1 / 12

Beam-gas Background Signatures in BaBar / PEP-II

Beam-gas Background Signatures in BaBar / PEP-II. Introduction: bremsstrahlung e - trajectories The ‘background zone’ concept Validation of beam-gas background simulations. W. Kozanecki, CEA-Saclay. Dipole (or offset Q). QF. QD. Nominal e - trajectory (curvilinear coordinates).

gwatson
Download Presentation

Beam-gas Background Signatures in BaBar / PEP-II

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Beam-gas Background Signatures in BaBar / PEP-II • Introduction: bremsstrahlung e- trajectories • The ‘background zone’ concept • Validation of beam-gas background simulations W. Kozanecki, CEA-Saclay

  2. Dipole (or offset Q) QF QD Nominal e- trajectory (curvilinear coordinates) Vacuum pipe / mask apertures • Only those e- are shown that • scattered between –26m & –4 m of the IR • hit an aperture within +- 8.5 m of the IR IP Bremsstrahlung e- trajectories (x) in the HER (zscat > -26 m)

  3. Coulomb e- trajectories (y) in the HER (-1996< zscat < -66 m) IP IP

  4. Coulomb scattering in Arcs (y-plane) IP e-Brems-strahlung in last 26 m (x-plane) Vacuum pipe / mask apertures Spatial origin of beam-gas backgrounds in the HER Normalized to: - uniform pressure profile of 1 nT - 1 A beam current IP

  5. Background zones • “Zones” are empirically defined based on observation that lost particles from different regions have differing characteristics • Physically, their boundaries correspond to • the edges of beam-line regions with repetetive properties (e.g. arcs) • the location of a horizontal (HER & LER) or vertical (LER only) bending magnet (dipole or strongly offset quad) HER Zone Range (m) 0 -4, 4 1 -4, -26 2 -26, -42 3 -42, -66 4 -66, -2196 LER Zone Range (m) 0 -4, 4 1 4, 10 2 10, 21 3 21, 36 4 36, 62 5 62, 2196

  6. Zone 1 Zone 2 X (mm) X (mm) Zone 4 Zone 3 X (mm) IP The “Background Zones” reflect the combined effect of.... • beam-line geometry (e.g. bends) • optics at the source and at the detector • aperture restrictions, both distant(good!) & close-by (bad!) Bremmsstrahlung Bremmsstrahlung in field-free region Coulomb scattering in Arcs Bremmsstrahlung

  7. Vacuum gauge reading (nT) Abort diode signal (mR/s) Pressure-bump experiment: NEG heating in BaBar straight • Create localized P-bumps • NEG heating • DIPS on/off • Measure response of  background monitors • Compare relative measured & simulated monitor response to validate Monte Carlo Zone 3 (-40 m) Zone 1 (-8 m) • Different • regions • ==> • diff. patterns • diff. abs. levels

  8. This pressure model is (badly) out-of-date: • the incoming-HEB straight vacuum was significantly upgraded in 2001 (-30  -10 m) • it is now known that a large fraction of the pump reading is due to a photoelectron signal Understandingthe absolute level of HER backgrounds (Sep 99) • Compare measured & predicted dose rates in HER: • Monte Carlo lost-particle simulation (Turtle + BBSIM) validated by p-bump experiments • Computed pressure profile in detector straight section (N2-equivalent, not vacuum-gauge units!) • Average ring pressure (from lifetime) for arcs & distant straights

  9. This pressure model is (badly) out-of-date: • the incoming-HEB straight vacuum was significantly upgraded in 2001 (-30  -10 m) • it is now known that a large fraction of the pump reading is due to a photoelectron signal Understandingthe absolute level of HER backgrounds (Sep 99) • Compare measured & predicted dose rates in HER: • Monte Carlo lost-particle simulation (Turtle + BBSIM) validated by p-bump experiments • Computed pressure profile in detector straight section (N2-equivalent, not vacuum-gauge units!) • Average ring pressure (from lifetime) for arcs & distant straights A new pressure model, based on “as-built” pumping speeds & conductances, and on a refined analysis of pump readings, is under construction

  10. Conclusions • Beam-gas backgrounds exhibit specific spatial patterns, that • depend on where the scattering occurs • are different in the LER & the HER • Those patterns are predicted by simulations • they can be understood in terms of simple properties of the beam line • the predictions can be verified by • dedicated pressure bump experiments (SVT diodes, for HER) • comparison with background-characterization data (EMC, HER & LER; DCH?) • parasitic background monitoring (DIRC) • In particular, the dominance of beam-gas backgrounds in the horizontal plane of the SVT is well understood, both qualitatively & quantitatively • Recent progress in understanding – and remediating – the thermal outgassing problem, will be discussed by M. Sullivan in a future meeting.

  11. Spares

  12. LEB current (mA) Beam abort Neutral-dominated VP 3091 (nT) VP 3071 (nT) Electron-dominated How to separate a photoelectron signal fromgenuine gas pressure ?

More Related