View
1
Download
0
Category
Preview:
Citation preview
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)
€
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
€
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
117
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
€
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
30
panoramic on accelerators!
topics
Fundamental discoveries in accelerator physics and technology
Historical perspective
Accelerator typologies Sources Linear accelerators Circular accelerators Special accelerators Synchrotrons
31
The everyone’s accelerator!
32
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;
33
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)
34
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 ?
35
36
37
38
39
40
41
42
43
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
44
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
45
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±
46
Antiproton source
horn lens
80÷150 GeV p+ target p- To a storage ring with
stochastic cooling
p+/p- yield typically ≈ 10-5
Recommended