Presentation on theme: "FysN15 Accelerators 4 Accelerators for high energy nuclear and particle physics You basically know how a synchrotron works. Synchrotrons used as storage."— Presentation transcript:
fysN15 Accelerators 4 Accelerators for high energy nuclear and particle physics You basically know how a synchrotron works. Synchrotrons used as storage rings with internal target Colliding, stored synchrotron beams Linear collider for future high energy electron collisions Free electron laser: future X-ray laser source, spinn off from linear collider development
fysN15 Accelerators 4 Storage rings, Why -The acceleration in a synchrotron takeslong time. At best you accelerate the ring content during a few seconds to full energy and extract the beam slowly for a few seconds to make collisions. Ramping down the magnets also takes a few seconds and then repeat the cycle. ca 10 times per minute depending on energy. -You have to use thin target material (mg/cm 2 ) in order to avoid secondary inteactions. -With extracted beam hitting a thin external target you are using only a small fraction (%) of the accelerated particles. -In a storage ring, noninteracting particles come back on the next turn you can keep the accelerated beam for hours, until you have used an optimal fraction of the beam. -Targets can be either extremely thin (ng/cm 2 ) gas jets (stationary target internal to the ring) or a colliding, stored synchrotron beams.
fysN15 Accelerators 4 Why colliding beams? B-field in practice limited to about 10 TESLA All kinetic energy of beams make available energy in CM frame Efficient use of accelerated particles. (come back next turn). Long storage time-accelerate seldom- cheaper magnets due to slow ramp. Particles to be detected have lower laboratory momenta. Better for particle id and P and in particular P t resolution Particles to be detected are more spread out in space which makes it easier to resolve them.
fysN15 Accelerators 4 FAIR at GSI, Future nuclear physics in Europé, >2014 Atomic phys with Naked ions Stored RIB P RIB Radioactive Ion Beam EOS GSI, Darmstadt 1AGeV
fysN15 Accelerators 4 Example fixed target at CERN SPS Pb at 160 A GeV
fysN15 Accelerators 4 Reconstructed event High p in lab system Focused forward in space Very long exp. setup
The alternating E-field keeps particles in bunches
fysN15 Accelerators 4 Electron cooling Gålnander (Uppsala) Electrons can obtain same velocity as the accelerated ions by electrostatic acc. Elastic collision e+ion Will decrease the relative momentum spread In the beam
fysN15 Accelerators 4 Storage rings with internal taget Very efficient. Storage times are long so you can run several such experiments at the same time.
fysN15 Accelerators 4 Large Electron Positron collider (LEP)
fysN15 Accelerators 4 Large Electron Positron collider (LEP) Closed down 2000 Collision energy s ~ 200 GeV
fysN15 Accelerators 4 Magnets keep particles in orbit A charged particle, moving in a magnetic field follows a circular orbit You want the highest possible magnetic field. This means very large current through the electromagnets. Superconducting is the solution circular orbit Magnetic field In LEP, e + and e - Opposite directions in same magnets
fysN15 Accelerators 4 LHC key numbers Vertical B field in the dipole bends the beam round via the Lorentz force Need very strong magnets to get the high energy beam around the circle. Superconducting (1.9 K) dipoles producing a field of 8.4 T - current 11,700 A 2-in-1 magnet design. Bending magnets (dipoles): 14.3 metres long. Cost: ~ 0.5 million CHF each. Need 1232 of them Quads etc to keep beam focused and the motion stable Stored magnetic energy up to 1.29 GJ per sector. Total stored energy in magnets = 11GJ One dipole weighs around 35 tonnes. 10-10 Torr (~3 million molecules/cm3)
fysN15 Accelerators 4 Make superconductive wire Ca 4mm diam wire
fysN15 Accelerators 4 Detector materials in a collider exp. Beams perpendicular to this view If warm magnet If cold magnet
fysN15 Accelerators 4 RHIC consists of two 3.8 km long rings, called Blue (clockwise) and Yellow (counter clockwise) It has six interaction regions (IR), four of which are equipped with detectors: PHENIX and some other less important experiments ;-) This year we have deuterons in the blue ring and Au in the yellow. The Run has just started. A briefing on RHIC
fysN15 Accelerators 4 Relativistic Heavy Ion Collider at Brookhaven National Laboratory (BNL) RHIC STAR PHENIX PHOBOS BRAHMS
fysN15 Accelerators 4 RHIC Injectors: Pictures (A.Drees) LINAC, since late 60s, accelerates (polarized) protons up to 200 MeV Tandem Van De Graaff, since 1970, accelerates 40 species, from hydrogen to uranium
fysN15 Accelerators 4 Pre-Accelerators A. Drees Booster, since 1991, accelerates up to 2 GeV, ¼ of AGS size Alternating Gradient Synchrotron (AGS) since 1960, 240 magnets, accelerates up to 10 (23) GeV
fysN15 Accelerators 4 RHIC Pictures Injection arcs to blue and yellow rings Blue and yellow rings Blue Dump Yellow Yellow Blue
fysN15 Accelerators 4 More RHIC Pictures Installation of final focussing triplets Rf storage cavities RHIC dipole magnet
fysN15 Accelerators 4 Basic Collider (and Accelerator) Concepts Ingredients for high performance: Good vacuum in both rings. Accelerating devices (so called “RF cavities”) to increase the particles energy (or speed) => ramp. Storage cavities to reduce bunch lengths. Good beam lifetimes (tunes, closed orbit) Maintain high beam currents and small profiles to get high collision rates.
fysN15 Accelerators 4 Accelerate total of 55 bunches per ring 12.8 s per revolution Abort gap Beam is accelerated by Radio Frequency (RF) cavities: / 28 MHz for acceleration / 200 MHz for storage to reduce bunch length 28 MHz defines the number of “ buckets ” = 360, length is 35 ns each (or 10 m) Coasting beam: continuous, no bunch structure (debunched), cannot be accelerated Bunched (or captured) beam: every 6 th bucket, i.e. 55+5 bunches per ring with 10 9 ions Currently: we are using 110 bunches per ring to increase total beam current. Bunch 1 Bunch 55
fysN15 Accelerators 4 RHIC ramp with 56 bunches Acceleration BLUE Fill 56 bunches YELLOW Fill 55 bunches Transition energy Storage energy Correction points (stepstones) Total Yellow current Bunched Yellow current Total Blue current Bunched blue current The beam is accelerated from Injection Energy (10 GeV) to Storage Energy (100 GeV). The acceleration process is called “ ramp ”. Injection energy
fysN15 Accelerators 4 Circulate: Betatron Motion Particles perform oscillations around closed orbit. The number of oscillations per revolution is called the “ tune ”. The quadrupole configuration ( “ optic ” ) defines the tune (betatron function). Integer and 1/2, 1/3, 1/4 … tunes would cause magnetic imperfections to be repetitive and resonant => beam loss This example: tune = 11.27 1 oscillation Number of oscillation is defined by the magnet configuration.
fysN15 Accelerators 4 Collision Rate Collision rate is defined to be the number of ‘ events ’ per second, i.e. the number of collisions happening in the center of one of the experiments (depends on the cross section) The collision rate can be increased if: o There is more beam/bunch in the two rings (N B,N Y ) o There are more bunches colliding (k b ) o The beam profiles, the size of the beam, at the interaction point, is small ( x, y ) -> * (cm -2 s -1 )
fysN15 Accelerators 4 Cross-section at collider R=L · σ (cm -2 s -1 ) σ is the cross-section R is the number of events per Second (corresponding to σ) We normally use the luminosity integrated over the time of the measure- ment. The sensitivity of the experiment is often given as inverse barns (or eg. inverse femtobarns for a sensitive experiment). 1/ σ = L So if we observe one event and the integrated L is one inverse femtobarn then the cross-section for this observation is 1 femtobarn.
fysN15 Accelerators 4 The Zero Degree Calorimeter (luminosity monitor, based on known crossection) 3 modules on either side of the Interaction Region (IR) Same detector at all IRs with experiments. About +/- 18 m distance from center behind DX => Only neutron sensitive Covers +/- 2.5 mrad forward angle Quite often the luminosty monitor uses some elastic reaction at small angles, whose crossection is possible to calculate. Nuclear collisions only
fysN15 Accelerators 4 Luminosity Monitoring during Au-Au @ 200 GeV cogging steering PHENIX * = 1 m PHOBOS * = 2 m STAR * = 2 m BRAHMS * = 2 m Clean, compatible signal from every IR ! ZDC rate
fysN15 Accelerators 4 LINAC principle I L n corresponds to half wavelength V V n =√2neV/m 1/2f=L n /v n so L n = v n /2f = v n λ/2c = β n λ/2 Can use fixed frequancy if L is made longer to match increase in velocity
fysN15 Accelerators 4 LINAC principle II Standing wave When v=c, L n can stay constant. For electrons this is the normal situation
fysN15 Accelerators 4 Why a linear collider for electrons? Energy loss per turn of a machine with an average bending radius : e+e+ e-e- ~15-20 km Linear Collider: no bends, but lots of RF ! For a E cm = 1 TeV machine: Effective gradient G = 500 GV / 15 km = 34 MV/m LEP: 100 GeV/beam with a circumference of 27 km 500 GeV/beam would require a circumference ~ 17.000 km cf the circumference of earth ~ 40.000 km
International Performance Specification – Initial maximum energy of 500 GeV, operable over the range 200- 500 GeV for physics running. – Equivalent (scaled by 500 GeV/ s) integrated luminosity for the first four years after commissioning of 500 fb -1. – Ability to perform energy scans with minimal changeover times. – Beam energy stability and precision of 0.1%. – Capability of 80% electron beam polarization over the range 200-500 GeV. – Two interaction regions, at least one of which allows for a crossing angle enabling collisions. – Ability to operate at 90 GeV for calibration running. – Machine upgradeable to approximately 1 TeV.
e+ production The undulator produces high energy γ A smaller linac gives possibility for X-Ray Laser We come to XFEL, Free Electron Laser
fysN15 Accelerators 4 ILC Projected Time Line 20052006200720082015 CDR TDR GDI process construction commissioning physics site selection International Funding EUROTeV Very aggressive!
fysN15 Accelerators 4 e+ production The undulator produces high energy γ A smaller linac gives possibility for X-Ray Laser We come to XFEL, Free Electron Laser 17.5GeV from electron LINAC Coherent X-Ray Femtosecond pulse X-ray production
fysN15 Accelerators 4 XFEl, X-ray laser Accelerator tunnel: 2.1 km Depth underground: 6 - 38 meters 1 underground experimental hall for 10 measuring stations Wavelength of X-ray radiation: 6 to 0.085 nanometers (nm) corresponding to electron energies of 10 to 17.5GeV), expandable to 20 GeV Length of radiation pulses: below 100 femtoseconds (fs) Expandable with a 2nd experimental complex of the same size Cost 10 9 € Ready 2014 Decision taken, Swedish partnership.
fysN15 Accelerators 4 What to study XFEL energies Max IV similar in wavelength but XFEL superior in pulse- length. Movie vs photograph
fysN15 Accelerators 4 XFL, science Femtochemistry Structural biology Materials research Cluster physics Plasma physics New experiments The European X-ray free-electron laser XFEL opens up new experi- mental areas that are inaccessible today, for nearly all the natural sciences. The resolution in time and space, are several orders of magnitude higher than for comparable X-ray sources, It will be possible to study dynamic processes, for instance chemical reactions forming matter. Up to now, in most cases only the static properties of matter could be investigated. Science at XFEL www.desy.de
fysN15 Accelerators 4 Concluding remark XFEL is one, in a long row of examples that fantastic measurement possibilities open up in applied science and technology, thanks to the development of instruments for basic science. Or in other words: Accelerator technology (with all its practical benefits to human life) would never have come near to where it is today, if it wasn’t driven by the curiosity of basic science. Profit and practical use is simply too short sighted for such competence buildup over several decades. One can compare with the space program