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What is an Antiproton . Keith Gollwitzer Antiproton Source Department Accelerator Division Fermilab 18 August 2007. p for proton p for antiproton. What is an Antiproton?. Government issued Webster’s Dictionary: “The antiparticle of the proton”

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what is an antiproton

What is an Antiproton

Keith Gollwitzer

Antiproton Source Department

Accelerator Division


18 August 2007

what is an antiproton1

p for proton

p for 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”
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
protons and antiprotons
Protons and Antiprotons
  • Protons
    • Plentiful
    • Get “free” protons by separating hydrogen components
      • 13.6eV to ionize electron from proton
  • Antiprotons
    • Scarce in nature
      • Created by cosmic rays interacting with the atmosphere.
        • The original “Fixed Target” experiment
  • Particle and Antiparticle when they met --- annihilate
    • One big physics question is why there is little antimatter
    • I’ll talk about Dan Brown later
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

Particle Collisions
fermilab collisions
Fermilab 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.
particle acceleration



Particle 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.
to higher energies
To Higher Energies

Scientific Prefixes

K (kilo) 1,000

M (mega) 1,000,000

G (giga) 1,000,000,000

T (tera) 1,000,000,000,000

TeVatron 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 acceleration
First 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 acceleration
Second Stage of Acceleration
  • A linear accelerator (LINAC)
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 magnets
Dipole 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 magnets
Quadrupole 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 acc

First stage of acceleration

Start with Hydrogen Bottle

Final Energy is 750keV


Final Energy of 400MeV

booster ring
Booster Ring

Final Energy of 8GeV

Uses combined function magnets

main injector ring
Main Injector Ring

Final Energy of 150GeV

2 mile circumference

Upper ring is the Recycler

tevatron ring
Tevatron Ring

Final Energy of 980GeV

4 mile circumference

Uses cryogenic superconducting dipoles

fixed target beam lines
Fixed Target Beam Lines

Fixed Target program has

run at 800GeV and

currently at 120GeV

Neutrino Program runs at two different energies 8GeV and 120GeV

antiproton source
Antiproton 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 station

29 cm




Li Lens


The Antiproton Target Station



Nickel Alloy

with air cooling

through the

copper disks

the antiproton target station1

29 cm




Li Lens


The Antiproton Target Station
hot beam
“Hot” 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 cooling
Stochastic 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 (a factor of 1015)
  • The opposite of the error signal is applied to the pbar at the kicker
    • The kicker signal can be as large as 2 kW
stacking 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 x 108 (200 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 - Debuncher
stacking 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

Stacking Cycle - Accumulator

Cyan = After injection before RF capture

Green = After RF is turned off

total antiprotons at fermilab







Total Antiprotons at Fermilab
  • Accumulation rate of 2 x 1011 (200 billion) pbars per hour
  • When reach 5 x 1011 (500 billion) pbars, transfer beam out of the Accumulator to the Main Injector into the Recycler Ring for storage until needed for Tevatron
  • 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
  • This last year produced
    • 825 trillion pbars (1.4ng)
dan brown and antiprotons
Dan Brown and Antiprotons
  • Page of “Facts” in a book of fiction
  • Fact: 0.5 grams of antiprotons mixed with 0.5 grams of protons would produce an explosion equivalent Hiroshima
  • Fiction: Can easily produce, capture and transport that much antimatter
    • Fact: Fermilab’s bottles are over 6 miles of rings and would take 80 million years
      • It would cost a lot

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

using antiprotons
Using 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 collider
Tevatron 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

You will be on tours in different areas

  • Including into the Antiproton Source tunnel
    • No smoking, eating or drinking in enclosure
    • Please be careful on the stairs and walking
      • Edges of components and cables do stick out
    • Tunnel is hot – 95oF!

Enjoy your time at Fermilab

Please take pictures

Please ask questions

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