Particle Accelerators: introduction, University of Oslo, Erik Adli, University of Oslo, August 2014,

Video: the LHC accelerator youtube: the LHC Accelerator

3 25 ns Event rate in ATLAS : N = L x  (pp)  10 9 interactions/s Mostly soft ( low p T ) events Interesting hard (high-p T ) events are rare Experimental High-Energy Particle Physics

Particle accelerators for HEP LHC: the world largest accelerator, both in energy and size) First collisions end 2009 Gradual commissioning with steadily increased luminosity and CM energy 27 fb -1 integrated luminosity delivered to the ATLAS up to 2014 lead to the Higgs Boson discovery

Future colliders for HEP The next big thing? After LHC, a high energy, high luminosity Linear Collider of several 10 km length, may be needed – why?

Particle collider Livingstone plot Way forward? CLIC ILC

Others accelerators The driving force of accelerator development was high- energy physics experiments Today there are estimated to be more than 30'000 particle accelerators in the world, and only a fraction is used in HEP Over half of them used in medicine Accelerator physics: a scientific discipline in itself, and growing field Some examples of particle accelerators for various applications on the following pages

Medical applications Therapy –The last decades: electron accelerators (converted to X-ray via a target) used successfully for cancer radiation therapy –Increasing popularity : particle therapy/hadron therapy - direct use of proton/ion beams - provide an improved alternative for various types of cancer. Energy deposition can be controlled better, however, significant accelerator physics challenges Imaging –Isotope production for PET scanners

Advantages of hadron therapy From U. Amaldi

Hadron therapy accelerators Heidelberg Ion-Beam Therapy Center (HIT) State of the art of commercial hadron therapy centers. Can particle accelerator R&D drive size and cost down? Linear accelerator Synchrotron Beam transport lines Beam delivery 25 m (gantry size)

Synchrotron Light Sources Synchrotron radiation emitted from accelerated charged particles can produce very intense radiation at X-ray frequencies The last decades, vast increase in the use of synchrony radiation for photon science. Some uses: material sciences; life sciences; earth sciences. Soleil, France Synchrotron radiation covered later in the course. Radiation from ultra-relativistic electrons: forward direction.

Neutron spallation sources (ESS) Neutron spallation sources: intense flux of protons at high energies. Lund, Sweden: building Europe’s first neutron spallation source, the European Spallation Source, using superconducting technology.

Thorium - Accelerator Driven Systems

Advanced acceleration research Cutting edge accelerator physics research. The target is to overcome the limitations in conventional rf based accelerator technology.

Plasma wakefield acceleration Ideas of ~100 GV/m electric fields in plasma, using W/cm 2 lasers: 1979 T.Tajima and J.M.Dawson (UCLA), Laser Electron Accelertor, Phys. Rev. Lett. 43, 267– 270 (1979) PWFA: plasma wakefield acceleration Drive a wake in plasma by the space charge field of an intense charged particle beam (beam-driven) or by the radiation pressure of an intense laser beam (laser-driven). * Typical plasma densities: /cm 3 * Length scales: p ~ um * Plasma usually modeled as collisionless We will treat this topic in separate lectures in October

Accelerator Physics Accelerator physics deals with the dynamics of charged particle beams, under the effect of collective electromagnetic forces in an accelerator. Extensive research in accelerator physics is in order to advance the high-energy particle physics. Proud Norwegian tradition : Rolf Wideröe Odd Dahl Bjørn Wiik Kjell Johnsen Professor og direktør ved Europas nest største akseleratorsenter (DESY i Hamburg) Pioneer både for betatronprinsippet og for lineære akseleratorer Leder av CERN PS prosjektet (en viktig del av LHC- komplekset den dag i dag) Leder av CERN ISR, og leder av CERN's gruppe for akseleratorforskning

Basic description of charged particle beams

Single particle coordinates We usually describe particle movement in a particle accelerator in a frame co-moving with a reference position at the beam center The state of a particle is characterized by the deviation from the reference position along the three spatial dimensions, – (x, y, z) and their complementary dimensions, for example – (x’ ≈ dx/ds, y’ ≈ dy/ds, E). The choices are not unique. The coordinates are usually given in the laboratory frame z y pzpz pypy y’≈dy/ds s: co-ordinate along accelerator

It’s about a beam, in 6D Any charged particle beams, taken at a given point in time, can be characterized as a distribution in 6D phase space.  x, y, z)

Description in terms of moments

Discrete distributions We may also use representations where each particles have different weight, in case the weight of each particle enters the above formulas.

Gaussian distributions

Some questions one may ask: What are the rms beam sizes? What are the correlations?  x, y, z)  x’, y’, E) The following example 6D distribution is from a simulation of an electron photo-injector line : Example distribution

 x, y)  y)  x, y, z)  x) Gaussian fit beam sizes  x = 9.4 um,  y = 5.6 um correlations ≈ 0

Example distribution The two transverse planes are often to a large degree uncoupled = 0. However, evidently the position and the angle of particles in a given plane are dynamically coupled, and the correlation, will change as the beam evolves in time. Below: the effect of letting the beam propagate in free space, from a time t 1 to a time t 2 : y phase space at t=t 1. ≈ 0y phase space at t=t 2. > 0

Beam dynamics: beta function and emittance Beta function,  s  : quantifies how well the beam is focussed. Minimum,  *, at the beam waist. Emittance,  : phase-space area preserved in the above case;  = √( - 2 ) Two key concepts that defines a charged particle beam: Evolution of the beam (y,y’) when propagating in free space along beamline, s :  y = √(  y  y (s))

Gaussian laser beams : - Rayleigh length Z R  * - Wavelength 4  -  =   ’ ~ w 0  - Evolution along beam path, s, given by : Charged particle beams : -  * represents focus depth and strength - Emittance, , is conserved (when?) - At waist:  = √( ) =   y  ’ y - Evolution along beamline, s, given by : Charged particle propagation versus laser beam propagation ss Beam propagates in s direction In the “transverse optics” part of the course we will treat this topic in detail.

Beam Parameters

Main parameters to characterize a charged particle beam Particle type Energy spectrum Charge Emittance Focusing Time structure … Luminosity Requirements from a High-Energy Physics point of view

Main parameters: particle type Hadron collisions: compound particles –Mix of quarks, anti-quarks and gluons: variety of processes –Parton energy spread –Hadron collisions  large discovery range Lepton collisions: elementary particles –Collision process known –Well defined energy –Lepton collisions  precision measurement SppS, LHC LEP, CLIC, ILC “If you know what to look for, collide leptons, if not collide hadrons”

Parameters: particle energy New physics can be found at larger unprobed energies Energy for particle creation: centre-of-mass energy, E CM Assume particles in beams with parameters m, E, E >> mc 2 –Particle beam on fixed target: –Colliding particle beams:  Much more efficient to collide beam Collision energy is affected by beam-beam interactions; an initial small energy spread maybe converted into a spectrum : Right: example spectrum from a 3 TeV CLIC design

Parameters: luminosity High energy is not enough, high event rate is as important in HEP Cross-sections, , for interesting processes are very small. E.g. Higgs production in e + e - colliders are ~ 100 fb = 10 −37 cm² –Depending on the process we want to study we need L >> cm -2 s -1 in order to observe a significant amount of interesting processes (1 year ~  x 10 7 ) L [cm -2 s -1 ] for “bunched colliding beams” depends on –number of particles per bunch (n 1, n 2 ) –bunch transverse size at the interaction point (  x,  y ) –bunch collision rate ( f)

Parameters: time structure Linear collider time structure : charge delivered in micro-bunched pulses Example for the International Linear Collider (500 GeV high lum.) -charge delivered in pulses of 1 ms, at 5 Hz -3 nC charge in each micro-bunch Circular collider time structure : constant collision rate E xample for LHC, nominal parameters -charge delivered in bunches at 25 ns spacing -16 nC charge in each bunch 2800 bunches in each beam, colliding at 40 GHz The collider time structure is driven by both accelerator design constraints and detector / data analysis constraints.

Parameters: LEP, LHC and CLIC LEPLHCCLIC Particle typee + and e - p, ions (Pb, Au)e + and e - Max. collision energy 209 GeVp: 14 TeV (~ 2-3 TeV mass reach, depending on physics) 3 TeV Time structure4 bunches circulating, 50 MHz collsion rate 2800 bunches circulating, 40 GHz collision rate 312 micro- bunches, colliding at 50 Hz repeition rate LuminosityPeak: cm -2 s - 1 Integrated L in total : ~ 1000 pb -1 (per experiment) cm -2 s -1 (IP1 / IP5) Integrated L up to now : ~ 27 fb -1 (per experiment) cm -2 s -1 CERN-based colliders, nominal parameters :

Accelerator lectures for FYS4550 Accelerator types, main parameters, basic Concepts Acceleration and Longitudinal Dynamics Basic Transverse Dynamics (single particle) Advanced Transverse Dynamics (multiple particles) Synchrotron radiation and collective effects Linear colliders and CLIC Advanced Accelerator Research with focus on plasma wakefield acceleration At CERN Visit to the CERN accelerator complex, LHC injectors and linear collider test facilities Focus: accelerators for high-energy physics, with thus emphasize high- energy accelerators, especially synchrotrons and linear colliders Goal: understand the basics of why and how we accelerate particles, plus the challenges and the limitations