question: What happens if pushing the MRI QUENCH button? How the superconductive magnet loses the superconductivity?
comment: > But how exactly pushing a button can make the coil temperature rise at the first place? It activates an electrical heating element on or very close to the magnet itself. There are dedicated circuits for this emergency stop process, and the goal is to heat the magnet quickly to the point where it gains electrical resistance and the circulating charge can dissipate into heat, stopping the strong magnetic field.
passages: In certain cases, superconducting magnets designed for very high currents require extensive bedding in, to enable the magnets to function at their full planned currents and fields. This is known as "training" the magnet, and involves a type of material memory effect. One situation this is required is in the case of particle colliders such as CERN's Large Hadron Collider. The magnets of the LHC were planned to run at 8 TeV (2×4 TeV) on its first run and 14 TeV (2×7 TeV) on its second run, but were initially operated at a lower energy of 3.5 TeV and 6.5 TeV per beam respectively. Because of initial crystallographic defects in the material, they will initially lose their superconducting ability ("quench") at a lower level than their design current. CERN states that this is due to electromagnetic forces causing tiny movements in the magnets, which in turn cause superconductivity to be lost when operating at the high precisions needed for their planned current. By repeatedly running the magnets at a lower current and then slightly increasing the current until they quench under control, the magnet will gradually both gain the required ability to withstand the higher currents of its design specification without quenches occurring, and have any such issues "shaken" out of them, until they are eventually able to operate reliably at their full planned current without experiencing quenches.
   An unintentional shut-down of a superconducting electromagnet, an event known as "quench", involves the rapid boiling of liquid helium from the device. If the rapidly expanding helium cannot be dissipated through an external vent, sometimes referred to as a 'quench pipe', it may be released into the scanner room where it may cause displacement of the oxygen and present a risk of asphyxiation.
   A large section of the superconducting magnets in CERN's Large Hadron Collider unexpectedly quenched during start-up operations in 2008, necessitating the replacement of a number of magnets. In order to mitigate against potentially destructive quenches, the superconducting magnets that form the LHC are equipped with fast-ramping heaters which are activated once a quench event is detected by the complex quench protection system. As the dipole bending magnets are connected in series, each power circuit includes 154 individual magnets, and should a quench event occur, the entire combined stored energy of these magnets must be dumped at once. This energy is transferred into dumps that are massive blocks of metal which heat up to several hundreds of degrees Celsius due to the resistive heating in a matter of seconds. Although undesirable, a magnet quench is a "fairly routine event" during the operation of a particle accelerator.
   BULLET::::- fast fault current limiters
  
  BULLET::::- high sensitivity particle detectors, including the transition edge sensor, the superconducting bolometer, the superconducting tunnel junction detector, the kinetic inductance detector, and the superconducting nanowire single-photon detector
  
  BULLET::::- railgun and coilgun magnets
  
  BULLET::::- electric motors and generators
  
  Section::::Low-temperature superconductivity.
  
  Section::::Low-temperature superconductivity.:Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR).
   Typical for a CCC is the use of a SQUID magnetometer as null detector for the magnetic field (SQUID = Superconducting Quantum Interference Device). These are capable of detecting extremely small changes of the magnetic field corresponding to fractions of the magnetic flux quantum = "h"/2"e" ≈ 2×10 V·s ("h" is Planck's constant and "e" the elementary charge). The function principle of a SQUID is based on macroscopic quantum interferences of electric currents, arising in superconducting circuits (loops) with tunnel junctions.
   A large section of the superconducting magnets in CERN's Large Hadron Collider unexpectedly quenched during start-up operations in 2008, necessitating the replacement of a number of magnets. In order to mitigate against potentially destructive quenches, the superconducting magnets that form the LHC are equipped with fast-ramping heaters which are activated once a quench event is detected by the complex quench protection system. As the dipole bending magnets are connected in series, each power circuit includes 154 individual magnets, and should a quench event occur, the entire combined stored energy of these magnets must be dumped at once. This energy is transferred into dumps that are massive blocks of metal which heat up to several hundreds of degrees Celsius—because of resistive heating—in a matter of seconds. Although undesirable, a magnet quench is a "fairly routine event" during the operation of a particle accelerator.
   One of the most challenging use of SC magnets is in the LHC particle accelerator. The niobium-titanium (Nb-Ti) magnets operate at 1.9 K to allow them to run safely at 8.3 T. Each magnet stores 7 MJ. In total the magnets store . Once or twice a day, as the protons are accelerated from 450 GeV to 7 TeV, the field of the superconducting bending magnets will be increased from 0.54 T to 8.3 T.
   The rapid switching on and off of the magnetic field gradients is capable of causing nerve stimulation. Volunteers report a twitching sensation when exposed to rapidly switched fields, particularly in their extremities. The reason the peripheral nerves are stimulated is that the changing field increases with distance from the center of the gradient coils (which more or less coincides with the center of the magnet). Although PNS was not a problem for the slow, weak gradients used in the early days of MRI, the strong, rapidly switched gradients used in techniques such as EPI, fMRI, diffusion MRI, etc. are capable of inducing PNS. American and European regulatory agencies insist that manufacturers stay below specified "dB/"dt" limits ("dB/"dt" is the change in magnetic field strength per unit time), or else prove that no PNS is induced for any imaging sequence. As a result of "d"B/"dt" limitation, commercial MRI systems cannot use the full rated power of their gradient amplifiers.
   In practice, magnets usually have safety devices to stop or limit the current when the beginning of a quench is detected. If a large magnet undergoes a quench, the inert vapor formed by the evaporating cryogenic fluid can present a significant asphyxiation hazard to operators by displacing breathable air.
   While most IVC filters are made of non-ferromagnetic materials, there are a few types that are weakly ferromagnetic. Accordingly, IVC filters fall under the MRI Safe and MRI Conditional categories depending mostly on type of material used during construction. Rarely will one find an MRI Not Safe IVC filter, as most of the steel, and other ferromagnetic material devices have been discontinued via the FDA.
   A contour map of the decaying magnetic fields is used to localize the sources containing bound NP. This map is produced from the field distribution obtained from an array of SQUID sensors, multiple positions of the sources under the sensors, or a combination of both. The magnetic moments of the sources is obtained during this procedure.
  
  Section::::Magnetic field decay of bound particles.
  
  The time of the NP decaying magnetic field for bound particles in SPMR measurements is on the order of seconds. Unbound particles of similar size decay on the order of milliseconds, contributing very little to the results.
   A quench is an abnormal termination of magnet operation that occurs when part of the superconducting coil enters the normal (resistive) state. This can occur because the field inside the magnet is too large, the rate of change of field is too large (causing eddy currents and resultant heating in the copper support matrix), or a combination of the two. More rarely a defect in the magnet can cause a quench. When this happens, that particular spot is subject to rapid Joule heating from the enormous current, which raises the temperature of the surrounding regions. This pushes those regions into the normal state as well, which leads to more heating in a chain reaction. The entire magnet rapidly becomes normal (this can take several seconds, depending on the size of the superconducting coil). This is accompanied by a loud bang as the energy in the magnetic field is converted to heat, and rapid boil-off of the cryogenic fluid. The abrupt decrease of current can result in kilovolt inductive voltage spikes and arcing. Permanent damage to the magnet is rare, but components can be damaged by localized heating, high voltages, or large mechanical forces. In practice, magnets usually have safety devices to stop or limit the current when the beginning of a quench is detected. If a large magnet undergoes a quench, the inert vapor formed by the evaporating cryogenic fluid can present a significant asphyxiation hazard to operators by displacing breathable air.
   BULLET::::- Magnetic field intensity: 0.15 teslas produced by a 1,200 kg permanent neodymium magnet
  
  BULLET::::- Original superconducting magnet: 2 coils of niobium-titanium at 1.8 K producing a central field of 0.87 teslas
  
  BULLET::::- 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/sec of data. This data is filtered and compressed to about 300 kbit/s for download to the operation center POCC at CERN.
  
  Section::::Design.
   Most IVC filters that have been tested have been labeled as “MRi safe”; the remainder of IVC filters that have been tested are “MR conditional.” Patients who have been treated with nonferromagnetic IVC filters can undergo MR examination any time after filter implantation. In patients who have been treated with a weakly ferromagnetic IVC filter (Gianturco bird nest IVC filter [Cook], stainless steel Greenfield vena cava filter [Boston Scientific]), it is advised that the patient wait at least six weeks before undergoing an MR examination (because these older devices initially may not be anchored as firmly in place as other devices discussed in the present context), unless there is a strong clinical indication to perform the MR examination sooner after implantation, and as long as there is no reason to suspect that the device is not positioned properly or that it is not firmly in place. Most studies of IVC filters have generally been conducted at 1.5 tesla or less, although many IVC filters have now been evaluated at 3 tesla and deemed acceptable for MR examination.
   The superconductor's "residual resistance" arises from several sources, such as random material defects, hydrides that can form on the surface due to hot chemistry and slow cool-down, and others that are yet to be identified. One of the quantifiable residual resistance contributions is due to an external magnetic field pinning magnetic fluxons in a Type II superconductor. The pinned fluxon cores create small normal-conducting regions in the niobium that can be summed to estimate their net resistance. For niobium, the magnetic field contribution to "R" can be approximated by
  
  where:
   A cryogenic, superconducting magnet system was developed for the AMS-02. With Obama administration plans to extend 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, its on-orbit operational time at ISS is expected to be 10 to 18 years versus only three years for the superconducting version. In January 2014 it was announced that funding for the ISS had been extended until 2024.
   In 2015 the CRESST detectors were upgraded by a sensitivity factor of 100 allowing dark matter particles with a mass around that of a proton to be detected.
   Intrauterine devices with copper are generally safe in MRI, but may become dislodged or even expelled, and it is therefore recommended to check the location of the IUD both before and after MRI.
  
  Section::::Projectile risk.
   Section::::Operation.:Magnet "training".
   In general, much care and attention to detail must be exercised in the experimental setup of SRF cavities so that there is not "Q" degradation due to RF losses in ancillary components, such as stainless steel vacuum flanges that are too close to the cavity's evanescent fields. However, careful SRF cavity preparation and experimental configuration have achieved the ideal "Q" not only for low field amplitudes, but up to cavity fields that are typically 75% of the magnetic field quench limit. Few cavities make it to the magnetic field quench limit since residual losses and vanishingly small defects heat up localized spots, which eventually exceed the superconducting critical temperature and lead to a thermal quench.
   As part of the 'routing' survey for MRI studies, patients who have IVC filters will often need verification from the doctor, or medical records, to state that the IVC is safe for the MRI. Most patients with weakly or non-safe ferromagnetic implants will be given a card, which they keep on their person at all time, that can help isolate if it is safe to do an MRI.
  
  For patients who have been denied MRI scans for safety reasons, doctors usually recommend the CT scan with contrast as an alternative.
  
  Section::::Side effects.:Labeling and recommendations.
   BULLET::::- the ion is Doppler cooled with 397 nm and 866 nm light, with 854 nm light on as well
  
  BULLET::::- the ion is spin polarized to the S(m=-1/2) state by applying a formula_36 397 nm light for the last few moments of the Doppler cooling process
  
  BULLET::::- sideband cooling loops are applied at the first red sideband of the D(m=-5/2) 729 nm transition
  
  BULLET::::- to ensure the population ends up in the S(m=-1/2) state, another formula_36 397 nm pulse is applied
  
  BULLET::::- manipulation is carried out and analysis is carried out by applying 729 nm light at the frequency of interest
   Section::::Importance of flux pinning.
  
  Flux pinning is desirable in high-temperature ceramic superconductors to prevent "flux creep", which can create a pseudo-resistance and depress both critical current density and critical field.
  
  Degradation of a high-temperature superconductor's properties due to flux creep is a limiting factor in the use of these superconductors. SQUID magnetometers suffer reduced precision in a certain range of applied field due to flux creep in the superconducting magnet used to bias the sample, and the maximum field strength of high-temperature superconducting magnets is drastically reduced by the depression in critical field.
  
  Section::::Flux pinning in the future.
   Section::::Construction.:Materials.
  
  The maximal magnetic field achievable in a superconducting magnet is limited by the field at which the winding material ceases to be superconducting, its "critical field", "H", which for type-II superconductors is its upper critical field. Another limiting factor is the "critical current", "I", at which the winding material also ceases to be superconducting. Advances in magnets have focused on creating better winding materials.
   Phase 2 has a new CaWO crystal with better radiopurity, improved detectors, and significantly reduced background. It began July 2013 to explore excess signals in the prior run. The results of Phase 2 showed no signal above expected background, proving that the result of Phase 1 had indeed been due to excess background by components of the detector.
  
  CRESST-II first detected the alpha decay of tungsten-180 (W). CRESST-II phase 1 full results were published in 2012. New phase 2 results have been presented on July 2014 with a limit on spin-independent WIMP-nucleon scattering for WIMP masses below 3 GeV/c.
  