fysn15 accelerators 4 accelerators for high energy nuclear and particle physics you basically know...

fysN15 Accelerators 4

Accelerators for high energy nuclear and particle physics

You basically know how a synchrotron works.

Synchrotrons used as storage rings with internal target

Colliding, stored synchrotron beams

Linear collider for future high energy electron collisions

Free electron laser: future X-ray laser source, spinn off from linear collider development


Storage rings, Why

-The acceleration in a synchrotron takeslong time. At best you accelerate the ring content during a few seconds to full energy and extract the beam slowly for a few seconds to make collisions. Ramping down the magnets also takes a few seconds and then repeat the cycle. ca 10 times per minute depending on energy. -You have to use thin target material (mg/cm2) in order to avoidsecondary inteactions.

-With extracted beam hitting a thin external target you are using only a small fraction (%) of the accelerated particles.

-In a storage ring, noninteracting particles come back on the next turn you can keep the accelerated beam for hours, until you have used an optimal fraction of the beam.

-Targets can be either extremely thin (ng/cm2) gas jets (stationary target internal to the ring) or a colliding, stored synchrotron beams.


Why colliding beams?

B-field in practice limited to about 10 TESLA

All kinetic energy of beams make available energy in CM frame

Efficient use of accelerated particles. (come back next turn).

Long storage time-accelerate seldom- cheaper magnets due to slow ramp.

Particles to be detected have lower laboratory momenta. Better for particle id and P and in particular Pt resolution

Particles to be detected are more spread out in space which makes it easier to resolve them.


FAIR at GSI,Future nuclear physics in Europé, >2014

Atomic phys withNaked ions

Stored RIB

PRIB

RIBRadioactiveIonBeam

EOS

GSI, Darmstadt

1AGeV


Example fixed target at CERN SPS Pb at 160 A GeV


Reconstructed event

High p in lab systemFocused forwardin spaceVery long exp. setup


Colliding Au beams

B


B


The alternating E-field keeps particles in bunches


Electron cooling

Gålnander (Uppsala)

Electrons can obtain same velocity as theaccelerated ions by electrostatic acc.

Elastic collision e+ionWill decrease the relative momentum spreadIn the beam


Storage rings with internal taget

Very efficient. Storage times are long so you can run severalsuch experiments at the same time.


Large Electron Positron collider (LEP)


Large Electron Positron collider (LEP) Closed down 2000

Collision energy s ~ 200 GeV


Magnets keep particles in orbit

A charged particle, moving in a magnetic field follows a circular orbit

You want the highest possible magnetic field. This means very large current through the electromagnets.

Superconducting is the solution

circular orbit

Magnetic field

In LEP, e+ and e- Opposite directions in

same magnets


CERN, accelerators

Internal target


LHC, pp@14TeV


LHC key numbers

•Vertical B field in the dipole bends the beam round via the Lorentz force •Need very strong magnets to get the high energy beam •around the circle. Superconducting (1.9 K) dipoles producing a field of 8.4 T - current 11,700 A •2-in-1 magnet design. •Bending magnets (dipoles): 14.3 metres long. Cost: ~ 0.5 million CHF each. Need 1232 of them •Quads etc to keep beam focused and the motion stable •Stored magnetic energy up to 1.29 GJ per sector. Total •stored energy in magnets = 11GJ •One dipole weighs around 35 tonnes.

10-10 Torr (~3 million molecules/cm3)


An LHC dipole magnet


Make superconductive wire

Ca 4mm diam wire


Detector materials in a collider exp.Beams perpendicular to this view

If warm magnet

If cold magnet


RHIC consists of two 3.8 km long rings, called Blue (clockwise) and Yellow (counter clockwise)

It has six interaction regions (IR), four of which are equipped with detectors: PHENIX and some other less important experiments ;-)

This year we have deuterons in the blue ring and Au in the yellow. The Run has just started.

A briefing on RHIC

SvOutPlaceObject


Relativistic Heavy Ion Collider at Brookhaven National Laboratory (BNL)

RHIC

STARPHENIX

PHOBOSBRAHMS


RHIC Injectors: Pictures (A.Drees)

LINAC, since late 60s, accelerates (polarized) protons up to 200 MeV

Tandem Van De Graaff, since 1970, accelerates 40 species, from hydrogen to uranium


Pre-Accelerators A. Drees

Booster, since 1991, accelerates up to 2 GeV, ¼ of AGS size

Alternating Gradient Synchrotron (AGS)since 1960, 240 magnets, acceleratesup to 10 (23) GeV


RHIC Pictures

Injection arcs to blue and yellow rings

Blue and yellow rings

Blue Dump Yellow

Yellow Blue


More RHIC Pictures

Installation of final focussingtriplets

Rf storage cavities

RHIC dipole magnet


Basic Collider (and Accelerator) Concepts

Ingredients for high performance: Good vacuum in both rings. Accelerating devices (so called “RF

cavities”) to increase the particles energy (or speed) => ramp. Storage cavities to reduce bunch lengths.

Good beam lifetimes (tunes, closed orbit) Maintain high beam currents and small profiles to

get high collision rates.


Accelerate

total of 55 bunches per ring12.8 s per revolution

Abort gap

Beam is accelerated by Radio Frequency (RF) cavities:

28 MHz for acceleration 200 MHz for storage to

reduce bunch length

28 MHz defines the number of “buckets” = 360, length is 35 ns each (or 10 m)

Coasting beam: continuous, no bunch structure (debunched), cannot be accelerated

Bunched (or captured) beam: every 6th bucket, i.e. 55+5 bunches per ring with 109 ions

Currently: we are using 110 bunches per ring to increase total beam current.

Bunch 1

Bunch 55


RHIC ramp with 56 bunches

Acceleration

BLUEFill 56bunches

YELLOWFill 55bunches Transition energy

Storage energy

Correction points (stepstones)

Total Yellow currentBunched Yellow current

Total Blue currentBunched blue current

The beam is accelerated from Injection Energy (10 GeV) to Storage Energy (100 GeV). The acceleration process is called “ramp”.

Injection energy


Circulate: Betatron Motion

Particles perform oscillations around closed orbit.

The number of oscillations per revolution is called the “tune”. The quadrupole configuration (“optic”) defines the tune (betatron function).

Integer and 1/2 , 1/3, 1/4 … tunes would cause magnetic imperfections to be repetitive and resonant => beam loss

This example: tune = 11.27

1 oscillation

Number of oscillation is

defined by the magnet

configuration.


Collision Rate

Collision rate is defined to be the number of ‘events’ per second, i.e. the number of collisions happening in the center of one of the experiments (depends on the cross section)

The collision rate can be increased if:o There is more beam/bunch in the two rings

(NB,NY) o There are more bunches colliding (kb)o The beam profiles, the size of the beam, at

the interaction point, is small (x,y) -> *

revb

yx

YB fkNN

L4

(cm-2s-1 )


Cross-section at collider

revb

yx

YB fkNN

L4

R=L · σ (cm-2s-1 )

σ is the cross-sectionR is the number of events perSecond (corresponding to σ)

We normally use the luminosity integrated over the time of the measure-ment. The sensitivity of the experiment is often given as inverse barns (or eg. inverse femtobarns for a sensitive experiment).

1/σ = L So if we observe one event and the integrated L is one inverse femtobarn then the cross-section for this observation is 1 femtobarn.


The Zero Degree Calorimeter (luminosity monitor, based on known crossection)

3 modules on either side of the Interaction Region (IR) Same detector at all IRs with experiments. About +/- 18 m distance from center behind DX

=> Only neutron sensitive Covers +/- 2.5 mrad forward angle

Quite often the luminosty monitor uses some elastic reaction at small angles, whose crossection is possible to calculate.

Nuclear collisionsonly


Luminosity Monitoring during Au-Au @ 200 GeV

cogging

steering

PHENIX * = 1 mPHOBOS * = 2 mSTAR * = 2 mBRAHMS * = 2 m

Clean, compatible signal from every IR ZDC rate


e+e- colliders


Hadron and ion colliders


LINAC principle I

Ln corresponds to half wavelength

V

Vn=√2neV/m

1/2f=Ln/vn so Ln= vn/2f = vnλ/2c = βnλ/2 Can use fixed frequancy if L is made longer to

match increase in velocity


LINAC principle II

Standing wave

When v=c, Ln can stay constant.For electrons this is the normal situation

http://en.wikipedia.org/wiki/Image:Standing_wave.gif

http://en.wikipedia.org/wiki/Image:Standing_wave.gif


Why a linear collider for electrons?

Energy loss per turn of a machine with an average bending radius :

e+ e-

~15-20 km

Linear Collider: no bends, but lots of RF !

For a Ecm = 1 TeV machine: Effective gradient G = 500 GV / 15 km= 34 MV/m

LEP: 100 GeV/beam with a circumference of 27 km 500 GeV/beam would require a circumference ~ 17.000 km

cf the circumference of earth ~ 40.000 km


International Performance Specification

– Initial maximum energy of 500 GeV, operable over the range 200-500 GeV for physics running.

– Equivalent (scaled by 500 GeV/s) integrated luminosity for the first four years after commissioning of 500 fb-1.

– Ability to perform energy scans with minimal changeover times.– Beam energy stability and precision of 0.1%.– Capability of 80% electron beam polarization over the range

200-500 GeV. – Two interaction regions, at least one of which allows for a

crossing angle enabling collisions.– Ability to operate at 90 GeV for calibration running.– Machine upgradeable to approximately 1 TeV.


e+ production

The undulator produces high energy γA smaller linac gives possibility for X-Ray LaserWe come to XFEL, Free Electron Laser


ILC Projected Time Line

2005 2006 2007 2008 2015

CDR

TDR

GDI process

construction

commissioningphysics

site selection

International Funding

EUROTeVVery aggressive!


e+ production

The undulator produces high energy γA smaller linac gives possibility for X-Ray LaserWe come to XFEL, Free Electron Laser

17.5GeV from electron LINAC

Coherent X-RayFemtosecond pulse

X-ray production


XFEl, X-ray laser

Accelerator tunnel: 2.1 km Depth underground: 6 - 38 meters 1 underground experimental hall for 10 measuring stations Wavelength of X-ray radiation: 6 to 0.085 nanometers (nm) corresponding to electron energies of 10 to 17.5GeV), expandable to 20 GeV Length of radiation pulses: below 100 femtoseconds (fs) Expandable with a 2nd experimental complex of the same size Cost 109€Ready 2014 Decision taken, Swedish partnership.


What to study

XFEL energies

Max IV similar in wavelengthbut XFEL superior in pulse-length.Movie vs photograph


XFL, science

Femtochemistry Structural biology Materials research Cluster physics Plasma physics

New experimentsThe European X-ray free-electron laser XFEL opens up new experi-mental areas that are inaccessible today, for nearly all the natural sciences. The resolution in time and space, are several orders of magnitude higher than for comparable X-ray sources, It will be possible to study dynamic processes, for instance chemical reactions forming matter. Up to now, in most cases only the static properties of matter could be investigated.

Science at XFEL www.desy.de


Concluding remark

XFEL is one, in a long row of examples that fantastic measurement possibilities open up in applied science and technology, thanks to the development of instruments for basic science.

Or in other words: Accelerator technology (with all its practical benefits to human life) would never have come near to where it is today, if it wasn’t driven by the curiosity of basic science.

Profit and practical use is simply too short sighted for such competence buildup over several decades.

One can compare with the space program

fysn15 accelerators 4 accelerators for high energy nuclear and particle physics you basically know...

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high energy beam

beam storage rings

accelerated beam

available energy

extracted beam

beam round

high energy nuclear

long storage time