Fermilab has been the world's premier high energy physics particle accelerator facility for well over 30 years. Fermilab has been instrumental in helping to complete our understanding of the Standard Model of Matter as depicted in the chart above. It will NOT be closing down on September 30, 2011. Only the Tevatron accelerator at Fermilab will cease to operate. Fermilab still has a number of on-going and future projects to keep it contributing to the field for several more years.
Because of the coming closure of the Tevatron and the recent news from CERN about neutrino measurements possibly exceeding light speed, it seemed appropriate to put the Fermilab story into a diary. More to follow below the squiggle. ⬇
Where is Fermilab Located |
Fermilab is about 40 miles directly west of downtown Chicago as shown below. Groundbreaking was in 1968. The area at that time was rural nestled between some west suburban small towns. Today, the surrounding area is bustling with activity.
This zoomed image below of the heart of the facility shows that much of it still retains the open spaces it once had. This link will provide a large amount of
information on the site's history.
As director of the National Accelerator Laboratory in 1967, Robert R. Wilson determined that this facility would provide certain leadership for scientific contributions to society beyond the high energy physics mission of the physicists. The nature of Fermilab, and its 6,800-acre site, has included inquiry into all fields of science. The Lab is a natural laboratory setting for studying use of vast open space including grasslands and woodlands and their wildlife populations.
Tevatron and 28 Years of Science |
The Tevatron accelerator is the set of red colored objects in the image below from Fermilab's Main Ring tunnel. The blue colored objects make up the accelerator originally installed before the Tevatron came into operation in the mid-80s.
The red and blue objects are 19 foot long electromagnets specially wound to produce vertical magnetic fields along their center lines. There are about 1000 magnets end to end in the main ring tunnel. The total circumference is nearly 4 miles. The blue ones are conventional water cooled magnets. The red ones are wound with
superconducting cable. By cooling them with liquid helium, they become superconducting. That means they have no resistance to electric current flow and generate no heat. The magnetic fields they can generate are much stronger.
More about the science of the accelerators at Fermilab a little later in the diary.
Shortly after 2 pm on September 30, 2011, the Tevatron magnets will be turned off. An operator at the laboratory in Batavia, Illinois, will divert the final bunches of protons and anti-protons into a solid metal block. The history and contributions of the Tevatron are highlighted in this interactive time line from the Fermilab office. It has had an illustrious 28 year history. But, much work is still unfinished. There are plans for the future described in more detail here.
During the next few years, the two detector collaborations that use the Tevatron, CDF (B0) and DZero (D0), will continue to analyze data, produce results and publish scientific papers. CDF and DZero explore the subatomic world to search for the origin of mass, extra dimensions of space and new particles and forces that would help explain the nature of our universe.
Fermilab will continue investigating the science behind our universe using present and future experiments at the frontiers of particle physics. While the Tevatron has been Fermilab’s major focus in the past few decades, the laboratory's particle physics portfolio is diverse. The laboratory will continue to operate most of the ten accelerators on site and use them to continue to produce and provide particle beams for experiments involving protons, neutrinos and muons.
Science of the Fermilab Accelerator System |
Fermilab starts with Hydrogen gas in a bottle. They end up with protons and anti-protons traveling at
99.999954 percent of the speed of light in opposite directions around a four-mile circumference.
The two beams collide at the centers of two 5,000-ton detectors positioned around the beam pipe at two different locations, (B0 and D0 in the zoomed image above). The collisions reproduce conditions in the early universe and probe the structure of matter at a very small scale.
Scientists at Fermilab also study particle collisions by directing beams into stationary targets to produce neutrino beams. (Fixed Target Area in the zoomed image above)
The Tevatron tunnel is buried 25 feet below grade, underneath an earthen berm. In the Tevatron, beams of particles travel through a vacuum pipe mostly surrounded by superconducting electromagnets. The magnets bend the beam in a large circle.
The Tevatron has more than 1,000 superconducting magnets, which produce much stronger magnetic fields than conventional magnets. Operating at negative 450 degrees Fahrenheit, the cable inside the magnets can conduct large amounts of electric current without resistance. The extra strength allows for the acceleration of particles to higher energy.
Higher energy means collisions can probe deeper into the structure of the protons and anti-protons to study the quarks within them. Protons are made of two up quarks and one down quark.
Protons Begin at the Cockcroft-Walton Generator |
Zoom in more on the Fermilab site above. It reveals the 16 story office building and some nearby buildings. Of note are C-W the Cockcroft-Walton generator, the Linac linear accelerator, the Booster Ring, and the edge of the Main Ring. Each part will get described below. First, let's take a look at C-W.
This sci-fi looking apparatus is called a Cockcroft-Walton generator. It is a high voltage generator reaching 750,000 volts. Within it is a bottle of Hydrogen gas which is slowly bled out into an evacuated chamber inside the rectangular heart of the machine. The gas is electrified and each molecule is given an extra electron to make it ionized and not neutral any more. As the gas escapes the chamber, the molecules feel the 750,000 volts of potential difference and accelerate up to high speed toward a positively charged electrode. In high energy physics language, we say the particles have acquired an energy of 750000 electron volts, 750000 ev, or 750 kev.
The 750 kev protons enter via an evacuated pipe into this 150 meter long linear accelerator. An oscillating electromagnetic field between the copper chambers hanging down from above speed up the protons to an energy of 400 million electron volts, 400 Mev, toward a carbon foil. As they pass through the foil, the electrons are stripped leaving a high speed proton. These protons pass through the vacuum pipe to the Booster Ring. Some of the electro-magnets of the booster are pictured below. In this stage, the protons are steered horizontally as they pass through each magnet. At one point, they receive a speed boost with each transit. After about 20,000 trips around they are at energy of 8 billion ev or 8 Gev.
The protons are passed to the Injector labeled in the first zoomed image of the full Fermilab facility. The Injector was operational in the spring of 1999 and performs a number of tasks. It can accelerate protons up to 150 GeV; it can produce 120 GeV protons for antiproton creation; it can increase antiproton energy to 120 GeV and it can inject protons or antiprotons into the Tevatron. The Tevatron can accelerate the particles from the Main Injector up to 980 GeV. The protons and antiprotons are accelerated in opposite directions, crossing paths in the B0 and D0 detectors to collide at 1.96 TeV. Until the collider was operational at CERN, this was the highest energy attained for particle collisions.
When the B0 and D0 detectors are not operating, Fermilab can work in Fixed Target Mode. Protons are shunted out of the Main Ring and toward a number of experiments in buildings north of the Main Ring. The lab has usually operated in Collider Mode several months and then in Fixed Target Mode for another several months before switching back.
Anti-Protons and Anti-Matter |
A few remarks might help here on the subject of anti-matter. When very high energy fast moving particles collide with something, they immediately slow down. That excess energy manifests itself in the formation of many smaller masses of particles. Mostly it is a lot of uninteresting stuff. But, a small number of those particles are anti-matter protons. They are sometimes called pbar.
According to this web page from Fermilab...
A beam of 120 GeV protons from the Main Injector is smashed on to a Nickel Target every 1.5 sec. In the collisions many particles are created. (remember E=mc2). For every 1 million protons that hit the target, only about twenty 8 GeV pbars survive to make it into the Accumulator.
They are rare. They must not be allowed to touch ordinary matter, or they annihilate. Their small numbers need to be accumulated and then injected into the Tevatron. Because they have the opposite charge of a proton and other characteristics the same, they will rotate in the same accelerator as the protons. But, they move the opposite direction around it.
Imagine a wisp of a bunch of protons moving 99.999954% the speed of light running directly into a wisp of a bunch of anti-protons. It is not likely for a perfectly head on collision to occur with any of them. So, the wisps are pinched down by magnets to beams more like knitting needles when they pass through each other. The odds of a head-on collision go up.
In a head-on collision, the total momentum will be zero, as it would for two identical cars in a head-on. The debris will tend to go to the sides. For the protons, it is a tougher challenge than you might think. Within each proton is a set of 3 quarks. In a head-on collision, you are only going to get 1 quark from each to be involved. And, the likelihood that they are perfectly head-on is very small. But, it does happen.
When it does, their collision annihilates them both, since one is an anti-matter quark. That energy, it is hoped, will be sufficient to create a Top Quark and an Anti-Top Quark pair. They will immediately decay into a particular and unique signature of particles which will identify them as having been present only briefly. Making these Top-anti-Top pairs of quarks was an important milestone in completing the Standard Model.
There has been an even tougher challenge faced by Fermilab in recent months. They are trying their best to gather evidence for the elusive Higgs Boson. They want to determine some of its characteristics before they shut down the Tevatron. They would like to do so before CERN does it.
Three Frontiers of Physics |
At Fermilab, a robust scientific program pushes forward on three interrelated frontiers. The Venn diagrams above illustrate the interlocking framework of those frontiers. Each frontier has a unique approach to making discoveries, and all three are essential to answering key questions about the laws of nature and the cosmos. Some questions can only be addressed by experiments at one frontier, but others require investigation on multiple fronts to create a complete picture.
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I lived near Fermilab in the 80's and taught physics in a local high school. In 1983, I was fortunate to be part of the first
Summer Science Teachers Institute offered by Fermilab. For two weeks, we heard lectures on topics in modern physics, and collaborated with others in the program to create lessons to incorporated the new ideas into our classes. From 1986-1992, I was the coordinator of the physics teacher group of the summer institutes. The physicists at Fermilab were the most interesting people to know. And they were eager to share their knowledge and enthusiasm with the teachers. I am very pleased to know that Fermilab and the affiliated
Fermilab Science Education Office will be there to offer assistance for several more years to come. Please visit the education link to see the many great programs they offer.