Batavia (IL) – TG Daily recently had an opportunity to visit the facilities of Fermilab, home of the Tevatron, currently the world’s highest energy particle accelerator. Join us on a tour through a stunning world of machinery that accelerates protons close to the speed of light to help scientists research topics of matter, space and time.
Caught between deadlines, press conferences and travel schedules, we easily oversee interesting technology topics that are right in front of our door. The NCSA was such a case, which we covered a few weeks ago in detail; even closer to our modest headquarters in the Western suburbs of Chicago, there is another high-profile science institution, which I usually drive by several times a week, but never really thought of including in one of our stories.
It was one of those strange accidents of knowing someone who knew someone that opened the door for me to go on a fantastic multi-hour tour through Fermilab and see what the largest employer (2000 people work at Fermilab) in my hometown is actually up to. Ron Moore, in charge of the Tevatron at Fermilab, took some time out of his calendar to take me through some of Fermilab’s facilities. Read on to get the detail of what is easily one of the most impressive research sites that exist in the U.S. today.
What is Fermilab?
Fermilab is operated by the Fermi Research Alliance (FRA). It is part of the Department of Energy (DoE) with a 2001 funding in the amount of $277 million, a good chunk of the department’s total annual budget of about $3.18 billion back then. The DoE spent a total of about $726 million on high-energy physics in 2001.
Located on the East side of Batavia, IL, the core research area at Fermilab is particle physics, which involves the very smallest building blocks of matter. Scientists investigate the foundations of matter to understand the forces that hold them together or force them apart.
On a 6800-acre site – just under 10 square miles – Fermilab operates a range of proton/anti-proton accelerators to enable various sub-atomic collisions. Using enormous amounts of energy, collisions can reveal exotic particles of matter, which are detected by special devices.
These experiments have allowed scientists to discover several new particles over the years, including the top quark in 1995, the last undiscovered quark of the six predicted to exist by current scientific theory; Fermilab was also the site of the discovery of the bottom quark in 1977 and the site where direct evidence for the tau neutrino was discovered (2000). Most recently, you may have heard of discovery of the “triple scoop” baryon, which contains one quark from each generation of matter.
Foremost, Fermilab serves as a service for students and international organizations to conduct their experiments. However, besides enabling research, which in some cases can last several years, Fermilab scientists also come up with what may appear to some of us as more practical solutions for our every day life: Fermilab contributes to finding new ways of working with electric currents and magnetism, new ways to treat cancer with particle beams, the staff develops superconducting magnets and acts as an early adopter for new technologies. Interestingly, particle physicists were also involved in the invention of the World Wide Web – or the Internet as we understand it today – which was originally developed at CERN, the European Particle Physics Laboratory in Geneva, Switzerland.
Brief history of Fermilab
Before we look at the accelerators, let’s have a look at the history of the site. Fermilab was built in 1967 with a total cost of $243 million. The site is dominated today by two major installations: The “Tevatron”, a high-energy, 4-mile long underground tunnel that houses a beam pipe ring (surrounded by superconducting magnets) to accelerate protons and anti-protons. The Tevatron was completed in 1983; the price tag was $120 million. If you are traveling in Kane County, Fermilab can be identified from a few miles away trough its “Wilson Hall” 16-story high-rise, which eclipses any other building in its mostly rural vicinity.
The name “Fermilab” honors Enrico Fermi, a professor of theoretical physics at the University of Rome and University of Chicago. The scientist was born in Pisa, Italy in 1901 and died in 1954 in the U.S. Among Fermi’s accomplishments is the theory of beta decay (1933) as well as a Nobel Prize in 1938 for the discovery of new radioactive elements. In Chicago, Fermi supervised the design and assembly of what is claimed to have been the first nuclear reactor. A plaque is dedicated to this event at the site of the University’s Stagg Field. It reads: “On December 2, 1942, man achieved here the first self-sustaining chain reaction and thereby initiated the controlled release of nuclear energy.”
The University of Chicago’s Institute for Nuclear Studies is named “The Enrico Fermi Institute” today.
Read on the next page: Fermilab’s Accelerator Chain
Fermilab’s Accelerator Chain
The installation houses the following components to create and “test” particle beams (in chronological order):
– Cockroft Walton (proton source)
– Linac (Linear Accelerator)
– Main Injector
– Antiproton Source
– Proton, Meson, Neutrino (fixed target facilities)
– Tevatron accelerator; CDF, DZero (detector facilities)
Any particle beam at Fermilab begins with the Cockroft Walton accelerator, which is located in the North-end of a skinny building, a little over 500 ft long, neighboring Wilson Hall to the North West. About two stories high, the Cockroft Walton is used to extract create negative ions, each consisting of two electrons and one proton, from hydrogen gas. With the help of a 1 Megawatt first-stage power amplifier, Moore said that the ions reach an energy of 750,000 electron volts (750 KeV), which compares to about 30 times the energy beam of the electron beam in a TV tube. The ions travel at a speed of about 8.8 million mph at this stage.
Linac (Linear Accelerator)
The next stage is the Linac, which consumes most of the skinny building mentioned before. Increasingly powerful amplification power sources with up to 5 Megawatt being applied in repeating stages and particles are accelerated in a radio-frequency cavity: Inside a solid copper tube, Particles are accelerated within electric fields that oscillate at the same rate as the electric fields of radio waves.
The Linac accelerates the beam to 400 million electron volts (400 MeV) or about 70% of the speed of light (about 469,431,640 mph). Just before the ions are sent into the “Booster”, the ions pass through a carbon foil, which removes electrons and enables the creation of positively charged protons.
The third stage is the “Booster”, which circumvents a small radial pond. Visitors to Fermilab will actually recognize a series of smaller and larger (artificial) ponds, which are located in direct proximity to the accelerators and, as Moore told me, are used as natural cooling sources.
The Booster is about 20 ft underground and is the first phase in which the particle beam has to be bent. Fermilab builds its own gigantic dipole, quadrupole and sextopole magnets which are used to bend (dipole) and focus the beam (quadrupole, sextopole). The beam itself widens over time, but is kept as thin as possible (it is only 30 to 40 microns wide when it ravels within the beam pipe at the beginning). Interestingly, while it is called a beam, it is not an uninterrupted beam, but travels in packets that are about 1.5 ns or 30 to 40 cm (12″ to 16″) long.
Visitors to the Booster tunnel (and Main Injector, Antiproton Source and Tevatron as well) mainly see a chain of magnets varying in size and weighing between 7 to 48 tons, each of which circumvents the beam pipe carrying the proton beam (and anti-protons in following stages).
The protons make about 20,000 circles in the Booster and are pumped to an energy level of 8,000,000 eV (8 GeV).
Main Injector and Antiproton Source
The next phase, and the phase just before protons are sent into the Tevatron, is the “Main Injector” (built in 1999). This device, consisting of two machine s in the same tunnel, is also called the “recycler” or “reservoir” and “particle switchyard” for protons and anti-protons. Besides accelerating protons from 8 GeV to 150 GeV, it also is used as the source for creating antiprotons that are required for collision experiments in the Tevatron.
120 GeV protons are sent into a nickel target that is located between the main injector ring and the Antiproton Source ring. From the outside, there are just three buildings positioned in a way to to create an imaginary triangle. In fact, the Antiproton Source is not an entirely circular ring, but makes up a triangular shape with three straight lines and three sharp curves.
When protons from the Main Injector collide with the nickel target. several secondary particles are created. Among those are anti-protons that are sent into a ring located in an underground tunnel of the Antiproton Source facility. You can imagine the tunnel system between and within each facility as a relatively dark, warm and humid environment with a very distinct heavy metal smell originating from the magnets as well as maintenance work on magnets, circuits and cooling system.
Antiprotons arriving from the nickel target arrive in an outside ring (made of the cable pipe surrounded by hundreds of magnets) in the tunnel. That beam pipe has a fork off to transition antiprotons to a second (inner) ring, called the “accumulator” ring. Antiprotons are circulating in this ring and when there is a sufficient number of antiprotons, they are sent back through another fork-off to the Main Injector where they are accelerated to 150 GeV. Antiprotons flow in the opposite direction to the circulating protons.
The Main Injector is called by the Fermilab staff “recycler” – a description that goes back to its function to work as, well, a recycler: The facility has the capability to store antiprotons that return from a trip through the Tevatron. However, according to Moore, while this feature was originally planned, it never has been used. Typically, about 95% of antiprotons are injected into the Tevatron.
Fermilab staff told us that it takes a minimum of 2.5 hours to generate a particle beam from the beginning to this stage.
Fixed target facilities
Depending on the experiment, the proton beam can be sent through a portion of the Tevatron and into a fixed target – the Proton, Neutrino, or Meson facilities.
The beam lines to these targets can actually be seen in applications such as Google Maps or Google Earth, as they are buried under substantial hills that are located between roads on the site. There are a total of five possible targets in these three locations. Typically, the experiments consist of putting different materials into the path of the particle beam to see how materials react and interact with each other. These fixed target facilities were used in the discovery of the bottom quark in 1977 and the tau neutrino in 2000.
The buildings are empty at the time of proton impact due to immense energy and radioactivity that is set free. The main radiation, however, is present within the accelerators and there is a certain “cool down” period after every experiment to allow the radiation to disappear (Moore noted that there are very short halftimes involved). Our visit, which we spent almost exclusively within the Antiproton Source, happened during a 10-week shutdown of the accelerators for general maintenance reasons.
We noticed Geiger Counters at the exit on buildings to measure radioactivity and, obviously, there was no noticeable radioactivity on our clothes. Moore actually used a device that stores the radioactivity reading, which is analyzed every few weeks to check, whether there are any radioactivity issues.
Read on the next page: Tevatron
The Tevatron is really what Fermilab is known for today. From the outside, it is a gigantic ring visible through a circular hill with a length of 4 miles and a radius of one mile. It uses a circular pond on its inside as natural cooling source and encloses vegetation on the inside to force the local fire department to apply a controlled burn to keep vegetative growth and fire risks under control.
Along the ring, there are several buildings, including the Collision Detector at Fermilab (CDF) and DZero, where the collision of proton and antiproton beams happen and are measured. There is also a liquid helium farm, which receives liquid helium from the on-site helium liquifier plant (production capacity: 6300 liters or 1685 gallons of liquid helium per hour).
The liquid helium (and liquid nitrogen as well) is used as cooling material for the superconducting magnets and is transported through pipes around the ring (there is a total of 15 miles of pipes of helium). Every few hundred feet, there are also smaller “refrigeration” buildings, some of which can act as pressure relieve, if the cryogenic system fails and liquid helium transitions into gas: In such a case, helium expands its volume by a factor of 700.
Underground is where it gets interesting. The Tevatron houses about 1000 superconducting magnets (772 dipoles, 240 quadrupoles): Superconductivity with zero resistance is achieved through liquid helium, which is in direct contact with the (hollow) cable carrying beam to cool down the magnet. The temperature of the liquid helium is 4.5 Kelvin or -450 degrees Fahrenheit or -268.5 degrees Celsius. Liquid nitrogen is used as a secondary cooling layer towards the outside of the beam pipe.
This environment allows the protons and antiprotons to be lifted into another energy dimension: Traveling at the speed of 670,616,429 mph – just 200 mph slower than the speed of light – the proton and antiproton beam top out at 0.98 TeV or 980 billion electron volts. On impact (within the CDF or DZero detector facilities), the energy set free is 1.7 TeV – which makes the Tevatron the highest energy collision test facility in the world today.
To put this energy in perspective, you could build a Tevatron yourself. If you take flat 3 Volt batteries, you would need a ring consisting of 333 billion of those batteries. The total length of this battery chain would be 1 million km or 621,300 miles.
Controlling a 0.98 tera electron volt (TeV) beam requires quite some precision: Even if just a portion of this beam gets out of control – scientists refer to this event as “beam loss” – a “quench” can happen and damage is done very quickly: While these quenches do not happen very often, a problem for example in the cryogenic system can cause the beam to leave its path. The Tevatron has an automated shutdown function in such a case, but the high energy causes damage even within short time periods: Within 16 ns, one beam burned through about 1.5 m (about 5 feet) of solid steel.
“If we do not get the current out quickly, magnets can get deformed,” Moore told us. He described quenches as “sudden violent impacts” that carry “explosive power.”
Detection on impact
So, how do you measure such extreme high energies, especially when they hit each other head on? Fermilab has two three-story tall, 5000-ton, multi-stage detector devices (CDF and DZero); the actual collision happens within a core round tube that is not quite a foot in diameter and not longer than your average desk. Remember, these protons are traveling nearly at the speed of light in a 4-mile circle – it gives you a sense of the precision that is at work here.
The impact of both beams translates into a 1.7 MHz collision. According to Moore, a level one trigger decides within 5 microseconds through dozens of thin and strategically placed silicon sensors (having the least possible resistance to pass through for the created particles) which collision results to store and which not. This first trigger tries to recognize the most unusual, interesting and rarest results, which translates into about 30 KHz of data of the total 1.7 MHz collision. While the decision is made, collisions obviously happen and particles are created: These results are buffered and put into memory. Two more triggers act as filters and leave the most interesting data for storage: Trigger 2 boils it down to about 1 KHz and Trigger 3 to about 70-100 Hz, Moore said. Experiments at Fermilab create a data volume of about 100 MB per second.
Data is stored offsite at Fermilab’s Feynman Computing Center. We were not able to get details on the available computing power at Fermilab (which includes the Feynman center as well as a Grid Computing Center), but Moore told us that the L3 Trigger uses “several hundred high-end off-the-shelf desktop PCs” for data analysis.
Read on the next page: Other interesting facts about Fermilab
I would have loved to actually have seen the facility during a test (you actually can see the protons as there is radiation that is in the visible spectrum), but the tour was fascinating enough even without witnessing a proton impact. However, there are some other facts I came by and that may be interesting to you as well. Let me go over these, without any particular order.
Fermilab draws its electricity directly from a ComEd plant, and it draws lots of it – 45 Megawatts on average. According to the Fermilab website, this consumption results in a power bill of about $12 to $18 million per year.
When you are walking through one of the tunnels housing the beam pipes and huge magnets, you can’t help wondering where Fermilab gets these magnets from and how they get them down there. The answer is, Fermilab does not buy magnets – they buy iron and build the magnets themselves. Huge cranes in maintenance buildings lift the magnets down into the tunnel system from where they are brought to their destination.
There are some nifty solutions how to deal with extremely heavy devices all around Fermilab: For example, some of the older power amplifiers have nozzles on the four corners of their square bases. To move the device, which weighs several tons, nitrogen gas is blown through those nozzles – which enables staff to simply push an amplifier from A to B.
To my surprise, there isn’t a whole lot of security at Fermilab. A few security cameras here and there, a security guard at the entrance of the site – that was it, at least to my untrained eyes. But then, who wants to steal magnets that weigh at least 7 tons?
However, I noticed a simple but very efficient security system to avoid accidents. There are hundreds of keys that allow access to certain parts of the facilities. Each key can only be removed through turning a “switch” which means that if a key is missing to facility, that facility can not be put under power. The central key distribution location is located in the main control room with several other areas housing keys around the site. Keys can only be removed with proper authentication (which happens visually through camera surveillance). Only when a key is put back, the switch is turned back and allows that part of the facility to go into operation.
As mentioned before, Fermilab was built in 1967, with many buildings added over time. Walking through the buildings can feel a bit like a time machine of technology. There is plenty of machinery that puts you on the set of the first James Bond movie (Dr. No), while I also noticed a brand new iMac, not even two weeks old in one corner of the Control Room (And yes, that iMac looks much nicer in reality than it does in pictures.)
A rather unexpected discovery within the Linac building was a poster that described cancer treatment with particle beams. In fact, there is cancer treatment happening on this site – in cases where cancer cells are hit with particle beams that are cut off from the main particle beam.
Moore said he was not aware of how dangerous or effective such a treatment is – or to whom it actually is available. A reliable source however told me that it is extremely expensive, even by medicine standards.
Main Control room
Yes, of course there is a main control room that oversees the activity around Fermilab. The control room is staffed 24 hours a day. From here, the particle beam is initiated and controlled – and automatically shut down in the case of a quench.
6800 acres of land provide lots of opportunity to preserve vegetation and wildlife. Arriving at Fermilab through its signature gate in fact feels much more like arriving at a park rather than a high-energy research site. Vegetation is brought back to its original prairie state; wildlife includes 277 bird species, 54 species of butterflies, about 18,000 Canada geese during migration cycles, more than 350 deer – and 45 bisons.
Read on the next page: Concluding notes
Visiting facilities such as Fermilab and bringing those observations to readers is one of the reasons why I enjoy my job. If you have a chance visiting Fermilab or other research facilities that are open to the public, I would highly recommend doing so.
When organizing my notes, pictures and thoughts about my visit, I was left disappointed by the fact that the Tevatron is scheduled for a complete and final shut down in October 2009, with active discussion to keep it alive for an additional year. CERN is working on its “Large Hadron Collider”, often referred to as “Big Bang machine”, which has a 27 km circle (as opposed to the Tevatron’s 6.4 km) and a maxium energy level of 7 TeV – seven times the energy that can be achieved by the Tevatron.
“What a waste,” was my first thought, thinking about the fact that this facility is likely to be abandoned and my young children will not have the opportunity to visit this facility when they are old enough to understand its importance.
According to Moore, there are currently no confirmations that would indicate a replacement of the Tevatron in the near future. Estimates stated that rebuilding a new, higher-energy facility is likely to cost several billions of dollars. However, back in 2002, the the High Energy Physics Advisory Panel to the Department of Energy and the National Science Foundation today revealed plans for a 30 km (18 mile) long linear collider (ILC or International Linear Collider)with an energy capacity of several hundred to about 1000 TeV as a next phase for the Fermilab accelerator facility and a plan to keep high-energy physics leadership for the next 20 years. The cost of such a collider was estimated in the range of $5 to $7 billion.
No decision has been made on the construction of such a collider.
My thanks go to Ron Moore for a great tour of Fermilab.
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