Thomas Jefferson National Accelerator Facility
Encyclopedia
Thomas Jefferson National Accelerator Facility (TJNAF), commonly called Jefferson Lab or JLab, is a U.S. national laboratory located in Newport News
, Virginia. Since June 1, 2006, it has been operated by Jefferson Science Associates, LLC, a joint venture between Southeastern Universities Research Association, Inc., and CSC Applied Technologies, LLC. Until 1996 it was known as the Continuous Electron Beam Accelerator Facility (CEBAF); this name is still commonly used for the main accelerator.
Founded in 1984, JLab employs over 675 people, and over 2,000 scientists from around the world have conducted research using the facility. Its stated mission is "to provide forefront scientific facilities, opportunities and leadership essential for discovering the fundamental structure of nuclear matter; to partner in industry to apply its advanced technology; and to serve the nation and its communities through education and public outreach."
source and injector and a pair of superconducting RF linear accelerators 7/8 mile (1400 m) in length, connected to each other by two arc sections which contain steering magnets. As the electron beam makes up to five successive orbits, its energy is increased up to a maximum of 6 GeV. This leads to a design that appears similar to a racetrack, compared to the classical ring shaped accelerator shape found at sites such as CERN
or Fermilab
. Effectively, CEBAF is a linear accelerator, like SLAC at Stanford, that has been folded up to a tenth of its normal length.
The design of CEBAF allows the electron beam to be continuous rather than the pulsed beam typical of ring shaped accelerators. (There is some beam structure but the pulses are very much shorter and closer together.) The electron beam is directed onto three potential targets (see below). One of the distinguishing features of JLab is the continuous nature of the electron beam, with a bunch length of less than 1 picosecond
. Another is JLab's use of superconducting RF
(SRF) technology, which uses liquid helium
to cool niobium
to approximately 4 K
(−452.5°F), removing electrical resistance and allowing the most efficient transfer of energy to an electron. To achieve this, JLab houses the world's largest liquid helium refrigerator, and was one of the first large-scale implementators of SRF technology. The accelerator is built 8 meters, or approximately 25 feet, below the Earth's surface, and the walls of the accelerator tunnels are 2 feet thick.
The beam ends in three experimental halls, labelled Hall A, Hall B, and Hall C. Each hall contains a unique spectrometer
to record the results of collision between the electron beam and a stationary target. This allows physicists to study the structure of the atomic nucleus
, specifically the interaction of the quark
s that make up proton
s and neutron
s of the nucleus.
from the beam, an "interaction", or "event", occurs, scattering particle
s into the hall. Each hall contains an array of particle detector
s that track the physical properties of the particles produced by the event. The detectors generate electrical pulse
s that are converted into digital values by analog to digital converters (ADCs), time to digital converters (TDCs) and pulse counters (scalers).
This digital data
must be gathered and stored so that the physicist
can later analyze the data and reconstruct the physics that occurred. The system of electronics and computers that perform this task is called a data acquisition system.
, with an output of over 14 kilowatts.
experiments. In nuclear and particle physics
experiments, the particle tracks are digitized by the data acquisition system, but the detectors are capable of generating a large number of possible measurements, or "data channels".
The ADC, TDC and other digital electronics are typically large circuit boards with connectors at the front edge that provide input and output for digital signals, and a connector at the back that plugs into a backplane
. A group of boards are plugged into a chassis
, or "crate", that provides physical support, power and cooling for the boards and backplane. This arrangement allows electronics
capable of digitizing
many hundreds of channels to be compressed into a single chassis.
In the CODA system, each chassis contains a board that is an intelligent controller
for the rest of the chassis. This board, called a ReadOut Controller (ROC), configures each of the digitizing boards upon first receiving data, reads the data from the digitizers, and formats the data for later analysis.
Newport News, Virginia
Newport News is an independent city located in the Hampton Roads metropolitan area of Virginia. It is at the southeastern end of the Virginia Peninsula, on the north shore of the James River extending southeast from Skiffe's Creek along many miles of waterfront to the river's mouth at Newport News...
, Virginia. Since June 1, 2006, it has been operated by Jefferson Science Associates, LLC, a joint venture between Southeastern Universities Research Association, Inc., and CSC Applied Technologies, LLC. Until 1996 it was known as the Continuous Electron Beam Accelerator Facility (CEBAF); this name is still commonly used for the main accelerator.
Founded in 1984, JLab employs over 675 people, and over 2,000 scientists from around the world have conducted research using the facility. Its stated mission is "to provide forefront scientific facilities, opportunities and leadership essential for discovering the fundamental structure of nuclear matter; to partner in industry to apply its advanced technology; and to serve the nation and its communities through education and public outreach."
Accelerator
The laboratory's main research facility is the CEBAF accelerator, which consists of a polarized electronElectron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
source and injector and a pair of superconducting RF linear accelerators 7/8 mile (1400 m) in length, connected to each other by two arc sections which contain steering magnets. As the electron beam makes up to five successive orbits, its energy is increased up to a maximum of 6 GeV. This leads to a design that appears similar to a racetrack, compared to the classical ring shaped accelerator shape found at sites such as CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
or Fermilab
Fermilab
Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...
. Effectively, CEBAF is a linear accelerator, like SLAC at Stanford, that has been folded up to a tenth of its normal length.
The design of CEBAF allows the electron beam to be continuous rather than the pulsed beam typical of ring shaped accelerators. (There is some beam structure but the pulses are very much shorter and closer together.) The electron beam is directed onto three potential targets (see below). One of the distinguishing features of JLab is the continuous nature of the electron beam, with a bunch length of less than 1 picosecond
Picosecond
A picosecond is 10−12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to 31,700 years....
. Another is JLab's use of superconducting RF
Superconducting Radio Frequency
Superconducting Radio Frequency science and technology involves the application of electrical superconductors to radio frequency devices. The ultra-low electrical resistivity of a superconducting material allows an RF resonator to obtain an extremely high quality factor, Q...
(SRF) technology, which uses liquid helium
Liquid helium
Helium exists in liquid form only at extremely low temperatures. The boiling point and critical point depend on the isotope of the helium; see the table below for values. The density of liquid helium-4 at its boiling point and 1 atmosphere is approximately 0.125 g/mL Helium-4 was first liquefied...
to cool niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
to approximately 4 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
(−452.5°F), removing electrical resistance and allowing the most efficient transfer of energy to an electron. To achieve this, JLab houses the world's largest liquid helium refrigerator, and was one of the first large-scale implementators of SRF technology. The accelerator is built 8 meters, or approximately 25 feet, below the Earth's surface, and the walls of the accelerator tunnels are 2 feet thick.
The beam ends in three experimental halls, labelled Hall A, Hall B, and Hall C. Each hall contains a unique spectrometer
Spectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
to record the results of collision between the electron beam and a stationary target. This allows physicists to study the structure of the atomic nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
, specifically the interaction of the quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s that make up proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s and neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s of the nucleus.
Particle behavior
Each time around the loop, the beam passes through each of the two LINAC accelerators, but through a different set of bending magnets. The electrons make up to five passes through the LINAC accelerators.Collision event
When a nucleus in the target is hit by an electronElectron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
from the beam, an "interaction", or "event", occurs, scattering particle
Subatomic particle
In physics or chemistry, subatomic particles are the smaller particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles...
s into the hall. Each hall contains an array of particle detector
Particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
s that track the physical properties of the particles produced by the event. The detectors generate electrical pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
s that are converted into digital values by analog to digital converters (ADCs), time to digital converters (TDCs) and pulse counters (scalers).
This digital data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
must be gathered and stored so that the physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
can later analyze the data and reconstruct the physics that occurred. The system of electronics and computers that perform this task is called a data acquisition system.
12 GeV upgrade
As of June 2010, construction has begun an additional end station, Hall D, on the opposite end of the accelerator from the other three halls, as well as an upgrade which doubles the beam energy to 12 GeV. Concurrently, an addition to the Test Lab, (where the SRF cavities used in CEBAF and other accelerators used worldwide are manufactured) is being constructed.Free electron laser
JLab houses the world's most powerful tunable free electron laserFree electron laser
A free-electron laser, or FEL, is a laser that shares the same optical properties as conventional lasers such as emitting a beam consisting of coherent electromagnetic radiation which can reach high power, but which uses some very different operating principles to form the beam...
, with an output of over 14 kilowatts.
CODA
Since CEBAF has three complementary experiments running simultaneously, it was decided that the three data acquisition systems should be as similar as possible, so that physicists moving from one experiment to another would find a familiar environment. To that end, a group of specialist physicists was hired to form a data acquisition development group to develop a common system for all three halls. CODA, the CEBAF Online Data Acquisition system, was the result http://coda.jlab.orgDescription
CODA is a set of software tools and recommended hardware that facilitate a data acquisition system for nuclear physicsNuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
experiments. In nuclear and particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
experiments, the particle tracks are digitized by the data acquisition system, but the detectors are capable of generating a large number of possible measurements, or "data channels".
The ADC, TDC and other digital electronics are typically large circuit boards with connectors at the front edge that provide input and output for digital signals, and a connector at the back that plugs into a backplane
Backplane
A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...
. A group of boards are plugged into a chassis
Chassis
A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...
, or "crate", that provides physical support, power and cooling for the boards and backplane. This arrangement allows electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
capable of digitizing
Digitizing
Digitizing or digitization is the representation of an object, image, sound, document or a signal by a discrete set of its points or samples. The result is called digital representation or, more specifically, a digital image, for the object, and digital form, for the signal...
many hundreds of channels to be compressed into a single chassis.
In the CODA system, each chassis contains a board that is an intelligent controller
Controller (computing)
In computing and especially in computer hardware, controller is a chip, an expansion card, or a stand-alone device that interfaces with a peripheral device...
for the rest of the chassis. This board, called a ReadOut Controller (ROC), configures each of the digitizing boards upon first receiving data, reads the data from the digitizers, and formats the data for later analysis.
External links
- Thomas Jefferson National Accelerator Facility, official site
- Google Hybrid Map of TJNAF
- MSN Virtual Earth Aerial Map
- Physics Division at Jefferson Lab (includes links to each of the experimental halls)
- Free-Electron Laser Program
- 12 GeV Upgrade
- K-12 Science Education