Studies of GDC on bending magnet chambers of Indus-2

Indus-2 is a Synchrotron radiation (SR) source dedicated to X-rays. The vacuum envelope is made of aluminium alloys. The whole ring is divided into 8 vacuum sectors (VS) each isolated from the adjacent sectors by RF shielded all metal gate valves. Each VS consists of two Bending Magnet (BM) chambers, the connecting straight section (St.S) chamber and the parts of straight section chambers at both the ends. Vacuum chambers were fabricated from Aluminium alloys. Vacuum in 10-10 mbar range (with the beam) is essential through out the ring for the specified life time (∼20 Hrs) of the electron beam. Towards the initial storage of the electron beam, tremendous pressure rise is commonly observed in electron storage rings, which is caused by the photo-electron induced desorption (PID) of gas molecules from the vacuum chambers, when they get exposed to Synchrotron radiation (SR). To reduce this effect, it is essential that the chambers should undergo a typical pretreatment -Glow discharge cleaning (GDC) with Argon+Oxygen (10%) mixture, prior to the assembly in the ring. The dose for this treatment was fixed after conducting experiments in the lab. The GDC treatment on the vacuum chambers was followed by baking. Residual gas analysis was done to confirm the effectiveness of the treatment. All the chambers (BM as well as St.S chambers) of Indus-2 have undergone this treatment. This paper gives the details of these experiments on BM chambers with results. (author)