Penning trap

Last updated
A cylindrical version of a Penning trap, with open endcaps to permit axial access. B indicates the magnetic field, and E indicates the electric field used for storage of the particles in the trap centre. Penning Trap.jpg
A cylindrical version of a Penning trap, with open endcaps to permit axial access. B indicates the magnetic field, and E indicates the electric field used for storage of the particles in the trap centre.

A Penning trap is a device for the storage of charged particles using a homogeneous magnetic field and a quadrupole electric field. It is mostly found in the physical sciences and related fields of study as a tool for precision measurements of properties of ions and stable subatomic particles, like for example mass, [1] fission yields and isomeric yield ratios. One initial object of study was the so-called geonium atoms, which represent a way to measure the electron magnetic moment by storing a single electron. These traps have been used in the physical realization of quantum computation and quantum information processing by trapping qubits. Penning traps are in use in many laboratories worldwide, including CERN, to store and investigate anti-particles such as antiprotons. [2] The main advantages of Penning traps are the potentially long storage times and the existence of a multitude of techniques to manipulate and non-destructively detect the stored particles. [3] [4] This makes Penning traps versatile tools for the investigation of stored particles, but also for their selection, preparation or mere storage.

Contents


History

The Penning trap was named after F. M. Penning (1894–1953) by Hans Georg Dehmelt (1922–2017) who built the first trap. Dehmelt got inspiration from the vacuum gauge built by F. M. Penning where a current through a discharge tube in a magnetic field is proportional to the pressure. Citing from H. Dehmelt's autobiography: [5]

Sectional view of a hyperbolic Penning trap as used by Dehmelt, with electric and magnetic field lines indicated. Penning Trap.svg
Sectional view of a hyperbolic Penning trap as used by Dehmelt, with electric and magnetic field lines indicated.

"I began to focus on the magnetron/Penning discharge geometry, which, in the Penning ion gauge, had caught my interest already at Göttingen and at Duke. In their 1955 cyclotron resonance work on photoelectrons in vacuum Franken and Liebes had reported undesirable frequency shifts caused by accidental electron trapping. Their analysis made me realize that in a pure electric quadrupole field the shift would not depend on the location of the electron in the trap. This is an important advantage over many other traps that I decided to exploit. A magnetron trap of this type had been briefly discussed in J.R. Pierce's 1949 book, and I developed a simple description of the axial, magnetron, and cyclotron motions of an electron in it. With the help of the expert glassblower of the Department, Jake Jonson, I built my first high vacuum magnetron trap in 1959 and was soon able to trap electrons for about 10 sec and to detect axial, magnetron and cyclotron resonances." – H. Dehmelt


H. Dehmelt shared the Nobel Prize in Physics in 1989 for the development of the ion trap technique.

Operation

Penning traps use a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially. [6] The static electric potential can be generated using a set of three electrodes: a ring and two endcaps. In an ideal Penning trap the ring and endcaps are hyperboloids of revolution. For trapping of positive (negative) ions, the endcap electrodes are kept at a positive (negative) potential relative to the ring. This potential produces a saddle point in the centre of the trap, which traps ions along the axial direction. The electric field causes ions to oscillate (harmonically in the case of an ideal Penning trap) along the trap axis. The magnetic field in combination with the electric field causes charged particles to move in the radial plane with a motion which traces out an epitrochoid.

The orbital motion of ions in the radial plane is composed of two modes at frequencies which are called the magnetronand the modified cyclotron frequencies. These motions are similar to the deferent and epicycle, respectively, of the Ptolemaic model of the solar system.

A classical trajectory in the radial plane for o + / o - = 8 {\displaystyle \omega _{+}/\omega _{-}=8} Penningtrajec.svg
A classical trajectory in the radial plane for

The sum of these two frequencies is the cyclotron frequency, which depends only on the ratio of electric charge to mass and on the strength of the magnetic field. This frequency can be measured very accurately and can be used to measure the masses of charged particles. Many of the highest-precision mass measurements (masses of the electron, proton, 2 H, 20 Ne and 28 Si) come from Penning traps.

Buffer gas cooling, resistive cooling, and laser cooling are techniques to remove energy from ions in a Penning trap. Buffer gas cooling relies on collisions between the ions and neutral gas molecules that bring the ion energy closer to the energy of the gas molecules. In resistive cooling, moving image charges in the electrodes are made to do work through an external resistor, effectively removing energy from the ions. Laser cooling can be used to remove energy from some kinds of ions in Penning traps. This technique requires ions with an appropriate electronic structure. Radiative cooling is the process by which the ions lose energy by creating electromagnetic waves by virtue of their acceleration in the magnetic field. This process dominates the cooling of electrons in Penning traps, but is very small and usually negligible for heavier particles.

Using the Penning trap can have advantages over the radio frequency trap (Paul trap). Firstly, in the Penning trap only static fields are applied and therefore there is no micro-motion and resultant heating of the ions due to the dynamic fields, even for extended 2- and 3-dimensional ion Coulomb crystals. Also, the Penning trap can be made larger whilst maintaining strong trapping. The trapped ion can then be held further away from the electrode surfaces. Interaction with patch potentials on the electrode surfaces can be responsible for heating and decoherence effects and these effects scale as a high power of the inverse distance between the ion and the electrode.

Fourier-transform mass spectrometry

Fourier-transform ion cyclotron resonance mass spectrometry (also known as Fourier-transform mass spectrometry) is a type of mass spectrometry used for determining the mass-to-charge ratio (m/z) of ions based on the cyclotron frequency of the ions in a fixed magnetic field. [7] The ions are trapped in a Penning trap where they are excited to a larger cyclotron radius by an oscillating electric field perpendicular to the magnetic field. The excitation also results in the ions moving in phase (in a packet). The signal is detected as an image current on a pair of plates which the packet of ions passes close to as they cyclotron. The resulting signal is called a free induction decay (fid), transient or interferogram that consists of a superposition of sine waves. The useful signal is extracted from this data by performing a Fourier transform to give a mass spectrum.

Single ions can be investigated in a Penning trap held at a temperature of 4 K. For this the ring electrode is segmented and opposite electrodes are connected to a superconducting coil and the source and the gate of a field-effect transistor. The coil and the parasitic capacitances of the circuit form a LC circuit with a Q of about 50 000. The LC circuit is excited by an external electric pulse. The segmented electrodes couple the motion of the single electron to the LC circuit. Thus the energy in the LC circuit in resonance with the ion slowly oscillates between the many electrons (10000) in the gate of the field effect transistor and the single electron. This can be detected in the signal at the drain of the field effect transistor.

Geonium atom

A geonium atom is a pseudo-atomic system that consists of a single electron or ion stored in a Penning trap which is 'bound' to the remaining Earth, hence the term 'geonium'. [6] The name was coined by H.G. Dehmelt. [8]

In the typical case, the trapped system consists of only one particle or ion. Such a quantum system is determined by quantum states of one particle, like in the hydrogen atom. Hydrogen consists of two particles, the nucleus and electron, but the electron motion relative to the nucleus is equivalent to one particle in an external field, see center-of-mass frame.

The properties of geonium are different from a typical atom. The charge undergoes cyclotron motion around the trap axis and oscillates along the axis. An inhomogeneous magnetic "bottle field" is applied to measure the quantum properties by the "continuous Stern-Gerlach" technique. Energy levels and g-factor of the particle can be measured with high precision. [8] Van Dyck, et al. explored the magnetic splitting of geonium spectra in 1978 and in 1987 published high-precision measurements of electron and positron g-factors, which constrained the electron radius.[ citation needed ]

Single particle

In November 2017, an international team of scientists isolated a single proton in a Penning trap in order to measure its magnetic moment to the highest precision to date. [9] It was found to be 2.79284734462(82)  nuclear magnetons . The CODATA 2018 value matches this. [10]

Related Research Articles

<span class="mw-page-title-main">Spectroscopy</span> Study involving matter and electromagnetic radiation

Spectroscopy is the field of study that measures and interprets electromagnetic spectrum. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum.

<span class="mw-page-title-main">Klystron</span> Vacuum tube used for amplifying radio waves

A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range. Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, while high-power klystrons are used as output tubes in UHF television transmitters, satellite communication, radar transmitters, and to generate the drive power for modern particle accelerators.

<span class="mw-page-title-main">Mass spectrometry</span> Analytical technique based on determining mass to charge ratio of ions

Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.

<span class="mw-page-title-main">Ion source</span> Device that creates charged atoms and molecules (ions)

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

Plasma diagnostics are a pool of methods, instruments, and experimental techniques used to measure properties of a plasma, such as plasma components' density, distribution function over energy (temperature), their spatial profiles and dynamics, which enable to derive plasma parameters.

Electron cyclotron resonance (ECR) is a phenomenon observed in plasma physics, condensed matter physics, and accelerator physics. It happens when the frequency of incident radiation coincides with the natural frequency of rotation of electrons in magnetic fields. A free electron in a static and uniform magnetic field will move in a circle due to the Lorentz force. The circular motion may be superimposed with a uniform axial motion, resulting in a helix, or with a uniform motion perpendicular to the field resulting in a cycloid. The angular frequency of this cyclotron motion for a given magnetic field strength B is given by

<span class="mw-page-title-main">Ion trap</span> Device for trapping charged particles

An ion trap is a combination of electric and/or magnetic fields used to capture charged particles — known as ions — often in a system isolated from an external environment. Atomic and molecular ion traps have a number of applications in physics and chemistry such as precision mass spectrometry, improved atomic frequency standards, and quantum computing. In comparison to neutral atom traps, ion traps have deeper trapping potentials that do not depend on the internal electronic structure of a trapped ion. This makes ion traps more suitable for the study of light interactions with single atomic systems. The two most popular types of ion traps are the Penning trap, which forms a potential via a combination of static electric and magnetic fields, and the Paul trap which forms a potential via a combination of static and oscillating electric fields.

Fourier-transform ion cyclotron resonance mass spectrometry is a type of mass analyzer (or mass spectrometer) for determining the mass-to-charge ratio (m/z) of ions based on the cyclotron frequency of the ions in a fixed magnetic field. The ions are trapped in a Penning trap (a magnetic field with electric trapping plates), where they are excited (at their resonant cyclotron frequencies) to a larger cyclotron radius by an oscillating electric field orthogonal to the magnetic field. After the excitation field is removed, the ions are rotating at their cyclotron frequency in phase (as a "packet" of ions). These ions induce a charge (detected as an image current) on a pair of electrodes as the packets of ions pass close to them. The resulting signal is called a free induction decay (FID), transient or interferogram that consists of a superposition of sine waves. The useful signal is extracted from this data by performing a Fourier transform to give a mass spectrum.

<span class="mw-page-title-main">Quadrupole ion trap</span> Type of apparatus for isolating charged particles

In experimental physics, a quadrupole ion trap or paul trap is a type of ion trap that uses dynamic electric fields to trap charged particles. They are also called radio frequency (RF) traps or Paul traps in honor of Wolfgang Paul, who invented the device and shared the Nobel Prize in Physics in 1989 for this work. It is used as a component of a mass spectrometer or a trapped ion quantum computer.

<span class="mw-page-title-main">History of mass spectrometry</span>

The history of mass spectrometry has its roots in physical and chemical studies regarding the nature of matter. The study of gas discharges in the mid 19th century led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. Improved capabilities in the separation of these positive ions enabled the discovery of stable isotopes of the elements. The first such discovery was with the element neon, which was shown by mass spectrometry to have at least two stable isotopes: 20Ne and 22Ne. Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb.

<span class="mw-page-title-main">Orbitrap</span> Type of ion separator used in mass spectrometry

In mass spectrometry, Orbitrap is an ion trap mass analyzer consisting of an outer barrel-like electrode and a coaxial inner spindle-like electrode that traps ions in an orbital motion around the spindle. The image current from the trapped ions is detected and converted to a mass spectrum by first using the Fourier transform of time domain of the harmonic to create a frequency signal which is converted to mass.

<span class="mw-page-title-main">Cyclotron resonance</span> Motion of charged particles

Cyclotron resonance describes the interaction of external forces with charged particles experiencing a magnetic field, thus moving on a circular path. It is named after the cyclotron, a cyclic particle accelerator that utilizes an oscillating electric field tuned to this resonance to add kinetic energy to charged particles.

Quantum electrodynamics (QED), a relativistic quantum field theory of electrodynamics, is among the most stringently tested theories in physics. The most precise and specific tests of QED consist of measurements of the electromagnetic fine-structure constant, α, in various physical systems. Checking the consistency of such measurements tests the theory.

Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field. It is used for accelerating ions in a cyclotron, and for measuring the masses of an ionized analyte in mass spectrometry, particularly with Fourier transform ion cyclotron resonance mass spectrometers. It can also be used to follow the kinetics of chemical reactions in a dilute gas mixture, provided these involve charged species.

Gerald Gabrielse is an American physicist. He is the Board of Trustees Professor of Physics and director of the Center for Fundamental Physics at Northwestern University, and Emeritus George Vasmer Leverett Professor of Physics at Harvard University. He is primarily known for his experiments trapping and investigating antimatter, measuring the electron g-factor, and measuring the electron electric dipole moment. He has been described as "a leader in super-precise measurements of fundamental particles and the study of anti-matter."

<span class="mw-page-title-main">Frans Michel Penning</span> Dutch physicist (1894–1953)

Frans Michel Penning was a Dutch experimental physicist. He received his PhD from the University of Leiden in 1923, and studied low pressure gas discharges at the Philips Laboratory in Eindhoven, developing new electron tubes during World War II. Many detailed observations of gas ionization were done with colleagues, finding notable results for helium and magnetic fields. He made precise measurements of Townsend discharge coefficients and cathode voltage fall. Penning made important contributions to the advancement of high resolution mass spectrometry.

High-precision experiments could reveal small previously unseen differences between the behavior of matter and antimatter. This prospect is appealing to physicists because it may show that nature is not Lorentz symmetric.

<span class="mw-page-title-main">Collision-induced dissociation</span> Mass spectrometry technique to induce fragmentation of selected ions in the gas phase

Collision-induced dissociation (CID), also known as collisionally activated dissociation (CAD), is a mass spectrometry technique to induce fragmentation of selected ions in the gas phase. The selected ions are usually accelerated by applying an electrical potential to increase the ion kinetic energy and then allowed to collide with neutral molecules. In the collision, some of the kinetic energy is converted into internal energy which results in bond breakage and the fragmentation of the molecular ion into smaller fragments. These fragment ions can then be analyzed by tandem mass spectrometry.

In physics a non-neutral plasma is a plasma whose net charge creates an electric field large enough to play an important or even dominant role in the plasma dynamics. The simplest non-neutral plasmas are plasmas consisting of a single charge species. Examples of single species non-neutral plasmas that have been created in laboratory experiments are plasmas consisting entirely of electrons, pure ion plasmas, positron plasmas, and antiproton plasmas.

<span class="mw-page-title-main">ISOLTRAP experiment</span>

The high-precision mass spectrometer ISOLTRAP experiment is a permanent experimental setup located at the ISOLDE facility at CERN. The purpose of the experiment is to make precision mass measurements using the time-of-flight (ToF) detection technique. Studying nuclides and probing nuclear structure gives insight into various areas of physics, including astrophysics.

References

  1. ↑ Eronen, T.; Kolhinen, V. S.; Elomaa, V. -V.; Gorelov, D.; Hager, U.; Hakala, J.; Jokinen, A.; Kankainen, A.; Karvonen, P.; Kopecky, S.; Moore, I. D. (2012-04-18). "JYFLTRAP: a Penning trap for precision mass spectroscopy and isobaric purification". The European Physical Journal A. 48 (4): 46. Bibcode:2012EPJA...48...46E. doi:10.1140/epja/i2012-12046-1. ISSN   1434-601X. S2CID   119825256.
  2. ↑ "Penning Trap | ALPHA Experiment". alpha.web.cern.ch. Retrieved 5 March 2019.
  3. ↑ Major, F. G. (2005). Charged particle traps : physics and techniques of charged particle field confinement. V. N. Gheorghe, G. Werth. Berlin: Springer. ISBN   3-540-22043-7. OCLC   62771233.
  4. ↑ Vogel, Manuel (2018). Particle confinement in Penning traps : an introduction. Cham, Switzerland. ISBN   978-3-319-76264-7. OCLC   1030303331.{{cite book}}: CS1 maint: location missing publisher (link)
  5. ↑ "Hans G. Dehmelt - Biographical". Nobel Prize. 1989. Retrieved June 1, 2014.
  6. 1 2 Brown, L.S.; Gabrielse, G. (1986). "Geonium theory: Physics of a single electron or ion in a Penning trap" (PDF). Reviews of Modern Physics. 58 (1): 233–311. Bibcode:1986RvMP...58..233B. doi:10.1103/RevModPhys.58.233. Archived from the original (PDF) on 2017-03-13. Retrieved 2014-05-01.
  7. ↑ Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. (1998). "Fourier transform ion cyclotron resonance mass spectrometry: A primer". Mass Spectrometry Reviews. 17 (1): 1–35. doi:10.1002/(SICI)1098-2787(1998)17:1<1::AID-MAS1>3.0.CO;2-K. PMID   9768511.
  8. 1 2 Dehmelt, Hans (1988). "A single atomic particle forever floating at rest in free space: New value for electron radius". Physica Scripta. T22: 102–110. Bibcode:1988PhST...22..102D. doi:10.1088/0031-8949/1988/T22/016. S2CID   250760629.
  9. ↑ Schneider, Georg; Mooser, Andreas; Bohman, Matthew; et al. (2017). "Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision". Science. 358 (6366): 1081–1084. Bibcode:2017Sci...358.1081S. doi: 10.1126/science.aan0207 . PMID   29170238.
  10. ↑ "2018 CODATA Value: proton magnetic moment to nuclear magneton ratio". The NIST Reference on Constants, Units, and Uncertainty. NIST . Retrieved 2020-04-19.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.