Recent Tevatron Operations

1. Implementing new sextupoles Issues along the way Orbit smoothing Pbars at 150 GeV Losses in squeeze Peak vs integrated luminosity Recent Tevatron Operations Ron Moore Fermilab – Tevatron Dept.

2. Chromaticity Correction Sextupoles • Correct 2nd order tune and β-function chromatic effects • Simulations show improved lifetimes (see previous talk by A. Valishev) • Plan – split off ¼ existing sextupole SF/SD elements for use in new circuits • Pull new cables (last long shutdown) • Run new circuits as “normal” chromaticity elements w/ new supplies (Feb 07) • New power supplies operate just fine – no failures • Turn OFF new circuits – necessary for injection, ramp, squeeze (early May) • Did major orbit smoothing as well (necessary, but added complications) • First HEP store in this configuration - # 5409 on May 3 • Difficult 2 weeks of running as we tuned up (limited proton intensities) • Accesses to change polarities of some of the new elements (May) • Necessary for low-β – that’s why we wanted to do previous step first • Studies for running new circuits @ low-β • Implement new circuits for HEP – first store # 5480 on June 7 • Ongoing evaluations and tweaks to improve performance We knew this would be tough R. Moore - FNAL

3. Why smooth orbits? • 150 GeV central orbit • Up to 4 mm offsets! • Not good • Turning off sextupoles gives up to 0.5 mm offsets • Motivates the big smooth R. Moore - FNAL

4. Issues @ 150 GeV After Turning OFF New Sextupoles • Losses at 150 GeV and early in ramp • Proton losses high enough to cause quenches • Requested smaller proton intensities for 1 week • Lifetimes were worse, too • New injection helix for 150 GeV and early in ramp • Improve losses and lifetimes – more separation / reduce beam-beam • Separation @ 150 GeV limited by aperture • Needed orbit bumps @ C49 to increase aperture for beams • Pbar emittance growth @ injection • Reduced peak luminosity • Found vertical tune too high → lowering solved problem R. Moore - FNAL

5. Turn off new sextupoles + orbit smoothing Lower pbar vert tune New helix + orbit bumps R. Moore - FNAL

6. Pbar Emittances @ Injection J. Annala R. Moore - FNAL

7. Losses during Squeeze • Proton loss is driven by beam-beam effects • Depends on pbar intensity and emittance • Higher brightness = intensity/emittance  more proton loss • Becoming more problematic with higher pbar intensities • Orbit changes were big impact • Where the lost beam lands can be problem • Loss spikes or integrated dose @ CDF or D0 • Quenches (like those @ D11 recently @ LBSEQ 17) • Chasing losses around with orbit bumps • e.g., decrease losses at D0, increase @ D11, CDF R. Moore - FNAL

8. Proton Losses Increase with Pbar Intensity R. Moore - FNAL

9. Store 5426 – before D0 horz angle changes early in squeeze Low-β LBSEQ A49H Sep [kV] Proton Intensity [109] LBSEQ 17 Init Collisions High D0 losses D0 BLM [Rad/s] CDF BLM [Rad/s] R. Moore - FNAL

10. Store 5450 – after D0 horz angle change early in squeeze Low-β LBSEQ A49H Sep [kV] LBSEQ 17 Proton Intensity [109] Init Collisions Higher CDF losses D0 BLM [Rad/s] CDF BLM [Rad/s] R. Moore - FNAL

11. Losses @ LBSEQ 17 • Proton losses at LBSEQ 17 is not a new feature • Longstanding pain from beam-beam effects • Horz separation minimal during switch from injection to collision helix • B17 horz separator goes to 0, switches polarity • Was requirement to get pbars on correct side for Roman pots • Depends on pbar intensity and emittance • Higher brightness = intensity/emittance  more proton loss • After solving pbar emittance growth at injection, saw high losses and 2 quenches @ D11 @ LBSEQ 17 • Requested reduced pbar intensity during investigation (~1 week) • Vertical angle bumps @ D0 helped reduce beam lost @ D11 • Lowered chromaticities, too • Ready to step up pbar intensities again • Still keeping an eye on losses • Could also try developing new helix, if needed R. Moore - FNAL

12. D11 Losses @ LBSEQ 17 Before bumps LBSEQ 17 [Rad/s] After bumps R. Moore - FNAL

13. Fixing LBSEQ 17 Once and For All (?) • Want to eliminate the source of beam loss → maintain larger beam separation • Flip horz helix in “short arc” to eliminate B17H separator polarity change • Protons and pbars swap horz orbit positions for HEP • B11H, B17H and C49H separators run in opposite polarities • Need extensive conditioning period → end of long shutdown • No collimators to flip in short arc R. Moore - FNAL

14. End of Squeeze • Transition from LBSEQ 24→25 (low-β) • New sextupoles come on + other associated changes (tunes, etc.) • Pbar loss and likely emittance growth • Coupling on pbar helix is large ~0.01 • Difficult to keep tunes away from resonances • Still a work in progress… • Orbit bumps can’t be explored fully since the IP positions / angles are constrained by experiments for low-β / collisions R. Moore - FNAL

15. Pbars at End of Squeeze – Shot 5542 New sextupoles turning on Low-β LBSEQ A49H Sep [kV] Proton Intensity [109] Poor pbar lifetime Pbar Intensity [109] Init Collisions D0 BLM [Rad/s] CDF BLM [Rad/s] R. Moore - FNAL

16. D0 Low-β Quad Motion • This interesting topic is a separate talk in its own right • Air flow / thermal gradients between Tev tunnel and collision hall causing support girder to twist, flex (?) • ~μm/~μradchanges in quads lead to ~mm changes in arcs • Recent hotter weather has led to more motion that causes significant orbit changes from shot to shot • Complicates investigation of losses & orbits in squeeze • Makes orbit smoothing difficult when quads move during shot-setup • Larger than desired D0 horz IP changes during HEP • Lattice measurements on Thursday needs to be repeated due to orbit changes over the few hour study rendered data useless • AD & D0 working together to develop new ideas to reduce motion R. Moore - FNAL

17. D0 Low-β Quad Motion D0 Lumi [μb-1/s] D1Q3 Roll [μrad] HC49 current [amps] D0 horz IP offset [μm] Temperature [deg F] R. Moore - FNAL

18. Chromaticities @ Low-β • Without new circuits Fit to parabola… Significantly non-linear Tune vs Frequency (Momentum) Offset • With new circuits • Much more linear! • Correct chromaticity as intended May 26 study R. Moore - FNAL

19. Evaluating New Sextupoles R. Moore - FNAL

20. Peak vs Integrated Luminosity • Peak luminosity is a sexy number... • …but integrated luminosity on tape is where the physics is • Yes, peak lumi is down from our record running in Jan/Feb • Let’s look further… R. Moore - FNAL

21. Sextupole work J. Crawford’s spreadsheet R. Moore - FNAL

22. J. Crawford’s spreadsheet R. Moore - FNAL

23. Average lumi @ recent peak lumi is as good or better! J. Crawford’s spreadsheet R. Moore - FNAL

24. To-Do List Before Shutdown • Understand effect on new sextupoles during HEP • More precise lattice measurements @ low-β • 2-3 hours proton-only differential orbit measurements • Tried once, need to be repeated… • Identify need for corrections, way to correct coupling on pbar helix • Pbar-only store to gather data for collision helix closure • Just a single transfer • Better than using protons and putting separators in opposite polarity • Higher risk of sparking on subsequent HEP stores and causing quench R. Moore - FNAL

25. Summary • Implementing 2nd order chromaticity correction sextupoles has been long • New circuits turned off and orbits smoothed in early May (#5409) • New sextupoles ON at low-β only since early June (#5480) • Needed orbit smoothing has had big impact on operations, too • Attacked various problems with additional orbit bumps • Losses at 150 GeV and early in ramp • Losses during squeeze, especially LBSEQ 17 • Complicated by recent weather exacerbating D0 low- β quad motion • Peak luminosity has been down, but integrating OK • Average luminosity for recent peak lumi is as good or up to 25% better! • New sextupoles correct chromaticity as desired, but still working on other lattice corrections to improve performance • Need to fix large coupling on pbar helix R. Moore - FNAL

26. Orbit Effect from Turning Off New Sextupoles • 150 GeV on 2/21 • Before smoothing central orbit to 0 R. Moore - FNAL

27. R. Moore - FNAL