Secondary Electron Emission Detector Research Articles

Improvement of Velocity Distribution Function Measurement of Hydrogen Atoms in ion Source Discharges

The efficiency of negative hydrogen (H-) ion surface production in an ion source should be highly dependent upon the velocity distribution function of neutral atomic hydrogen (H0) striking the plasm grid (PG). A system composed of forming an atom beam, rotating beam chopper, ionizer and pulse count unit has been constructed to measure H0 velocity distribution functions. The background noise due to stagnation of hydrogen gas in the region between the beam formation skimmer and the ion source PG was improved by inserting a flow reflection structure. The short life time of the secondary electron emission detector (SEM) was prolonged by properly setting the hydrogen ion trajectories from the ionizer to the the first dynode of the SEM. The system is running stably to record the velocity distribution function but statistical noise synchronized to the trigger pulse of the chopper must be removed before the measurment of change in H0 velocity distribution functions dependin upon the type of discharge.

Commissioning and initial heating results of the neutral beam injection system in Versatile Experiment Spherical Torus

The initial neutral beam heating experiment in Versatile Experiment Spherical Torus (VEST) has been conducted via neutral beam characterizations such as neutralization efficiency, beam fraction, and shine-through loss. For the neutralization efficiency and shine-through loss estimation, a secondary electron emission (SEE) detector, which can be used in rapidly changing plasma, has been developed. The measurement results of the monatomic fraction by Doppler shift spectroscopy and the neutralization efficiency by SEE detector are 65%, and 70%, respectively. The shine-through loss measurement shows that the injection of a 12 keV neutral beam into a typical ohmic discharge of VEST results in a large amount of shine-through loss. To reduce the shine-through loss, a new target plasma discharge (0.17 T, 120 kA, 13 ms) with increased plasma density of ~2×1019m−3 is developed by providing additional gas injection. The electron-heating effect has been successfully observed for this target plasma with a 200 kW neutral beam injection at the beam energy of 12 keV. The electron temperature increases from 20 to 68 eV without significant density change when the neutral beam is injected.

Gas-Filled Ionization Chamber and Secondary-Emission Detector for Measuring γ-Ray Dose Rate

The design of a KGK-2 γ-ray dose rate detector is described. The basic characteristics of the detector are presented. The readings of a KGK-2 gas-filled ionization chamber detector and VED-2 secondary-electron emission detector during power startup of BR-K1 and BR-1M reactors are compared. It is shown that by using KGK-2 and VED-2 detectors in combination the γ-ray dose rate can be measured in the interval 1 μGy/sec to 10 GGy/sec with the linear sections of the regulation curves overlapping to at least four decimal orders.

Erratum: “Secondary electron emission detectors for neutral beam characterization on C-2W” [Rev. Sci. Instrum. 89, 10I123 (2018)

Erratum: “Secondary electron emission detectors for neutral beam characterization on C-2W” [Rev. Sci. Instrum. 89, 10I123 (2018)

Secondary electron emission detectors for neutral beam characterization on C-2W.

Heating, current drive, and partial fueling from neutral beam injection are essential to sustainment of C-2W field-reversed configuration plasmas. C-2W has eight 2.1 MW neutral beams (16.8 MW of total electrical power), capable of providing a beam of 15 keV hydrogen neutrals for 30 ms. To maximize the effectiveness of neutral beam injection, duct losses must be minimized by maintaining beam alignment and optimizing beam current for minimum divergence. Each beam terminates on a vertical and horizontal array of secondary electron emission detectors (nine in the vertical, seven in the horizontal, and sharing one in the middle). The molybdenum detectors are spatially separated to characterize the beam size and alignment. With knowledge of the geometry of the vacuum ducts and horizontal and vertical beam profiles from test stand measurements, the focal length, divergence, and power loss were calculated. Through characterization, the set of neutral beams are optimized to inject up to 12 MW of power into the confinement vessel throughout the plasma discharge.

Spatial profile monitors for keV and MeV antiproton beams

A parallel plate ionization chamber and a secondary electron emission detector were developed to non-destructively measure the spatial profiles of antiproton beams with kinetic energies K = 5 – 21 MeV . The position-sensitive electrodes in these monitors were manufactured by using a laser trimmer to cut strip patterns on metalized polyester foils. Microwire secondary electron emission detectors were also developed to measure antiprotons at the lowest ( K = 10 – 100 keV ) energies. This detector was operated in ultrahigh vacuum ( p ∼ 10 - 8 Pa ) , low temperatures ( T < 100 K ) , and strong magnetic fields ( B > 0.1 T ) .

Scanning electron microscope studies of bone samples: Influence of simulated microgravity

A scanning electron microscope (SEM) with backscatter and secondary electron emission detectors plus a Si(Li) detector for photon yield measurements was used to study bone samples from skull and leg of mice and rats. These animals were either suspended by their tail to induce simulated microgravity, characterized as hind-limb suspension (HLS) or not suspended (control). Analyses of the SEM images and energy dispersive spectrometer (EDS) spectra using Si(Li) detector indicate variation in the lattice structures, and in intensities of the characteristics X-rays, produced from the exposed bone surface due to its interaction with the electron beam. Using Flame software, the X-ray spectra were analyzed and normalized ratios of the elements determined. The elemental analysis indicated a variation in the density of calcium, potassium, and oxygen near the knee joints and near the sutures in the skull bones. The comparison of simulated microgravity subjected samples of the rat skull bones with that of the control samples revealed that in the suture region there was a large increase in the ratio of calcium, and to some degree for phosphorus, suggesting simulated microgravity affects distribution of these elements. Elemental composition for control samples with depth (within the cross section of the leg bones) revealed decrease of oxygen and increase of calcium in the first millimeter of the bone depth after which the relative percentage of elements stayed constant.

A secondary electron emission detector for measuring the intensity of synchrotron radiation

A secondary electron emission detector can be used as a high-intensity radiation beam monitor because the absence of ion recombination extends the upper dose range of the monitor. The characteristics of saturation, linearity, sensitivity, reproducibility, and current stability of the monitor were measured with respect to synchrotron radiation from undulators at SPring-8. Thin aluminum-evaporated electrodes were used in a vacuum chamber. Linearity was observed at 1011–1013photons∕s between 10 and 30keV. Even at the highest intensity of 1015photons∕s, current linearity was achieved to some extent. Sensitivity ranged from 27to55pC∕Gy∕cm2, and increased with decreasing energy. During long irradiation, the current decreased gradually with time; the degree became larger with the dose. When irradiation was interrupted, however, the current recovered to its initial value at the next irradiation.

Observation of Antiproton Beams and Nonneutral Plasmas

Diagnostics of antiproton beams and nonneutral plasmas are described in this chapter. Parallel plate secondary electron emission detectors are used to non-destructively observe the beam position and intensity without loss. Plastic scintillation tracking detectors are useful in determining the position of annihilations of antiprotons in the trap. Three-dimensional imaging of antiprotons in a Penning trap is discussed. The unique capability of antimatter particle imaging has allowed the observation of the spatial distribution of particle loss in a trap. Radial loss is localized to small spots, strongly breaking the azimuthal symmetry expected for an ideal trap. By observing electrostatic eigen-modes of nonneutral plasmas trapped in the Multi-ring electrode trap, the non-destructive measurement of plasma parameters is performed.

Parallel plate chambers for monitoring the profiles of high-intensity pulsed antiproton beams

Two types of beam profile monitor with thin parallel-plate electrodes have been used in experiments carried out at the Low Energy Antiproton Ring (LEAR) and Antiproton Decelerator (AD) of CERN. The detectors were used to measure non-destructively the spatial profiles, absolute intensities, and time structures of 100–300-ns-long beam pulses containing between 10 7 and 10 9 antiprotons. The first of these monitors was a parallel plate ionization chamber operated at gas pressure P=65 mbar . The other was a secondary electron emission detector, and was operated in the ultra-high vacuum of the AD. Both designs may be useful in medical and commercial applications. The position-sensitive electrodes in these detectors were manufactured by a novel method in which a laser trimmer was used to cut strip patterns on metallized polyester foils.

Real-time secondary electron emission detector for high-rate X-ray crystallography

We present the first results of the application of a novel digital X-ray imaging detector, based on secondary electron emission from a solid converter, to high-rate crystallographic studies. Results from diffraction and small-angle scattering experiments from several crystallized proteins, performed at the European Synchrotron Radiation Facility, ESRF, Grenoble, are presented and compared with a phosphor-based imaging system. Future developments of this detector system are proposed.

An ion beam apparatus for collinear photodetachment experiments

A new collinear laser-ion beams apparatus, designed for laser photodetachment experiments, is described. The apparatus differs mainly in four aspects from other similar facilities. First, the angular distribution of the electrons emitted in the photodetachment process can be measured although the laser and ion beams are collinearly aligned. This gives an increase of the signal with more than two orders of magnitude in comparison with the conventional crossed beams experiments. Second, a new type of secondary electron emission detector is used to detect neutral atoms produced in the photodetachment process. The detector is capable of preventing the detection of electrons produced by the photoelectric effect induced by the laser radiation; therefore, pulsed lasers, with their high photon fluxes, can be used in experiments with the apparatus. Third, a simplified design of an electrostatic quadrupole deflector, used to bend the ion beam into the laser beam, has been implemented in the apparatus. Finally, a surface ionizer, giving a very low energy spread of the ions, is used to produce the negative ions. A detailed description of the apparatus is given, and examples of measurements of total and differential cross sections and an example of a mass spectrum are presented in the paper.

Characteristics of a novel X-ray detector for real-time radiographic imaging

Abstract New detectors for fast, real-time, high resolution X-ray imaging at high photon fluxes are described. A thin solid photoconverter is coupled to a multistage gaseous electron multiplier operating at low pressure. The readout electronics connected to the wire electrodes of the chamber provides two-dimensional localization of single registered photons. Prototype detectors were tested with Csl, Ag and Ta converters in the photon energy range of 8–60 keV. Radiographic digital images are presented compared to that of X-ray films. It is shown that compared to the film technique the secondary electron emission detector provides radiographic images of an equivalent contrast at an order of magnitude lower exposure. This novel type of detector is suited for static and dynamic in-line quality control on industrial production lines and for medical imaging.

Collinear photodetachment spectroscopy

A new ion beam apparatus, designed for collinear photodetachment experiments, has been constructed. Negative ions are formed on a surface ionizer, mass selected in a sector magnet and directed into a field-free region where they are merged with a laser beam along a 50 cm long path. A new secondary electron emission detector has been constructed in order to detect neutral atoms formed in the photodetachment process. The design of the detector makes it possible to use pulsed lasers which, in combination with a gated detection, gives a very good signal-to-background ratio. In a first experiment, the electron affinity of atomic iodine has been determined to be 3.059038(10) eV. The onset of the photodetachment process was observed when the wavelength of the laser light was scanned, and the result was fitted to the Wigner law in order to determine the photodetachment threshold.

H atom detection and energy analysis by use of thin foils and TOF technique

It has been shown experimentally that detection and energy analysis of H atoms with energy 600-3000 eV can be performed successfully by means of a time-of-flight technique using secondary electron emission detectors and thin foils. The registration of particle fluxes in the presence of a superior ultraviolet background is possible. This technique may be applied to diagnostics of high-temperature and space plasmas.

Umladungsmessungen an Lithium-Ionen im Energiebereich von 3 bis 10 keV

An ion source is described where a beam of lithium ions is directly emitted from a platinum filament coated with the lithium mineralΒ-eucryptite. Charge exchange cross sections were measured in the energy range from 3 to 10 keV for the gases A, N2, N2O, H2, O2, CH4, CCl2F2 and air. The results in this energy range agree with the adiabatic hypothesis of Massey. The uncharged particles were detected by means of a secondary electron emission detector. The secondary electron emission yield for a Cu-Be and a Ag-Mg surface by bombardment with lithium ions was measured.