Cryogenic particle detectors
Encyclopedia
Cryogenic particle detectors operate at very low temperature, typically only a few degrees above absolute zero
. These sensors interact with an energetic elementary particle
(such as a photon
) and deliver a signal which can be related to the type of particle and the nature of the interaction. While many types of particle detectors might be operated with improved performance at cryogenic
temperatures, this term generally refers to types which take advantage of special effects or properties occurring only at low temperature.
and electrical resistivity, particularly superconductivity
; other designs are based on superconducting tunnel junction
s, quasiparticle
trapping, roton
s in superfluid
s, magnetic bolometer
s, and other principles.
Originally, astronomy pushed the development of cryogenic detectors for optical and infrared radiation. Later, particle physics and cosmology motivated cryogenic detector development for sensing known and predicted particles such as neutrino
s, axion
s, and weakly interacting massive particles (WIMPs).
is a device which measures the amount of heat
deposited in a sample of material. A calorimeter differs from a bolometer
in that a calorimeter measures energy while a bolometer measures power
.
Below the Debye temperature of a crystalline dielectric
material (such as silicon
), the heat capacity decreases inversely as the cube of the absolute temperature. It becomes very small so that the sample's increase in temperature for a given heat input may be relatively large. This makes it practical to make a calorimeter that has a very large temperature excursion for a small amount of heat input, such as that deposited by a passing particle. The temperature rise can be measured with a standard type of thermistor
, as in a classical calorimeter. In general, small sample size and very sensitive thermistors are required to make a sensitive particle detector by this method.
In principle, several types of resistance thermometers can be used. The limit of sensitivity to energy deposition is determined by the magnitude of resistance fluctuations, which are in turn determined by thermal fluctuations. Since all resistor
s exhibit voltage fluctuations that are proportional to their temperature, an effect known as Johnson noise, a reduction of temperature is often the only way to achieve the required sensitivity.
(TES) takes advantage of superconductivity
. Most pure superconductors have a very sharp transition from normal resistivity to superconductivity at some low temperature. By operating on the superconducting phase transition, a very small change in temperature resulting from interaction with a particle results in a significant change in resistance.
. Quasiparticles can also tunnel across the barrier, although the quasiparticle current is suppressed for voltages less than twice the superconducting energy gap. A photon absorbed on one side of a STJ breaks Cooper pairs and creates quasiparticles. In the presence of an applied voltage across the junction, the quasiparticles tunnel across the junction, and the resulting tunneling current is proportional to the photon energy. The STJ can also be used as a heterodyne detector by exploiting the change in the nonlinear current-voltage characteristic
that results from photon-assisted tunneling. STJs are the most sensitive heterodyne detectors available for the 100 GHz - 1 THz frequency range and are employed for astronomical observation at these frequencies.
(KID) is based on measuring the change in kinetic inductance
caused by the absorption of photons in a thin strip of superconducting
material. The change in inductance is typically measured via the change in the resonant frequency of a microwave
resonator
, and hence these detectors are also known as microwave kinetic inductance detectors (MKIDs).
and excludes the field completely excluded from its interior. If it is held slightly below the transition temperature, the superconductivity vanishes on heating by particle radiation, and the field suddenly penetrates the interior. This field change can be detected by a surrounding coil. The change is reversible when the grain cools again. In practice the grains must be very small and carefully made, and carefully coupled to the coil.
rare earth
ions have been used as particle sensors by sensing the spin flips of the paramagnetic atoms induced by heat absorbed in a low heat capacity material. The ions are used as a magnetic thermometer.
or nearly so. In crystalline materials at very low temperature this is not necessarily the case. A good deal more information can be found by measuring the elementary excitations of the crystal lattice, or phonon
s, caused by the interacting particle. This can be done by several methods including superconducting transition edge sensors.
(SNSPD) is based on a superconducting wire cooled well below the superconducting transition temperature and biased with a dc current
that is close to but less than the superconducting critical current. The SNSPD is typically made from ≈ 5 nm thick niobium nitride
films which are patterned as narrow nanowires (with a typical width of 100 nm). Absorption of a photon breaks Cooper pairs and reduces the critical current below the bias current. A small non-superconducting section across the width of the nanowire is formed. This resistive non-superconducting section then leads to a detectable voltage pulse of a duration of about 1 nanosecond. The main advantages of this type of photon detector are its high speed (a maximal count rate of 2 GHz makes them the fastest available) and its low dark count rate. The main disadvantage is the lack of intrinsic energy resolution.
the elementary collective excitations are phonon
s and roton
s. A particle striking an electron or nucleus in this superfluid can produce rotons, which may be detected bolometrically or by the evaporation of helium atoms when they reach a free surface. 4He is intrinsically very pure so the rotons travel ballistically and are stable, so that large volumes of fluid can be used.
is acts similarly to a superconductor. Pairs of atoms are bound as quasiparticle
s similar to Cooper pairs with a very small energy gap of the order of 100 nanoelectronvolt
s. This allows building a detector
analogous to a superconducting tunnel detector. The advantage is that many (~109) pairs
could be produced by a single interaction, but the difficulties are that it is difficult
to measure the excess of normal 3He atoms produced and to prepare and maintain much
superfluid at such low temperature.
Absolute zero
Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....
. These sensors interact with an energetic elementary particle
Elementary particle
In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which...
(such as a photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
) and deliver a signal which can be related to the type of particle and the nature of the interaction. While many types of particle detectors might be operated with improved performance at cryogenic
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...
temperatures, this term generally refers to types which take advantage of special effects or properties occurring only at low temperature.
Introduction
The most commonly cited reason for operating any sensor at low temperature is the reduction in thermal noise, which is proportional to the square root of the absolute temperature. However, at very low temperature, certain material properties become very sensitive to energy deposited by particles in their passage through the sensor, and the gain from these changes may be even more than that from reduction in thermal noise. Two such commonly used properties are heat capacityHeat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
and electrical resistivity, particularly superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...
; other designs are based on superconducting tunnel junction
Tunnel junction
A tunnel junction is any junction between two different materials, where electrons move through the junction by quantum tunneling. Tunnel junctions serve a wide variety of different purposes....
s, quasiparticle
Quasiparticle
In physics, quasiparticles are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space...
trapping, roton
Roton
A roton is an elementary excitation, or quasiparticle, in superfluid Helium-4. The dispersion relation of elementary excitations in this superfluid shows a linear increase from the origin, but exhibits first a maximum and then a minimum in energy as the momentum increases...
s in superfluid
Superfluid
Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...
s, magnetic bolometer
Bolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
s, and other principles.
Originally, astronomy pushed the development of cryogenic detectors for optical and infrared radiation. Later, particle physics and cosmology motivated cryogenic detector development for sensing known and predicted particles such as neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
s, axion
Axion
The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics...
s, and weakly interacting massive particles (WIMPs).
Calorimetric particle detection
A calorimeterCalorimeter
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal microcalorimeters, titration calorimeters and accelerated rate calorimeters are among the most common...
is a device which measures the amount of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
deposited in a sample of material. A calorimeter differs from a bolometer
Bolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
in that a calorimeter measures energy while a bolometer measures power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
.
Below the Debye temperature of a crystalline dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
material (such as silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
), the heat capacity decreases inversely as the cube of the absolute temperature. It becomes very small so that the sample's increase in temperature for a given heat input may be relatively large. This makes it practical to make a calorimeter that has a very large temperature excursion for a small amount of heat input, such as that deposited by a passing particle. The temperature rise can be measured with a standard type of thermistor
Thermistor
A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...
, as in a classical calorimeter. In general, small sample size and very sensitive thermistors are required to make a sensitive particle detector by this method.
In principle, several types of resistance thermometers can be used. The limit of sensitivity to energy deposition is determined by the magnitude of resistance fluctuations, which are in turn determined by thermal fluctuations. Since all resistor
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
s exhibit voltage fluctuations that are proportional to their temperature, an effect known as Johnson noise, a reduction of temperature is often the only way to achieve the required sensitivity.
Superconducting transition edge sensors
A very sensitive calorimetric sensor known as a transition edge sensorTransition edge sensor
A transition edge sensor or TES is a type of cryogenic particle detector that exploits the strongly temperature-dependent resistance of the superconducting phase transition.-Principle of operation:...
(TES) takes advantage of superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...
. Most pure superconductors have a very sharp transition from normal resistivity to superconductivity at some low temperature. By operating on the superconducting phase transition, a very small change in temperature resulting from interaction with a particle results in a significant change in resistance.
Superconducting tunnel junctions
The superconducting tunnel junction (STJ) consists of two pieces of superconducting material separated by a very thin (~nanometer) insulating layer. It is also known as a superconductor-insulator-superconductor tunnel junction (SIS), and it is a type a Josephson junction. Cooper pairs can tunnel across the insulating barrier, a phenomenon known as the Josephson effectJosephson effect
The Josephson effect is the phenomenon of supercurrent across two superconductors coupled by a weak link...
. Quasiparticles can also tunnel across the barrier, although the quasiparticle current is suppressed for voltages less than twice the superconducting energy gap. A photon absorbed on one side of a STJ breaks Cooper pairs and creates quasiparticles. In the presence of an applied voltage across the junction, the quasiparticles tunnel across the junction, and the resulting tunneling current is proportional to the photon energy. The STJ can also be used as a heterodyne detector by exploiting the change in the nonlinear current-voltage characteristic
Current-voltage characteristic
A current–voltage characteristic is a relationship, typically represented as a chart or graph, between an electric current and a corresponding voltage, or potential difference.-In electronics:...
that results from photon-assisted tunneling. STJs are the most sensitive heterodyne detectors available for the 100 GHz - 1 THz frequency range and are employed for astronomical observation at these frequencies.
Kinetic inductance detectors
The kinetic inductance detectorKinetic inductance detector
The kinetic inductance detector — also known as a microwave kinetic inductance detector — is a type of superconducting photon detector first developed by scientists at the California Institute of Technology and the Jet Propulsion Laboratory in 2003. These devices operate at cryogenic...
(KID) is based on measuring the change in kinetic inductance
Kinetic inductance
Kinetic inductance is the manifestation of the inertial mass of mobile charge carriers in alternating electric fields as an equivalent series inductance. Kinetic inductance is observed in high carrier mobility conductors Kinetic inductance is the manifestation of the inertial mass of mobile charge...
caused by the absorption of photons in a thin strip of superconducting
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...
material. The change in inductance is typically measured via the change in the resonant frequency of a microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
resonator
Resonator
A resonator is a device or system that exhibits resonance or resonant behavior, that is, it naturally oscillates at some frequencies, called its resonant frequencies, with greater amplitude than at others. The oscillations in a resonator can be either electromagnetic or mechanical...
, and hence these detectors are also known as microwave kinetic inductance detectors (MKIDs).
Superconducting granules
The superconducting transition alone can be used to directly measure the heating caused by a passing particle. A type I superconducting grain in a magnetic field exhibits perfect diamagnetismDiamagnetism
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the...
and excludes the field completely excluded from its interior. If it is held slightly below the transition temperature, the superconductivity vanishes on heating by particle radiation, and the field suddenly penetrates the interior. This field change can be detected by a surrounding coil. The change is reversible when the grain cools again. In practice the grains must be very small and carefully made, and carefully coupled to the coil.
Magnetic calorimeters
ParamagneticParamagnetism
Paramagnetism is a form of magnetism whereby the paramagnetic material is only attracted when in the presence of an externally applied magnetic field. In contrast with this, diamagnetic materials are repulsive when placed in a magnetic field...
rare earth
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
ions have been used as particle sensors by sensing the spin flips of the paramagnetic atoms induced by heat absorbed in a low heat capacity material. The ions are used as a magnetic thermometer.
Phonon particle detection
Calorimeters assume the sample is in thermal equilibriumThermal equilibrium
Thermal equilibrium is a theoretical physical concept, used especially in theoretical texts, that means that all temperatures of interest are unchanging in time and uniform in space...
or nearly so. In crystalline materials at very low temperature this is not necessarily the case. A good deal more information can be found by measuring the elementary excitations of the crystal lattice, or phonon
Phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...
s, caused by the interacting particle. This can be done by several methods including superconducting transition edge sensors.
Superconducting nanowire single-photon detectors
The superconducting nanowire single-photon detectorSuperconducting nanowire single-photon detector
The superconducting nanowire single-photon detector is a type of near-infrared and optical single-photon detector based on a current-biased superconducting nanowire. It was first developed by scientists at Moscow State Pedagogical University in 2001....
(SNSPD) is based on a superconducting wire cooled well below the superconducting transition temperature and biased with a dc current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
that is close to but less than the superconducting critical current. The SNSPD is typically made from ≈ 5 nm thick niobium nitride
Niobium nitride
Niobium nitride is a compound of niobium and nitrogen with the chemical formula NbN. At low temperatures , niobium nitride becomes a superconductor, and is used in detectors for infrared light.-Uses:...
films which are patterned as narrow nanowires (with a typical width of 100 nm). Absorption of a photon breaks Cooper pairs and reduces the critical current below the bias current. A small non-superconducting section across the width of the nanowire is formed. This resistive non-superconducting section then leads to a detectable voltage pulse of a duration of about 1 nanosecond. The main advantages of this type of photon detector are its high speed (a maximal count rate of 2 GHz makes them the fastest available) and its low dark count rate. The main disadvantage is the lack of intrinsic energy resolution.
Roton detectors
In superfluid 4HeHelium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...
the elementary collective excitations are phonon
Phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...
s and roton
Roton
A roton is an elementary excitation, or quasiparticle, in superfluid Helium-4. The dispersion relation of elementary excitations in this superfluid shows a linear increase from the origin, but exhibits first a maximum and then a minimum in energy as the momentum increases...
s. A particle striking an electron or nucleus in this superfluid can produce rotons, which may be detected bolometrically or by the evaporation of helium atoms when they reach a free surface. 4He is intrinsically very pure so the rotons travel ballistically and are stable, so that large volumes of fluid can be used.
Quasiparticles in superfluid 3He
In the B phase, below 0.001 K, superfluid 3HeHelium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...
is acts similarly to a superconductor. Pairs of atoms are bound as quasiparticle
Quasiparticle
In physics, quasiparticles are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space...
s similar to Cooper pairs with a very small energy gap of the order of 100 nanoelectronvolt
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
s. This allows building a detector
analogous to a superconducting tunnel detector. The advantage is that many (~109) pairs
could be produced by a single interaction, but the difficulties are that it is difficult
to measure the excess of normal 3He atoms produced and to prepare and maintain much
superfluid at such low temperature.
See also
- Detector
- Superconductors
- Josephson effectJosephson effectThe Josephson effect is the phenomenon of supercurrent across two superconductors coupled by a weak link...
- BolometerBolometerA bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
- MicrobolometerMicrobolometerA microbolometer is a specific type of bolometer used as a detector in a thermal camera. Infrared radiation with wavelengths between 7.5-14 μm strikes the detector material, heating it, and thus changing its electrical resistance. This resistance change is measured and processed into temperatures...