TFTR ultrahigh-vacuum pumping system incorporating mercury diffusion pumps
NOTICE Raeareh and Lkvclepmcnt Adminiatntion, nor any of their cmpbysu, nor any 01 their mntractorr. r u b n l m c t o n , or thcu employes. m a t s any arursnty cxpreu or implied, or a5umcr any legal liability o r responsibility lor the accuracy, completenen or urlvlnm of any inlormalion. Ppparatw, product or pm-d'wlolol~d. or represents that its w would not ~!STRIBUT\ON OF THIS ABSTRACT The TFTR vacuum vessel w i l l have a system of four 61 cm diameter mercury diffusion pumps to -8 -9
... mps to -8 -9 provide a base pressure i n the 10 -10 Torr range as we1 I as a low impurity level within the vessel. The system, called the Torus Vacuum Pumping System (TVPS), w i l l be employed 0 with the aid of an occasional 250 C bakeout i n situ as well as periodic applications of aggressive 2 discharge'cleaning. The total interior surface area of the vessel i s 1200 m , and its volume i s 63,300 liters. In addition to evacuating the main vessel volume, the twelve bellows guard regions -4 of the toroidal vessel (total volume -600 liters) w i l l be exhausted to a pressure of -10 Torr. The vacuum system backing the mercury diffusion pumps consists of four mechanical pumping units, a 1000 liter holding tank to contain the exhausted gases from the mechanical pumps, two zirconium aluminum getter pumping units, two residual gas analyzer units, and a Dry Gas.supply. The TVPS i s an ultrahighvacuum (UHV) system using no elastomers as well as being a closed system with respect to tritium or any tritiated gases. The backing system employing --75 al lmetal isolation valves i s designed with the features of redundancy and flexibility employed i n a variety of ways to meet the fundamental requirements and functions enumerated for the TVPS. . Since the design, as presented i n this report, i s one which i s a modification of the conceptual design of the TVPS, those features which have changed are discussed. Calculations are presented for the maior performance parameters anticipated for the TVPS and include conductances, effective pumping speeds, base pressures, operating parameters, getter pump parameters, and calculations of time constants associated with leak checking. 4 The effective hydrogen pumping speed of the four two-trap diffusion pump stacks i s -2 x 10 liter/sec a t the vessel. Each stack i s connected through similar ducts directly lo the brus such that the neuirol beam injector ducts are no longer utilized as pump ducts. The backing system i s located i n the basement of the TFTR facility and detailed descriptions of the main units and the arrangement of valving and vacuum lines connecting them are given. The foreline arrangement i s i n the fo'rm o f a stack with the mechanical pumps arranged two-by-two on the floor, the zirconium aluminum getter units at an intermediate level above the floor, and the residual gas analyzers a t an upper level. The configuration provides easy maintenance access for the vacuum lines and units. The effect on operating parameters of locating the backing system directly under the device in the basement pit area i s also investigated. $ Modifications i n the vacuum pumping system for the guard regions on the twelve bellows sections are presented so that it i s compatible with the main TVPS. The bellows pumping system consists of a mechanical pump unit, a zirconium aluminum getter pump unit and a residual gas analyzer. ,. * The control and management of the TVPS i s described with particular attention given to providing both manual and automatic control at a local station and at the TFTR Central Control. Such operations as testing, maintenance, leak checking, startup, bakeout, and various other operations are considered i n some detail. Various aspects related to normal pulsing, discharge cleaning, non-tritium operations and tritium operations were also taken into consideration.