An ion source has an arc chamber having a body defining and interior region. A liner defined an exposure surface of the interior region that is exposed to a plasma generated within the arc chamber. An electrode has a shaft with a first diameter that passes through the body and the liner. The electrode is electrically isolated from the body where the liner is a plate having a first surface with an optional recess having a second surface. A hole is defined through the recess for the shaft to pass through. The hole has a second diameter that is larger than the first diameter, and an annular gap exists between the plate and the shaft. The plate has a lip extending from the second surface toward the first surface that surrounds the hole within the recess and generally prevents particulate contaminants from entering the annular gap.