acceleratori

what are accelerators ?!

topics

  Accelerators: what for ?

  Some accelerator typologies   Fundamental research versus technological uses   Fixed target versus collider accelerators   Leptons versus hadrons accelerators

  Overview of existing accelerators and of their present use

  Overview of future projects

Introductory remarks (1/2)!  Particle accelerators are technological black boxes

producing   either flux of particles impinging on a fixed target   or debris of interactions emerging from colliding particles

  In trying to clarify what the black boxes are one can   list the technological problems   describe the basic physics and mathematics involved

  Most of the phenomena in a particle accelerator can be described with

➊ classical mechanics ➋ electro-dynamics ➌ special relativity ➍ quantum mechanic is required in a couple of cases just for leptons

(synchrotron radiation, pinch effect)!

Introductory remarks (2/2)!

  However there are some complications:   many non-linear phenomena   many particles interacting to each other and with a complex surroundings   the observables are averaged over large ensembles of particles

  to handle high energy high intensity beams a complex technology is required

  large scale vacuum   high power microwaves   superconducting technology   very strong and precise magnets   computer control   large scale project management   accelerator physics (beam dynamics)

Why accelerators ?!

  Particle accelerators can produce charged particle beams of   protons (and anti-protons)   ions   electrons (and positrons)   muons   neutrons   other secondary particles

  Common applications are   Fundamental research (creation of new particles, observation of new

interactions)   Ultra-precise Proton and Electron Microscopy   High Brightness Photon Sources for Material Analysis and Modification,

Spectrometry, … .   Ion Implanters, for Surface Modification and for Sterilization and

Polymerization   Radiation Surgery and Therapy of Cancer

Ultra-precise microscopy!  Probing particles are required for studies of the elementary

constituents   The associated de Broglie wavelength λ of a probing particle

defines the minimum object size that can be resolved: microstructure can be identified if probing particle λ < dim (structures to be studied <10-15 m, visible light ~500 nm)

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λ =hp

= h × cE

with h = 4 × 10−15

eVs (Plank constant)p = momentum, E = energy

⎧ ⎨ ⎩

Resolving Smaller Objects Requires Higher Momentum Probe Particles

Example of probe wavelength   electrons with p = 1 keV/c ⇒ λ = 4×10-12 m   photons with E = 1 keV ⇒ λ = h×c/E ~ 1.2 x 10-9 m.   electrons have ~ 300 times better resolution than

photons (electron-microscopy !)

Typical microscopic sizes   Atom 10-10 m   Nucleus 10-14 m   Proton 10-15 m   Quark 10-19 m

Microscopic scale of λ!

Quarks and leptons can be sensed down to distances of 10-19 meters by means of particles from giant accelerators with particle energies of > 1000 GeV

The living cell is commonly studied by means of an optical microscope which receives scattered photons of visible light.

  living cell are investigated by optical microscopes   objects of the atomic dimension by electron microscopes   nucleus and sub-nuclear objects by particle accelerators

Sub-micron objects such as the constituents of a living cell are often investigated in electron microscopes where electrons, accelerated typically to a few hundred kilovolts, are used to hit the objects and scatter from them

The full scale of λ!

Ener

gy

 Why accelerators: need to produce under controlled conditions HIGH INTENSITY, at a CHOSEN ENERGY particle beams of GIVEN PARTICLE SPECIES to do an EXPERIMENT

 An experiment consist of colliding particles either onto a fixed target or with another particle beam.

 The cosmo is already doing this with different mechanisms: while I am speaking about 66 109 particles/cm2/s are traversing your body, with this spectrum before being filtered by the atmosphere.

Why particle accelerators in fundamental reserch?

The universe is able to accelerate particles up to 106 MeV protons,…but in uncontrolled conditions

  Particles from accelerators colliding to each other or with target particles may lead to the creation of new matter

  New mass is created from the collision energy according to the formula E=mc2

  It is thus by conversion to mass of excess kinetic energy in a collision that particles, antiparticles and exotic nuclei can be created.

Creating matter!

Matter constituent and interaction!In an accelerator for fundamental physics discovery we need:

  enough energy to produce directly the different particles   enough intensity (i.e. particle interaction) to produce enough particles

In the last 100 year, the history of accelerator physics is  a continuous fight to get energy and intensity to study known and

unknown particles and their interactions

…some accomplishments

Technological development required for each step different particle species used in the different colliders:

electron-positrons and hadron colliders (either p-pbar as Tevratron, or p-p as LHC)

Different approaches: fixed target versus collider

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ECM = 2 Ebeammc2 +m2c 4( )

€

ECM = 2 Ebeam +mc 2( )

B. Tuschek

N1 particles beam population N1 target density ρ cross section σ no. of target particles N2 = ρlA effective interaction area Aeff = σN2 = σρlA probability of interaction P = Aeff/A = σρl reaction rate R = P•dN1/dt = σρl•dN1/dt

Fixed target!

A

l

Collider Advantage!

Luminosity bunch population in beam 1 N1 bunch population in beam 2 N2 rms beam radius σ beam area 2πσ2, reaction rate R L = R/σ = ρl•dN1/dt = N2/A•dN1/dt L = frevN1N2/4πσ2

Energy and interaction rate

The proper particle for the proper goal

  Pros: with a single energy possible to scan different processes at different energies. Discovery machine (LHC)

  Cons: the energy available for the collision is lower than the accelerator energy, e.g. reduced collision energy

Electrons and positrons are (so far) point like particles: no internal structure

The energy of the collider is totally transferred into the collision ECM= Eb1+ Eb2= 2×Eb (= 200 GeV in LEP)

Protons (and antiprotons) are formed by quarks (uud) kept together by gluons

The energy of each beam is carried by the proton constituents, and it is not the entire proton which collides, but one of his constituents ECM < 2×Eb (≈ 1 TeV in LHC)

  Pros: the energy can be precisely tuned to scan for example, a mass region. Precision measurement (LEP)

  Cons: above a certain energy is no more convenient to use electron because of too high synchrotron radiation

Lepton versus hadron circular colliders

->!

(At the parton level )!

RF is a major concern

magnets are a major concern

Synchrotron radiation

€

U =e2

3ε0β 3γ 4

ρ

U MeV[ ] = 0.0885E 4 GeV[ ]ρ m[ ]

Energy loss per turn

◆  Polarized light ◆  Fan in the bending plane

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Type of accelerators (1990)!

Main accelerators for research!

Colliders in operation (2001/11)

Main accelerators for research!

Colliders under investigation or in construction (2011)

Type Facility Ecm (GeV) Luminosity (1033cm-2 s-1)AuAu two ring collider BNL RHIC (US) 100/nucleon 10-6Electron Microtron CEBAF (US) 4 -Electron linac Bates (US) 0.3-1.1 -Proton synchrotron IUCF (US) 0.5 -Isochronous heavy-ion cyclotron MSU NSCL (US.) 0.5Isochronous cyclotron TRIUMF(Canada) 0.5 -Isochronous cyclotron PSI (Switzerland) 0.5 -

Accelerators in operation for nuclear physics research (2011)

Other applications!

Field Accelerator Topics of studyAtomic Physics Low energy ion beams Atomic collision processes - study of excited

states - electron-ion collisions - electronicstopping power in solids

Condensed matterphysics

Synchrotron radiationsources

X-ray studies of crystal structure

Condensed matterphysics

Spallation neutronsources

Neutron scattering studies of metals andcrystals - liquids and amorphous materials

Material science Ion beams Proton and X-ray activation analysis ofmaterials - X-ray emission studies -accelerator mass spectrometry

Chemistry andbiology

Synchrotron radiationsources

Chemical bonding studies: dynamics andkinetics - protein and virus crystallography -biological dynamics

Other applications!

◆  Oil well logging with neutron sources from small linacs ◆  Archaeological dating with accelerator mass spectrometry ◆  Medical diagnostics using accelerator-produced radioisotopes ◆  Radiation therapy for cancer: X-rays from electron linacs, neutron-

therapy from proton linacs, proton therapy; pion and heavy-ion therapy ◆  Ion implantation with positive ion beams ◆  Radiation processing with proton or electron beams:

polymerization,vulcanization and curing, sterilization of food, insect sterilization,production of micro-porous membranes

◆  X-ray microlithography using synchrotron radiation ◆  Inertial confinement fusion using heavy-ion beams as the driver ◆  Muon-catalyzed fusion ◆  Tritium production, and radioactive waste incineration, using high energy

proton beams

CATEGORY NUMBER Ion implanters and surface modifications 7'000 Accelerators in industry 1'500 Accelerators in non-nuclear research 1'000 Radiotherapy 5'000 Medical isotopes production 200 Hadrontherapy 20 Synchrotron radiation sources 70 Research in nuclear and particle physics 110 TOTAL        15'000

How many accelerators today?!

The data have been collected by W. Scarf and W. Wiesczycka (See U. Amaldi Europhysics News, June 31, 2000)

2010 data

The way for fundamental research!

ELECTRONS (e+e-): LEP 113 GeV ILC 500 GeV CLIC 3 TeV

  LHC and its upgrades   e+e-linear colliders: ILC and CLIC   Neutrino beams, factory   Muon collider   Synchrotron light sources, Free Electron Lasers   Neutron sources   Advanced accelerator concepts

PROTONS (pp): LHC 7 TeV VLHC 30 -200TeV

The proton colliders!

VLHC (pp) > 20 TeV IN DISCUSSION:  ENERGY 30 –50 TeV  UPGRADEBLE TO 100 -200 TeV  CIRCUMFERENCE UP TO ~ 600 km

Scaling of the cost

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Bρ[Tm] =1

0.29979p[GeV/c]

€

cost ∝ρ∝ E

EnricoFermi’s (1954) Space-Based World Machine

The electron colliders!

Scaling of the cost

€

Circular electron collider

power∝ E4

ρ2

\cost ∝ρ∝ E2

€

Linear Collidercost ∝ l ∝ E

Compare to

Medical therapy!

Light sources!Synchrotron light

X-Ray Laser fully coherent source of 1 Å X-rays 1012 photons pulses Short pulses: femto-to atto-seconds

reminder

  The accelerators are basic tools for physics discovery: new ideas and technological breakthrough sustained an impressive exponential progress of their performance for almost a century

  Many different type of accelerator are used for particle and nuclear physics research, however the large majority of the existing accelerators is used for a multitude of practical applications

  The synchrotrons are the backbone of accelerator complex, however old ideas and concepts are still revisited and upgraded to achieve more demanding requirements

  Colliders are the master tool in the quest of the highest energy, whilst fixed target operation allow reaching the highest rates

  Hadron and lepton colliders play complementary roles for discovery and high-resolution investigations

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panoramic on accelerators!

topics

  Fundamental discoveries in accelerator physics and technology

  Historical perspective

  Accelerator typologies   Sources   Linear accelerators   Circular accelerators   Special accelerators   Synchrotrons

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The everyone’s accelerator!

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Important discoveries I! 1900 to 1925 radioactive source experiments à la Rutherford -> request for

higher energy beams;  1928 to 1932 electrostatic acceleration ->

  Cockcroft & Walton -> voltage multiplication using diodes and oscillating voltage (700 kV);

  Van der Graaf -> voltage charging through mechanical belt (1.2 MV);  1928 resonant acceleration -> Ising establish the concept, Wideroe builds the

first linac;  1929 cyclotron -> small prototype by Livingstone (PhD thesis), large scale by

Lawrence;  1942 magnetic induction -> Kerst build the betatron;  1944 synchrotron -> MacMillan, Oliphant and Veksel invent the RF phase stability

(longitudinal focusing);  1946 proton linac -> Alvarez build an RF structure with drift tubes (progressive

wave in 2π mode);  1950 strong focusing -> Christofilos patent the alternate gradient concept

(transverse strong focusing);  1951 tandem -> Alvarez upgrade the electrostatic acceleration concept and build

a tandem;

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Important discoveries II! 1955 AGS -> Courant, Snider and Livingstone build the alternate gradient

Cosmotron in Brookhaven;  1956 collider -> Kerst discuss the concept of colliding beams;  1961 e+e- collider -> Touschek invent the concept of particle-antiparticle collider;  1967 electron cooling -> Budker proposes the e-cooling to increase the proton

beam density;  1968 stochastic cooling -> Van der Meer proposes the stochastic cooling to

compress the phase space;  1970 RFQ -> Kapchinski & Telyakov build the radiofrequency quadrupole;  1980 to now superconducting magnets -> developed in various laboratories to

increase the beam energy;  1980 to now superconducting RF -> developed in various lab to increase the RF

gradient.  1983 sc magnets with two-in-one concept  2005 first evidence of laser-plasma acceleration mechanisms (1 GeV/c in 1 mm

length)

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The Livingstone’s diagram! Livingstone plot (invented in 1950).

 The accelerator energy is expressed in semi-logarithmic scale as a function of the year of construction

 The curve shows a linear growth, e.g. the energy increases by a factor 33 every decade, thanks to discoveries and technological advances.

Recent signs of saturation ?

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Sources (1/3)!

Surface source

Volume source

Penning source Magnetron source Ion sources: ◆  positive ions sources

■  formed from electron bombardment of a gas ■  extracted from the resulting plasma:

species ranging from H to U (multiply charged)

◆  negative ion sources: principal interest is in H-, for charge exchange injection ■  surface sources: in a plasma, H picks up electrons from an activated surface ■  volume sources: electron attachment or recombination in H plasma ■  polarized ion sources: e.g., optically pumped source -> some penalty in intensity,

relatively high (> 65 %) polarization

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Electron sources ◆  electron production mechanism:

■  thermo ionic emission (pulse duration controlled by a pulsed grid) ■  photocathode irradiation by pulsed laser (laser pulse width

determines the pulse duration) ◆  initial acceleration methods

■  DC HV guns -> 50-500 keV acceleration ■  RF guns: cathode forms one wall of the RF cavity

-> rapid acceleration to > 10 MeV in a few cells -> mitigates space charge effects, -> makes for low emittance

Sources (2/3)!

NLC Electron Source layout, for polarized and un-polarized sources

RF gun

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Positron sources ◆  “conventional” positron source: can get from 10-3 :1 up to ~1:1 positron/electron as

electron energy rises from 0.2 to 20 GeV

◆  positron production through high energy photons:

RF linac

solenoid!helical undulator sweep magnet converter

high energy e- e-

e-

γ γ e+ e+

matching solenoid

RF linac

solenoid!

target 0.2 to 20 GeV e-

e+ e+

Sources (3/3)!

◆ µ± source is similar to p- source

Protons produce π±, which in turn produce µ±

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Antiproton source

horn lens

80÷150 GeV p+ target p- To a storage ring with

stochastic cooling

p+/p- yield typically ≈ 10-5