Channel Electron Multiplier Array Research Articles

The Plasma Ion and Electron Instruments for the Genesis Mission

The Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM) provide 3- dimensional plasma measurements of the solar wind for the Genesis mission. These measurements are used onboard to determine the type of plasma that is flowing past the spacecraft and to configure the solar wind sample collection subsystems in real-time. Both GIM and GEM employ spherical-section electrostatic analyzers followed by channel electron multiplier (CEM) arrays for detection and angle and energy/charge analysis of incident ions and electrons. GIM is of a new design specific to Genesis mission requirements whereas the GEM sensor is an almost exact copy of the plasma electron sensors currently flying on the ACE and Ulysses spacecraft, albeit with new electronics and programming. Ions are detected at forty log-spaced energy levels between ∼ 1 eV and 14 keV by eight CEM detectors, while electrons with energies between ∼ 1 eV and 1.4 keV are measured at twenty log-spaced energy levels using seven CEMs. The spin of the spacecraft is used to sweep the fan-shaped fields-of-view of both instruments across all areas of the sky of interest, with ion measurements being taken forty times per spin and samples of the electron population being taken twenty four times per spin. Complete ion and electron energy spectra are measured every ∼2.5 min (four spins of the spacecraft) with adequate energy and angular resolution to determine fully 3-dimensional ion and electron distribution functions. The GIM and GEM plasma measurements are principally used to enable the operational solar wind sample collection goals of the Genesis mission but they also provide a potentially very useful data set for studies of solar wind phenomena, especially if combined with other solar wind data sets from ACE, WIND, SOHO and Ulysses for multi-spacecraft investigations.

Design considerations, calibration and applications of an array detector for a four-sector tandem mass spectrometer

A focal plane detector consisting of a channel electron multiplier array, phosphor-coated fiber optics and photodiode array has been constructed and installed at the final detector of a four-sector tandem mass spectrometer. The active length of the detector is 2 in., incorporating 2048 photodiodes and covering 6.6% of mass range. To obtain a complete tandem mass spectrum, a number of consecutive segments are recorded and assembled. Data acquisition and processing are carried out by a dedicated processor and a VAX 750 computer, respectively. Mass and gain calibration of the detector is carried out by using CsI ionized by fast atom bombardment in the first mass spectrometer. Experiments with two peptides, renin substrate ( M r 1757.9) and ACTH (18–39) ( M r 2464.2), gave excellent product ion spectra when 10 and 50 pmol were used, respectively. This represents at least a 50-fold decrease in sample requirement (compared with conventional detectors), whereas the quality of the spectra and mass assignments are equal to those of conventional detectors, or better. The detector functions equally well in the negative ion mode, as demonstrated with a ganglioside (GM 1) of M r 1545.9. All elements of the array detector, including the diode array, are mounted within the vacuum envelope of the mass spectrometer. It can be adjusted in angle and position through a bellows arrangement for focusing or adaptation to other modes of operation in which the focal plane of the spectrometer changes angle or position.

Wave-vector imaging photoelectron spectrometer

We have developed an imaging photoelectron spectrometer based on a simple electrostatic immersion lens with the capability of measuring photoemission intensity as a function of the parallel component of electron wave vector throughout the Brillouin zone. The image is a simple rectilinear mapping of the k∥ component of the wave vector in reciprocal space. Using a retarding field-energy selection system, it is possible to energy select and image the various states below the Fermi energy. We obtain an energy resolution of 0.3 eV and a k∥ resolution of 0.04 Å−1. The distribution of photocurrent is amplified onto a phosphor screen by a channel electron multiplier array. The image on the screen is then picked up with a charge-coupled device (CCD) camera so that the digitized image can be both position and energy analyzed. The performance of the system is demonstrated by imaging the photoelectron distribution from a Cu(001) single crystal. We find that the intensity distribution of emission in k space reflects the dispersion of the projected bulk energy band structure.

Channel electron multiplier arrays for scintillating fibre readout

A Channel Electron Multiplier Array is a readout well suited to detect the low light output of small diameter scintillating fibers.

252Cf plasma desorption mass spectrometry using a Mamyrin reflectron in a low voltage regime

A 252Cf plasma desorption mass spectrometer was constructed using a linear Mamyrin reflectron in a low voltage regime with acceleration potentials ranging from +40 to +500 V. The Mamyrin reflectron is an electrostatic reflector which allows ions with slightly greater velocities to travel longer flight paths, resulting in velocity focusing. This design includes a novel electron conversion dynode ion detection system. The conversion dynode consists of an aluminum plate coated with CsI maintained at a high negative potential. The reflected ions strike the dynode and electrons are ejected which travel the flight path, pass through the reflectron, and are detected by a channel electron multiplier array. Experimental results demonstrate the successful performance of the detector system and the establishment of the velocity focusing conditions at several acceleration voltages.

Reciprocal Space Imaging of Photoelectron Distributions

We present details of a display type photoelectron spectrometer, based on the principal of mirror-electron-microscopy employing an electrostatic projection lens system, which is capable of imaging photoelectrons as a linear function of their parallel wavevector throughout the entire Brillouin zone. The photocurrent is amplified onto a phosphor screen via a channel electron multiplier array. The very low light levels are then picked up with a specially developed CCD camera so that the digitized image can be both position and energy analysed. The system has the advantage over existing display type analysers in that the image is a rectilinear mapping of k||-space independent of both photon energy used or binding energy of the electronic states selected. It is possible to energy select various states at or below the Fermi energy with a retarding field analyser to a resolution of 0.3 eV.The performance of this electrostatic lens system is demonstrated by imaging the photoelectron distribution from the valence band states of a clean Cu(001) surface. Analysis of the results shows good agreement with the energy band diagram of copper and with results obtained by conventional angle-resolved photoelectron spectroscopy.

Magnetic-dipole wavelength measurements in the n=3 configurations of highly ionized Cu, Zn, Ga, As, Kr, and Y.

Magnetic dipole (M1) transitions between the levels of the ground configurations in the 3${s}^{2}$3${p}^{x}$ Al-like through Cl-like and the 3s3p Mg-like isoelectronic sequences of Cu, Zn, Ga, As, Kr, and Y have been observed. These elements were introduced into the Texas experimental Tokomak plasma by laser ablation of metallic thin films and gas puffing. The spectral lines were recorded by using three monochromators with photoelectric detection and a spectrometer with a channel electron multiplier array detector. Twenty-eight newly observed M1 lines were measured and classified.

Applications of accelerator-based low-energy positron beams in atomic physics

Applications of LINAC-based positron beams in atomic physics are described. The following broad subject areas are treated; e+ mobility and momentum transfer cross section determinations, angularly resolved and integral cross sections for e+-atomic processes plus charge transfer (Ps formation) type experiments, experiments with tunable positronium beams and experiments with thermal Ps sources. In addition, some discussion is given concerning the use of channel electron multiplier arrays (CEMAs) in conjunction with charge coupled devices (CCDs) as position sensitive detectors.

High-resolution VUV spectrometer with multichannel detector for absorption studies of transient species

A new high-resolution VUV spectrometer is demonstrated for applications in the 40–900-Å wavelength range. The instrument is comprised of a laser-plasma VUV source, which provides continuum background illumination, 1.5-m grazing incidence spectrometer, and a 1024-channel VUV optical multichannel analyzer (VUV-OMA). The VUV-OMA is of new design, featuring a special resolution enhanced channel electron multiplier array in an overall configuration chosen to optimize the spatial resolution of the detector while maintaining single-photoelectron sensitivity.

A High-Resolution VUV Spectrometer With Electronic Parallel Spectral Detection

We demonstrate a new high resolution grazing incidence spectrometer system for spectroscopic applications in the range 50 to 400 Å. The instrument is comprised of a laser-plasma VUV continuum source, a 1.5 m grazing incidence spectrometer, and a 1024-channel VUV optical multichannel analyzer (VUV-OMA). The VUV-OMA is of new design, featuring a special resolution-enhanced channel electron multiplier array in an overall configuration chosen to optimize the spatial resolution of the detector while maintaining single-photoelectron sensitivity. The instrument has the capability of bringing the advantages of linear response and parallel spectral detection to general VUV photoabsorption studies of atoms, ions, molecules, and thin solid samples, as well as studies involving laboratory plasmas. The instrument has the additional special capability of performing time resolved absorption spectroscopy of transient species. The characteristics of the source and detector, along with various applications of the instrument to atomic physics will be discussed.

Quantum efficiency of opaque CsI photocathodes with channel electron multiplier arrays in the extreme and far ultraviolet

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Christopher Martin and Stuart Bowyer, "Quantum efficiency of opaque CsI photocathodes with channel electron multiplier arrays in the extreme and far ultraviolet," Appl. Opt. 21, 4206-4207 (1982) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Response of a chevron microchannel plate to 2.5 and 14 MeV neutrons

The response of a large area (4.6×13 cm) multianode channel electron multiplier array (CEMA) detector to energetic neutrons was investigated. The measured neutron detection efficiencies of the chevron microchannel plate (MCP) were 1.7×10−3 and 6.4×10−3 counts/neutron, respectively, for 2.5 MeV-DD and 14 MeV-DT neutrons. The apparently higher efficiency observed for the 14 MeV neutrons is attributed to neutron-induced background gamma radiation.

An image intensifier for electron microscopy of polymers

A unique manipulator for a channel electron multiplier array (CEMA) is described. It allows for easy installation into the viewing chamber of a transmission electron microscope. This device, through a series of motions, positions the CEMA normal to the electron beam, thus amplifying the electron flux while preserving its image. This increase in image brightness permits operation of the microscope with a greatly reduced flux of electrons passing through the sample, thereby decreasing radiation damage while simultaneously extending the time available for examination of the specimen. The manipulator can then move the CEMA to a remote area of the chamber, thus returning the microscope to its normal operating mode.

An electro-optical detector for spark source mass spectrometry.II. quantitative measurements

A channel electron multiplier array detector (CEMA) for spark source mass spectrometry (SSMS) has been evaluated for possible quantitative analytical applications. CEMA with SSMS in the quantitative mode offers real-time data acquisition and the ability to monitor several ions simultaneously, which permits rapid optimization of instrumental parameters. Compared to a discrete dynode electron multiplier, CEMA displays similar sensitivities and resolutions. Measurement precisions are intermediate between rapid logarithmic scan and the slower peak switching methods. For isotope dilution analysis, CEMA shows a precision of about ⊥5% RSD up to a 5 : 1 spike/sample ratio compared to about ′ 10% at a 3 : 1 ratio for photographic detectors. Suggestions are offered for improving the CEMA detector.

An electro-optical ion detector for spark source mass spectrometry

An ion detector for spark source mass spectrometry is described which utilizes a channel electron multiplier array in the chevron configuration with phosphor screen display. An optical flange positions the detector in the focal plane of an AEI-MS702R mass spectrometer. The photographic plate detection mode of the spectrometer is also available with a minimum of change-over time. Preliminary results are shown for several modes of electronic data collection.

H2 and rare gas field ion source with high angular current

We have built and carried out initial tests on a field ion source that has been designed to operate at very low temperatures with a physisorbed surface supply to the ionization region. This mode has been found to give beams of high angular current density and is expected to have low energy spread in the beam. Presently we have measured dI/dΩ?10 to 60/sr with a probable energy spread of ?l eV. The UHV system allows processing of the field emitter under clean, high vacuum conditions. A liquid He cooled finger maintains the tip at controlled temperatures from that of liquid He to room temperature. The tip is mounted on a sapphire block to provide both excellent thermal conduction and electrical insulation to ?30 kV. Differential pumping allows a high supply pressure of H2, He, Ar, etc. in the region of the tip (≳ 10−2 Torr) and a low pressure in the rest of the system. Observation on the characteristics of the field ionization pattern are made under varying conditions of pressure, temperature, field and tip processing, and orientation by using a channel electron multiplier array and phosphor screen (CEMA). An alignable aperture defines the angular divergence.

Novel Faraday cup for the simultaneous observation and measurement of ion‐beam currents

A novel Faraday cup is described which allows the simultaneous observation and measurement of ion‐beam currents. The Faraday cup is constructed around a Galileo channel electron multiplier array (CEMA), which serves as the basis of an internal image intensification system (a gain of ≳104) for the observation of the ion beam; the CEMA also acts as a collector for the ion current which is measured by a Keithley 602 electrometer. The ion current is integrated by a simple and inexpensive dosimeter; the electronic circuit for the dosimeter is described. The application of the Faraday cup to the observation and measurement of a 30‐keV Ar+ ion beam is presented as an illustrative example. We have also employed this Faraday cup to observe and measure 30‐keV Cr+, Mo+, or W+, and 18‐keV Au+ ion beams employed for the in situ irradiation of field‐ion microscope specimens.

Areal detection efficiency of channel electron multiplier arrays

The areal detection efficiency of a channel electron multiplier array (CEMA) and the nature of its secondary emission surface were investigated with the ion microprobe mass analyzer (IMMA). Previous speculations of detection efficiency based on simple geometric arguments of channel-to-interchannel area ratios are shown to be in error. With a positive bias applied to a front electrode surface of high secondary yield, areal detection efficiency of a CEMA may approach 100% even for single-ion impacts. The secondary emission properties of a CEMA are shown to be determined by an alkali-rich surface layer on each channel wall, and not a concentration of Pb or PbO as previously thought. Both reversible and irreversible gain degradation observed when heating a CEMA in vacuum are interpreted as a change in the composition of this layer.

An electro—optical detector for focal plane mass spectrometers

An electro—optical ion detector for a Mattauch—Herzog focal plane mass spectrometer is described. The detector consists of a channel electron multiplier array, phosphor screen, fiber optic image dissector and vidicon camera system. Experimental verification of the concept is discussed with particular attention given to intense stray magnetic fields, resolving power, sensitivity and channel electron multiplier array geometry.

Amplification factors of a CEMA (channel electron multiplier array) for organic, noble gas and Hg ions

Channel electron multiplier array (CEMA) amplification factors were determined for organic ions in the mass range of 31–614 amu, noble gas and Hg ions by direct comparison of the output signals of the CEMA (Mullard G 40 25 ) and a Faraday cage collector, both placed at the detector end of a mass spectrometer. Empirical formulae are discussed to represent the gain as a function of the mass, the structure, and the energy of the ion.