Real Accelerators: a facility overviewthe nuts and bolts…and gaskets and resistors

United States Particle Accelerator School – Accelerator FundamentalsIndiana University/Baton Rouge6 – 17 January 2003Elvin HarmsBeams Division/FermilabHarms@fnal.gov

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Introduction

‘Scratch the surface’ overviewWhat goes into making a real working acceleratorPerspective of ‘big’ machinesPrinciples applicable to all types of acceleratorsInteractive

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Scale

Table topE. O. Lawrence

early cyclotron ‘dees’

Berkley, California USA

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Scale

Big machine

LHC – 27 kilometers

(under construction)

CERNGeneva,

Switzerland

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What makes up an Accelerator?

Two primary components– Magnet system

• Keep the beam focused• Keep the beam on course

– Radiofrequency system• Impart energy to the particle beam

AccelerationMaintain beam’s energy

(synchrotron light)Maintain structure (colliding beams)

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Magnets

Electromagnets– Conventional

• Water or air-cooled• Copper or aluminum coils• Iron shapes and contains the field

– Superconducting• Liquid helium cooled• Higher fields > higher energies• Ramp slowly• Coil placement critical to field

Permanent

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Magnets

Gradient or ‘Combined function’– Steering and focusing by a single element

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Magnets

Separated function– Focusing and bending are done by separate

magnets• Quadrupole for focusing• Dipole for bending

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Magnets

Flavors– Dipoles– Quadrupoles– Correctors

• ‘trim’ dipoles• (skew) quadrupoles• sextupoles• even higher order• Special purpose

– Injection/Extraction– Light sources

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Magnets

Flavors

Quadrupole Sextupole

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Magnets

Flavors– Undulator/Wiggler

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Magnets

Superconducting

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Radiofrequency systems

Low level– Frequency– Amplitude (voltage)– feedback

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Radiofrequency systems

High level– Amplification– Accelerating cavities

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Piecing the machine together

A true complex, not just a machine

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Piecing the machine together

Cascade of accelerators– Different technologies are more efficient in different

energy regimes• Ion sources• Injectors• Collectors• Transfer lines• End accelerator

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Piecing the machine together

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Piecing the machine together

Power– Accelerators require

lots of it!– Stable and reliable

source

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Piecing the machine together

Power– Magnets connected in series

• Distribution• Regulation/feedback loops• Current changes through a component leads to changes

in beam behavior (never better…)

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Piecing the machine together

Contain the beam in a pipeVacuum– Particles travel a long way while being accelerated/in

storage– Scattering by air can lead to reduced beam quality

• emittance growth• energy loss

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Piecing the machine together

Vacuum– Quality: 10-7 mbar and lower for

circular machines– Distributed pumping– Ion pumps, TSP’s, cryo

pumping– Pick the correct materials and

seals– Meticulous cleaning beforehand– UHV: bake the chamber in

place

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Piecing the machine together

Cooling– Virtually every component requires some sort of

external cooling, electronics, too– Water is most common medium– Superconducting components require cryogens– Coolant should be in as direct contact with heat load

as possible (best thermal transfer)

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Piecing the machine together

Water Cooling– Conventional magnet coils

typically have a coolant hole through middle of conductor

– Control the chemistry• Water must be low conductivity

(deionized) since water & current flow together

• Remove the dissolved oxygen• Minimize particulates – small

orifices– Regulate the temperature

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Piecing the machine together

Cryogenic Cooling– Superconducting

coils bathed in liquid helium at 4.6K or less

– Lots of refrigeration (significant power use)

– Low heat loss– Magnets are super

“thermos” bottles

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Piecing the machine together

Enclosure– Electrical and Radiation

hazards when operating– Personnel protection

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Piecing the machine together

Equipment housing– Want power supplies and other interface equipment

as close as possible, but accessible

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Keeping it all together / Making it work

Alignment– Keep it in line!

– Tevatron 150 to 800 GeV in 30 seconds

– 0 = 21s– C ~4 miles– > 1.4 million miles traveled

during acceleration alone

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Keeping it all together / Making it work

Alignment– Where is it?

• Position of components with respect to each other

• Macro-positioning

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Keeping it all together / Making it work

Alignment– Move it

• Reference system• Fixturing• Component stands• Remote positioning

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Keeping it all together / Making it work

Diagnostics– Where’s the beam, what does it look like, how many

particles?• Beam Position Monitor• Beam Loss Monitor• Profile Monitor/Wire scanner• Schottky detector• Toroid• Resistive Wall Monitor• Damper• …

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Keeping it all together / Making it work

Diagnostics

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Keeping it all together / Making it work

Diagnostics

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Keeping it all together / Making it work

Controls system– Monitor and Control– Timing– Fast response– Beam removal– Coordination– Human interface

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Where does the beam go?

Experiments / End Users– Internal to machine

• Interaction regions• Beam quality/size

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Where does the beam go?

Experiments / End Users– External

• Rate, energy, size, and location to deliver beam

– Single-turn– Resonant extraction– Synchrotron light

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Resources

People are the most important componentOther resources– Books– Schools, Workshops, conferences– Web