1. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA Linear Collider Luminosity Related Issues Nick Walker (DESY)

2. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Content Luminosity Issues –oft quoted advantages of s.c. RF in a nutshell Main linac dynamics –emittance tuning Bunch Compressor Undulator-Based Positron Source Damping Ring –many critical issues Beam Delivery System –head-on collision scheme –machine (collimator) protection philosophy Luminosity Stabilisation & Feedback

3. Nick Walker DESYITRP Meeting - RAL - 28.02.04 The Luminosity Issue

4. Nick Walker DESYITRP Meeting - RAL - 28.02.04 The Luminosity Issue Low repetition rate: 5 Hz limited by cryogenics power impact on ground motion stabilisation (feedback)

5. Nick Walker DESYITRP Meeting - RAL - 28.02.04 The Luminosity Issue Compensated by long bunch train: n b = 2800 – fast intra-train orbit stabilisation (feedback) High bunch charge: N = 2×10 10

6. Nick Walker DESYITRP Meeting - RAL - 28.02.04 The Luminosity Issue Emittance Preservation: low wakefields (low frequency) relatively loose tolerances

7. Nick Walker DESYITRP Meeting - RAL - 28.02.04 10  6 10  5 10  4 10  3 Ratio of deflecting wakefield to accelerating field for 1mm offset Wakefields (alignment tolerances) Transverse Wakefield Kick  f 3 TESLA C-band X-band CLIC

8. Nick Walker DESYITRP Meeting - RAL - 28.02.04 The Luminosity Issue High Beam-Beam Disruption (Enhancement) factor ~2 for luminosity collision is unstable (kink instability) tighter tolerance on emittance dilution banana effect

9. Nick Walker DESYITRP Meeting - RAL - 28.02.04 500 GeV C.M. Parameters

10. Nick Walker DESYITRP Meeting - RAL - 28.02.04 the TESLA TDR linear collider ML dynamics Damping Ring Sources (e + ) Beam Delivery & IR Luminosity Issues:

11. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA Linac Beam Dynamics Emittance Preservation Alignment tolerances Beam based alignment

12. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA Long Range Wakes All modes damped below 1  10 5 36 cavity average, 0.1% frequency spread 337 ns bunch spacing Random detuning HOM absorbers

13. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA Long Range Wakes bunch number vertical offset (  m) Effect of 1  y oscillation along linac Pattern remains the same (difference at nm level) Result of loose tolerances (cavity offsets) Static part (almost all) can be fixed with feed forward

14. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Single Bunch Wakefields z (  m) V/pC/m Accurate calculation of single-bunch transverse wakefield 30% less transverse kick than previous TDR estimate. I. Zagorodnov, T. Weiland (2003)

15. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Assumed Alignment Errors quad offsets:300  m cavity offsets:300  m cavity tilts:300  rad BPM offsets:200  m CM offsets:200  m BPM resolution:10  m wrt CM axis single-shot these values have been used in simulations of linac tuning

16. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Dispersion Free Steering The effect of upstream beam jitter on DFS simulations for the TESLA linac. 1  y initial jitter 10  m BPM noise average over 100 random machines TDR budget uncorrected cavity tilts cause problems for TESLA

17. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Ballistic Alignment Less sensitive to model errors beam jitter average over 100 seeds systematically turn off sections of linac Use ‘ballistic beam’ to define (straight) reference line.

18. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Ballistic Alignment Less sensitive to model errors beam jitter average over 100 seeds systematically turn off sections of linac Use ‘ballistic beam’ to define (straight) reference line. 3% Energy Spread from Bunch Compressor

19. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Ballistic Alignment We can tune out linear and correlation using bumps or dispersion correction in BDS average over 100 seeds

20. Nick Walker DESYITRP Meeting - RAL - 28.02.04 100 Random Machines dispersion corrected 94% 85%

21. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Ballistic Alignment TO DO Control of Ballistic Beam –Show that ‘fat’ ballistic beam can be safely transported through linac Large cavity irises (Ø70mm) a benefit Study additional potential problems –stray magnetic fields etc. Confident we can achieve desired budget

22. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Other Sub-Systems Spin Rotation / Bunch Compression Source –‘dog bone’ damping ring –undulator-driven positron source Beam Delivery System critical TESLA systems

23. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TDR Bunch Compressor Compression factor of 20 in single stage  z = 6 mm  300  m  rms = 1.3‰  3% RF (4 cryomodules) with V pk ~1 GeV,  = -155°   V = -423 MV Wiggler section (~100 m) to generate required R 56 Problems: –Cavity Tilts in Module (see later) –Large 3%  P/P –Tuning!

24. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TDR Ring-to-Linac (RTL) Spin Rotator Bunch Compressor Diag- nostics (emittance measurement) RFwiggler

25. Nick Walker DESYITRP Meeting - RAL - 28.02.04 BC Cavity Tilts Slope of tilted RF results in correlated z-y kick along long bunch (  z = 6 mm) 300  rad RMS tilts gives average of  y ~140% for TDR design!

26. Nick Walker DESYITRP Meeting - RAL - 28.02.04 BC Cavity Tilts cavity tilt kick acceleration (along bunch) Resulting correlation (dispersion)

27. Nick Walker DESYITRP Meeting - RAL - 28.02.04 BC Cavity Tilts Results of tracking simulations. Emittance estimated at exit of RF section Emittance after removing  correlation [best you can achieve] mean: 138% mean: 2% different scale! 1000 random seeds

28. Nick Walker DESYITRP Meeting - RAL - 28.02.04 RTL Emittance Dilution Tuning ‘dispersion’ (bunch tilt) out downstream –requires tuning knobs (bumps) –emphasis on emittance measurement final achievable emittance set by resolution (10% ?) Re-think of design –stronger focusing in RF section (smaller  ) –possible two-stage compression system No  budget in TDR –assumed  = 0

29. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA TDR Positron Source Photons (~20 MeV  ) produced by high energy electron beam in undulator placed at exit of e  linac (upstream of BDS and IR) Thin target (0.4X 0 ) converts the  to e + e  pairs

30. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TDR e + Source Parameters SLCTESLA e+/pulse(3-5)×10 10 5.6×10 13 bunches/pulse12820 pulse duration3 ps0.95 ms bunch spacing8.3 ms337 ns rep. frequency120 Hz5 Hz

31. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TDR e + Source Parameters undulator length135 m (TDR: 100m) av. photon power135 kW av. deposited target power5 kW photon beam size on target0.7 mm capture efficiency16% e + / e  ~2 see damping ring

32. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Advantages significantly reduced power deposition in thin target (~5 kW) smaller emittance beam produced –less multiple coulomb scattering –reduced acceptance requirements for DR no pre-DR foreseen much cheaper / less complex than equivalent ‘conventional source’ for TESLA –if conventional source is even possible! Naturally allows upgrade to polarised e + source

33. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Disadvantages Requires e-linac with  150 GeV –TDR solution to use main e- linac –coupling e- to e+ production raises questions of operability reliability commissioning strategy Never been done before –although physics is well understood! –E166 experiment at SLAC can be mitigated through R&D no real show stoppers

34. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA Damping Ring TESLA bunch train 2820 × 337 ns = 950  s  285 km long Extract every bunch separately, bunch spacing given by shortest kicker rise/fall time  20 ns × 2820  56  s  17 km long Save tunnel cost: DR in main linac tunnel and short return arcs  dogbone

35. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Dogbone DR Concept  B 2 dl= 605 T 2 m Permanent Magnet Wiggler with B max = 1.6 T, =0.4 m Radiated Power (160 mA) over 450 m : 3 MW Need ~450m of wiggler to achieve required damping time (28 msec)

36. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TESLA DR Parameters e+e+ ee Injected RMS Emittance 0.01 m4×10 -5 m Ejected Emittance hor / ver8×10 -6 m / 2×10 -8 m Injected Energy Spread0.5 % Ejected Bunch Length6 mm Damping Time28 msec44 msec Number of Bunches2820 Ejected Bunch Spacing337 ns Particles per Bunch2×10 10

37. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Wiggler

38. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Space Charge Tune Shift Unusually large circumference / energy ratio –final emittance is space-charge limited! –Quantitive effect on steady-state  y unknown, but probably >factor 2 increase. Solutions: –Increase energy difficult lattice in arc more RF needed cost optimum turns out to be at 4-5 GeV –increase transverse beam size in long straight sections through local x-y coupling radical! –multiple ring designs (cost!)

39. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Kicker Requirements 337 ns 40 ns 0.6 mrad ±0.05% 0.01 Tm Ripple: 0.05% 2820 pulses with 3 MHz repetition rate 5 Hz repetition rate of macro-pulse

40. Nick Walker DESYITRP Meeting - RAL - 28.02.04 RF Kicker RF kicker system –Delahaye 93 –Koshkarev 95 –Gollin et al. 2002 –INFN-LNF 2003 With enough harmonics very sharp pulse possible No flexibiliy for different bunch distances

41. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Stripline Kicker Stripline Kicker (1996) C-Yoke Kicker (2000-.....) Kicker technology available Main Challenge: Pulser –IGBT Transformer Switch –MOSFET Stacks ongoing R&D (XFEL needs fast kickers too!)

42. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TTF Measurements Frank Obier (DESY), Guido Blokesch (IPP) averaged over 50 pulses / point

43. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Dynamic Aperture Large average injected beam power –224 kW Wiggler dominated dynamics leads to too small (dynamic) aperture for e+ ring: –acceptance approx. factor 2 too small –culprit: wiggler non-linearities Needs additional study –R&D on wiggler to reduce non-linearities –introduction of octupoles into lattice Do have factor 2 safety margin in e+ production –requires careful collimation in DR transfer line to reduce losses in ring

44. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Emittance Control BPM and H+V steerer at each quadrupole (800) Skew windings on every sextupole (300) Combined orbit and dispersion correction with steerer Skew correction linear response approach

45. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Emittance Control horizontalvertical Quadrupole00.1 mm Sextupole00.1 mm BPM resolution0 1  m BPM (relative to quadrupole)00.1 mm Simulated alignment errors BPM resolution critical for required level of dispersion control for all LC DR

46. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Emittance Control (simulation) goal Simulation of vertical emittance after application of orbit tuning algorithm 100 random alignment seeds 88% of machines below achieved <14 nm (goal) space-charge coupling bumps not included (vertical correction only).

47. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Emittance Stability Quadrupole vibration of 350 nm (RMS) gives 10% increase in emittance Slow drifts [based on ATL model] indicate the following corrections will be needed: –closed-orbit correction every 2 minutes –dispersion correction every 11 hours

48. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Collective Effects IBS no issue because of high energy Coupled Bunch –HOM‘s suppresed by SC cavities –resistive wall damped with feedback –ion trapping requires P  1×10 -10 mbar in straight sections (nb: no synch. rad.) – more studies needed for fast beam ion instability (common problem) – e-cloud seems OK because of bunch distance [input from LHC] e+/e- e- e+ e+/e-

49. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Stray Field Problems Time varying stray fields at beginning of linac beam pulse from Klystron turn-on Measured to be > 1  T Effect checked by simulating 5  T m at each klystron position (every 48 m)

50. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Stray Field Problems Leads to variation of closed orbit –dispersion at extraction Blow-up of projected emittance Fast correction needed: –dispersion correction (difficult) –fast turn-by-turn distributed orbit feedback [accuracy 75 mm RMS]

51. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam Delivery System Issues To large extent linac techology independent Two possible areas of difference: –possibility of a head-on collision –spoiler protection philosophy

52. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Head-On Collision Large bunch spacing (337ns) puts first parasitic crossing at 50 m from IP –outside of physics detector –allows for a head-on collision arrangement Head-on scheme does not require ‘compact final quadrupole’ –relatively large aperture s.c. magnet based on LHC can be used Some potential benefit for physics –small angle tagging etc. (still under discussion) or: “too cross, or not too cross: that is the question”

53. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Head-on collision pros –no crab-crossing cavities required –no tilted solenoid field –no need for compact final quad solution compact s.c. design from BNL looks very promising! –low angle physics contentious –comparatively cheap single tunnel – no separation shafts

54. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Head-on collision cons –extraction system complex requires electrostatic separators and a septum magnet (reliability/operability?) –masking and collimation difficult beamstrahlung stay-clear difficult current TDR solution does not work! –difficult to optimise extraction line for diagnostic use All said: TESLA does have the choice! solutions under consideration

55. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Machine Protection long bunch train + large bunch spacing allows to abort pulse within the train –fast kickers can extract beam to the dump in the case of a fault –beam can be ‘turned off’ at the DR from BDS approx. 200/2820 bunch delay

56. Nick Walker DESYITRP Meeting - RAL - 28.02.04 TDR BDS Layout

57. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Fast Extraction can achieve ‘single bunch delay’

58. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Luminosity Stability Ground motion –vibration; slow drifts Fast Intra-Train Feedback –beam-beam collision feedback Effect of slow drifts –Importance of orbit control (BDS: critical) High-Disruption Regime –beam-beam kink instability makes TESLA ‘sensitive’

59. Nick Walker DESYITRP Meeting - RAL - 28.02.04 IP Fast (orbit) Feedback Beam-beam kick Long bunch train: 2820 bunches t b = 337 ns

60. Nick Walker DESYITRP Meeting - RAL - 28.02.04 IP Fast (orbit) Feedback Systems successfully tested at TTF Simulation of system with realistic errors

61. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Long Term Stability 10 days 1 hour 1 day 1 second

62. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Long Term Stability 10 days 1 hour 1 day 1 second No Feedback

63. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Long Term Stability 10 days 1 hour 1 day 1 second With Fast Beam-Beam Feedback

64. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Long Term Stability 10 days 1 hour 1 day 1 second With FBBF and (slower) BDS orbit correction

65. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam-Beam Issues: Bananas TESLA: high disruption regime: long. correlated emittance growth causes excessive luminosity loss (‘banana’ effect) Brinkmann, Napoly, Schulte, TESLA-01-16

66. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam-Beam Issues TESLA luminosity as a function of linac emittance growth D. Schulte. PAC03, RPAB004 Note:  y will contain a correlated component due to wakefields

67. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam-Beam Issues Rigid bunch approximation D. Schulte. PAC03, RPAB004

68. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam-Beam Issues GUINEAPIG result ‘banana effect’ Now optimise (scan) collision offset and angle (collision feedback) D. Schulte. PAC03, RPAB004

69. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam-Beam Issues optimise beam-beam offset D. Schulte. PAC03, RPAB004

70. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Beam-Beam Issues optimise beam-beam offset and angle OK for ‘static’ effect dynamic effects still a problem D. Schulte. PAC03, RPAB004

71. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Simulating the Dynamic Effect Realistic simulated ‘bunches’ at IP linac (PLACET, D.Schulte) BDS (MERLIN, N. Walker) IP (GUINEAPIG, D. Schulte) FFBK (SIMULINK, G. White) bunch trains simulated with realistic errors, including ground motion and vibration Luminosity assumed measured by fast lumi (e+e- pair) monitor LINACBDSIRBDSIR IP FFBK

72. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Simulating the Dynamic Effect IP beam angleIP beam offset intra-train fast feedback scans angle/offset at IP to optimise luminosity

73. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Simulating the Dynamic Effect 2  10 34 cm  2 s  1 (one seed) currently studying cause of 30% reduction room for improvement (additional key feedbacks)

74. Nick Walker DESYITRP Meeting - RAL - 28.02.04 Last Word LINAC technology is mature and [we believe] ready to go (cf. talk by RB) TESLA’s ‘?’ lie mostly in the other critical sub-systems: –dogbone DR –e+ source –bunch compressor No show stoppers International Design Team effort