Advanced Beam Emittance Measurement Techniques at CERN

1. “emittance” Extended Frank Zimmermann LTC – Chamonix@CERN Many thanks to: Ilya Agapov, Gianluigi Arduini, Ralph Assmann, Elena Benedetto, Enrico Bravin, Oliver Bruning, Helmut Burkhardt, Fritz Caspers, Bernd Dehning, Massimo Giovannozzi, Steve Hutchins, Rhodri Jones, Verena Kain, Thibaut Lefevre, Alick MacPherson, Laurette Ponce, Rogelio Tomas, Jan Uythoven

2. topics • transverse target emittance • measuring LHC beam emittances • transfer line to LHC matching • minimizing emittance blow up during injection, ramp, and squeeze • longitudinal emittance

3. transverse target emittance

4. LHC transverse emittance target: from SPS: ge=3.5 mmLHC at top energy: ge=3.75 mm→ total emittance growth allowed=7%possible sources of emittance growth:optical mismatch, dispersion mismatch, injection oscillations, p.c. decay & snapback, ramp, squeeze, beam-beam effects, wake fields, instabilities, damper noise, rf noise, damper noise, intrabeam scattering, residual-gas scattering, electron cloud,… require individual contributions < 2% (smaller than typical measurement resolution)

5. can we relax the LHC emittance tolerances during commissioning? No, LHC emittance targets cannot be relaxed, LHCCWG no.39 (M. Giovannozzi) but smaller emittances are available from the SPS!!

6. SPS emittance - dependence on #bunches & bunch intensity nominal 25-ns 25-ns 75-ns TOTEM 75-ns TOTEM pilot data from G. Arduini, LHC MAC 20, Dec. 2006

7. proposed strategy: blow up every beam to the design emittance of 3.5 micron in the SPS with “pink noise” injection into the transverse damper before extracting to the LHC if the additional LHC emittance increase is found to be too large, we can then reduce the TFB-noise blow up in the SPS until LHC target emittances are obtained

8. measuring LHC beam emittances

9. transverse beam-size diagnostics • 1-pass OTR screens for transfer lines & injection • OTR screen matching monitors • wire scanners • synchrotron light monitors • ionization profile monitor • collimator scans • Schottky monitors

10. transverse beam diagnostics in IR4 LHC Design Report & EDMS 599636 ~ 90 m ~ 150 m ~ 25 m OTR screen beam 1 gas monitor beam 1 SL monitor beam 2 wire scanner beam 2 OTR screen beam 2 gas monitor beam 2 SL monitor beam 1 wire scanner beam 1 calibration of SLM with wire scanner: short distance, no quadrupoles

11. OTR screens in LHC LHC Design Report dispersion > 1 m dispersion ~ 0 m beam intensity limits from screen damage (at 450 GeV)1.5x1014 protons x turns for Ti screens 1.5x1013 protons x turns for Al2O3 screens EDMS 821083

12. wire scanners (B. Dehning) beam intensity limits 450 GeV : 25 % of nominal limit for wire damage,                  quench level limit much higher 7 TeV: limited by both quench and damage of wire                 5 % of nominal for quench                 7 % of nominal for wire damage emittance increase due to single wire scan: SPS at 26 GeV: ~0.05 mm (14%) SPS at 450 GeV: negligible (a few 1e-5) (F. Roncarolo and B. Dehning, CERN-AB-2005-042 )

13. synchrotron light monitor available at all beam intensities switch from 5-T undulator radiation to D3 radiation at ~2 TeV full beam turn by turn fast camera for bunch-by-bunch measurements averaged over 20 ms (bunch-by-bunch turn-by-turn with intensifier, probably not in year 1) light optics slightly out of focus at injection set up for optimized performance at 7 TeV beam-size resolution < 10% at all conditions

14. expected SR image at 7 TeV: 5 pixels/s vertical , 8 pixels/s horizontal → emittance resolution from discretization <1% (Steve Hutchins)

15. ionization profile monitor requires pressure bump for proton pilot bunch if nominal vacuum, not in year 1 could we not perhaps inject an inert gas to improve signal while protecting the adjacent NEG chambers (as for LHCb)? main application for ion beams, s~Z2

16. beam size from scraping Tevatron example 11.17.2002 X.L. Zhang, V. Shiltsev, F. Zimmermann lost fraction of beam f vs.collimator position; fit gives the beam size at collimator and hence the emittance we here assumed a Gaussian distribution alternatively we can reconstruct the shape

17. LHC “collimator calibration” - + Scraper Collimator  Get beam offset from measured jaw positions x1 x2 Measure half gap  R. Assmann, LHCCWG no 5, May 2006

18. Local beta functions at collimators More difficult for skew collimators! Measure gap  beta beat Measure gap, emittance & normalized edge  absolute beta This feature is the result of: Having two opposite jaws: not possible for TEVATRON or RHIC! Direct measurement of gap with calibration during production! R. Assmann, LHCCWG no 5, May 2006

19. Schottky monitor antiprotons transverse emittance measurement with 1.7 GHz Schottky monitor at Tevatron; comparison with wire scans; at LHC 4.8 GHz Schottky pick-ups available in “BI Phase-II” protons A.Jansson, HHH-ABI Chamonix’07

20. beam size → emittance? • 3 nearby monitors → b, a, e • 5 nearby monitors w.intermediate bends→ b, a, e, D, D’ • 6 nearby monitors w.interm. bends→ b, a, e, D, D’, drms • [+ and x-y b ratio > 2 for coupling information; • e.g. fit 15 independent covariance matrix elements] • example: OTR screens in TLs and injection region • however, most monitors are single devices; then • - high-accuracyb function measurement (~1%) • at the profile monitors; 3 BPMs / monitor w/o quad • two nearby quadrupoles equipped with K modulation • “quadrupole” scan, i.e. measure beam sizes for • different quadrupole settings • beware: dynamic b beat tolerance ~8% for collimation

21. transfer line to LHC matching

22. emittance growth • - from injection oscillation • w. transverse damper • - from dispersion mismatch • from betatron mismatch • from geometric TL tilt & coupling De/e<2% → |Dx|<0.2 s (equal to required trajectory stability) De/e<2% → |Dx|<1.5 s (for DQtot~5x10-4, ndamp~50) De/e<2% → |DD|<20 cm & |DD’|<4 mrad (for Dp/prms~5x10-4) De/e<2% → Db/b<22% De/e~1%

23. transfer line matching – procedure use techniques from TT2/TT10, and TI2&TI8 commissioning suggested steps (G. Arduini): (1) dispersion matchingby changing the energy from SPS (2) optical parameters & emittances in transfer line (screens); screen measurements with single bunch (to avoid interference from bunch-to-bunch offsets) (3) if optics problem found, check orbit response(4) use LHC matching monitor(s)as final verification (5) monitorblow-up TL-ring & mismatch during running note: LHC optics must be known (and stable) ; in TI2/8 commissioning no need to correct (one exception)

24. distribution and number of monitors in each transfer line “triplet” “triplet” “triplet” J. Wenninger, EDMS 328136 3 emittance numbers along the line; 4-5% accuracy of beam-size measurement → expected emittance precision ~10%, relative precision ~5%

25. J. Uythoven LTC, 5.12.07 TI2 dispersion match

26. J. Uythoven LTC, 5.12.07 TI2 b off-line match

27. J. Uythoven LTC, 5.12.07 MAD-X matching tools in preparation (I. Agapov) TI2 on-line b match

28. TI2 Twiss measurements From: 19:12:28 to 19:28:43 (during dispersion measurements) Hx Hy PRELIMINARY RESULTS Elena Benedetto

29. J. Uythoven LTC, 5.12.07 TI2 corrector response measurements

30. (B. Goddard et al, PAC’05) we have ~5% right here, leaving ~2-3% for other effects

31. possible sources of injection errors • errors & changes can arise in SPS, LHC, or transfer line; • examples: • magnetic stray field at extraction • kicker ripple • transfer line optics errors (energy error, • misalignments, magnet calibration, ) • optics errors in the LHC • tune changes in the SPS or LHC • b* changes in IP2 or 8 at injection • changes of crossing angle / separation bump • configuration & spectrometer polarity changes (H. Burkhardt, Chamonix XIV)

32. A. Koschik et al, EPAC’06 • LHC aperture at injection is tight • transfer line optics strongly constrained by phase advance relations between transfer line collimator • 20% change in bcan change phase advance between TCDIs by 15o & reduce protected aperture by 10% (H. Burkhardt, Chamonix XIV) • dispersion matching on “cm” level using orbit bumps in the LHC not practical (A. Koschik et al, EPAC’06)

33. Matching monitor Expected resolution De/e ~1%!! EDMS 328146 One fast camera is available, which has to be positioned at the chosen matching screen. The camera is radiation sensitive and needs to be taken out of the tunnel after the measurements. From year 2, also SLM (& IPM) with fast camera & intensifier might detect mismatch (B. Dehning)

34. matching monitor test @ SPS turn-by-turn beam size measured & and expected from the optics parameters (dispersion and Twiss) observed in TT2-TT10 ~sin(4pqx) Hx~1.03 expected beam size computed assuming: • r.m.s momentum spread: dp/p=0.94 10-3 (→ measured in PS ) • r.m.s. normalized emittance (H&V) < 3mm (→ fitted from the first 3 turns measurements) fast decay!? no dispersion at this monitor Hy~1.00 PRELIMINARY RESULTS Elena Benedetto

35. matching monitor test @ SPS pixel offset problem still to be understood RAW data PRELIMINARY RESULTS Elena Benedetto

36. records on LHC matching monitor “For matching studies at injection a matching monitor is needed in each ring…” C. Fischer, EDMS 328147 (2003). LHC Design Report vol. 1, chapter 13.4.2 (2004). “… it is currently not foreseen to install the acquisition system and develop the necessary software for this monitor before Stage II.” (75 ns operation) R. Jones, Chamonix XV@Divonne (2006).

37. minimizing emittance blow up during injection, ramp, and squeeze

38. example emittance growth from Tevatron emittance growth of 12 antiproton bunches in first 10 minutes of store: 5-20% increase due to beam-beam, asymmetry so-called “scallops effect”; after 0.5-1 h the blow up flattens V. Shiltsev, EPAC’04

39. minimizing emittance blow up detecting such blow up needs cross-calibration of monitors (wire scanner – SR from undulator, wire scanner – SR from dipole, SR – collimator scans, SPS-LHC, etc.) tools for minimizing emittance growth: - transverse damper (on or off) • stabilization of orbit, tunes, coupling, chromaticity by feedbacks (tune kicker 1.6-0.4 s, excites ~1/12th of the ring → emittance growth 2% for 1-20 kicks) • standardized magnet cycles • optics studies & corrections, changes to tunes chromaticity etc.

40. Tevatron “calibration” example we tried to resolve factor >2 discrepancy between flying wires & SL monitor by scraping 11.17.2002 X.L. Zhang, V. Shiltsev, F. Zimmermann pbar horizontal and vertical 6s2 normalized emittances (in mm) prior to scraping, measured by three different methods. 2002 to 08 ~50 papers in FNAL DocDB on Synclite & calibration!

41. longitudinal emittance

42. longitudinal requirements at injection emittance must be small, <1 eVs, to fit within 400-MHz RF bucket at 7 TeV it should be increased to 2.5 eVs to reduce IBS effect, t~e/N, t||,nom~60 h emittance should grow like energy1/2 to avoid decrease in beam stability increase is accomplished by applying band-limited RF noise; procedure tested in SPS

43. J. Tuckmantel, Chamonix IX

44. SPS emittance - dependence on #bunches & bunch intensity nominal 25-ns, & 75-ns 25-ns 75-ns TOTEM TOTEM pilot data from G. Arduini, LHC MAC 20, Dec. 2006

45. longitudinal emittance diagnostics • wall-current monitor, 2.3 GHz • Schottky monitor • SL longitudinal-density monitor (year 2?)

46. records on longitudinal density monitor “The high sensitivity longitudinal profile monitor should provide as well the nominal bunch core parameters (bunch length and energy spread, density distribution and possibly longitudinal oscillations of the core). This information will be used for cross calibration of other devices like electro-magnetic detectors (faster but less accurate).” “This instruments profits from the Transv. Profile Monitor Light Source with the aim of using synchrotron light to measure bunch profiles with a dynamic range of 105, enabling measurements and monitoring of bunch lengths, …. An alternative system is to use an array of fast Single Photon detectors (SPD) … A decision for the best system for LHC will be made in 2004.” C. Fischer, EDMS 328145 (2003) LHC Design Report, vol. 1, 13.5 (2004) “The LDM collaboration with  Politecnico di Milan and Harriot-Watt should be pursued with the second highest priority.” 35th LTC, 8.12.2004

47. Schottky monitor momentum spread measurement with 1.7 GHz Schottky monitor at Tevatron; comparison with RW wide band pick up; at LHC 4.8 GHz Schottky pick-ups A.Jansson, HHH-ABI Chamonix’07

48. conclusions • nominalemittance targetsaretight, but growth tolerances can be relaxed for the commissioning by injecting beams withsmaller initial emittance from SPSif needed • many diagnostics toolsare available for cross checks and cross-calibration • based on experience so fartransfer lines should be stablewith residual unavoidable blow up < 5%; however,expected changes in b, D, & orbitmust be accommodated • correction may not be easy– neither in LHC nor in the transfer line • main uncertainty aresize & stability of optics errorsin the LHC (dynamic beta beat, spurious dispersion, local coupling,…) • for commissioning beams,longitudinal emittance budget looks tighterthan the transverse one

49. references • Y. Alexahin, “On the Emittance Growth due to Noise in Hadron Colliders and Methods of its Suppression,” NIM A, V. 391, 1, 73-76 (1997). • G. Arduini, “Mismatch Measurements,” Chamonix IX, 1999. • G. Arduini, “Status and Performance of the LHC (Proton) Injector Complex,” LHC MAC no. 20, December 2006 • G. Arduini et al., “Analysis and Measurement of Coupling Effects in the Transfer Line from PS to SPS for the LHC Proton Beam,” PAC 2001 Chicago. • E. Benedetto, “Optics Studies for the LHC Beam in the TT2-TT10 Line…”, APC 30.03.07 • E. Benedetto, “Optics Changes for Protons and Ions in TT2/TT10,” APC 18.01.2008 • A. Burns, “Beam Instrumentation,” Chamonix X, 2000. • H. Burkhardt, “Overview of the LHC Injection and Transfer Line Optics Configurations and Tolerances,” Chamonix XIV • H. Burkhardt et al, “Collimation in the Transfer Lines to the LHC,” PAC 2005 Knoxville. • A. Guerrero Ollacarizqueta,S. Hutchins, “SPS Matching Tests,” APC 09.02.2007 • A. Jansson, “Schottky Observations in the Tevatron,” CARE-HHH-ABI workshop Chamonix’07 • J. Uythoven, “TI2 Beam Test,” LTC 5 December 2007. • C. Fischer, “Functional Specification – High Sensitivity Measurement of the Longitudinal Distribution of the LHC Beams,” LHC-B-ES-0005.00 rev. 2.0 (2003). • C. Fischer et al., “Functional Specification – Measurement of the Transverse Distribution in the LHC Rings,” LHC-B-ES-0006 rev. 1.0 (2003). • B. Goddard et al., “Expected Emittance Growth and Beam Tail Repopulation from Errors at Injection into the LHC,” PAC2005 Knoxville (2005). • B. Goddard et al., “Functional Specification – Interlocking of LHC BTV Screens,” LHC-BTV-ES-0001 rev. 1.0 (2007). • K. Hanke, “Betatron Matching and Dispersion Matching,” Chamonix IX, 1999. • A. Koschik et al, “Optics Flexibility and Dispersion Matching at Injection into the LHC,” EPAC 2006. • O.R. Jones, “LHC Beam Instrumentation,” PAC07 Albuquerque 2007. • F. Roncarolo, B. Dehning, “Transverse Emittance Blow-Up due to the Operation of Wire Scanners…,” CERN-AB-2005-042 (2005). • E. Shaposhnikova, “Longitudinal Phenomena during the LHC Cycle,” Chamonix XI, 2001 • E. Shaposhnikova, “Longitudinal Stability of the LHC Beam in the SPS,” CERN SL-Note-2001-035 HRF, 2001. • V. Shiltsev, X.L.Zhang, F. Zimmermann, “Tevatron Study Report: Pbar Tunes & Pbar Removal 11/17/02, “CERN-AB-Note-2003-007 (MD) • V. Shiltsev, “Status of Tevatron Collider Run II and Novel Technologies for Luminosity Upgrades,” EPAC’04 Lucerne. • J. Tuckmantel, “The SPS/LHC Longitudinal Interface,” Chamonix IX, 1999. • J. Wenninger, “Functional Specification – Instrumentation for the Ti2 and Ti8 Transfer Lines,” LHC-B-ES-0004 rev.. 2.0 (2002). • “Engineering Change Order – Class 1: Layout of the Beam Instrumentation in LSS4 Left and Right,” LHC-L3-EC-0009 ver. 1.0 (2005). • LHC Design Report, Chapter 13