Position-sensitive Microchannel Plate Detector Research Articles

Applying machine learning methods for the analysis of two-dimensional mass spectra

In a measurement of isomeric yield-ratios in fission, the Phase-Imaging Ion-Cyclotron-Resonance technique, which projects the radial motions of ions in the Penning trap (JYFLTRAP) onto a position-sensitive micro-channel plate detector, has been applied. To obtain the yield ratio, that is the relative population of two states of an isomer pair, a novel analysis procedure has been developed to determine the number of detected ions in each state, as well as corrections for the detector efficiency and decay losses. In order to determine the population of the states in cases where their mass difference is too small to reach full separation, a Bayesian Gaussian Mixture model was implemented. The position-dependent efficiency of the micro-channel plate detector was calibrated by mapping it with ^{133}Cs^+ ions, and a Gaussian Process was trained with the position data to construct an efficiency function that could be used to correct the recorded distributions. The obtained numbers of counts of excited and ground-state ions were used to derive the isomeric yield ratio, taking into account decay losses as well as feeding from precursors.

A position-sensitive large-area microchannel plate detector with digital data-acquisition system for studies of exotic nuclei

Development of a position-sensitive large-area microchannel plate (MCP) detector based detection system is reported. Two MCPs with 120 mm active diameter, mounted in chevron configuration, with delay-line anode are read out by a digital data-acquisition system consists of fast-timing amplifier unit and CAEN v1751 waveform digitizer. Details of the digital pulse processing, programmed triggering and calibration setup are described. The obtained position resolution was studied using α-particles, the best resolutions on X and Y axes are 460 ± 1μm and 579 ± 1μm in FWHM, respectively.

First application of the phase-imaging ion-cyclotron resonance technique at TRIGA-Trap

The phase-imaging ion cyclotron resonance technique (PI-ICR) has been implemented at TRIGA-Trap together with a newly built five-pole cylindrical trap. In PI-ICR the total phase of trapped ions is measured by projecting the ion motion onto a position-sensitive delay-line micro-channel plate detector. The systematic uncertainties have been investigated and first mass measurements on stable Pb isotopes have been performed with PI-ICR. The new technique offers higher mass-resolving power, allows checking for the presence of contaminant ion species, and it proved useful in tuning the harmonicity of the trapping potential as well as in aligning the trap symmetry axis with respect to the magnetic field axis by visualizing the radial ion motion. This is a non-scanning technique where every detected ion contributes equally, therefore it is more sensitive than the previously used time-of-flight ion-cyclotron-resonance (ToF-ICR) technique, which is based on the scanning of the sideband-frequency of trapped ions and recording their time of flight after ejection. It will enable us to carry out high-precision mass measurements in the actinide region with uncertainties on the ppb level.

Radial position sensitive microchannel plate detector with ring-strip resistive anode and integrated electronics

Using a ring-strip resistive anode and a pair of integrated spectroscopy amplifiers, a circular radius-sensitive microchannel plate (MCP) detector is developed for future studies of ion-atom collisions. The detector is tested by a 55Fe X-ray source and a radial resolution of 0.2 mm is achieved.

A versatile ion beam spectrometer for studies of ion interaction with 2D materials.

We present an ultrahigh vacuum setup for ion spectroscopy of freestanding two-dimensional solid targets. An ion beam of different ion species (e.g., Xe with charge states from 1 to 44 and Ar with charge states from 1 to 18) and kinetic energies ranging from a few 10 eV to 400 keV is produced in an electron beam ion source. Ions are detected after their transmission through the 2D target with a position sensitive microchannel plate detector allowing the determination of the ion's exit charge state as well as the scattering angle with a resolution of approximately 0.04°. Furthermore, the spectrometer is mounted on a swiveling frame covering a scattering angle of ±8° with respect to the incoming beam direction. By utilizing a beam chopper, we measure the time-of-flight of the projectiles and determine the energy loss when passing a 2D target with an energy uncertainty of about 2%. Additional detectors are mounted close to the target to observe emitted secondary particles and are read-out in coincidence with the position and time information of the ion detector. A signal in these detectors can also be used as a start trigger for time-of-flight measurements, which then yield an energy resolution of 1% and an approximately 1000-fold larger duty cycle. First results on the interaction of slow Xe30+ ions with a freestanding single layer of graphene obtained with the new setup are compared to recently published data where charge exchange and energy were measured by means of an electrostatic analyzer.

A two-dimensional position-sensitive microchannel plate detector realized with two independent one-dimensional resistive anodes.

A two-dimensional position-sensitive microchannel plate detector, with a Ø100 mm sensitive area and equipped with four integrated amplifiers, is realized with a new anode scheme. The anode is constructed by two independent one-dimensional resistive anodes, each consisting of an array of parallel copper strips connected by resistors in series on a printed circuit board (PCB). The arrays are perpendicularly aligned to realize two-dimensional position resolution, with the intervals between the adjacent strips on the PCB nearer to the microchannel plate cut out to allow electrons passing through. The detector is tested with an 55Fe x-ray source, and a position resolution of 0.38 mm is achieved.

Achieving high spatial resolution using a microchannel plate detector with an economic and scalable approach

A second generation position-sensitive microchannel plate detector using the induced signal approach has been realized. This detector is presently capable of measuring the incident position of electrons, photons, or ions. To assess the spatial resolution, the masked detector was illuminated by electrons. The initial, measured spatial resolution of 276 μm FWHM was improved by requiring a minimum signal amplitude on the anode and by employing digital signal processing techniques. The resulting measured spatial resolution of 119 μm FWHM corresponds to an intrinsic resolution of 98 μm FWHM when the effect of the finite slit width is de-convoluted. This measurement is a substantial improvement from the last reported spatial resolution of 466 μm FWHM using the induced signal approach. To understand the factors that limit the measured resolution, the performance of the detector is simulated.

Note: A two-dimensional position-sensitive micro-channel plate detector with a cross-connected-pixels resistive anode and integrated spectroscopy amplifiers.

Based on the charge-division method, a compact detector system for charged particles is constructed. The system consists of a pair of micro-channel plates, a novel two-dimensional position-sensitive cross-connected-pixels resistive anode, and specially designed front-end electronics that can directly drive analog-to-digital converters. The detector is tested with an 241Am α-source. A position resolution of better than 0.3 mm and a maximum distortion within 0.5 mm in the active dimensions of 100 mm diameter are achieved.

Test-beam and laboratory characterisation of the TORCH prototype detector

The TORCH time-of-flight (TOF) detector is being developed to provide particle identification up to a momentum of 10GeV/c over a flight distance of 10m. It has a DIRC-like construction with 10mm thick synthetic amorphous fused-silica plates as a Cherenkov radiator. Photons propagate by total internal reflection to the plate periphery where they are focused onto an array of customised position-sensitive micro-channel plate (MCP) detectors. The goal is to achieve a 15ps time-of-flight resolution per incident particle by combining arrival times from multiple photons. The MCPs have pixels of effective size 0.4mm×6.6mm2 in the vertical and horizontal directions, respectively, by incorporating a novel charge-sharing technique to improve the spatial resolution to better than the pitch of the readout anodes. Prototype photon detectors and readout electronics have been tested and calibrated in the laboratory. Preliminary results from testbeam measurements of a prototype TORCH detector are also presented.

A position-sensitive micro-channel plate detector with a parallel-strip resistive anode and integrated charge-sensitive amplifiers

A one-dimensional position-sensitive micro-channel plate detector with parallel-strip resistive anode and dedicated amplifiers has been constructed. The detector is tested by a 241Am α -source and the spatial resolution of 0.2 mm is achieved.

An experimental set up for studying the fusion edge plasma facing materials using TOF mass spectrometry

A new experimental set up is developed to study the fusion edge plasma facing materials under impact of low-energy (40–10,000eV) atomic and molecular ions. The primary ions are obtained from a low-pressure D.C. gas discharge Colutron ion source. The product ions resulting from the ion–surface interactions involving different processes, for example, surface-induced dissociation (SID), surface-induced reaction (SIR), chemical- and sputtering are detected and identified by using a single-field linear time-of-flight (TOF) mass spectrometer coupled with a time- and position-sensitive dual micro-channel plate detector. The mass spectra of secondary ions are recorded by employing a pulsed extraction and acceleration technique. The experimental set up, experimental technique and data acquisition methodology are presented and discussed. A test experiment is conducted on the developed set up to demonstrate the performance and reliability of the apparatus. For this, a primary beam of 427eV N2+ ions was chosen to interact with a hydrocarbons covered surface of platinum target kept at room temperature. SID of N2+ into N+ and TOF mass spectra of sputtered, reflected and chemically formed ions from the ion–surface interaction are analyzed. A noticeable feature in the spectra is observed which shows that the odd-electron ions of sputtered hydrocarbons are preferentially produced in the interaction in addition to the other product ions. The nominal mass resolution (M/ΔM) of the present tandem mass spectrometer system is estimated to be about 600, while energy and spatial spreads of the primary ion beam are determined to be about 518meV and 2.8±0.3mm respectively. The survival probability of the incident ions is found to be 6.6% suggesting that the major process of ion–surface interaction at the considered impact energy is neutralization.

Momentum spectrometer for electron-electron coincidence studies on superconductors

We present a new experimental setup to study electron-electron coincidences from superconducting surfaces. In our approach, electrons emitted from a surface are projected onto a time- and position-sensitive microchannel plate detector with delayline position readout. Electrons that are emitted within 2 π solid angle with respect to the surface are detected in coincidence. The detector used is a hexagonal delayline detector with enhanced multiple hit capabilities. It is read out with a Flash analog-to-digital converter. The three-dimensional momentum vector is obtained for each electron. The intrinsic dead time of the detector has been greatly reduced by implementing a new algorithm for pulse analysis. The sample holder has been matched to fit the spectrometer while being capable of cooling down the sample to 4.5 K during the measurement and heating it up to 420 K for the cleaning procedure.

Using induced signals to sense position from a microchannel plate detector

We demonstrate a novel concept for a position sensitive microchannel plate detector. This detector provides sub-millimeter spatial resolution by examining the signal induced on a wire harp by the electron cloud from a microchannel plate detector. Wires in the harp are efficiently read out by coupling them to a delay line.

Transmission of 16 keV Cu− ions through Al2O3 nano-capillaries

The interaction of 16keV Cu− ions with Al2O3 nano-capillaries of 50nm diameter and 10μm length was studied. The angular and charge state distributions of the transmitted particles were measured by a position-sensitive microchannel plate detector. It shows that transmitted particles appear as two peaks and consist of three charge states, Cu−, Cu0 and Cu+. As the tilt angle increases, more Cu− ions lose electrons resulting in the formation of Cu0 and Cu+ during multiple collisions with the capillary walls. Unlike previously reported results on highly charged ions, keV-energy Cu− ions undergo significant charge exchange processes with the inner walls of the capillaries. This indicates that the guiding effect is absent in the negative ion transmission under the very low ion current conditions.

Absence of a guiding effect and charge transfer in the interaction of keV-energy negative ions with Al2O3nanocapillaries

In this work, the efficient electron loss process was observed for the transmission of 10- to 18-keV Cu${}^{\ensuremath{-}}$ and Cl${}^{\ensuremath{-}}$ ions through Al${}_{2}$O${}_{3}$ nanocapillaries. The fractions of the scattered particles were simultaneously measured using a position-sensitive microchannel plate detector. The neutrals were guided through the capillary via multiple grazing scattering. In particular, the scattered Cl${}^{\ensuremath{-}}$ ions were observed in the transmission, whereas no Cu${}^{\ensuremath{-}}$ ion was formed. In contrast to highly charged ions, these results support strongly the fact that the scattering events dominate the transport of negative ions through the nanocapillaries and that there is no direct evidence for the formation of negative charge patches inside the capillaries which are able to repulse and guide negative ions efficiently.

Nanogram amounts of selected rare earth elements measured by AMS

Results are presented from a series of measurements on nanogram quantities of selected rare earth elements. The work was performed at the NRL trace element AMS facility using a multi-cathode cesium-sputtering negative-ion source. The possibility to simultaneously inject, transmit and analyze a relatively broad mass range is a unique feature of our AMS system. The detection system, placed in the focal plane of the split-pole magnetic spectrograph, consists of a combination of position-sensitive microchannel plate and ion-implanted Si detectors. The small amounts of rare earth elements to be measured were chemically extracted from the surface of metallic samples. Calibration curves were built using standards containing 3 and 10ng of the material of interest. Extensive studies were performed to develop a method of normalizing the data by adding known amounts of a given element to the samples and to the standard material. Dedicated software was written to allow for event-by-event data acquisition as well as for data reduction. Results are shown for samples containing from less than 100pg to almost 10ng of material with uncertainties of the order of 15%. Further upgrades of the experimental method are underway.

Structure of an Er silicide film on a Si(111) substrate using three-dimensional medium-energy ion scattering

A three-dimensional medium-energy ion scattering (3D-MEIS) spectrometer has been developed for crystallographic structure analysis of materials. In 3D-MEIS, a pulsed He+ ion beam at 100keV is incident upon a sample and scattered (and/or recoiled) particles are detected by a three-dimensional detector. The three-dimensional detector used is a position-sensitive and time-resolving microchannel plate detector with two delay-line anodes intersecting at right angles. 3D-MEIS has been employed to analyze the structure of an Er silicide film on a Si(111) substrate. A blocking pattern based on the structure of the Er silicide was clearly observed. The results indicate that 3D-MEIS is effective for crystallographic structural analysis of materials.

Development of three-dimensional medium-energy ion scattering spectroscopy

A three-dimensional medium-energy ion scattering spectrometer has been developed for crystallographic structure analysis of nanomaterials. Three-dimensional medium-energy ion scattering spectroscopy (3D-MEIS) is an outgrowth of medium-energy coaxial impact-collision ion scattering spectroscopy (ME-CAICISS). A pulsed He + ion beam at 100 keV is incident upon a sample, and scattered (and/or recoiled) particles are detected by a position-sensitive and time-resolving microchannel plate (MCP) detector with two delay-line anodes, which provides information on the two-dimensional blocking pattern and flight time of scattered (and/or recoiled) particles. Preliminary experiments using 3D-MEIS have been made for a Si(1 1 1) crystal. The blocking pattern of a Si crystal was clearly observed, which indicated that the performance of the spectrometer was satisfactory.

A position sensitive detector for SPIDR—a mission to map the cosmic web

The primary goal of the Spectroscopy and Photometry of the IGM's Diffuse Radiation (SPIDR) mission is to detect and map the huge filamentary structures, the “cosmic web”, predicted to be present in the IGM. To accomplish this task the SPIDR instrument comprises six imaging spectrographs providing high-resolution spatial maps of IGM features in the critical OVI and CIV lines at both rest and red-shifted wavelengths. Each spectrograph uses a two-dimensional position sensitive microchannel plate detector to image UV dispersed by a normal incidence grating, encoding spectral and spatial information. Two-dimensional imaging is recovered by tomographic reconstruction of data from the slowly spinning spacecraft. The detector configuration utilizes an open faced microchannel plate stack coated with a UV photocathode. The conservative imaging requirements are met by a wedge and strip anode whose performance has been enhanced by using the image charge technique. Image charge provides a highly stable and predictable detector response which has enabled us to use software simulation to improve the linearity of the readout considerably.

Multiple electron stripping of 3.4 MeV/amu Kr7+ and Xe11+ in nitrogen

Use of heavy ions beams with ∼10 MeV/amu mass ∼200, and average charge state of 1+ has been proposed as a driver for heavy ion fusion. Stripping of the ion beam by background gas can lead to an increase in the space charge density of the beam, which may make focusing the intense ion beam onto small targets more complex. Knowledge of the electron loss cross sections is essential to understand and address the problem. Currently, there are no 10 MeV/amu mass=200, charge state=1 beams available, and the theories that calculate electron loss cross sections can be experimentally tested only by using available beams of somewhat lower energy and higher initial charge state. The charge state distribution of ions produced in single collisions of 3.4 MeV/amu Kr7+ and 3.4 MeV/amu Xe11+ in N2 have been measured at the Texas A&M Cyclotron Institute using a windowless gas cell. The charge states of the outgoing ions are determined by magnetic analysis using a position-sensitive microchannel-plate detector. The cross sections for single and multiple electron loss are determined, and the results indicate that substantial multiple-electron loss occurs. The relative cross section for loss of i+1 electrons is 0.3–0.7 times that for i electron loss. The average number of electrons removed per one collision (sum of the electron-weighted cross sections normalized to the total cross section) is 1.86 for Kr and 1.97 for Xe.