Experimental observations of in situ secondary electron yield reduction in the PEP-II particle accelerator beam line

Abstract

Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron

Effect of the surface processing on the secondary electron yield of Al alloy samples

“…Where lower SEY are desired it seems that the only possibility to use Al vacuum chambers for accelerator rings is to coat the inner walls with a stable thin film of a low max material, suitable to hinder the interaction of the Al surface with the oxidizing species that inevitably develop during machine running. A similar strategy was also suggested by preliminary studies performed in the Positron low-energy ring of the PEP-II accelerator [8].…”

“…For other technical surfaces as TiN and Cu [6][7][8]12,13] it has been observed that electron conditioning reduces the high max values measured on the as-received samples to values of the order of 1.3 or even lower, and this behavior has been related to the desorption of contaminants as well as to the formation of a graphitic film upon the interaction of the electron beam with C containing surface adsorbates. For the PETRA III Al alloy sample, however, in spite of the large quantity of C at the surface, a similar growth of a graphitic layer has not been observed.…”

“…The estimation of such effects with the available EC simulation codes requires a clear determination of the secondary electron yield (SEY) of the chamber wall [5]. Furthermore it is crucial to investigate whether EC effects induce a conditioning of the accelerator environment, which changes the chemical state of the chamber surface and leads to a permanent lower SEY [6][7][8][9][10][11][12][13].…”

“…The investigations carried out so far on technical Al samples have emphasized the impossibility to obtain surfaces with a low SEY even after extensive conditioning [14,15], indicating the difficulty to modify in the desired direction the state of the Al surface via the impact of charged particles. On the other hand the large spread of the max values reported in the literature for different Al and Al alloys [6,8,[14][15][16] ( max being the maximum of the measured SEY curves) denotes the importance of the chemical state of the metal surface, but also to the properties of the specific alloy, in determining the secondary electron yield. This poses a crucial issue as the simulation codes developed to correctly analyze, predict, and possibly mitigate the EC-related unwanted effects for PETRA III necessitate, among other input parameters, a reliable max value.…”

DAΦNEOperation with Electron-Cloud-Clearing Electrodes

“…Various types of methods have been proposed, studied and experimentally verified in order to provide a solution to the e-cloud problems. There are two basic approaches for suppressing the ecloud effects: the first one is to modify the chamber surface properties thus reducing the Secondary Emission Yield (SEY) by the application of surface coatings [25][26][27][28][29][30][31][32][33] or by an artificial surface roughness, like grooves [32,[34][35][36][37]. Also the conditioning of the vacuum chamber surfaces by exposing it to synchrotron radiation or generated e-cloud (scrubbing) can partially reduce the SEY [30,33,38,39].…”