Method and apparatus for radio frequency cavity

A particle accelerator comprising:

• a conductive housing including a cell, the cell defining a cavity, the cell having a substantially monolithic structure that has no seams or joints internal to the cell;
• a charged particle source for emitting charged particles into the cavity;
• a wave guide coupled to the housing for guiding a micro wave into the cavity;
• an opening disposed in a wall of the conductive housing for guiding the charged particles emitted into the cavity out from the cavity to form an electron beam;
• and
• a flow path through which coolant flows to forcibly cool the conductive housing;
• wherein the conductive housing comprises a cylinder having an inner circumferential surface and a toroid like protrusion from the inner circumferential surface toward a center axis of the conductive housing;
• wherein the flow path enters an external wall of the conductive housing from an outer circumferential surface, the flow path circulates around a through hole defined in a central area of the protrusion, and then returns to the outer circumferential surface of the conductive housing;
• and
• wherein the flow path comprises a portion following a curved path.