Measuring the ion-stimulated desorption coefficient on a model of the vacuum chamber of the accelerating-storage complex at the temperature of 300 and 77 K

For studying the vacuum-technical performance of a model of the vacuum chamber of the IHEP accelerating-storage facility the ion-stimulated desorption coefficient eta is measured. The vacuum chamber with the nitrogen coating of the 3.8 m length, 70 mm diameter and 1 mm wall thickness is made of the 12 Kh18N10T stainless steel. Glow discharge treatment of the chamber in argon is carried out at 2.5x10-2 mm Hg. eta is determined according to the ratio of the number of gas molecules extracted from the chamber walls into the gas phase during ion bombardment and the number of ions passed through the discharge during the same period of time. The eta dependences on the ion integral dose for different discharge voltages and eta dependences on the discharge voltage at 77 K and for two ion integral doses at 300 K are presented. It follows from the dependences that at first, at small ion doses, the eta coefficient has a relatively great value, and then it decreases and yields to the steady value with the ion dose increase at voltages > 1100 V. At 800 V and 500 V the eta value linearly decreases at doses higher than 6x106 ionxcm-2. At the fixed ion dose eta linearly increases with the ion energy increase. At 77 K temperature in the chamber the eta value, remaining negative, approaches zero with the increase of energy or ion integral dose