09.12.2012 Views

Abstracts Brochure - CERN

Abstracts Brochure - CERN

Abstracts Brochure - CERN

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

MOPCH131<br />

MOPCH132<br />

MOPCH133<br />

26-Jun-06 16:00 - 18:00 MOPCH — Poster Session<br />

SNS Ring Commissioning Results<br />

M.A. Plum, A.V. Aleksandrov, S. Assadi, W. Blokland, I.E. Campisi,<br />

P. Chu, S.M. Cousineau, V.V. Danilov, C. Deibele, G.W. Dodson, J.<br />

Galambos, M. Giannella, S. Henderson, J.A. Holmes, D.-O. Jeon,<br />

S.-H. Kim, T.A. Pelaia, T.J. Shea, A.P. Shishlo, Y. Zhang (ORNL)<br />

86<br />

The Spallation Neutron Source (SNS) comprises<br />

a 1.5-MW, 60-Hz, 1-GeV linac, an accumulator<br />

ring, associated beam lines, and a<br />

spallation neutron target. Construction began<br />

in 1999 and the project is on track to be<br />

completed in June 2006. By September 2005<br />

the facility was commissioned up through the end of the superconducting linac, and in January 2006 commissioning<br />

began on the High Energy Beam Transport beam line, the accumulator ring, and the Ring to Target Beam Transport<br />

beam line up to the Extraction Beam Dump. In this paper we will discuss early results from ring commissioning<br />

including a comparison of achieved vs. design beam machine parameters and the maximum beam intensity achieved<br />

to date.<br />

Coupled Maps for Electron and Ion Clouds<br />

Contemporary electron cloud models and<br />

U. Iriso, S. Peggs (BNL)<br />

simulations reproduce second order phase<br />

transitions, in which electron clouds grow<br />

smoothly beyond a threshold from "off" to "on". In contrast, some locations in the Relativistic Heavy Ion Collider<br />

(RHIC) exhibit first order phase transition behaviour, in which electron cloud related outgassing rates turn "on" or<br />

"off" precipitously. This paper presents a global framework with a high level of abstraction in which additional<br />

physics can be introduced in order to reproduce first (and second) order phase transitions. It does so by introducing<br />

maps that model the bunch-to-bunch evolution of coupled electron and ion clouds. This results in simulations that<br />

run several orders of magnitude faster, reproduce first order phase transitions, and show hysteresis effects. Coupled<br />

maps also suggest that additional dynamical phases (like period doubling, or chaos) could be observed.<br />

An Analytic Calculation of the Electron Cloud Linear Map Coefficient<br />

The evolution of the electron density during<br />

U. Iriso, S. Peggs (BNL)<br />

multibunch electron cloud formation can often<br />

be reproduced using a bunch-to-bunch<br />

iterative map formalism. The coefficients that parameterize the map function are readily obtained by fitting to results<br />

from compute-intensive electron cloud simulations. This paper derives an analytic expression for the linear map<br />

coefficient that governs weak cloud behaviour from first principles. Good agreement is found when analytical results<br />

are compared with linear coefficient values obtained from numerical simulations. This analysis is useful in predicting<br />

thresholds beyond which electron cloud formation occurs, and thus in determining safety regions in parameter space<br />

where an accelerator can be operated without creating electron clouds. The formalism explicitly shows that the<br />

multipacting resonance condition is not a sine qua non for electron cloud formation.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!