What is an Antiproton? What is an Antiproton?

Keith Gollwitzer

Antiproton Source Department

Accelerator Division

Fermilab

8 August 2009

What is an Antiproton?What is an Antiproton?

• Government issued Webster’s Dictionary:– “The antiparticle of the proton”

• Antiparticle definition “subatomic particle having the same mass, average lifetime, spin, magnitude of magnetic moment but opposite direction, magnitude of electric charge but opposite sign, opposite intrinsic parity”

• What about “Antimatter”?– “Matter made from antiparticles”

• What is a Pbar?– Shortened name for Antiproton based upon symbol

used in physics– Over-line or bar above symbol means “anti”

p for proton

p for antiproton

• So what are protons?– With neutrons form

different atomic nuclei• Simplest is Hydrogen

nucleus of a single proton

– Made up of quarks (up and down)

• Proton is uud• Neutron is ddu

• Antiproton is uud– Antiquarks

Matter and AntimatterMatter and Antimatter• Matter

– Plentiful and “free” by separating hydrogen components • 13.6eV to ionize electron from proton

• Antimatter – Scarce in nature

• Created by cosmic rays interacting with the atmosphere. – The original “Fixed Target” experiment

• Positrons are by product of normal everyday radioactivity

• Particle & Antiparticle when they met --- annihilate – Who first informed us of this?

Where else Antimatter recently?Where else Antimatter recently?• Dan Brown’s Angels & Demons

• We will come back to this later• Move back to reality and what Fermilab does

History: Particle CollisionsHistory: Particle Collisions

• Originally studied Cosmic Ray Particles Cosmic rays are energetic

• No human control of energy, type, when

– Detection done at high altitudes

– Discovered many types of particles that are not everyday matter

• Accelerators allow control of collisions– Allowed study of many new

particles• Some with masses greater

than the initial particles

Fermilab CollisionsFermilab Collisions• Fixed Target

– In the Fixed Target mode, ½ of the experiment is at rest.

– The other ½ is moving at high energy.

– There is a big “relativistic” penalty to be paid because of the conservation of momentum.

• Collider Mode– In the Collider mode, two particles

of equal mass and energy travel directly at each other.

– The total momentum of the system is zero, so there is no “relativistic” penalty to be paid.

– Most of the energy goes directly into making new particles.

2targetbeamCM 2 cmEE

beamCM 2EE

Particle AccelerationParticle Acceleration

• A charged particle will be accelerated by a voltage potential.– Opposite charges attract.

• One electron Volt (eV) is the energy gained by an electron (or any particle of unit charge) when it is accelerated through a potential of 1 Volt.

+

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To Higher EnergiesTo Higher Energies

Scientific PrefixesK (kilo) 1,000

M (mega) 1,000,000

G (giga) 1,000,000,000

T (tera) 1,000,000,000,000TeVatron accelerates beam to nearly 1 trillion electron Volts

Batteries are 1Volt per inch

A trillion inches is 15.8 million miles

First Stage of the AccelerationFirst Stage of the Acceleration• Crockoft-Walton Accelerator

– Can be thought of as a 750,000V DC voltage source.– The maximum voltage is limited by how much the air

can “stand-off” before sparking.

Second Stage of AccelerationSecond Stage of Acceleration

• A linear accelerator (LINAC)

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.secv

Lt

.secv

L2t

Drift Tube LinacDrift Tube Linac

SynchrotronsSynchrotrons• The Fermilab Linac is 130

meters long and reaches an energy of 400 MeV (1 million Volts per foot)

• To get to 980 billion volts, a Linac would have to be

– 200 miles long at 1 million Volts per foot

• What about using the Linac over and over?

– The drift tube spacing at the beginning of the Linac would be wrong for higher energy particles

• But a Synchrotron could be used!

– Dipoles are used to bend particles

– Quadrupoles are used to focus particles

– RF cavities are used to accelerate particles

Dipole MagnetsDipole Magnets• Dipole magnets

are used to bend the particle’s path

• The magnet body confines or concentrates the magnetic field

• The pole faces shape the magnetic field

Quadrupole MagnetsQuadrupole Magnets• Quadrupoles are needed for

focusing particles• Not all the particles are on the

“perfect” orbit.– If the particle is on the right

orbit – don’t bend.– If the particle is on the inside

– bend to the outside.– If the particle is on the outside

– bend to the inside.

Pre-AccPre-Acc

First stage of acceleration

Start with Hydrogen Bottle

Final Energy = 750KeV

LinacLinac

Final Energy of 400MeV

Booster RingBooster RingFinal Energy of

8GeV

Uses combined function magnets

Main Injector RingMain Injector RingFinal Energy of 150GeV

2 mile circumference

Upper ring is the Recycler

Tevatron RingTevatron RingFinal Energy of

980GeV

4 mile circumference

Uses cryogenic superconducting

dipoles

Fixed Target Beam LinesFixed Target Beam Lines

Fixed Target program hasrun at 800GeV and currently at 120GeV

Neutrino Program runs at two different energies

8GeV and 120GeV

Antiproton SourceAntiproton Source

120GeV protons from Main Injector hit (fixed) production target.

Antiproton Source beam lines and rings capture and collect 8GeV pbars

8GeV pbars are sent to the rest of accelerator complex to be injected into the Tevatron for the collider program

The Antiproton Target StationThe Antiproton Target Station

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Pul

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Mag

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29 cm 81cmB

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Aft

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Nickel Alloywith air cooling

through the copper disks

The Antiproton Target StationThe Antiproton Target Station

3

Tar

get

Li L

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Pul

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Mag

net

29 cm 81cm

““Hot” BeamHot” Beam• The pbars leave the target at a wide range of energies,

positions, and angles.• This randomness is equivalent to temperature. The pbar

beam is “hot” coming off the target.– This “hot” beam will have a difficult time fitting into a beam pipe of

reasonable dimensions.– Also, this “hot” beam is very diffuse and not very “bright”. Bright

beams are needed in the collider in order to increase the odds that the particles collide with particles in the other beam

• Stochastic cooling is a technique that is used to remove the randomness of the “hot” beam on a particle by particle basis.

Stochastic CoolingStochastic Cooling• Stochastic cooling uses feedback• A pickup electrode measures an

“error” signal for a given pbar. – This error signal could be the

pbar’s position or energy– The pickup signal can be

extremely small, on the order of 1pW

– The Debuncher pickups are cooled to 4 Kelvin to reduce the effect of thermal noise and 300 Kelvin “shine”

• This signal is processed and amplified– The gain of the Debuncher

systems is about 150 dB• The opposite of the error signal is

applied to the pbar at the kicker– The kicker signal can be as large

as 2 kW

Stochastic Cooling PickupsStochastic Cooling Pickups

Stacking Cycle - DebuncherStacking Cycle - Debuncher• Every 2.2 seconds

– 8 x 1012 (8 trillion) 120GeV protons onto target

– Beam line transfers negatively charged 8GeV particles to the Debuncher

• Other particles decay or radiate away in a few turns

• Beam circulates every 1.6 microseconds

– 0.0000016 seconds

– 2.5 x 108 (250 million) 8GeV pbars circulate in the Debuncher

• Stochastic cooling reduces the phase space by a factor of ten

– Transfer all pbars to the Accumulator

Stacking Cycle - AccumulatorStacking Cycle - Accumulator• RF system decelerates from

injection to deposition orbit• Stochastic Cooling

• 2-4 GHz stacktail– Pushes and compresses

beam into the core

• 2-4 & 4-8 GHz core momentum– Gathers beam from the

stacktail

• 4-8 GHz transverse slotted waveguide pickups

– Increase particle density by factor of 5000

– Factor of 3-5 decrease in both transverse phase space dimensions

Cyan = After injection before RF captureGreen = After RF is turned off

• Accumulation rate of 2.5 x 1011 (250 billion) antiprotons per hour

• When reach 4 x 1011 (400 billion) pbars, transfer beam out of the Accumulator to the Main Injector into the Recycler Ring for storage until needed for the Tevatron collider program

• Most number of antiprotons that have been on site at Fermilab at one time (Accumulator, Recycler and Tevatron)– 6 x 1012 (6 trillion) pbars

• 10pg = 0.000 000 000 01grams

• In 2008 produced – 1400 trillion pbars (2.3ng)

p

ppp

pp

Total Antiprotons at FermilabTotal Antiprotons at Fermilab

Using AntiprotonsUsing Antiprotons•Antiprotons are collected in Recycler Ring at 8GeV for a day

•Then antiprotons are sent in 36 batches to Main Injector to be accelerated to 150GeV

•Antiprotons are transferred to the Tevatron which already has 36 proton batches

•Both beams are accelerated to 980GeV

Tevatron ColliderTevatron Collider• Two beams in one

accelerator going in opposite directions!– Electrostatic separators

keep beams on different helical orbits during acceleration

• Bring beams into collisions by collapsing helix orbits at desired interaction points– Middle of detectors

Angels & DemonsAngels & Demons + Antiprotons + Antiprotons

• Page of “Facts” in a book of fiction

• Antimatter exists

• 0.25 grams of antimatter mixed with 0.25 grams of matter would produce an explosion equivalent Hiroshima (wipe out the Vatican)

Angels & DemonsAngels & Demons + Antiprotons + Antiprotons• Can easily produce 0.25 grams of

antimatter– Fact: Fermilab is the world leader for

producing antiprotons/antimatter– It would take 100 million years

• Can easily transport that much antimatter– Fact: Fermilab’s bottles are over 6

miles of rings

• It would cost a lot

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pbarkg

hrpbars

hrMWMW/102940$

1000107.1102

/50$20 *12

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*2940 trillion $ ~ 420 x U.S. GNP

Antimatter UsesAntimatter Uses• Scientific Studies

– Laboratories use antimatter to collide with matter– Study why no antimatter today

• Applications– Example is Positron Emission Tomography (PET Scans)

• Not Spaceships

SafetySafetyYou will be on tours in different areas

– Including into the Antiproton Source tunnel

• No smoking, eating or drinking in the tunnel enclosure

• Please be careful on the stairs and walking

– Edges of components and cables do stick out

Tunnel is hot – 90oF!

TodayToday

Enjoy your time at Fermilab

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Hope that you have learned a little about antiprotons, particle accelerators and what goes on at Fermilab