Patent ID: 8790071

Claim:
A turbomolecular pump comprising a plurality of first vane stages each of which comprises a plurality of moving vane blades formed so as to extend radially from a rotating assembly, and a plurality of second vane stages each of which consists of a plurality of stationary vane blades arranged so as to extend radially with respect to a rotation shaft of the rotating assembly, arranged alternately; and including, with respect to the vane stages that are adjacent along the rotation shaft direction, at least one vane stage that satisfies a first relational equation “Xo(R)>Xo(S)” and a second relational equation “Xi(R)<Xi(S)” in connection with a dimensionless number X that is a ratio of an inter-vane distance S to a chord length C for the moving vane blades and the stationary vane blades, with the dimensionless numbers at an outer circumferential portion and an inner circumferential portion of the first vane stage being termed Xo(R) and Xi(R) and the dimensionless numbers at an outer circumferential portion and an inner circumferential portion of the second vane stage being termed Xo(S) and Xi(S).