N. Petersohn(1), J.C. Boissin(2), D. Murdoch(3) , A. Mack(1)
(1) Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany
(2) L'Air Liquide, Division des Techniques Avances, B.P. 15, 38360
Sassenage, France
(3) The NET Team, Max Planck Inst. fur Plasmaphysik, Boltzmannstr. 2, 85748
Garching, Germany
A cryopump as ITER primary vacuum pump is developed at FZK under the European Fusion Technology Programme. The ITER vacuum system comprises 16 cryopumps as primary vacuum pumps operating in a cyclic mode. Prior to the construction of a prototype cryopump, the concept is tested on a reduced scale Model Pump. Content of this paper is a description of the detailed design of the Model Pump.
The pumping principle of the Model Pump, as well as for the ITER cryopump, is cosorption on a 80 K baffle and a set of 5 K croypanels which are covered with activated charcoal. The cryopanels with a total area of 4 m2 are installed laterally in the pump housing. The cooling of the cryopanels is performed by a forced flow of 5 K supercritical helium through the cooling chanels of the cryopanals which are designed in quilted design. The total stainless steel mass which has to be cooled to 5 K is 60 kg. The 80 K louvre baffle consists of 10 stainless steel rings. The rings, 70 mm in width, are inclined by an angle of 45 degrees to the pump inlet. Therefore, the baffle is both optically tight to the pump inlet and open for the molecular flow with the best possible conductance. To the outside the cryopanels are thermally proteced by a 80 K cylindrical shield. The shield consists of 4 seperable parts in order to allow easy mounting and dismantling of the Model Pump components. The total 80 K stainless steel mass is 260 kg. The inner system is surrounded by a pump housing with an outer diameter of 1200 mm and a length of 1350 mm. The pump housing is attached to a pump plug which is used for the installation of the Model Pump in the test vessel. The pump inlet is closed by a valve disc with a diameter of 700 mm. The valve disc is driven by a pneumatic actuator from the back side of the pump. The actuator has a piston with a diamter of 300 mm and is operated with 2 MPa pressured nitrogen. The valve shaft with a stroke of 400 mm is sealed to the inner volume of the pump by a metal bellow.