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1 House, Apr 25, 2004 Accelerator Physics from the Tevatron to the LHC Steve Peggs, BNL - How to increase the luminosity - Beam-Beam.

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Presentation on theme: "1 House, Apr 25, 2004 Accelerator Physics from the Tevatron to the LHC Steve Peggs, BNL - How to increase the luminosity - Beam-Beam."— Presentation transcript:

1 1 House, Apr 25, 2004 Accelerator Physics from the Tevatron to the LHC Steve Peggs, BNL - How to increase the luminosity - Beam-Beam interactions nonlinear dynamics - Energy stored in the beam 350 MJ materials testing? - “Snap-back” effect superconducting magnet physics - Summary

2 2 House, Apr 25, 2004 US-LHC Accelerator Research Program LARP is BNL, FNAL, LBNL, & SLAC ~ $10m/yr by FY06 Goals - more luminosity, earlier - interaction region (luminosity) upgrade - use and enhance unique US capabilities

3 3 House, Apr 25, 2004 How to increase Luminosity

4 4 House, Apr 25, 2004 How to make Luminosity Collision frequency Protons/bunch in beams 1 & 2 Beam size (round) Number of bunches Beam-beam parameters Angular beam size Engineering Physics

5 5 House, Apr 25, 2004 Interaction Region optics - a nonlinear problem in quad gradients and lengths - “pole tip” field has a maximum - larger radius magnets are weaker and further away - result: angular aperture and are constrained !

6 6 House, Apr 25, 2004 Lose the anti-protons: - use 2-in-1 magnets to avoid long range Beam-Beam - put in LOTS of bunches - worry about the stored energy

7 7 House, Apr 25, 2004 Beam-Beam Interactions

8 8 House, Apr 25, 2004   r  Nonlinear dynamics A test particle in bunch 1 is deflected transversely by the nonlinear electro-magnetic fields of bunch 2 - (and vice versa) - “collision” can be HEAD-ON (in an experiment) - or LONG RANGE (eg in Tevatron arcs)

9 9 House, Apr 25, 2004 Tevatron dipole cross-section Protons and anti-protons follow helically intertwined closed orbits around most of the Tevatron

10 10 House, Apr 25, 2004 Beam-beam tune shifts TUNE - a test particle oscillates about its closed orbit - its displacement on INTEGER turn number t is where Q is the “betatron tune” HEAD-ON TUNE SHIFT - a small amplitude test particle in beam 1 is shifted in tune by from a single HEAD-ON beam-beam collision

11 11 House, Apr 25, 2004 LONG RANGE TUNE SHIFT - if the closed orbits have a big separation then a test particle is shifted in tune by Tevatron TOTAL TUNE SHIFT - with 2 head-on and 70 long range collisions, and - typical helix separation of 6 sigma You can't put 3,600 bunches in the Tevatron !

12 12 House, Apr 25, 2004 Who's afraid of a large tune shift? Fear the resonance “bed of nails”! (How long are they?)

13 13 House, Apr 25, 2004 Energy stored in the beam

14 14 House, Apr 25, 2004 How much is 350 MJoules? Kinetic energy - 1 small aircaft carrier of 10 4 tonnes going 30 kph automobiles of 2 tonnes going 100 kph Chemical energy - 80 kg of TNT - 70 kg of (swiss?) chocolate Thermal energy - melt 500 kg of copper - raise 1 cubic meter of water 85 C: “a tonne of tea” (Suggesting that “physical intuition” is tuned to instantaneous power?)

15 15 House, Apr 25, 2004 LHC collimation scheme Primary collimators scrape the beam “halo” Secondaries scrape particles scattered by primaries Protection devices act as a last resort - fuses Consider the size of Spain on a 1 Euro piece...

16 16 House, Apr 25, 2004 Tevatron: < 1 MJ is bad enough!

17 17 House, Apr 25, 2004 Hole drilled through primary collimator

18 18 House, Apr 25, 2004 Severely damaged secondary collimator

19 19 House, Apr 25, 2004 Should NOT look like Baked Alaska

20 20 House, Apr 25, 2004 Quenches Superconducting magnets can QUENCH: - a small amount of local energy (eg particles) turns SUPER conductor into NORMAL conductor... - resistively generating more heat, etc, etc, - magnet is not (usually) destroyed, but.. - quenches recovery takes many hours LHC at 450 GeV (injection) - a FAST loss of of the beam quenches a magnet - Tevatron, RHIC, HERA lose a “few %” of the beam as acceleration begins – but “not so fast”? LHC at 7 TeV (store) - a FAST loss of of the beam quenches a magnet

21 21 House, Apr 25, 2004 “The complexity of the system is also worrying for (the) operations (group)” with more than 100 jaws to adjust:

22 22 House, Apr 25, 2004 Control system challenge Accelerator control systems thrive in the face of complexity But the physical system to control (eg closed orbit) is usually - linear (response matrix) - hysteresis free - fast Score 0 (?) out of 3 for the 100 collimator control problem, whether the task is - machine protection - quench avoidance - background reduction This ill conditioned task may well be painfully slow...

23 23 House, Apr 25, 2004 The LHC project party line

24 24 House, Apr 25, 2004 The “snap-back” effect

25 25 House, Apr 25, 2004

26 26 House, Apr 25, 2004 Vortex currents circulate around quantum fluxoids in a Type II superconducting filament I Quantum fluxoids Need a fluxoid density gradient to get a net transport current

27 27 House, Apr 25, 2004 Persistent currents A quadratic density gradient drives a current gradient... Like eddy currents, these “persistent currents” - depend on the history of the “external” field - decay (SLOWLY) with time

28 28 House, Apr 25, 2004 Persistent current (gradients) drive quadratic field errors which drive the chromaticity potentially causing disastrous tune spreads and BEAM LOSS unless which requires strong corrections that change quickly !! Time-dependent chromaticity

29 29 House, Apr 25, 2004 Tevatron persistent current hysteresis loop This is an injection problem – how long does it take?

30 30 House, Apr 25, 2004 LHC predictions “Snap-back” is not SO fast, but the chromaticity jump is huge

31 31 House, Apr 25, Challenges: - reproducibility (predictability) from fill-to-fill - real time chromaticity measurements and feedback

32 32 House, Apr 25, 2004 Summary

33 33 House, Apr 25, ) Eschew anti-protons 2) Make luminosity with lots of bunches 3) Fear the 350 MJ beam stored energy 4) Snap-back is a major challenge But, all participants should remember 5) The LHC will be a huge success, even if...


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