Cryopump

Abstract

A cryopump includes: a cryopump vessel that defines an inlet; a refrigerator including a first stage and a second stage housed in the cryopump vessel, the second stage being cooled to a lower temperature than that of the first stage; a first cryopanel thermally connected to the first stage and surrounded by the cryopump vessel; and a second cryopanel thermally connected to the second stage and surrounded by the first cryopanel. The first cryopanel includes a plate member having an inlet aperture at the inlet. The inlet aperture is formed in the plate member such that a ratio of a conductance of the plate member with respect to an aperture conductance of the inlet is 6% or less.

What is claimed is: 
     
         1 . A cryopump comprising:
 a cryopump vessel that defines a cryopump inlet;   a refrigerator comprising a first stage and a second stage housed in the cryopump vessel, the second stage being cooled to a lower temperature than that of the first stage;   a first cryopanel thermally connected to the first stage and surrounded by the cryopump vessel; and   a second cryopanel thermally connected to the second stage and surrounded by the first cryopanel,   wherein the first cryopanel comprises an inlet cryopanel having an inlet aperture at the cryopump inlet,   wherein the inlet aperture is formed in the inlet cryopanel such that a ratio of a conductance of the inlet cryopanel with respect to an aperture conductance of the cryopump inlet is 6% or less.   
     
     
         2 . The cryopump according to  claim 1 , wherein the inlet aperture is formed in the inlet cryopanel such that the ratio of the conductance of the inlet cryopanel with respect to the aperture conductance of the cryopump inlet is 1% or more or 4% or more. 
     
     
         3 . The cryopump according to  claim 1 , wherein the inlet cryopanel comprises an orifice member located in the cryopump inlet, and the inlet aperture is implemented by at least one opening formed in the orifice member,
 wherein an area ratio of the at least one opening with respect to the cryopump inlet is 6% or less.   
     
     
         4 . The cryopump according to  claim 3 , wherein the area ratio is 1% or more or 4% or more. 
     
     
         5 . The cryopump according to  claim 3 , wherein the orifice member is a single orifice plate covering the cryopump inlet. 
     
     
         6 . The cryopump according to  claim 3 , wherein the cryopump inlet is a circular opening having a first diameter,
 wherein the orifice member comprises a circular plate having a second diameter smaller than the first diameter and an annular plate covering the cryopump inlet along with the circular plate, and the at least one opening is formed in the circular plate.   
     
     
         7 . The cryopump according to  claim 3 , wherein the at least one opening is implemented by a large number of holes. 
     
     
         8 . The cryopump according to  claim 1 , wherein a diameter of the cryopump inlet is in a range from 180 mm to 340 mm. 
     
     
         9 . The cryopump according to  claim 1 , wherein a side surface of the inlet cryopanel defining the inlet aperture is black. 
     
     
         10 . The cryopump according to  claim 1 , wherein the inlet cryopanel is located above a front end of the cryopanel vessel that defines the cryopanel inlet.