PARTICLE BEAMS, TOOLS FOR MODERN SCIENCEHans-H. Braun, CERN

History and Physics Principles of Particle AcceleratorsOriginsFrom Zyklotron to Synchrotron Defocusing + Focusing = FocusingParticle Colliders

An Overview of Accelerator ApplicationsSynchrotron Radiation, from Nuisance to Bright LightBeams for MedicineParticle Accelerators for Particle Physics

Introduction to Linear e+/e- Colliders and CLICLinear Colliders - Motivation and ConceptTechnical Challenges for Linear CollidersCLIC

5th Particle Physics Workshop

National Centre for Physics

Quaid-i-Azam University Campus, Islamabad

PARTICLE BEAMS, TOOLS FOR MODERN SCIENCEHans-H. Braun, CERN

1st LectureHistory and Physics Principles of Particle Accelerators

o Origins

o From Zyklotron to Synchrotron

o Defocusing + Focusing = Focusing

o Particle Colliders

5th Particle Physics Workshop

National Centre for Physics

Quaid-i-Azam University Campus, Islamabad

One of the first particle beam set-up’s

The Rutherford-Geiger-Marsden Experiment (1906-1913)

Showed that the Thomson (or Plum Pudding) model of the atom is wrong !Atoms consists of extremely small nucleus of positive electric charge, carrying almost all the mass of the atoms. The nucleus is surrounded by a diffuse cloud of almost weightless electrons with negative charged.

Origins

(Marsden didn’t get a stamp)

Rutherford experiment startedinterest in subatomic length scales

Ernest Rutherford cajoled for years British industry to push development of high voltage sources as replacement for the α-emitters in his experiments.

Why ?

• Higher flux of particles

• Particles of higher velocity ⇔ higher momentum ⇔ higher kinetic energy

Motivations for higher beam energies I

Theory of microscope:

Only objects larger than the wavelength λ of light can be resolved

Louis De Broglie 1923:

Particles have wave properties with wavelength given by

Uqmh

Emh

Ph

KIN 22===λ

106 107 108 10910-16

10-15

10-14

Accelerating Voltage (MV)

λ (m

)de Broglie wavelength of α particles vs. kinetic energy

strongest αsources

size of proton

Coulomb barrier for charged-particle reactions

++++

+electric

force

Motivations for higher beam energies II

Einstein* 1905: Energy equivalent to mass

E = m c2

⇒ Collisions of energetic particles can createnew particles, if kinetic energy is sufficient

*many stamps

Traces of particles produced in collision of gold atoms at 100 GeV

Motivations for higher beam energies III

Electrostatic Generators

Van de Graaff Generator, 1931

Limited to 20MV

by electrical sparking

Linear accelerator (Rolf Wideroe 1928)

Lengths of drift tubes follow increasing velocity

Particle gains energy at each gap, total acceleration NGAP ·VRF

Applied acceleration is N times higher than electric voltage !

fvL

21

=

… and half an RF period later

In 1928 voltage from RF oscillators was small and the linear accelerator,(or LINAC ) not competitive with electrostatic accelerators

RADAR technology boosted the development of RF sources duringWorld War II. This eventually made LINAC’s the accelerator ofchoice for many applications.

Wiederoe’s first LINAC

Fermilab proton linac (400MeV)

Inside proton linac

Electrically coupled TM010 resonant cavities

Condition for acceleration Δϕ = ω/c·d, with Δϕ the phase difference between adjacent cells

Electron LinacsBecause of higher particle velocity (≈c0), higher frequency (1.3-30 GHz) and different accelerating structure types.

Most common building block it traveling wave structure.

pulsed RFPowersource

d

RF load

Electric field RF wall currents

)structures ngaccelerati copperfor valueQ (typical

107,

bygiven lossPower

)405.2(2

)(2

W

Energy Stored

! oft independen

405.2 function, Bessel of

zero 1by given frequency Resonant

)sin()(

)cos()(

8

21

220

0

2

0 0

220

st

10

00

fQW

Q-P

JREd

dzddrrBcE

dRc

trJc

EB

trJEE

Z

d R

Z

c

cZ

⋅≈=

=

+=

=

−=

=

∫ ∫ ∫

ω

επ

φε

ω

ω

ω

ω

π

φ

ωφ

ω

mode"cavitybox "pill 010TM

EZ

Bφ

0 0.5 1 1.5 2 2.50

50

100

ω/c r

EZ (M

V/m

)

0 0.5 1 1.5 2 2.50

0.1

0.2

Bφ (T

)

d

R

23

0

0

)(1

)(1

110

)cos21(

sin velocity Group

wavenumber

cosa21 relation Dispersion

;,,Ansatz

0

kda

kddadkdv

dk

eEeEeE

EaEEE

G

tii

tii

tii

iii

+==⇒

=

+=⇒

===

=″+″++″

−+

+−

+−

ωω

ϕϕ

ωω

ω

ϕωωϕω

resonators of chain Coupled

d

ω

ϕ

ELECTRONP vdk

v ===ϕ

ωω

ω0

i i+1i-1

3 GHz accelerating structure of CTF3

Input power 30 MWPulse length 1.5 μsLength 1 mBeam current 3.5 AAcceleration 9 MVFrequency 2.99855 GHz

SiC load

Damping slot

Dipole modes suppressed by slotted iris damping (first dipole’s Q factor < 20)and HOM frequency detuning

Cyclotron Lawrence & Livingston 1932

The same acceleration gaptraversed many times !

! velocity oft Independen

2

frequency Cyclotron m

Befπ

=

22 timeRevolution

y trajectorof Radius

Force lCentrifuga Force Lorentz2

Bem

vRT

BevmR

RvmBve

ππ==

=

=

=

R

Example: a typical proton Zyklotron

( ) MeV 77.86J10247.12

MHz 25.922

m 0.75T 1.7

112

=⋅==

==

==

−

PKIN m

RBeE

mBef

RB

π

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

=

20

0 1

? velocity oft Independen

2

frequency Cyclotron

cmEmm

mBef

KINeffective

π

⇒ Cyclotron principle works only for beam energies

EKIN m0 c2

For example for protons

EKIN 938 MeV

(with some tricks 600 MeV can be obtained)

Theory of relativity

E.M. McMillan V. Veksler

The Synchrotron

Proposed independently and simultaneously 1945by McMillan in the USA and Veksler in the USSR

N

S

Electromagnet ofvariable strength

RF electric field withvariable frequency f=g(t)

Beam on circular orbitwith constant radius

injection

extraction

accelerat

ion

injectiontime

mag

netic

fiel

d Magnetic cycle synchrotron

injection

extraction

accelerat

ion

injectiontime

mag

netic

fiel

d Magnetic cycle synchrotron

To make synchrotron work magnetic field, RF frequency and voltage have to be controlled following a system of coupled equations:

Taken relativistic mass increase into account !

22

42

42

22

)(1)(

2)(

1)()(

)(

cm(t)Ecmctv

Rπv(t)tf

cmcm(t)E

RecmtB

tfVedt

(t)dE

kin

kin

RFkin

+−=

=

−+

=

=

⇒ Synchrotron can be build for very high energies.For proton beams limits are given by achievable magnetic fieldand size.Largest synchrotron LHC at CERN (under construction),27km circumference, BMAX=8.3 T, EKIN=7.000.000 MeV

f(t) VRF

B(t)

EKIN(t)

Layout of an early proton synchrotron

Variation of parameters with time in a proton synchrotron

0 0.2 0.4 0.6 0.8 1Time@sD

1000

2000

3000

4000

5000

Eciteni

KVe

M

Proton Synchrotron, R=10m, VRF=10 kV, EKinetic at injection=10MeV

0 0.2 0.4 0.6 0.8 1Time@sD

1

2

3

4

5

fnoitulove

R@zHMD

0 0.2 0.4 0.6 0.8 1Time@sD

0.25

0.5

0.75

1

1.25

1.5

1.75

2

citengam

dleif@TD

0 0.2 0.4 0.6 0.8 1Time@sD

5 ´ 107

1 ´ 108

1.5´ 108

2 ´ 108

2.5´ 108

3 ´ 108

elcitrapyticolev@m�sD

An electromagnet in quadrupole configurationwill have a similar effect on a particle beam.

However there is one big difference, considering the direction of Lorentz forceyou find that it focuses in one plane,but defocuses in the other !

In light optics an array of focusing lenses is used to keep light rays together

The action of each lens can be describedas an angle change of the trajectory

How to keep beam particles together ?

xΔφ

fx

−=Δφ

N

N S

S

iron yoke

coil

quadrupole magnet

1952 Courant, Snyder and Livingston propose “alternating gradient focusing”

focusing + defocusing = focusing

defocusing + focusing = focusing

Introduction of AG focusing had tremendous impact on beam quality and accelerator size and cost !

In turned out that Christofilos from Athens had filed an U.S. patent on this idea already in 1950, but nobody had noticed !

E. Courant H. Snyder

N. Christofilos

S. Livingston

Cell

FODO latticefor synchrotron

Quadrupolefocusing

Quadrupoledefocusing

Dipole (B=Bend)

Particle CollidersFrascati and Novosibirsk, 1961

B. Touschek*

Det

ecto

rs

Synchrotron

Reaction products

“Fixed target”

extracted beam

Detectors

Storage ring

Reaction products “Interaction point”

injection

extraction

acceleration

injectiontime

mag

netic

fiel

d Magnetic cycle synchrotron

time*with Lola

injection

storage

acceleration

mag

netic

fiel

d Magnetic cycle storage ring

A. Budker

What is the advantage of collider?

T

Xm

cmE 2

22

>2

2cmXE >

particle at rest of mass mT

beam particlewith energy E new particle

of mass mX

interaction

particle of clockwise beam with energy E new particle

of mass mX

interaction

particle of counterclockwisebeam with energy E

Fixed target Colliding beams

Conservation of energy and momentum

Same pages from Bruno Touscheks1960 notebook

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

e+/e-

p/pp/pp/p

e+/e-

e+/e-

e+/e-

e+/- /pe+/e-

e+/e-

e+/e-

e+/e-

e+/e-

p/p and Pb/Pb1961 VEP 1, Novosibirsk, USSR e-/e-

1971 ISR, CERN, Switzerland p/p2000 RHIC, Brookhaven, USA ion/ion

2007

DAΦNE

LNF Frascati500 MeV e+/e- collider

In the tunnel of the CERN SppS proton antiproton collider450.000 MeV, 7 km circumference

1967 Unified Theory of electromagnetic and weak interactionField quanta γ, W± and Z0

1979 Nobel price for Glashow, Weinberg, Salam

1983 Discovery of W± and Z0 at SppS /CERN

1984 Nobel price for Rubbia and van der Meer

UA1 detector

W event

SppS7 km

Electron, proton and ion sourcesVacuum systemsMagnet technology

Iron/copper magnetsFast pulsed ferrit magnetsSuperconducting magnetsPermanent magnets

RF power sources Accelerating RF structures

Normal conducting Superconducting

Cryogenic SystemsElectromagnetic sensorsHigh speed electronicsHigh precision electronicsElectric power systemsLarge scale precision alignmentLarge scale computer control systemsLaserTunnel construction techniques. . .

Accelerators

Enabling technologies for accelerators

Many technological developments were promoted by accelerator needs

Recommended literatureAccelerator physics generalH. Wiedemann, “Particle Accelerator Physics,” (2 volumes), Springer 1993K. Wille, “The Physics of Particle Accelerators : An Introduction,”Oxford University Press, 2001 S.Y. Lee, “Accelerator Physics,” World Scientific, 2004 A. Chao and M. Tigner (editors), “Handbook of Accelerator Physics and Engineering,”World Scientific, 1999T. Wangler, “RF Linear Accelerators,” John Wiley 1998M. Minty and F. Zimmermann, “Measurement and Control of Charged Particle Beams,”Springer 2003Accelerator key technologiesM.J. Smith and G. Phillips, “Power Klystrons Today,” John Wiley 1995M. Sedlacek, “Electron Physics of Vacuum and Gaseous Devices,” John Wiley 1996H. Padamsee, J. Knobloch, T. Hays, “RF Superconductivity for Accelerators,”Wiley 1998J. Tanabe, “Iron Dominated Magnets,” World Scientific 2005K. Mess, P. Schmüser, S. Wolff, “Superconducting Accelerator Magnets,”World Scientific, 1996

For more accelerator book references http://uspas.fnal.gov/book.html

PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE Hans-H. Braun, CERN

2nd LectureExamples of Modern Applications and their Technological Challenges

o Synchrotron Radiation, from Nuisance to Bright Light

o Beams for Medicine

o Particle Accelerators for Particle Physics