: a first pump turbo molecular pump, a large holding volume, and a semi-continuously operating pump. By only pumping ion beam source vacuum chamber and by only semi-continuously operating the ion beam source vacuum based on sensor readings about the holding volume, the lifetime of the semi-continuously operating pump is extended.