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Luminosity Tuning

Luminosity Tuning. Franz-Josef Decker 26-Oct-2006. Hints for tuning areas What tools are available besides tunes Examples for coupling and dispersion What is changing How to change a beta beat By 4 pattern tuning reveals coupling effect of parasitic crossing

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Luminosity Tuning

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  1. Luminosity Tuning Franz-Josef Decker 26-Oct-2006 • Hints for tuning areas • What tools are available besides tunes • Examples for coupling and dispersion • What is changing • How to change a beta beat • By 4 pattern tuning reveals coupling effect of parasitic crossing • Lifetime bumps [found due to trouble during wiggler experiment]

  2. We get hints from our “regular” characterization, where improvements might be helpful Fit with kick here

  3. Control system gives you 6*8*2 = 96 bumps

  4. Effects and uses of sextupole bumps [picture from SLC Final Focus paper] Anti-symmetric: (2 phases: ,’) In y: y-dispersion, fixes eta_y due to orbit variations In x: x-dispersion, used for LER x-emittance control Symmetric: (4 phases: xy, yx) In y: Coupling, SD: xy, SF: yx In x: Beta beat and (tune shift) SD for y, SF for x (only ONE phase per arc!) [two “canceling” sym x in SDs increases lifetime!]

  5. Symmetric y-bumps at SD2s (coupling): 50 m causes 2.5% less luminosity Howard Smith

  6. Anti-symmetric y-bumps (dispersion): 210 m causes 2.5% less luminosity Howard Smith

  7. Measured Luminosity Sensitivity Bumps necessary to reduce luminosity by 2.5 % ARC 11 ARC 05 Symmetric bumps 165 um 50 um 90 um 70 um (coupling) Anti-symmetric bumps 560 um 210 um 410 um 285 um (y-dispersion) Dispersion is about 4 times less sensitive than coupling, so it is better to use SYM and ASY knobs than individual sextupole bumps. Operators fine tune these to about half these offsets or 0.5% luminosity change

  8. Q2 chamber seen as Q4 raft motion causes luminosity dips up to half an hour after filling from scratch Q4R raft motions 25% Luminosity dips

  9. LER: Low current minus high current orbit difference Big kicks near septum (?) and at Q2 chamber. After new Q2 chamber HER injection was impossible without lowering septum bump. 20% of nominal

  10. Dispersion Bumps in Numbers • Correctors Dispersion for 1mm bump • Chicane: + –– + zero • 60 deg lattice: + – + 2 mm HER • 90 deg lattice: + + 4 mm LER • Double bump: + – 8 mm • ASYM SF1: 74 mm • ASYM SF2: 140 mm • ASYM SD1: 152 mm • ASYM SD2: 294 mm • 4-corrector: 7 mm • Septum-bump: 80 mm (for 12 mm bump) • (not compensated in design)

  11. How to change a beta beat Design • Find location with • clear max or min • at sextupole pair • (SF for x, SD for y) • 2. Sym. +x bump will • will make quad • stronger • Like IP with • dynamic beta • more focusing • reduces beta • Therefore move • to –x in this case • Depending on tune • amount is about • 1-2 mm for a beat • of 4 • 6. Fix tune change

  12. Luminosity Tuning for By 4 Pattern (no parasitic crossing) Parasitic crossing has HUGE coupling effect,: 550 um sym. y-bump necessary [(550/50)^2 * -2.5% = -300% ?] By 2 By 4 1 hr tuning

  13. Heating due to wiggler Here we have 2000 mA in LER and we need about a limit of 175 deg F to be able to go all the way to 3000 mA. Synchrotron light is linear.

  14. Wiggler bump (anti-symmetric in x) to reduce eta_x at wiggler to have mainly a damping wiggler (15% more damping  5% more luminosity) nux nuy beam lifetime 15% bump: -781E-6 0.0110 103 minutes 30% bump: -468E-5 0.0253 103 minutes 40% bump: -664E-5 0.0398 very low • Summary of Wiggler Experiment • The Bad: • Need to raise 150F limit to 175F for 3000 mA • LER x-emittance too big, low luminosity • Nu_y change not understood • Eta_x reducing wiggler bumps create VERY low lifetime • The Good: • Found quadrupole solution which directly reduces curly H • VERY low lifetime triggered search for cause and finally • found lifetime knobs.

  15. Lifetime Bumps Effects of x-bumps at FOUR sextupole pairs SD1 SD2 SD2 SD1  typical arc x x X X X X x x 180 90 180 90 180 90 180 Bump signs: + + y-beta beat and tune change – – + + y-beta beat only – – – – + + y-beta beat just in between big effect on lifetime! After bumps of -400 um and +200 um in three LER arcs: Less loss at septum: 120,000  20,000 [counts] More lifetime: 45  150 [min] Less DCH background: 1000  800 [counts]

  16. Wrong way LER beam loss monitor at septum reduced from 120,000 to 40,000 after first arc bumps. Reduced Drift Chamber background -12% and -8%

  17. Yuri Nosochkov showed, that the beta beat has a small effect while the created phase shift can cancel the third order chromaticity. Before (design) after bumps

  18. Summary • Tuning is still very necessary • We have knobs which control: • a) dispersion x and y • b) coupling xy, yx • c) beta beat in x and y • d) new: lifetime • e) Wx, Wy [G. Yocky’s talk] • 3. Often machine changes, like By4, MIA solutions, wiggler, etc • require big tuning efforts • 4. Many thanks especially to the newest operators, which push the • machine to higher luminosity peaks!

  19. Outlook More cross fertilization between tuning to modeling 1. Tuning  Modeling [tune shift, dynamic beta, coupling] not in model yet: a) beam-beam crossing at IP (partly done) b) beam-beam effect at parasitic crossing c) distributed tune shift due to elliptic chambervs local compensation d) higher order effects 2. Modeling  Tuning a) more tries to dial in dispersion or coupling solutions into machine b) localizing strong coupling changes by looking at “coupled phase”

  20. 69: PR06 1072 SD2 -2.1 mm+1.8kG 126: PR04 1022 SCX3 ? 133: PR02 4112 SCY3/SK6 ? 147: PR02 3149 SK4 +1.4 kG more 210: PR12 3092 SKG2 -1.6 kG

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