The Tevatron (background) and Main Injector rings |
|
| Intersecting Storage Rings | CERN, 1971–1984 |
|---|---|
| Super Proton Synchrotron | CERN, 1981–1984 |
| ISABELLE | BNL, cancelled in 1983 |
| Tevatron | Fermilab, 1987–2011 |
| Relativistic Heavy Ion Collider | BNL, 2000–present |
| Superconducting Super Collider | Cancelled in 1993 |
| Large Hadron Collider | CERN, 2009–present |
| Super Large Hadron Collider | Proposed, CERN, 2019– |
| Very Large Hadron Collider | Theoretical |
The Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory (also known as Fermilab), just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider (LHC). The Tevatron is a synchrotron that accelerates protons and antiprotons in a 6.28 km (3.90 mi) ring to energies of up to 1 TeV, hence its name.[1] The Tevatron was completed in 1983 at a cost of $120 million ($265 million today[2]) and significant upgrade investments were made in 1983-2011. (The 'Energy Doubler', as it was known then, produced its first accelerated beam — 512 GeV — on July 3, 1983.[3]) The Main Injector was the most substantial addition, built over five years from 1994 at a cost of $290 million ($639 million today[2]).
The Tevatron ceased operations on 30 September, 2011,[4] due to budget cuts;[5] it is not as powerful as the LHC, which began operations in early 2010. The main ring of the Tevatron will probably be reused in future experiments, and its components may be transferred to other particle accelerators.[6]
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The acceleration occurs in a number of stages. The first stage is the 750 keV Cockcroft-Walton pre-accelerator, which ionizes hydrogen gas and accelerates the negative ions created using a positive voltage. The ions then pass into the 150 meter long linear accelerator (linac) which uses oscillating electrical fields to accelerate the ions to 400 MeV. The ions then pass through a carbon foil, to remove the electrons, and the charged protons then move into the Booster.[7]
The Booster is a small circular synchrotron, around which the protons pass up to 20,000 times to attain an energy of around 8 GeV. From the Booster the particles pass into the Main Injector, which was completed in 1999 to perform 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 antiprotons are created by the Antiproton Source. 120 GeV protons are collided with a nickel target producing a range of particles including antiprotons which can be collected and stored in the accumulator ring. The ring can then pass the antiprotons to the Main Injector.
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 CDF and DØ detectors to collide at 1.96 TeV. To hold the particles on track the Tevatron uses 774 niobium-titanium superconducting dipole magnets cooled in liquid helium producing 4.2 teslas. The field ramps over about 20 seconds as the particles are accelerated. Another 240 NbTi quadrupole magnets are used to focus the beam.[1]
The initial design luminosity of the Tevatron was 1030 cm−2 s−1, however the accelerator has following upgrades been able to deliver luminosities up to 4x1032 cm−2 s−1.[8]
On September 27, 1993 the cryogenic cooling system of the Tevatron Accelerator was named an International Historic Landmark by the American Society of Mechanical Engineers. The system, which provides cryogenic liquid helium to the Tevatron's superconducting magnets, was the largest low-temperature system in existence upon its completion in 1978. It keeps the coils of the magnets, which bend and focus the particle beam, in a superconducting state so that they consume only 1/3 of the power they would require at normal temperatures.[9]
Sensors on underground magnets in the Tevatron are capable of detecting minute seismic vibrations from earthquakes thousands of miles away. The Tevatron recorded vibration spikes emanating from the 2004 Indian Ocean earthquake, the 2005 Sumatra earthquake, New Zealand's 2007 Gisborne earthquake, the 2010 Haiti earthquake and the 2010 Chile earthquake.[10]
In 1995, the CDF and DØ collaborations announced the discovery of the top quark, and by 2007 they measured its mass to a precision of nearly 1%.
In 2006, CDF made the first measurement of Bs oscillations, and observed two types of sigma baryon. [11]
In 2007, the DØ and CDF experiments reported direct observation of the "Cascade B" (Ξ−
b) Xi baryon. [12]
In September 2008, the DØ experiment reported detection of the Ω−
b, a "double strange" Omega baryon [13] [14] with the measured mass significantly higher than the quark model prediction. In May 2009 the CDF collaboration made public their results on search for Ω−
b based on analysis of data sample roughly four times larger than the one used by DZero experiment.[15] CDF measured mass to be 6,054.4±6.8 MeV/c2 in excellent agreement with Standard Model prediction. No signal has been observed at DZero reported value. The two results differ by 111±18 MeV/c2 or by 6.2 standard deviations and therefore are inconsistent. Excellent agreement between CDF measured mass and theoretical expectations is a strong indication that the particle discovered by CDF is indeed the Ω−
b. It is anticipated that new data from LHC experiments will clarify the situation in the near future.
On April 7, 2011, the CDF team at Fermilab announced the discovery of a possible new particle after a new non-Higgs particle appeared in their data. However, an independent analysis of data from trillions of particle collisions by the DØ team was not able to reproduce the detection of the new particle, thus suggesting that the initial observation was a statistical fluke and that, in fact, no new particle had been discovered. Although disappointed that the data did not yield a new discovery, scientists were quick to point out that this is exactly how science is supposed to work - data and discoveries must be independently replicated and verified by numerous measurements and teams. In this case, the scientific process worked perfectly.