Alpha Magnetic Spectrometer
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The Alpha Magnetic Spectrometer (AMS-02) is a
particle physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...
experiment module that is mounted on the
International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
(ISS).Kristine Rainey (April 2, 2013)
Alpha Magnetic Spectrometer (AMS): How It Works
NASA. Retrieved June 2, 2019.
The experiment is a recognized
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...
experiment (RE1). The module is a detector that measures
antimatter In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding subatomic particle, particles in "ordinary" matter, and can be thought of as matter with reversed charge and parity, or go ...
in
cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...
s; this information is needed to understand the formation of the
universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
and search for evidence of
dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
. The principal investigator is
Nobel laureate The Nobel Prizes (, ) are awarded annually by the Royal Swedish Academy of Sciences, the Swedish Academy, the Karolinska Institutet, and the Norwegian Nobel Committee to individuals and organizations who make outstanding contributions in th ...
particle physicist Samuel Ting. The launch of flight
STS-134 STS-134 (ISS assembly sequence, ISS assembly flight ULF6) was the penultimate mission of NASA's Space Shuttle program and the 25th and last spaceflight of . This flight delivered the Alpha Magnetic Spectrometer and an ExPRESS Logistics Carrier ...
carrying AMS-02 took place on May 16, 2011, and the
spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...
was installed on May 19, 2011. By April 15, 2015, AMS-02 had recorded over 60 billion cosmic ray events and 90 billion after five years of operation since its installation in May 2011. In March 2013, Professor Ting reported initial results, saying that AMS had observed over 400,000
positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
s, with the positron to electron fraction increasing from 10 GeV to 250 GeV. (Later results have shown a decrease in positron fraction at energies over about 275 GeV). There was "no significant variation over time, or any preferred incoming direction. These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations." The results have been published in ''
Physical Review Letters ''Physical Review Letters'' (''PRL''), established in 1958, is a peer-reviewed, scientific journal that is published 52 times per year by the American Physical Society. The journal is considered one of the most prestigious in the field of physics ...
''. Additional data are still being collected.


History

The alpha magnetic spectrometer was proposed in 1995 by the Antimatter Study Group, led by MIT particle physicist Samuel Ting, not long after the cancellation of the Superconducting Super Collider. The original name for the instrument was Antimatter Spectrometer, with the stated objective to search for primordial antimatter, with a target resolution of antimatter/matter ≈10−9. The proposal was accepted and Ting became the principal investigator.


AMS-01

An AMS prototype designated AMS-01, a simplified version of the detector, was built by the international consortium under Ting's direction and flown into space aboard the on STS-91 in June 1998. By not detecting any antihelium, the AMS-01 established an upper limit of 1.1×10−6 for the antihelium-to-helium flux ratio and proved that the detector concept worked in space. This shuttle mission was the last shuttle flight to the ''Mir'' space station.


AMS-02

After the flight of the prototype, the group, now labelled the AMS Collaboration, began the development of a full research system designated AMS-02. This development effort involved the work of 500 scientists from 56 institutions and 16 countries organized under
United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...
(DOE) sponsorship. The instrument which eventually resulted from a long evolutionary process has been called "the most sophisticated particle detector ever sent into space", rivaling very large detectors used at major
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies to contain them in well-defined particle beam, beams. Small accelerators are used for fundamental ...
s, and has cost four times as much as any of its ground-based counterparts. Its goals have also evolved and been refined over time. As built it is a more comprehensive detector which has a better chance of discovering evidence of
dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
along with other goals. The power requirements for AMS-02 were thought to be too great for a practical independent spacecraft, so AMS-02 was designed to be installed as an external module on the International Space Station and use power from the ISS. The post- plan was to deliver AMS-02 to the ISS by space shuttle in 2005 on station assembly mission UF4.1, but technical difficulties and shuttle scheduling issues added more delays. AMS-02 completed final integration and operational testing at
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...
in Geneva, Switzerland which included exposure to energetic
proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
beams generated by the CERN SPS particle accelerator. AMS-02 was then shipped b
specialist hauler
to ESA's European Space Research and Technology Centre (ESTEC) facility in the
Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...
, arriving February 16, 2010. Here it underwent thermal vacuum, electromagnetic compatibility, and electromagnetic interference testing. AMS-02 was scheduled for delivery to the
Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the NASA, National Aeronautics and Space Administration's (NASA) ten NASA facilities#List of field c ...
in
Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
, United States, in late May 2010. This was, however, postponed to August 26, as AMS-02 underwent final alignment beam testing at CERN. A cryogenic,
superconducting magnet A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire has no electrical resistance and therefore can conduct much ...
system was initially installed on the AMS-02. When the Obama administration extended International Space Station operations beyond 2015, the decision was made by AMS management to exchange the AMS-02 superconducting magnet for the non-superconducting magnet previously flown on AMS-01. Although the non-superconducting magnet has a weaker
field strength In physics, field strength refers to a value in a vector-valued field (e.g., in volts per meter, V/m, for an electric field ''E''). For example, an electromagnetic field has both electric field strength and magnetic field strength. Field str ...
, its on-orbit operational time at ISS is expected to be 10 to 18 years versus only three years for the superconducting version. In December 2018, it was announced that funding for the ISS had been extended to 2030. In 1999, after the successful flight of AMS-01, the total cost of the AMS program was estimated to be $33 million, with AMS-02 planned for flight to the ISS in 2003. After the Space Shuttle ''Columbia'' disaster in 2003, and after a number of technical difficulties with the construction of AMS-02, the cost of the program ballooned to an estimated $2 billion.


Installation on the International Space Station

For several years it was uncertain if AMS-02 would ever be launched because it was not manifested to fly on any of the remaining
Space Shuttle The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...
flights. After the 2003 ''Columbia'' disaster, NASA decided to reduce shuttle flights and retire the remaining shuttles by 2010. A number of flights were removed from the remaining manifest, including the flight for AMS-02. In 2006, NASA studied alternative ways of delivering AMS-02 to the space station, but they all proved to be too expensive. In May 2008, a bill was proposed to launch AMS-02 to the ISS on an additional shuttle flight in 2010 or 2011. The bill was passed by the full U.S.
House of Representatives House of Representatives is the name of legislative bodies in many countries and sub-national entities. In many countries, the House of Representatives is the lower house of a bicameral legislature, with the corresponding upper house often ...
on June 11, 2008. The bill then went before the Senate Commerce, Science and Transportation Committee where it also passed. It was then amended and passed by the full
Senate A senate is a deliberative assembly, often the upper house or chamber of a bicameral legislature. The name comes from the ancient Roman Senate (Latin: ''Senatus''), so-called as an assembly of the senior (Latin: ''senex'' meaning "the el ...
on September 25, 2008, and was passed again by the House on September 27, 2008. It was signed into law by President
George W. Bush George Walker Bush (born July 6, 1946) is an American politician and businessman who was the 43rd president of the United States from 2001 to 2009. A member of the Bush family and the Republican Party (United States), Republican Party, he i ...
on October 15, 2008. The bill authorized NASA to add another space shuttle flight to the schedule before the space shuttle program was discontinued. In January 2009, NASA restored AMS-02 to the shuttle manifest. On August 26, 2010, AMS-02 was delivered from
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...
to the
Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the NASA, National Aeronautics and Space Administration's (NASA) ten NASA facilities#List of field c ...
by a
Lockheed C-5 Galaxy The Lockheed C-5 Galaxy is a large military transport aircraft designed and built by Lockheed Corporation, Lockheed, and now maintained and upgraded by its successor, Lockheed Martin. It provides the United States Air Force (USAF) with a heavy ...
jet. It was delivered to the
International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
on May 19, 2011, as part of station assembly flight ULF6 on shuttle flight
STS-134 STS-134 (ISS assembly sequence, ISS assembly flight ULF6) was the penultimate mission of NASA's Space Shuttle program and the 25th and last spaceflight of . This flight delivered the Alpha Magnetic Spectrometer and an ExPRESS Logistics Carrier ...
, commanded by
Mark Kelly Mark Edward Kelly (born February 21, 1964) is an American politician, retired astronaut, and former United States Navy, naval officer serving as the Seniority in the United States Senate, senior United States senator from Arizona, a seat he ha ...
. It was removed from the shuttle cargo bay using the shuttle's robotic arm and handed off to the station's robotic arm for installation. AMS-02 is mounted on top of the
Integrated Truss Structure The Integrated Truss Structure (ITS) of the International Space Station (ISS) consists of a linear arranged sequence of connected trusses on which various unpressurized components are mounted such as logistics carriers, radiators, ISS Solar Arra ...
, on USS-02, the
zenith The zenith (, ) is the imaginary point on the celestial sphere directly "above" a particular location. "Above" means in the vertical direction (Vertical and horizontal, plumb line) opposite to the gravity direction at that location (nadir). The z ...
side of the S3-element of the truss.


Operations, condition and repairs

By April 2017, only one of the 4 redundant coolant pumps for the silicon trackers was fully working, and repairs were being planned, despite AMS-02 not being designed to be serviced in space. By 2019, the last pump was being operated intermittently. In November 2019, after four years of planning, special tools and equipment were sent to the ISS for in-situ repairs requiring four EVAs. Liquid carbon dioxide coolant was also replenished. The repairs were conducted by the ISS crew of
Expedition 61 Expedition 61 was the 61st Expedition to the International Space Station, which began on 3 October 2019 with the undocking of the Soyuz MS-12 spacecraft. The Expedition was commanded by European Space Agency, ESA astronaut Luca Parmitano, who be ...
. The spacewalkers were the expedition commander and ESA astronaut
Luca Parmitano Luca Parmitano (born 27 September 1976 in Paternò, Sicily) is an Italian astronaut in the European Astronaut Corps for the European Space Agency (ESA). He was selected as an ESA astronaut in May 2009. Parmitano is also a colonel and test pilot ...
, and
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
astronaut Andrew Morgan. Both of them were assisted by NASA astronauts Christina Koch and Jessica Meir who operated the
Canadarm2 The Mobile Servicing System (MSS) is a robotic system on board the International Space Station (ISS). Launched to the ISS in 2001, it plays a key role in station assembly and maintenance; it moves equipment and supplies around the station, suppo ...
robotic arm from inside the Station. The spacewalks were described as the "most challenging since he last Hubble repairs". The entire spacewalk campaign was a central feature of the Disney+ docuseries Among The Stars.


First spacewalk

The first spacewalk was conducted on November 15, 2019. The spacewalk began with the removal of the debris shield covering AMS, which was jettisoned to burn up in the atmosphere. The next task was to install three handrails in the vicinity of AMS to prepare for the next spacewalks and remove zip ties on the AMS' vertical support strut. This was followed by the "get ahead" tasks: Parmitano removed the screws from a carbon-fibre cover under the insulation and passed the cover to Morgan to jettison. The spacewalkers also removed the vertical support beam cover. The duration of the spacewalk was 6 hours and 39 minutes.


Second spacewalk

The second spacewalk was conducted on November 22, 2019. Parmitano and Morgan cut a total of eight stainless steel tubes, including one that vented the remaining carbon dioxide from the old cooling pump. The crew members also prepared a power cable and installed a mechanical attachment device in advance of installing the new cooling system. The duration of the spacewalk was 6 hours and 33 minutes.


Third spacewalk

The third spacewalk was conducted on December 2, 2019. The crew completed the primary task of installing the upgraded cooling system, called the upgraded tracker thermal pump system (UTTPS), completed the power and data cable connections for the system, and connected all eight cooling lines from the AMS to the new system. The intricate connection work required making a clean cut for each existing stainless steel tube connected to the AMS, then connecting it to the new system through
swaging Swaging () is a forging process in which the dimensions of an item are altered using Die (manufacturing), dies into which the item is forced. Swaging is usually a cold working process, but also may be hot working, hot worked. The term swage ma ...
. The astronauts also completed an additional task to install an insulating blanket on the
nadir The nadir is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direction opposite of the nadir is the zenith. Et ...
side of the AMS to replace the heat shield and blanket they removed during the first spacewalk to begin the repair work. The flight control team on Earth initiated power-up of the system and confirmed its reception of power and data. The duration of the spacewalk was 6 hours and 2 minutes.


Fourth spacewalk

The fourth spacewalk was conducted on January 25, 2020. The astronauts conducted leak checks for the cooling system on the AMS and opened a valve to pressurize the system. Parmitano found a leak in one of the AMS's cooling lines. The leak was fixed during the spacewalk. Preliminary testing showed the AMS was responding as expected. Ground teams worked to fill the new AMS thermal control system with
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
, allowed the system to stabilize, and powered on the pumps to verify and optimize their performance. The tracker, one of several detectors on the AMS, began collecting science data again before the end of the week after the spacewalk. The astronauts also completed an additional task to remove degraded lens filters on two high-definition video cameras. The duration of the spacewalk was 6 hours and 16 minutes.


Specifications

*Mass: *Structural material: Stainless steel *Power: 2,500 W *Internal data rate: 7 Gbit/s *Data rate to ground: 2 Mbit/s (typical, average) *Primary mission duration: 10 to 18 years * Design life: 3 years. *Magnetic field intensity: 0.15 tesla produced by a permanent
neodymium magnet A nickel-plated neodymium magnet on a bracket from a hard disk drive file:Nd-magnet.jpg">Nickel-plated neodymium magnet cubes Left: high-resolution transmission electron microscopy image of Nd2Fe14B; right: crystal structure with unit cell mar ...
*Original superconducting magnet: 2 coils of niobium-titanium at 1.8 K producing a central field of 0.87 tesla (not used in the actual device) *AMS-02 flight magnet changed to non-superconducting AMS-01 version to extend experiment life and to solve reliability problems in the operation of the superconducting system About 1,000 cosmic rays are recorded by the instrument per second, generating about one GB/s of data. This data is filtered and compressed to about 300 kbit/s for download to the operation center POCC at CERN. A mockup of the machine is present inside the operations center at CERN.


Design

The detector module consists of a series of detectors that are used to determine various characteristics of the radiation and particles as they pass through. Characteristics are determined only for particles that pass through from top to bottom. Particles that enter the detector at any other angles are rejected. From top to bottom the subsystems are identified as: * Transition radiation detector measures the velocities of the highest energy particles; *Upper time of flight counter, along with the lower time of flight counter, measures the velocities of lower energy particles; *Star tracker determines the orientation of the module in space; *Silicon tracker (9 disks among 6 locations) measures the coordinates of charged particles in the magnetic field; **Has 4 redundant coolant pumps *Permanent magnet bends the path of charged particles so they can be identified; *Anti-coincidence counter rejects stray particles that enter through the sides; *
Ring imaging Cherenkov detector The ring-imaging Cherenkov, or RICH, detector is a device for identifying the type of an electrically charged subatomic particle of known momentum, that traverses a transparency and translucency, transparent refractive medium, by measurement of the ...
measures velocity of fast particles with extreme accuracy; *Electromagnetic calorimeter measures the total energy of the particles.


Scientific goals

The AMS-02 uses the unique environment of space to advance knowledge of the Universe and lead to the understanding of its origin by searching for antimatter,
dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
and measuring
cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...
s.


Antimatter

Experimental evidence indicates that our galaxy is made of
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...
; however, scientists believe there are about 100–200 billion galaxies in the observable Universe and some versions of the
Big Bang The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...
theory of the origin of the Universe require equal amounts of matter and antimatter. Theories that explain this apparent asymmetry violate other measurements. Whether or not there is significant antimatter is one of the fundamental questions of the origin and nature of the Universe. Any observations of an
antihelium In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter, and can be thought of as matter with reversed charge and parity, or going backward in time ...
nucleus would provide evidence for the existence of antimatter in space. In 1999, ''AMS-01'' established a new upper limit of 10−6 for the antihelium/helium flux ratio in the Universe. AMS-02 was designed to search with a sensitivity of 10−9, an improvement of three orders of magnitude over ''AMS-01'', sufficient to reach the edge of the expanding Universe and resolve the issue definitively.


Dark matter

The visible matter in the Universe, such as stars, adds up to less than 5 percent of the total mass that is known to exist from many other observations. The other 95 percent is dark, either dark matter, which is estimated at 20 percent of the Universe by weight, or
dark energy In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
, which makes up the balance. The exact nature of both still is unknown. One of the leading candidates for dark matter is the
neutralino In supersymmetry, the neutralino is a hypothetical particle. In the Minimal Supersymmetric Standard Model (MSSM), a popular model of realization of supersymmetry at a low energy, there are four neutralinos that are fermions and are electrically ...
. If neutralinos exist, they should be colliding with each other and giving off an excess of charged particles that can be detected by AMS-02. Any peaks in the background
positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
,
antiproton The antiproton, , (pronounced ''p-bar'') is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived, since any collision with a proton will cause both particles to be annihilated in a burst of energy. The exis ...
, or
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
flux could signal the presence of neutralinos or other dark matter candidates, but would need to be distinguished from poorly known
confounding In causal inference, a confounder is a variable that influences both the dependent variable and independent variable, causing a spurious association. Confounding is a causal concept, and as such, cannot be described in terms of correlatio ...
astrophysical signals.


Strangelets

Six types of
quark A quark () is a type of 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 nucleus, atomic nuclei ...
s ( up, down,
strange Strange may refer to: Fiction * Strange (comic book), a comic book limited series by Marvel Comics * Strange (Marvel Comics), one of a pair of Marvel Comics characters known as The Strangers * Adam Strange, a DC Comics superhero * The title c ...
,
charm Charm or Charms may refer to: Arts and entertainment * The Charms, an American garage rock band * Otis Williams and the Charms, an American doo-wop group * The Charm (Bubba Sparxxx album), ''The Charm'' (Bubba Sparxxx album), 2006 * Charm (Danny! ...
, bottom and
top Top most commonly refers to: * Top, a basic term of orientation, distinguished from bottom, front, back, and sides * Spinning top, a ubiquitous traditional toy * Top (clothing), clothing designed to be worn over the torso * Mountain top, a moun ...
) have been found experimentally; however, the majority of matter on Earth is made up of only up and down quarks. It is a fundamental question whether there exists stable matter made up of strange quarks in combination with up and down quarks. Particles of such matter are known as
strangelet A strangelet (pronounced ) is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter, small enough to be ...
s. Strangelets might have extremely large mass and very small charge-to-mass ratios. It would be a totally new form of matter. AMS-02 may determine whether this extraordinary matter exists in our local environment.


Space radiation environment

Cosmic radiation Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Sol ...
during transit is a significant obstacle to sending humans to Mars. Accurate measurements of the cosmic ray environment are needed to plan appropriate countermeasures. Most cosmic ray studies are done by balloon-borne instruments with flight times that are measured in days; these studies have shown significant variations. AMS-02 operates on the ISS, gathering a large amount of accurate data and allowing measurements of the long term variation of the cosmic ray flux over a wide energy range, for nuclei from
proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
s to
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
. In addition to understanding the radiation protection required for astronauts during interplanetary flight, this data will allow the interstellar propagation and origins of cosmic rays to be identified.


Results

By late 2016, it was reported that AMS-02 had observed over 90 billion cosmic rays. In February 2013, Samuel Ting reported that in its first 18 months of operation AMS had recorded 25 billion particle events including nearly eight billion fast electrons and positrons. The AMS paper reported the positron-electron ratio in the mass range of 0.5 to 350
GeV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...
, providing evidence about the
weakly interacting massive particle Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter. There exists no formal definition of a WIMP, but broadly, it is an elementary particle which interacts via gravity an ...
(WIMP) model of dark matter. On March 30, 2013, the first results from the AMS experiment were announced by the
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...
press office. The first physics results were published in ''
Physical Review Letters ''Physical Review Letters'' (''PRL''), established in 1958, is a peer-reviewed, scientific journal that is published 52 times per year by the American Physical Society. The journal is considered one of the most prestigious in the field of physics ...
'' on April 3, 2013. A total of 6.8 million
positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
and
electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
events were collected in the energy range from 0.5 to 350 GeV. The positron fraction (of the total electron plus positron events) steadily increased from energies of 10 to 250 GeV, but the slope decreased by an order of magnitude above 20 GeV, even though the fraction of positrons still increased. There was no fine structure in the positron fraction spectrum, and no anisotropies were observed. The accompanying ''Physics'' Viewpoint said that "The first results from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays." These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations. Ting said "Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin." On September 18, 2014, new results with almost twice as much data were presented in a talk at CERN and published in ''Physical Review Letters''. A new measurement of positron fraction up to 500 GeV was reported, showing that positron fraction peaks at a maximum of about 16% of total electron+positron events, around an energy of 275 ± 32 GeV. At higher energies, up to 500 GeV, the ratio of positrons to electrons begins to fall again. The AMS team presented for 3 days at CERN in April 2015, covering new data on 300 million proton events and helium flux. It revealed in December 2016 that it had discovered a few signals consistent with antihelium nuclei amidst several billion helium nuclei. The result remains to be verified, and the team is currently trying to rule out possible contamination. A study from 2019, using data from NASA's
Fermi Gamma-ray Space Telescope The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is ...
discovered a halo around the nearby
pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...
Geminga. The accelerated electrons and positrons collide with nearby starlight. The collision boosts the light to much higher energies. Geminga alone could be responsible for as much as 20% of the high-energy positrons seen by the AMS-02 experiment. The AMS-02 on the ISS has, as of 2021, recorded eight events that seem to indicate the detection of antihelium-3. Over a twelve-year period aboard the ISS, the AMS has accumulated a dataset of more than 230 billion cosmic rays, spanning energies reaching multi-TeV levels. The precise measurements obtained by the magnetic spectrometer enable data presentation with an accuracy approaching ~1%. Particularly significant is the high-energy data regarding elementary particles such as electrons, positrons, protons, and antiprotons, which presents challenges to theoretical frameworks. Additionally, observations of nuclei and
isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
s reveal energy dependencies that deviate from theoretical predictions. In a presentation at the 2024 APS April meeting, the AMS collaboration argued that the dataset they have collected necessitates a reevaluation of existing models of the cosmos.


See also

*
List of space telescopes This list of space telescopes (astronomy, astronomical space observatory, space observatories) is grouped by major frequency ranges: gamma ray, x-ray, ultraviolet, visible light, visible, infrared, microwave and radio. Telescopes that work in mult ...
(Astronomical Space Observatories) *
Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) was a cosmic ray research module attached to an Earth orbiting satellite. ''PAMELA'' was launched on 15 June 2006 and was the first satellite-based experiment ded ...
(PAMELA) – an Italian-international cosmic ray mission launched in 2006 with similar goals *
Scientific research on the ISS Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...


References


Further reading

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External links


AMS Collaboration Homepage

AMS Homepage
at
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...
. Inc. construction diagrams
AMS Homepage
at the
Johnson Space Center The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight in Houston, Texas (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight controller, flight control are conducted. ...

NASA AMS-02 Project Fact Sheet


with real-time cosmic ray count
An animated movie of the STS-134 mission showing the installation of AMS-02 (72 MB)

Alpha Magnetic Spectrometer – image collection – AMS-02 on Facebook


* ttp://www.route-to-space.eu/index.php/en/projects/alpha-magnetic-spectrometer Route To Space Alliance – European Transport for The Space and Aeronautic Industries *Record fo
AMS-02
experiment on
INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1 ...
*Record fo
AMS-01
experiment on
INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1 ...
{{Orbital launches in 2011 Particle experiments Cosmic-ray experiments Components of the International Space Station International Space Station experiments Experiments for dark matter search Spacecraft launched in 2011 Space science experiments Piggyback mission CERN experiments