An ion trap is a combination of electric or magnetic fields that captures ions in a region of a vacuum system or tube. Ion traps have a number of scientific uses such as mass spectrometery and trapping ions while the ion's quantum state is manipulated. The two most common types of ion traps are the Penning trap and the Paul trap (quadrupole ion trap).
When using ion traps for scientific studies of quantum state manipulation, the Paul trap is most often used. This work may lead to a trapped ion quantum computer and has already been used to create the world's most accurate atomic clocks.
In an electron gun (a device emitting high-speed electrons, such as those in CRTs), an ion trap may be implemented above the cathode (using an extra, positively-charged electrode between the cathode and the extraction electrode) to prevent its degradation by positive ions accelerated backward by the fields intended to pull electrons away from the cathode.
Ion trap mass spectrometers
An ion trap mass spectrometer may incorporate a Penning trap (Fourier transform ion cyclotron resonance), Paul trap or the Kingdon trap. The Orbitrap, introduced in 2005, is based on the Kingdon trap. Other types of mass spectrometers may also use a linear quadrupole ion trap as a selective mass filter.
Penning ion trap
A Penning trap stores charged particles using a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially. The Penning Trap was named after Frans Michel Penning by Hans Georg Dehmelt who built the first trap. Penning traps are well suited for measurements of the properties of ions and stable subatomic particles which have an electric charge.
Penning traps can be used in quantum computation and quantum information processing and are used at CERN to store antiprotons. Penning traps form the basis of Fourier transform ion cyclotron resonance mass spectrometry for determining the mass-to-charge ratio of ions based on the cyclotron frequency of the ions in a fixed magnetic field.
Paul ion trap
A Paul trap is a type of quadrupole ion trap that uses static direct current (DC) and radio frequency (RF) oscillating electric fields to trap ions. Paul traps are commonly used as a components of a mass spectrometer. The invention of the 3D quadrupole ion trap itself is attributed to Wolfgang Paul who shared the Nobel Prize in Physics in 1989 for this work. The trap consists of two hyperbolic metal electrodes with their foci facing each other and a hyperbolic ring electrode halfway between the other two electrodes. Ions are trapped in the space between these three electrodes by the oscillating and static electric fields.
Kingdon trap and orbitrap
A Kingdon trap consists of a thin central wire and an outer cylindrical electrode. A static applied voltage results in a radial logarithmic potential between the electrodes. In a Kingdon trap there is no potential minimum to store the ions; however, they are stored with a finite angular momentum about the central wire and the applied electric field in the device allows for the stability of the ion trajectories. It consists of a thin central wire, an outer cylindrical electrode and isolated end cap electrodes at both ends. A static applied voltage results in a radial logarithmic potential between the electrodes. In 1981, Knight introduced a modified outer electrode that included an axial quadrupole term that confines the ions on the trap axis. The dynamic Kingdon trap has an additional AC voltage that uses strong defocusing to permanently store charged particles. The dynamic Kingdon trap does not require the trapped ions to have angular momentum with respect to the filament. An Orbitrap is a modified Kingdon trap has been used for mass spectrometry. Though the idea has been suggested and computer simulations performed neither the Kingdon nor the Knight configurations were reported to produce mass spectra, as the simulations indicated mass resolving power would be problematic.
Cathode ray tubes
Devices known as ion traps were used in early television receivers, prior to the introduction of aluminized CRT faces in approximately 1958. The ion trap must be delicately adjusted for maximum brightness. The purpose of these devices was to prevent ions from discoloring the phosphor screen.
Trapped ion quantum computer
A trapped ion quantum computer is a type of quantum computer that uses a Paul trap to store ions. Units of quantum information known as qubits are stored in stable electronic states of each ion, and quantum information can be processed and transferred through the collective quantized motion of the ions in the trap, interacting through the Coulomb force. Lasers are applied to induce coupling between the qubit states (for single qubit operations) or coupling between the internal qubit states and the external motional states (for entanglement between qubits).
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