JLab Vocabulary

Absolute zero: defined by scientists as the complete absence of heat. Measured at -273.2° Celsius, 0° Kelvin, and -459.7° Fahrenheit. At absolute zero, molecules stop moving and thus do not generate heat. Absolute zero has never been achieved, though scientists have come within millionths of a degree.

Accelerator: any machine used to impart large amounts of kinetic energy to charged particles. These particles are used to explore nuclear or sub-nuclear phenomena.

Atom: a unit of matter consisting of a nucleus orbited by negatively charged electrons.

Beam: a thin stream of particles moving in one direction. The CEBAF beam is made of electrons.

Cavity: the components of CEBAF's machine in which the electron beam is accelerated. CEBAF has 338 superconducting cavities that boost the beam with radio-frequency waves.

Central Helium Liquefier: CEBAF's refrigeration plant-the largest in the world at 2 Kelvin (-456° Fahrenheit) that provides liquid helium for superconducting cavity operation.

Continuous beam: a beam of particles that travels in a steady stream, as opposed to large pulses separated by significant periods of time. A constant stream of electrons ensures a steady flow of distinct nuclear collisions, enabling scientists to effectively record each collision.

Cryogenics: the science and technology of extremely low-temperature phenomena.

Cryomodule: four cryounits welded together containing a total of eight cavities.

Cryounit: a refrigeration container that encases the liquid helium around a pair of cavities keeping them superconductive.

Detector: a device that measures subatomic interactions and reactions. CEBAF's three detectors are spectrometers that will observe and measure electron-quark interactions.

Electron: a negatively-charged particle that orbits the nucleus of an atom. Electrons can be forced to move from atom to atom through a conductor, forming an electric current.

Electron volt (eV): a measure of the amount of energy gained by one electron when it traverses a potential of one volt. In a television set, each electron that contributes to image formation in the picture tube has an energy of about 20,000 eV. The CEBAF accelerator operates at ~6 GeV (6 billion eV).

Elementary particle: a particle that cannot be further divided.

Experimental Hall: the destination of CEBAF's electron beam where it will collide with nuclear targets. CEBAF's three experimental halls are called Halls A, B and C.

Klystron: a device that generates radio-frequency power for cryomodules in the CEBAF accelerator.

Linac: short for linear accelerator, the linac accelerates particles to extremely high energies. CEBAF uses two main linacs, recirculating the electron beam up to 5 times.

Liquid Helium: Helium, one of the lightest elements known, is a gas at room temperature. When its temperature is reduced to nearly absolute zero, it becomes a liquid. Liquid helium is used at CEBAF to maintain the cavities at low, superconducting temperatures.

Magnet: CEBAF's magnets guide the beam from one linac to the next by generating a magnetic field. Other magnets focus and steer the beam, and are used in experiments.

Mass: the measure of a body's resistance to acceleration.

Matter: an entity displaying gravitation and inertia when at rest as well as when in motion.

MCC: the Machine Control Center houses the computer system used to control all accelerator operations. The MCC tracks, manages and responds to more than 300,000 simultaneous signals and approximately 100,000 hardware control points.

Neutrons: subatomic particles with no electric charge, which, with protons, form the nucleus.

Niobium (Nb): metallic element with special properties enabling it to be superconductive at extremely low temperatures. CEBAF's superconducting cavities are made of niobium.

Nucleus: the core of an atom, containing positively-charged protons and neutral neutrons.

Proton: the positively-charged particle in the nucleus. Protons are more than 1,000 times more massive than electrons.

Quark: particles that in triplets make up each proton and neutron in the nucleus. CEBAF experiments will explore the quark structure of matter.

SRF superconducting radio frequency: CEBAF's accelerator uses radio waves within the cavities to establish the electric fields that boost electrons. Jefferson Lab is the first physics laboratory to employ large-scale SRF technology.

Superconductivity: a unique condition in which certain substances lose all resistance to the flow of an electric current.

Target: the substance that will be hit by the beam in an accelerator experiment.