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Lecture I&II RHIC The Relativistic Heavy Ion Collider

Lecture I&II RHIC The Relativistic Heavy Ion Collider. Particle accelerators. Large scientific instruments that produce and accelerate subatomic particles and ‘smashes them’ Fixed target Collider. Particles: electrons, positrons, protons, anti-protons, ions…..

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Lecture I&II RHIC The Relativistic Heavy Ion Collider

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  1. Lecture I&IIRHICThe Relativistic Heavy Ion Collider

  2. Particle accelerators Large scientific instruments that produce and accelerate subatomic particles and ‘smashes them’ Fixed target Collider Particles: electrons, positrons, protons, anti-protons, ions….. (atoms stripped of electrons: nuclei) Nuclei  protons + neutrons  quarks + gluons Varenna, July 2011

  3. RHIC @ Brookhaven National Lab p 1st Collisions: 13/06/2000 Jet/C-Polarimeters 12:00 o’clock RHIC ANDY 2:00 o’clock What do we collide ? PHENIX 8:00 o’clock RF 4:00 o’clock Polarized protons 24-250 GeV STAR 6:00 o’clock LINAC NSRL EBIS Booster ERL Test Facility Light ions (d,Si,Cu) Heavy ions (Au,U) 5-100 GeV/u AGS Polarized light ions He3 16 - 166 GeV/u Tandems Varenna, July 2011

  4. The RHIC Complex PHENIX STAR RHIC pC Polarimeters Absolute Polarimeter (H jet) ANDY 100 GeV/u 79+ Siberian Snakes Spin Rotators Partial Siberian Snake Pol. Proton Source 500 mA, 300 ms Stripping Au 77+ to 79+ Strong AGS Snake LINAC 9 GeV/u 77+ BOOSTER AGS 200 MeV Polarimeter AGS Internal Polarimeter 1 MeV/u 32+ AGS pC Polarimeters Rf Dipoles MP7 MP6 Varenna, July 2011 Tandem Van der Graaf

  5. The RHIC Accelerator System AGS Booster Ring Switchyard TandemVan de Graaff Yellow Ring RHIC Blue Ring Varenna, July 2011

  6. What does RHIC do? RHIC accelerates goldnuclei in two beams to about 100 GeV/nucleon each (i.e., to kinetic energies that are over 100 times their rest mass-energy) and brings these beams into a 200 GeV/nucleon collision. RHIC accelerates polarized protons up to 250 GeV and brings them into up to 500 GeV collision Three experiments, STAR,PHENIX, and ANDY study these collisions. Varenna, July 2011

  7. The RHIC project chronology 1989 RHIC design 1991 construction starts 1996 commissioning AtR injection lines 1997 sextant test (1/6 of the ring) 1999 RHIC engineering/test run 2000 first collisions 2001-02 Au-Au run, polarized p run 2003 deuteron-Au run, pp 2004 Au-Au physics run and 5 weeks pp development 2005 ….. RHIC is also a giant engineering challenge: magnets (3000+ industry and lab built superconducting magnets) cryogenics (2 weeks to cool down to 4.2K) ,instrumentation, etc. Varenna, July 2011

  8. RHIC operations The operation of RHIC and its injectors is a rather challenging endeavor…. RHIC operates for ~5-6 months/year – 24h/day 7 days/week RHIC Shutdown 6-7 months, for machine improvements (other programs are run by the injectors, Tandem delivering ions for industrial R&D, Booster delivering ions for NASA experiments, etc.) • CONTROL ROOM : remote access to instrumentations and controls • Accelerator physicists, shift leaders (machine initial set-up, new developments, beam experiments) • Operations group: operation coordinator, operators (“routine’ operations, shifts 1 OC + 2 operators) • Technical support (engineers and technicians on call and/or site for system diagnosis and trouble-shooting) Varenna, July 2011

  9. inject, accelerate, collide......! Beam intensities Beta* squeeze cogging re-bucketing collimation steering collisions transition Start acceleration Pilot bunch time acceleration Store (collisions) collisions Set-up injection preparation Varenna, July 2011

  10. A day in the life of RHIC… Varenna, July 2011

  11. A week in the life of RHIC… Week 9 Feb to 17 Feb [66% of calendar time in store] 60x109Auintensity Beam experiments enhancedluminosity designluminosity Varenna, July 2011

  12. A few years in the life of RHIC… Polarized proton runs Operated modes (beam energies): Au–Au 3.8/4.6/5.8/10/14/32/65/100 GeV/n d–Au* 100 GeV/n Cu–Cu 11/31/100 GeV/n p–p 11/31/100, 250 GeV Planned or possible future modes: Au – Au 2.5 GeV/n (~ SPS cm energy) U – U 100 GeV/n p – Au* 100 GeV/n Cu – Au* 100 GeV/n(*asymmetric rigidity) Achieved peak luminosities (100 GeV, nucl.-pair): Au–Au 1951030 cm-2 s -1 p–p 601030 cm-2 s -1 Other large hadron colliders (scaled to 100 GeV): Tevatron (p – pbar) 431030 cm-2 s -1 LHC (p – p) 371030 cm-2 s -1 Varenna, July 2011

  13. AnDY in Run-11 (250 GeV pp) x/IP = 0.005 visible impact, few percent loss to STAR/PHENIX small impact x/IP = 0.004 PHENIX STAR loss rates AnDY • Beam envelope function b* = 3.0 m at IP2 • Reduced IP2 crossing angle from initially 2.0 mrad to zero • Added 3rd collision with following criteria (last instruction): • Nb ≤ 1.5x1011 • Beam loss rate <15%/h in both beams • Not before first polarization measurement 3h into store Varenna, July 2011

  14. ANDY an getting Lumi ANDY got ~ 6.5/pb in run11 with b*=3m systematically increased thresholds for IP2 collisions ~0mr crossing angle ~1.6mr crossing angle ~2mr crossing angle Varenna, July 2011

  15. Future operation of AnDY Run-11 luminosity at AnDY: max ~0.5 pb-1/store With improvements: ~3x increase, ~10 pb-1/week (max) pp in Run-4 (100 GeV) Can reduce b* at IP2have run with b* = 2.0 m previously for BRAHMSb* = 1.5 m probably ok, needs to be tested Longer stores 10h instead of 8h in Run-11 (depends on luminosity lifetime and store-to-store time) Collide earlier in store when conditions are metneeds coordination with polarization measurement, PHENIX and STAR Electron lenses (see later) if AnDY runs beyond Run-13 increases max beam-beam tune spread, currently DQmax,bb ≈ 0.015 can be used for to increase x~Nb/e and/or number of collisions Varenna, July 2011

  16. Polarized proton beams Or How to do magic with an accelerator Varenna, July 2011

  17. What is Spin? From Google… • revolve quickly and repeatedly around one's own axis, "The dervishes whirl around and around without getting dizzy” • twist and turn so as to give an intended interpretation, "The President's spokesmen had to spin the story to make it less embarrassing” • a distinctive interpretation (especially as used by politicians to sway public opinion), "the campaign put a favorable spin on the story" Varenna, July 2011

  18. What is Spin? Classical definition the body rotation around its own axis Particle spin: an intrinsic property, like mass and charge a quantum degree freedom associated with the intrinsic magnetic moment. q: electrical charge of particle m: particle mass • G: anomalous gyromagnetic factor, describes • the particle internal structure. • For particles: • point-like: G=0 • electron: G=0.00115965219 • muon: G=0.001165923 • proton: G=1.7928474 Varenna, July 2011

  19. spin vector and spin-orbit interaction I  • Spin: single particle • pure spin state aligned along a quantization axis • Spin vector S: a collection of particles • the average of each particles spin expectation value • along a given direction • Spin orbit interaction S S N N Varenna, July 2011

  20. Figure of merit of polarized proton collider Luminosity: number of particles per unit area per unit time. The higher the luminosity, the higher the collision rates beam polarization Statistical average of all the spin vectors. zero polarization: spin vectors point to all directions. 100% polarization: beam is fully polarized if all spin vectors point to the same directions. # of particles in one bunch # of bunches Transverse beam size Varenna, July 2011

  21. Basics of circular accelerator • bending dipole • Constant magnetic field • Keeps particles circulating around the ring • quadrupole • Magnetic field proportional to the distance from the center of the magnet. • Keeps particles focused • radio frequency cavities • Electric field for acceleration and keeping beam bunched longitudinally Varenna, July 2011

  22. Closed orbit in a circular accelerator Closed orbit: particle comes back to the same position after one orbital revolution Closed orbit in a perfect machine: center of quadrupoles Closed orbit in a machine with dipole errors Varenna, July 2011

  23. Betatron oscillation in a circular accelerator Betatron tune: number of oscillations in one orbital revolution Beta function Varenna, July 2011

  24. Spin motion in circular accelerator: Thomas BMT Equation In a perfect accelerator, spin vector precesses around the bending dipole field direction: vertical Spin tune Qs: number of precessions in one orbital revolution. In general, B beam Spin vector in particle’s rest frame Varenna, July 2011

  25. polarized proton acceleration challenges: preserve beam polarization Depolarization (polarization loss) mechanism Come from the horizontal magnetic field which kicks the spin vector away from its vertical direction Spin depolarizing resonance : coherent build-up of perturbations on the spin vector when the spin vector gets kicked at the same frequency as its precession frequency y y y beam beam beam z z z x x x 2nd full betatron Oscillation period 1st full betatron Oscillation period Initial Varenna, July 2011

  26. spin depolarizing resonance Imperfection resonance Source: dipole errors, quadrupole mis-alignments Resonance location: G = k k is an integer • Intrinsic resonance • Source: horizontal focusing field from betatron oscillation • Resonance location: • G = kP±Qy • P is the periodicity of the accelerator, • Qy is the vertical betatron tune Varenna, July 2011

  27. Spin depolarization resonance in RHIC • For protons, imperfection spin resonances are spaced • by 523 MeV • the higher energy, the stronger the depolarizing resonance Intrinsic spin resonance Qx=28.73, Qy=29.72, emit= 10 Varenna, July 2011

  28. Innovative polarized proton acceleration techniques: Siberian snake • First invented by Derbenev and Kondratenko from Novosibirsk in 1970s • A group of dipole magnets with alternating horizontal and vertical dipole fields • rotates spin vector by 180o Varenna, July 2011

  29. Particle trajectory in a snake: Varenna, July 2011

  30. How to preserve polarization using Siberian snake(s) • Use one or a group of snakes to make the spin tune to be 1/2 • Break the coherent build-up of the perturbations on the spin vector y y beam beam z z Varenna, July 2011

  31. Accelerate polarized protons in RHIC Varenna, July 2011

  32. Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes Spin flipper PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS Alternating Gradient Synchrotron 200 MeV Polarimeter AGS Polarimeters Strong AGS Snake ANDY(p) Varenna, July 2011

  33. Polarized proton acceleration setup in RHIC • Energy: 23.8 GeV ~ 250 GeV (maximum store energy) • A total of 146 imperfection resonances and about 10 strong intrinsic resonances from injection to 100 GeV. • Two full Siberian snakes Varenna, July 2011

  34. How do we know the protons are polarized Varenna, July 2011

  35. What is beam polarization? Simple example: spin-1/2 particles (proton, electron) Can have only two spin states relative to certain axis Z: Sz=+1/2 and Sz=-1/2 |P|<1 Varenna, July 2011

  36. How to measure proton beam polarization There are several established physics processes sensitive to the spin direction of the transversely polarized protons Scattering to the left Scattering to the right AN – the Analyzing Power (|AN|<1) (left-right asymmetry for 100% polarized protons) Once AN is known: Varenna, July 2011

  37. Polarization Measurements pC elastic scattering AN depends on the process and kinematic range of the measurements -t=2MCEkin Precision of the measurements N=NLeft+NRight For (P)=0.01 and AN~0.01  N~108 ! • Requirements: • Large AN or/and high rate (N) • Good control of kinematic range Varenna, July 2011

  38. RHIC and Polarimetry Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes RHIC PHENIX (p) STAR (p) Siberian Snakes Spin Rotators Solenoid Snake LINAC BOOSTER Pol. Proton Source 500 mA, 400 ms AGS Warm Snake 200 MeV Polarimeter AC Dipole AGS pC CNI Polarimeter Cold Snake ANDY (p) Varenna, July 2011

  39. RHIC Polarimetry • Polarized hydrogen Jet Polarimeter (HJet) • Source of absolute polarization (normalization to other polarimeters) • Slow (low rates  needs lo-o-ong time to get precise measurements) • Proton-Carbon Polarimeter (pC) • Very fast  main polarization monitoring tool • Measures polarization profile (polarization is higher in beam center) • Needs to be normalized to HJet • Local Polarimeters (in PHENIX and STAR experiments) • Defines spin direction in experimental area • Needs to be normalized to HJet All of these systems are necessary for the proton beam polarization measurements and monitoring Varenna, July 2011

  40. Polarized H-Jet Polarimeter Left-right asymmetry in elastic scattering due to spin-orbit interaction: interaction between (electric or strong) field of one proton and magnetic moment associated with the spin of the other proton Beam and target are both protons Forward scattered proton RHIC proton beam H-jet target recoil proton Ptarget is provided by Breit Rabi Polarimeter Varenna, July 2011

  41. H-jet system target • Height: 3.5 m • Weight: 3000 kg • Entire system moves along x-axis 10 ~ +10 mm to adjust collision point with RHIC beam. Recoil proton RHIC proton beam IP12 Varenna, July 2011

  42. HJet target system |1> |2> H = p++e |1> |2> |3> |4> Hyperfine structure H2 desociater Separating Magnet (Sextuples) Atomic Beam Source RF transitions (WFT or SFT) P+ OR P Scattering chamber Holding magnet |1> |3> |2> |4> Breit-Rabi Polarimeter 2nd RF-transitions for calibration Separating magnet |1> |2> Ion gauge Varenna, July 2011 Ion gauge

  43. HJet: Identification of Elastic Events ToF vs Energy Forward scattered proton proton beam proton target recoil proton Energy vs Channel # YELLOW mode BLUE mode Array of Si detectors measures TR & ToFof recoil proton. Channel # corresponds to recoil angle R. Correlations (TR & ToF ) and (TR & R )  the elastic process Varenna, July 2011

  44. HJet: Ptarget Source of normalization for polarization measurements at RHIC • Breit-Rabi Polarimeter: • Separation of particles with different spin states in the inhomogeneous magnetic field (ala Stern-Gerlach experiment) Nuclear polarization • Nuclear polarization of the atoms: • 95.8%  0.1% • After background correction: • Ptarget = 92.4%  1.8% 1 day Very stable for entire run period ! Polarization cycle (+/ 0/  ) = (500/50/500) s Varenna, July 2011

  45. HJet: Example from Run-2006 εtarget Use the same statistics (with exactly the same experimental cuts) to measure beamand target (selecting proper spin states either for beam or for target)  Many systematic effects cancel out in the ratio εbeam t=-2MpEkin Ekin (MeV) Ekin (MeV) Provides statistical precision (P)/P ~ 0.10 in a store (6-8 hours) HJet Provides very clean and stable polarization measurements but with limited stat. precision  Need faster polarimeter! Varenna, July 2011

  46. P-Carbon Polarimeter: 6 1 2 5 3 4 Left-right asymmetry in elastic scattering due to spin-orbit interaction: interaction between (electric or strong) field of Carbon and magnetic moment associated with the spin of the proton Carbon target Polarized proton Recoil carbon Ultra thin Carbon ribbon Target (5 mg/cm2) Target Scan mode (20-30 sec per measurement) Stat. precision 2-3% Polarization profile, both vertical and horizontal Normalized to H-Jet measurements over many fills (with precision <3%) 18cm Si strip detectors (TOF, EC) Varenna, July 2011

  47. pC: AN pC Analyzing Power Run04 Phys.Rev.Lett.,89,052302(2002) unpublished zero hadronic spin-flip With hadronic spin-flip (E950) Ebeam = 100 GeV Elastic scattering: interference between electromagnetic and hadronic amplitudes in the Coulomb-Nuclear Interference (CNI) region Ebeam = 21.7GeV Varenna, July 2011

  48. Polarization Profile If polarization changes across the beam, the average polarization seen by Polarimeters and Experiments (in beam collision) is different H-Jet pC Collider Experiments ~1 mm 6-7 mm x=x0 P1,2(x,y) – polarization profile, I1,2(x,y) – intensity profile, for beam #1 and #2 Varenna, July 2011

  49. Pol. Profile and Average Polarization Scan C target across the beam In both X and Y directions Carbon Intensity I Ideal case: flat pol. profile (P=  R=0) Run-2009: Ebeam=100 GeV: R~0.1  5% correction Ebeam=250 GeV: R~0.35  15% correction Polarization P Target Position Varenna, July 2011

  50. pC+HJet: Polarization vs Fill Run-2009 results (Ebeam=100 GeV) • Normalized to HJet • Corrected for polarization profile (by pC) “Blue” beam P/P < 5% • Dominant sources of syst. uncertainties: • ~3% - HJet background • ~3% - pC stability • (rate dependencies, gain drift) • ~2% - Pol. profile “Yellow” beam Varenna, July 2011

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