Particle Accelerators: introduction Erik Adli, University of Oslo, September 2017, Erik.Adli@cern.ch , v2.30

FYS4550 - Experimental high energy physics Particle accelerator physics The study of relativistic charged particle beams in electromagnetic fields Data analysis Particle detectors With focus on track reconstruction and probability The study of charged particle interaction with matter

Video: the LHC accelerator youtube: the LHC Accelerator

Experimental High-Energy Particle Physics 25 ns Event rate in ATLAS : N = L x  (pp)  109 interactions/s Mostly soft ( low pT ) events Interesting hard (high-pT ) events are rare

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 58 fb-1 integrated luminosity delivered to the ATLAS as of today 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 CLIC ILC Way forward?

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 Beam transport lines Synchrotron Linear accelerator 25 m (gantry size) Beam delivery 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?

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. Synchrotron radiation covered later in the course. Radiation from ultra-relativistic electrons: forward direction. Soleil, France

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.

European Spallation Source, Lund, Sweden Under construction: first beam around 2020

Accelerator Driven Systems : Thorium Technology very similar to linac

Plasma wakefield acceleration Ideas of ~100 GV/m electric fields in plasma, using 1018 W/cm2 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: 1014-18/cm3 * Length scales: lp~10-1000 um * Plasma usually modeled as collisionless We will treat this topic in separate lectures in October

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

Accelerator Physics Bjørn Wiik Rolf Wideröe Odd Dahl Kjell Johnsen 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 : Bjørn Wiik Rolf Wideröe Professor og direktør ved Europas nest største akseleratorsenter (DESY i Hamburg) Pioneer både for betatronprinsippet og for lineære akseleratorer Odd Dahl Kjell Johnsen 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 y py y’≈dy/ds pz z s: co-ordinate along accelerator

It’s about a beam, in 6D y(x, y, z) Any charged particle beam, taken at a given point in time, can be characterized with a charge density distribution in 6D phase space [C/m3].

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

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

Example distribution y(x, y) y(x, y, z) y(x) y(y) Gaussian fit beam sizes sx = 9.4 um, sy = 5.6 um correlations <x y> ≈ 0

Example distribution y phase space at t=t1. <y y’> ≈ 0 The two transverse planes are often to a large degree uncoupled <x y> = 0. However, evidently the position and the angle of particles in a given plane are dynamically coupled, and the correlation <x x’>, <y y’> will change as the beam evolves in time. Below: the effect of letting the beam propagate in free space, from a time t1 to a time t2 : y phase space at t=t1. <y y’> ≈ 0 y phase space at t=t2 . <y y’> > 0

Beta function and emittance Evolution of the transverse phase-space in free space along the beamline : s= √(eb (s)) Two key concepts that defines a charged particle beam: Beta function, b(s): how well the beam is focussed. Minimum, b*, at the beam waist. Emittance, e: beam quality, phase-space area; e = √(<y2><y’2> - <y y’>2)

Charged particle propagation versus laser beam propagation Beam propagates in s direction s s Charged particle beams : - b* represents focus depth and strength - Emittance, e, is conserved (when?) - At waist: e = √(<y2><y’2>) = s*y s’y - Evolution along beamline, s, given by : Gaussian laser beams : - Rayleigh length ZR <-> b* - Wavelength l <-> 4pe - e = s s’ ~ w0 q - Evolution along beam path, s, given by : 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, energy spectrum Emittance Focusing Charge per time Time structure … Luminosity Requirements from a High-Energy Physics point of view

Requirements: Energy Ephoton = 2mec2 + Ek l = h / p 2012 Energy requirement for pair production: Ephoton = 2mec2 + Ek 1996 1983 1974 1977 ~1975 (1968) Colliders: Heavy particles  more energetic collisions are required. ECM >= mc2 1936 1968 Year : Accelerator discovery Year : Non-accelerator discovery Probe wavelength: Particles are waves. Wavelength of probe should be smaller than the object you want to study. De Broglie wavelength : 1897 l = h / p 2000 1962 (~ 1 Å for 100 MeV e-) 1956

Energy : fixed target versus colliding beams Colliding beams are needed in order to reach the highest center of mass energies. m2

Requirements: particle type Hadron production from lepton collisions Lepton collisions: elementary particles (leptons, muons…) Collision process known Well defined energy Lepton collisions  precision measurement Hadron collisions: compound particles (protons, ions…) Mix of quarks, anti-quarks and gluons: variety of processes Parton energy spread Hadron collisions  large discovery range Lepton production from hadron collisions “If you know what to look for, collide leptons, if not collide hadrons”

Requirements: luminosity High energy is not enough, production rate are as important, because the events we are looking for are rare. The probability for particle physics processes to occur are quantified by “cross section”, s, an area, with units in “barns”, b = 10-28 m2. In particle collisions, the higher the cross section, and the more collisons per second, the higher reaction rate R for a given process is : The proportional factor, L, called the luminosity [cm-2s-1], depends on the colliding beam parameters as : * n1, n2 :particles per bunch * x, y : bunch transverse size at the interaction point * bunch collision rate ( f)

Requirements: time structure Time structure may be driven by accelerator (collective effects) and/or detector (read-out) constraints. Circular collider time structure : constant collision rate Example for LHC, nominal parameters charge delivered in bunches at 25 ns spacing 16 nC charge in each bunch LHC: four collision points 2800 bunches in each beam, colliding at 40 GHz 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

Parameters: LEP, LHC and CLIC CERN-based colliders, nominal parameters : LEP LHC CLIC Particle type e+ and e- p, ions (Pb, Au) Max. collision energy 209 GeV p: 14 TeV (~ 2-3 TeV mass reach, depending on physics) 3 TeV Time structure 4 bunches circulating, 50 MHz collsion rate 2800 bunches circulating, 40 GHz collision rate 312 micro-bunches, colliding at 50 Hz repeition rate Luminosity Peak: 1032 cm-2s-1 Integrated L in total : ~ 1000 pb-1 (per experiment) 1034 cm-2s-1 (IP1 / IP5) Integrated L up to now : ~ 27 fb-1 (per experiment)

Accelerator lectures for FYS 4550 Accelerator types, main parameters, basic Concepts - today Basic Transverse Dynamics (linear optics) – week 38 Transverse Dynamics with energy spread (dispersion, chromaticity) – week 43 Advanced Accelerator Research,plasma wakefield acceleration – week 44 Linear colliders (CLIC), plasma wakefield acceleration (AWAKE) – at CERN Also 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