Pumping characteristics of the St707 non-evaporable getter (Zr 70-V 24.6-Fe 5.4 wt%)

The room temperature pumping speeds of the St707 Non-Evaporable Getter (NEG) have been measured both for individual gases and for gas mixtures as a function of the quantities of gas pumped. The interesting feature of this NEG consists in its moderately low activation temperature. Therefore particular attention has been devoted to defining the optimum temperature and duration of the activation process to obtain the highest possible pumping speed in a given practical situation. It has been found that heating at 400° C for about one hour or at 350° C for one day, results in pumping speeds of about 1000 ls-1m-1 for H2 , 2000 ls-1m-1 for CO and 450 ls-1m-1 for N2, values very close to those obtained after activation at the higher temperature of 740° C. The St707 NEG is therefore particularly suitable for passive activation during bakeout of stainless steel vacuum systems, avoiding the need of electrical insulation and feedthroughs which are mandatory when activation is carried out by resistive heating

Diffusion of oxygen in niobium during bake-out

Bake-outs at temperatures between 100 C and 150 C for a duration up to two days have become customary for optimising the performance of bulk niobium cavities. This treatment results in the diffusion of oxygen, originating from the surface oxide, into the niobium. The theoretical oxygen profile has been simulated using the diffusion equations, and compared with some experimental results

Ultimate pressures achieved in TiZrV sputter-coated vacuum chambers

Two metre long, cylindrical vacuum chambers of diameter ranging from 34 to 100 mm, coated with TiZrV getter films by sputtering, have been baked for about 24 h at temperatures from 120 to 250 degrees C. The ultimate pressures achieved after bakeout were found to correspond to the ratio of the pressure gauge degassing to the effective pumping speed provided by the chamber at the location of the gauge. The results covering a pressure range from 10/sup -11/ Torr down to 10 /sup -13/ Torr are presented and discussed. (6 refs)

Niobium films produced by magnetron sputtering using an Ar-He mixture as discharge gas

Superconducting RF accelerating cavities have been produced at CERN by sputter-coating, with a thin niobium layer, cavities made of copper. In the present work, the discharge behaviour and niobium film properties have been investigated when part of the argon sputtering gas is replaced with helium. Helium is chosen because of its low mass, which reduces the energy lost by the niobium atoms colliding with the sputter gas atoms. The higher niobium atom energy should lead to higher adatom mobility on the substrate and, hence, to a larger grain size, a feature which is highly desirable to reduce the cavity surface resistance. It has been found that helium addition effectively helps to maintain the discharge at considerably lower argon pressures, via metastable-neutral ionisation and high secondary electron yield. However, a large amount of helium is trapped in the film, amount which is proportional to the helium partial pressure during the discharge, resulting in a reduction of both Residual Resistivity Ratio and grain size

Production and Test of 352 MHZ Niobum-Sputtered Reduced-β\beta Cavities

Three types of 352 MHz single-cell cavities foreseen for different particle speeds (v/c=0.8, 0.625 and 0.48) have been designed and built with the niobium sputtered on copper technique. We report on the results of the cold tests at 4.5 and 2.5 K and the actual status of the data analysis

Various methods of manufacturing superconducting accelerating cavities

We report on experience in superconducting cavity production methods gained in shaping, joining and thin film coating with various materials and techniques (Pb, Nb, Nb$_{3}$Sn, NbN, NbTiN) with emphasis on their potential to reduce mass production costs