Electrostatic analyzer
Encyclopedia
An electrostatic analyzer or ESA is an instrument used in ion optics
that employs an electric field
to allow the passage of only those ions or electrons that have a given specific energy
. It usually also focuses these particles (concentrates them) into a smaller area. ESA’s are typically used as components of space instrumentation, to limit the scanning (sensing) energy range and, thereby also, the range of particles targeted for detection and scientific measurement. The closest analogue in photon optics
is a filter
.
component of the velocity of a charged particle is changed by an ESA since the potential on the plates only varies in the radial direction if one considers the geometry in cylindrical coordinates. Poisson's Equation
can be then used to calculate the magnitude of the electric field pointing radially inwards. The resultant inward-pointing force generated by this electric field will cause the particles' trajectories to curve in a uniform circular motion. Depending on initial energy (velocity), only certain particles will therefore have the "correct" motion to exit the analyzer by tracing its physical structure, while others will collide into the walls of the instrument. In addition to the energy, the angle of entry will also have an impact on the particles' time-of-flight through the analyzer as well as exit angle. In practice, the plates are usually oppositely charged and at very high potentials. Also, the inner surface of the analyzer, usually made of aluminum for space missions, is sometimes plated
with black chrome or even Ebonol C to absorb stray light, instead of allowing it to bounce its way through.
ESAs are usually designed and analyzed using an off-the-shelf ion-optics simulation-software package, such as SimIon, which includes the capability of performing Monte Carlo
simulations on known test particles, thus providing the designer a better understanding of the response characteristics of the analyzer itself.
Ion optics
Ion optics involves the focusing of plasmas and ion streams, usually in mass spectrometry.-Electric field manipulation:* Electrostatic lens** Einzel lens* Electrostatic analyzer...
that employs an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
to allow the passage of only those ions or electrons that have a given specific energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
. It usually also focuses these particles (concentrates them) into a smaller area. ESA’s are typically used as components of space instrumentation, to limit the scanning (sensing) energy range and, thereby also, the range of particles targeted for detection and scientific measurement. The closest analogue in photon optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
is a filter
Filter (optics)
Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....
.
Radial cylindrical analyzer
Electrostatic analyzers are designed in different configurations. A simple version is a radial cylindrical analyzer, which consists of two curved parallel plates at different potentials. Ions or electrons enter the analyzer at one end and either pass through the other end or collide with the walls of the analyzer, depending on their initial energy. In these types of analyzers, only the radialRadius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
component of the velocity of a charged particle is changed by an ESA since the potential on the plates only varies in the radial direction if one considers the geometry in cylindrical coordinates. Poisson's Equation
Poisson's equation
In mathematics, Poisson's equation is a partial differential equation of elliptic type with broad utility in electrostatics, mechanical engineering and theoretical physics...
can be then used to calculate the magnitude of the electric field pointing radially inwards. The resultant inward-pointing force generated by this electric field will cause the particles' trajectories to curve in a uniform circular motion. Depending on initial energy (velocity), only certain particles will therefore have the "correct" motion to exit the analyzer by tracing its physical structure, while others will collide into the walls of the instrument. In addition to the energy, the angle of entry will also have an impact on the particles' time-of-flight through the analyzer as well as exit angle. In practice, the plates are usually oppositely charged and at very high potentials. Also, the inner surface of the analyzer, usually made of aluminum for space missions, is sometimes plated
Plating
Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years, but it is also critical for modern technology...
with black chrome or even Ebonol C to absorb stray light, instead of allowing it to bounce its way through.
Face-field cylindrical energy analyzer
The Face-Field Cylindrical Energy Analyzer is a very new class of cylindrical analyzers. It uses a cylindrical field, restricted by concentric cylindrical electrodes and two flat electrodes perpendicular to the axis of symmetry. The inner electrode is usually connected with the flat electrodes, and the outer one, which is electrically isolated, has an electric potential that can either be constant or variable. (Potential is negative (-) for an electron beam, and positive (+) for a positive-ion beam.) The focusing field becomes very different from that of the simple-cylinder type (such as in the well-known CMA) near the flat-face boundaries; namely, it can achieve a very high energy resolution for a beam entering through the entrance window of one of the face electrodes. This new class of analyzer can be used in a variety of applications. It do remote sensing such as measuring the flow of charged particles in space; e.g., scanning-electron/Auger-electron spectroscopy for analyzing large objects.ESAs are usually designed and analyzed using an off-the-shelf ion-optics simulation-software package, such as SimIon, which includes the capability of performing Monte Carlo
Monte Carlo method
Monte Carlo methods are a class of computational algorithms that rely on repeated random sampling to compute their results. Monte Carlo methods are often used in computer simulations of physical and mathematical systems...
simulations on known test particles, thus providing the designer a better understanding of the response characteristics of the analyzer itself.
Use in space instrumentation
Examples of space instruments or missions using Electrostatic Analyzers:- The CAPS (Cassini Plasma Spectrometer) instrument on the Cassini-HuygensCassini-HuygensCassini–Huygens is a joint NASA/ESA/ASI spacecraft mission studying the planet Saturn and its many natural satellites since 2004. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan, although it has also returned...
spacecraft - IBEX-Hi and IBEX-Lo instruments on the future Interstellar Boundary ExplorerInterstellar Boundary ExplorerInterstellar Boundary Explorer is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. The IBEX satellite was launched with a Pegasus-XL rocket on October 19, 2008, at 17:47:23 UTC...
spacecraft - Mariner 10Mariner 10Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...
- The SWAP (Solar Wind Analyser around Pluto) instrument on the New HorizonsNew HorizonsNew Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
spacecraft - Pioneer 6, 7, and 8 missions
- Ranger 1Ranger 1Ranger 1 was a spacecraft in the Ranger program of unmanned space missions. Its primary mission was to test the performance of those functions and parts necessary for carrying out subsequent lunar and planetary missions; a secondary objective was to study the nature of particles and fields in...
- THEMISTHEMIS (satellite)The Time History of Events and Macroscale Interactions during Substorms mission was originally a constellation of five NASA satellites to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles...
mission