| Paper |
Title |
Page |
| MOPLT044 |
Longitudinal Positron Polarisation in HERA-II
|
644 |
| |
- E. Gianfelice-Wendt, D.P. Barber, F. Brinker, W. Decking, J. Keil, M. Vogt, F.J. Willeke
DESY, Hamburg
|
|
| |
Following the installation of two more pairs of spin rotators in the course of the HERA Luminosity Upgrade, longitudinal positron spin polarisation has now been generated simultaneously at all three positron(electron) interaction points in HERA at the routine energy of 27.5 GeV. The maximum attained so far is 54 percent. The theoretical maximum for this configuration and in the presence of realistic errors is 57.0 percent. This is the first time in the history of high energy electron storage ring physics that the naturally occurring vertical polarisation has been, with the aid of spin rotators, converted to longitudinal polarisation at three interaction points simultaneously. We describe the measures needed to attain polarisation in light of the HERA Upgrade and the resulting recent performance.
|
|
| MOPLT046 |
Overcoming Performance Limitations due to Synchrobetatron Resonances in the HERA Electron Ring
|
650 |
| |
- F.J. Willeke
DESY, Hamburg
|
|
| |
The HERA Electron Ring was suffering from strong synchrobetatron resonances which have been particularly detrimental after the HERA luminosity upgrade because of a reduced sychrotron tune due to stronger transverse focusing and a shift in the damping distribution in favor of transverse damping. It turned out to be most difficult to store a beam at the preferred working point for high electron spin polarization between the 2nd and the 3rd synchro-betatron satellite of the horizontal integer resonance. A comparative study of the resonance strength did not reveal any significant additional disadvantage of the new beam optics. However, a mechanism driven by closed orbit distortions was discovered which can increase the width of the resonance Qx+2Qs=0 by a large factor. This explains the operational difficulties. The remedy against this effect is quite straight forward. The Fourier component of the closed orbit near the horizontal tune must be avoided. This is enforced in HERA operations by rigerous orbit corrections and an orbit feedback system which reproduces well-corrected orbits reliably. Synchrobetatron resonances do not constitute a performance limitation of polarized lepton proton collisions in HERA any more.
|
|
| THPLT045 |
A more Accurate Approach to Calculating Proton Bunch Evolution under Influence of Intra-beam Scattering in a Storage Ring.
|
2580 |
| |
- I.V. Agapov, F.J. Willeke
DESY, Hamburg
|
|
| |
Some perturbations of discrete nature are known to influence the performance of a proton storage ring, contributing to parasitic background, decay of beam currents and bunch tail buildup. Such are, for example, intra-beam scattering and residual gas scattering .These processes are to a big extent described by existing analytical theory. The latter, employing a large amount of averaging, usually neglects effects arising from system nonlinearity. So, the motion of tail particles in the presence of a sufficiently nonlinear RF voltage under influence of intra-beam scattering strongly deviates from the average across the bunch and the analytical approach seems inadequate for it. To overcome this situation we have developed more accurate numerical methods for calculations of bunch evolution under influence of a rather broad class of jump-like perturbations. Here we present the computational algorithms and their application to assessment of coasting beam and proton background in HERA-p.
|
|