Application of Saturated NEG at Interaction Regions

Abstract

Activated non evaporable getter (NEG) coating has shown excellent surface properties, such as low secondary electron yield and low electron impact desorption rate, etc. Since usually the activation is difficult or sometimes not possible at interaction regions, the activated then saturated NEG coating could be used there, which does not require in-situ activation while still keeps many attractive surface properties. In this article, the experimental background problem at RHIC and the surface property of NEG coating are reviewed. The issues relevant to the application of saturated NEG at interaction regions are discussed. IntroductionThe non evaporable getter coating was developed primarily for the linear pumping [1], however, it was found that the activated NEG surface can also suppress the gas desorption induced by photon and electron bombardments [2]. Furthermore, the NEG surface has shown the reduced secondary electron yield (SEY) [3], and also the reduced desorption rate by ion impact [4]. The surface property of NEG coating (at least SEY) is probably only slightly changed after the saturation [3], which means that the low SEY is kept at the saturation.The surface property of beam chamber at interaction regions is an important aspect in improving experimental background. Since the NEG activation 1 at interaction regions is often limited in temperature or even not possible at all, the use of saturated NEG is of interest.To this end, some questions need to be answered.1. What surface property is relevant in the reduction of experimental background? These properties include SEY, electron and ion desorptions, and beam halo scrapping effects.2. What do we know about these surface property for NEG coating and the saturated NEG coating?3. How to improve the relevant surface properties in terms of coating and saturation methods and conditions? How to measure it?4. Other questions such as the aging and lifetime of saturated NEG, and the installation and maintenance as well.In this article, the RHIC experimental background problem in heavy ion and polarized proton operations is reviewed and several concerned surface properties of beam chamber at interaction region are discussed. This is followed by a review of NEG coating properties according to the bench test and machine studies performed at various laboratories. The issues that are not sufficiently understood are then discussed for further development. Experimental background 3.1 RHIC experienceLuminosities of RHIC heavy ion operations are affected by the experimental background problem in past several years, including collisions of Au-Au, dAu, and Cu-Cu.Since the bunch intensity has a quadratic relation to the luminosity, beams with highest possible bunch intensity are used as far as the beambeam and inter-beam scattering limits are not reached, which is the case for past and the current RHIC operations. The number of bunches then can be increased to raise luminosity. In 2003 d-Au run, however, the bunch number had to be reduced from 110 to 55 [5]. In 2004 A...