Micromegas detector
Encyclopedia
The “Micromegas “ detector is a gaseous particle detector
coming from the development of wire chamber
. Invented in 1992 by Georges Charpak
and Ioannis Giomataris, the Micromegas detectors are mainly used in experimental physics, in particular in particle physics
, nuclear physics
and astrophysics
for the detection of ionising particles.
The Micromegas are light detectors in order to minimize the perturbation on the impinging particle. From their small amplification gap, they have fast signals in the order of 100 nanoseconds. They are precise detectors with a spatial resolution below one hundred of micrometer
. Nowadays, the use of the Micromegas technology is growing over the different fields of experimental physics.
is used to detect a passing particle
and obtain information such as its position
, arrival time and momentum
. In experimental physics, the particle is usually coming from a particle accelerator
but it can also come from space (cosmic ray
) or from a nuclear reactor
.
The Micromegas detector, as every gaseous detector, detects particles by amplifying the charges that have been created by ionisation in the gas
volume. In a Micromegas detector, this gas
volume is divided in two by a metallic micro-mesh (“Micromesh” on the schematic) placed between
and 
of the readout electrode
(Strips on the schematic). The micro-mesh is the key element since it allows, at the same time, a high gain
of
with and a fast signal of 100ns.
/ion
pair (1). When no electric field
is applied, the ion
/electron
pair recombines and nothing happen. But here, within an electric field
in the order of
the electron will drift (2) toward the amplification electrode (the mesh) and the ion toward the cathode
. When the electron arrives closed to the mesh (3), it enters an intense electric field (typically in the order of
) in the amplification gap.
Accelerated by this field, the electron reaches enough energy to produce ion
/electron
pairs that will also ionise the gas, creating pairs; it’s the avalanche effect
(4). By this mean, it’s several thousand of pairs that are created from an hundred of primary charges coming from by the interaction with the impinging particle. The primary charges need to be multiplied to create a significant signal. A last, we read the electronic signal on the readout electrode (5) by a charge amplifier
. The readout electrode is usually segmented in strips and/or pixels in order to obtain the position of the impinging particle in the detector. The amplitude and the shape of the signal, read via the electronic on the readout electrode, gives information on the time and energy of the particle.
by the movement of charges between the micro-mesh and the readout electrode (this volume is called the amplification gap). The 100 nanoseconds signal consists of an electron peak (blue) and an ion tail (red). Since the electron mobility
in gas is over 1000 times faster than the ion
mobility, the electronic signal is much shorter (below 3ns) than the ionic one. That is why it is used to measure precisely the time. The ionic signal caries more than half of the signal and is used to reconstruct the energy
of the particle.
at the Hadron Blind Detector experiment, I. Giomataris and G. Charpak
reduced the amplification gap of a parallel plate detector (a type of spark chamber) in order to speed up the signal. A 1 mm amplification gap prototype was build for the HDB experiment but the gain
was not uniform enough to be used in the experiment. The millimetre gap was not enough controlled and created large gain
fluctuations.
Nevertheless the benefits of a reduce amplification gap has been demonstrated and the Micro-Mesh gaseous structure or Micromegas concept was born in October 1992, shortly before the announcement of the Nobel prize
attribution to Georges Charpak
for the invention of the wire chambers. Georges Charpak
used to say that this detector and some other new concepts belonging to the family of micro-pattern gaseous detectors (MPGDs) will revolutionise nuclear and particle physics just as his detector did.
, the Micromegas technology has been developed in order to obtain more stable, reliable, precise and faster detectors. In 2001, twelve large Micromegas detectors plane of
) were used for the first time in a large scale experiment at COMPASS situated on the Super Proton Synchrotron
accelerator at CERN
. Since 2002 they have been detecting millions of different particles per seconds and still continue today.
Another example of the development of the Micromegas detectors is the invention of the “bulk” technology. The “bulk” technology consists of the integration of the micro-mesh with the printed circuit board (that carries the readout electrodes) in order to build a monolithic detector. Such a detector is very robust and can be produce within an industrial process (a successful try has been conducted with the 3M
firm in 2006) allowing public applications. For instance, by modifying the micro-mesh in order to make it photo-sensitive to UV
light, the Micromegas can be used to prevent forest fires.
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...
coming from the development of wire chamber
Wire chamber
A multi-wire chamber is a detector for particles of ionizing radiation which is an advancement of the concept of the Geiger counter and the proportional counter....
. Invented in 1992 by Georges Charpak
Georges Charpak
Georges Charpak was a French physicist who was awarded the Nobel Prize in Physics in 1992.-Life:Georges Charpak was born to Jewish family in the village of Dąbrowica in Poland . Charpak's family moved from Poland to Paris when he was seven years old...
and Ioannis Giomataris, the Micromegas detectors are mainly used in experimental physics, in particular in 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...
, nuclear physics
Nuclear 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...
and astrophysics
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
for the detection of ionising particles.
The Micromegas are light detectors in order to minimize the perturbation on the impinging particle. From their small amplification gap, they have fast signals in the order of 100 nanoseconds. They are precise detectors with a spatial resolution below one hundred of micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
. Nowadays, the use of the Micromegas technology is growing over the different fields of experimental physics.
Working principle
A particle detectorParticle 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...
is used to detect a passing particle
Particle
A particle is, generally, a small localized object to which can be ascribed physical properties. It may also refer to:In chemistry:* Colloidal particle, part of a one-phase system of two or more components where the particles aren't individually visible.In physics:* Subatomic particle, which may be...
and obtain information such as its position
Position
Position may refer to:* Position , a player role within a team* Position , the orientation of a baby prior to birth* Position , a mathematical identification of relative location...
, arrival time and momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
. In experimental physics, the particle is usually coming from a 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...
but it can also come from space (cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
) or from a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
.
The Micromegas detector, as every gaseous detector, detects particles by amplifying the charges that have been created by ionisation in the gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
volume. In a Micromegas detector, this gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
volume is divided in two by a metallic micro-mesh (“Micromesh” on the schematic) placed between
and of the readout electrodeElectrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
(Strips on the schematic). The micro-mesh is the key element since it allows, at the same time, a high gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
of
with and a fast signal of 100ns.Ionisation and charge amplification
While passing through the detector, a particle will ionise the gas atoms by pulling up an electron creating 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...
/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...
pair (1). When no electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
is applied, the 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...
/electron
Electron
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...
pair recombines and nothing happen. But here, within an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
in the order of
the electron will drift (2) toward the amplification electrode (the mesh) and the ion toward the cathodeCathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
. When the electron arrives closed to the mesh (3), it enters an intense electric field (typically in the order of
) in the amplification gap.Accelerated by this field, the electron reaches enough energy to produce 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...
/electron
Electron
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...
pairs that will also ionise the gas, creating pairs; it’s the avalanche effect
Avalanche effect
In cryptography, the avalanche effect refers to a desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions. The avalanche effect is evident if, when an input is changed slightly the output changes significantly...
(4). By this mean, it’s several thousand of pairs that are created from an hundred of primary charges coming from by the interaction with the impinging particle. The primary charges need to be multiplied to create a significant signal. A last, we read the electronic signal on the readout electrode (5) by a charge amplifier
Charge amplifier
A charge amplifier is a current integrator driven by an electrical source with capacitive nature such as a piezoelectric sensor. Contrary to what its name may suggest, a charge amplifier does not amplify the electric charge present at its input...
. The readout electrode is usually segmented in strips and/or pixels in order to obtain the position of the impinging particle in the detector. The amplitude and the shape of the signal, read via the electronic on the readout electrode, gives information on the time and energy of the particle.
Analog signal of a Micromegas
The signal is inducedElectromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
by the movement of charges between the micro-mesh and the readout electrode (this volume is called the amplification gap). The 100 nanoseconds signal consists of an electron peak (blue) and an ion tail (red). Since the electron mobility
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...
in gas is over 1000 times faster than the 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...
mobility, the electronic signal is much shorter (below 3ns) than the ionic one. That is why it is used to measure precisely the time. The ionic signal caries more than half of the signal and is used to reconstruct the energy
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
of the particle.
First concept at the Hadron Blind Detector
In 1991, to improve the detection of hadronsHadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
at the Hadron Blind Detector experiment, I. Giomataris and G. Charpak
Georges Charpak
Georges Charpak was a French physicist who was awarded the Nobel Prize in Physics in 1992.-Life:Georges Charpak was born to Jewish family in the village of Dąbrowica in Poland . Charpak's family moved from Poland to Paris when he was seven years old...
reduced the amplification gap of a parallel plate detector (a type of spark chamber) in order to speed up the signal. A 1 mm amplification gap prototype was build for the HDB experiment but the gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
was not uniform enough to be used in the experiment. The millimetre gap was not enough controlled and created large gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
fluctuations.
Nevertheless the benefits of a reduce amplification gap has been demonstrated and the Micro-Mesh gaseous structure or Micromegas concept was born in October 1992, shortly before the announcement of the Nobel prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
attribution to Georges Charpak
Georges Charpak
Georges Charpak was a French physicist who was awarded the Nobel Prize in Physics in 1992.-Life:Georges Charpak was born to Jewish family in the village of Dąbrowica in Poland . Charpak's family moved from Poland to Paris when he was seven years old...
for the invention of the wire chambers. Georges Charpak
Georges Charpak
Georges Charpak was a French physicist who was awarded the Nobel Prize in Physics in 1992.-Life:Georges Charpak was born to Jewish family in the village of Dąbrowica in Poland . Charpak's family moved from Poland to Paris when he was seven years old...
used to say that this detector and some other new concepts belonging to the family of micro-pattern gaseous detectors (MPGDs) will revolutionise nuclear and particle physics just as his detector did.
The Micromegas technology research and development
Since 1992, at the CEA Saclay and at CERNCERN
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...
, the Micromegas technology has been developed in order to obtain more stable, reliable, precise and faster detectors. In 2001, twelve large Micromegas detectors plane of
) were used for the first time in a large scale experiment at COMPASS situated on the Super Proton SynchrotronSuper Proton Synchrotron
The Super Proton Synchrotron is a particle accelerator of the synchrotron type at CERN. It is housed in a circular tunnel, in circumference, straddling the border of France and Switzerland near Geneva, Switzerland. The SPS was designed by a team led by John Adams, director-general of what was...
accelerator at 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...
. Since 2002 they have been detecting millions of different particles per seconds and still continue today.
Another example of the development of the Micromegas detectors is the invention of the “bulk” technology. The “bulk” technology consists of the integration of the micro-mesh with the printed circuit board (that carries the readout electrodes) in order to build a monolithic detector. Such a detector is very robust and can be produce within an industrial process (a successful try has been conducted with the 3M
3M
3M Company , formerly known as the Minnesota Mining and Manufacturing Company, is an American multinational conglomerate corporation based in Maplewood, Minnesota, United States....
firm in 2006) allowing public applications. For instance, by modifying the micro-mesh in order to make it photo-sensitive to UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light, the Micromegas can be used to prevent forest fires.
Micromegas detectors in experimental physics
The Micromegas detectors are now used in several experiments :- HadronicHadronIn particle physics, a hadron is a composite particle made of quarks held together by the strong force...
physics: COMPASS, NA48, and projects for the ILC-TPCTPCTPC may stand for terms related to:engineering and computing:* Thin Plated Copper cathode* Tonnes per centimeter, used in maritime cargo plans and hydrostatic calculations, relates a vessel's displacement to its draft * Total Plant Cost in relation to electricity generation facilities* Transmission...
and CLAS12 at J-labThomas Jefferson National Accelerator FacilityThomas Jefferson National Accelerator Facility , 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...
are under active study - ParticleParticleA particle is, generally, a small localized object to which can be ascribed physical properties. It may also refer to:In chemistry:* Colloidal particle, part of a one-phase system of two or more components where the particles aren't individually visible.In physics:* Subatomic particle, which may be...
physics: T2K, CAST, HELAZZ - Neutron physicsNeutron transportNeutron transport is the study of the motions and interactions of neutrons with materials. Nuclear scientists and engineers often need to know where neutrons are in an apparatus, what direction they are going, and how quickly they are moving. It is commonly used to determine the behavior of nuclear...
: nTOF, Spallation Neutron Source (SNS)