Workpiece processing uses a transfer chamber in cooperation with a process chamber. The workpiece is to be heated to a treatment temperature, at a preheating pressure, and subsequently exposed to a plasma at a treatment pressure, which is less than the preheating pressure. The process chamber pressure does not exceed the preheating pressure, yet very rapid pressure increases can be induced in the process chamber in transitioning from the treatment pressure to the preheating pressure. The transfer chamber pressure can be maintained at the treatment pressure, the preheating pressure or raised to a selected pressure to backfill the process chamber to the preheating pressure. A backfill arrangement can selectively induce rapid pressure increases in the process chamber. A bypass arrangement provides selective pressure communication between the transfer and process chambers and can be used for backfilling the process chamber from the transfer chamber.