Patent ID: 6898229

Claim:
A gas circulation fan for an excimer laser apparatus circulating laser gas in a chamber by fan rotation, comprising: a rotary shaft on which said fan is attached, and driven to rotate by a motor; a controllable magnetic bearing having an electromagnet supporting, in a non-contact manner, said rotary shaft, and a position sensor detecting a position of said rotary shaft; and a control circuit controlling an output of said electromagnet based on an output signal of said position sensor; said control circuit including a front-stage circuit adjusted in accordance with variation in characteristic resulting from individual differences of a rotating body including said fan and said rotary shaft and of said controllable magnetic bearing, and outputting a control signal based on the output signal of said position sensor, and a back-stage circuit supplying a current to said electromagnet according to said control signal, said front-stage circuit constituting a mechanical body unit together with said rotating body and said controllable magnetic bearing, said back-stage circuit being provided in a replaceable manner, separately from said mechanical body unit.