Beam dump
Encyclopedia
A beam dump is a device that absorbs a beam. This may be a beam of photons ("light") such as a laser
beam, or a beam of electrically charged particles
.
element used to absorb a beam of light. Major design concerns in a beam dump typically include the management and reduction of back reflections and scattering as well as the dissipation of heat generated by absorption. For low-power systems and less demanding applications, the device can be as simple as a piece of black velvet
or flock
paper glued onto a stiff backing, but higher-power beam dumps must often incorporate more elaborate features to avoid back-reflection, overheating, or excessive noise. Dumping the beam with a simple flat surface may scatter unacceptably large amounts of light for some applications, even though the direct reflection may be effectively reduced. To minimize scattering, it is common to use deep, dark cavities lined with an absorbing material to dump the beam. A particularly simple and relatively inexpensive approach is to use a stack of razor blades
with the sharp edges facing the beam, so that the spaces between the blades form very deep cavities from which little light escapes.
A commonly available type of beam dump suitable for most medium-power laser
s is a cone of aluminum with greater diameter than the beam, anodized
to a black color and enclosed in a canister with a black, ribbed interior. Only the point of the cone is exposed to the beam head-on; mostly, incoming light grazes the cone at an angle, which eases performance requirements. Any reflections from this black surface are then absorbed by the canister. The ribs both help to make light less likely to escape, and improve heat transfer to the surrounding air.
Extremely high-power beam dumps have been made using water
with controlled amounts of colored salt
s (e.g., copper (II) sulfate) to give a moderate absorbance of the beam. The water is circulated through a long pipe with a window at one end, and chilled using a heat exchanger
.
, or ion
s. This is necessary when, for example, a circular particle accelerator
has to be shut down. Dealing with the heat deposited can be an issue, since the powers of the beams to be absorbed can run into the megawatts.
Materials used for such beam dumps include blocks of copper
, aluminum, carbon
, beryllium
, and tungsten
. The block often has a long conical hole where the beam hits it, so as to spread the heating over a larger region of the block. If the beam to be absorbed is high powered, these blocks may be up to several meters long and water-cooled. Pools of mercury
have also been used.
If the particles in the beam are energetic enough, induced radioactivity
, production of neutron
s by spalling
, radiation
embrittlement
, and production of secondary particles can also be issues.
Considerable quantities of material may be put around the beam dump, especially "downstream" of the beam dump, to serve as radiation shielding. Also, the beam may be carefully not aimed at anything critical (such as people or particle detector
s), and angled down into the earth before it hits the beam dump, so that soil serves as a radiation shield.
The most challenging beam dump design to date is that of the Large Hadron Collider
. Each of the two beam dumps, in case, for instance, of a dipole magnet
quench, must be able to dissipate 362 MJ of beam energy in the 90 μs
circulation time, which equates to a power of 4 TW
.
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
beam, or a beam of electrically charged particles
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...
.
Optical beam dumps
An optical beam dump is an opticalOptics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
element used to absorb a beam of light. Major design concerns in a beam dump typically include the management and reduction of back reflections and scattering as well as the dissipation of heat generated by absorption. For low-power systems and less demanding applications, the device can be as simple as a piece of black velvet
Velvet
Velvet is a type of woven tufted fabric in which the cut threads are evenly distributed,with a short dense pile, giving it a distinctive feel.The word 'velvety' is used as an adjective to mean -"smooth like velvet".-Composition:...
or flock
Flocking (texture)
Flocking is the process of depositing many small fiber particles onto a surface. It can also refer to the texture produced by the process, or to any material used primarily for its flocked surface. Flocking of an article can be performed for the purpose of increasing its value in terms of the...
paper glued onto a stiff backing, but higher-power beam dumps must often incorporate more elaborate features to avoid back-reflection, overheating, or excessive noise. Dumping the beam with a simple flat surface may scatter unacceptably large amounts of light for some applications, even though the direct reflection may be effectively reduced. To minimize scattering, it is common to use deep, dark cavities lined with an absorbing material to dump the beam. A particularly simple and relatively inexpensive approach is to use a stack of razor blades
Razor
A razor is a bladed tool primarily used in the removal of unwanted body hair through the act of shaving. Kinds of razors include straight razors, disposable razors and electric razors....
with the sharp edges facing the beam, so that the spaces between the blades form very deep cavities from which little light escapes.
A commonly available type of beam dump suitable for most medium-power laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
s is a cone of aluminum with greater diameter than the beam, anodized
Anodising
Anodizing, or anodising in British English, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit...
to a black color and enclosed in a canister with a black, ribbed interior. Only the point of the cone is exposed to the beam head-on; mostly, incoming light grazes the cone at an angle, which eases performance requirements. Any reflections from this black surface are then absorbed by the canister. The ribs both help to make light less likely to escape, and improve heat transfer to the surrounding air.
Extremely high-power beam dumps have been made using water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
with controlled amounts of colored salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s (e.g., copper (II) sulfate) to give a moderate absorbance of the beam. The water is circulated through a long pipe with a window at one end, and chilled using a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
.
Charged particle beam dumps
The purpose of a charged particle beam dump is to safely absorb a beam of charged particles such as electrons, protons, nucleiAtomic 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...
, or ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. This is necessary when, for example, a circular particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
has to be shut down. Dealing with the heat deposited can be an issue, since the powers of the beams to be absorbed can run into the megawatts.
Materials used for such beam dumps include blocks of copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, aluminum, carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
, and tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
. The block often has a long conical hole where the beam hits it, so as to spread the heating over a larger region of the block. If the beam to be absorbed is high powered, these blocks may be up to several meters long and water-cooled. Pools of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
have also been used.
If the particles in the beam are energetic enough, induced radioactivity
Induced radioactivity
Induced radioactivity occurs when a previously stable material has been made radioactive by exposure to specific radiation. Most radioactivity does not induce other material to become radioactive....
, production of 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 by spalling
Spallation
In general, spallation is a process in which fragments of material are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection or vaporization of material from a target during impact by a projectile...
, radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
embrittlement
Embrittlement
Embrittlement is a loss of ductility of a material, making it brittle. Various materials have different mechanisms of embrittlement.* Hydrogen embrittlement is the effect of hydrogen absorption on some metals and alloys....
, and production of secondary particles can also be issues.
Considerable quantities of material may be put around the beam dump, especially "downstream" of the beam dump, to serve as radiation shielding. Also, the beam may be carefully not aimed at anything critical (such as people or 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), and angled down into the earth before it hits the beam dump, so that soil serves as a radiation shield.
The most challenging beam dump design to date is that of the Large Hadron Collider
Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
. Each of the two beam dumps, in case, for instance, of a dipole magnet
Dipole magnet
A dipole magnet, in particle accelerators, is a magnet constructed to create a homogeneous magnetic field over some distance. Particle motion in that field will be circular in a plane perpendicular to the field and collinear to the direction of particle motion and free in the direction orthogonal...
quench, must be able to dissipate 362 MJ of beam energy in the 90 μs
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
circulation time, which equates to a power of 4 TW
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
.