Microchannel Plate Research Articles

Performance of a prototype TORCH time-of-flight detector

TORCH is a novel time-of-flight detector, designed to provide charged particle identification of pions, kaons and protons in the momentum range 2–20 GeV/c over a 9.5 m flight path. A detector module, comprising a 10 mm thick quartz plate, provides a source of Cherenkov photons which propagate via total internal reflection to one end of the plate. Here, the photons are focused onto an array of custom-designed Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMTs) which measure their positions and arrival times. The target time resolution per photon is 70 ps which, for 30 detected photons per charged particle, results in a 10–15 ps time-of-flight resolution. A 1.25 m length TORCH prototype module employing two MCP-PMTs has been developed, and tested at the CERN PS using a charged hadron beam of 8 GeV/c momentum. The construction of the module, the properties of the MCP-PMTs and the readout electronics are described. Measurements of the collected photon yields and single-photon time resolutions have been performed as a function of particle entry points on the plate and compared to expectations. These studies show that the performance of the TORCH prototype approaches the design goals for the full-scale detector.

Radiation, optical, power flow, and electrical diagnostics at the Z facility: Layout and techniques utilized to operate in the harsh environment.

The Z machine is a current driver producing up to 30 MA in 100ns that utilizes a wide range of diagnostics to assess accelerator performance and target behavior conduct experiments that use the Z target as a source of radiation or high pressures. We review the existing suite of diagnostic systems, including their locations and primary configurations. The diagnostics are grouped in the following categories: pulsed power diagnostics, x-ray power and energy, x-ray spectroscopy, x-ray imaging (including backlighting, power flow, and velocimetry), and nuclear detectors (including neutron activation). We will also briefly summarize the primary imaging detectors we use at Z: image plates, x-ray and visible film, microchannel plates, and the ultrafast x-ray imager. The Z shot produces a harsh environment that interferes with diagnostic operation and data retrieval. We term these detrimental processes "threats" of which only partial quantifications and precise sources are known. We summarize the threats and describe techniques utilized in many of the systems to reduce noise and backgrounds.

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.

Compact high repetition rate Thomson parabola ion spectrometer.

We present the development of a compact Thomson parabola ion spectrometer capable of characterizing the energy spectra of various ion species of multi-MeV ion beams from >1020W/cm2 laser produced plasmas at rates commensurate with the highest available from any of the current and near-future PW-class laser facilities. This diagnostic makes use of a polyvinyl toluene based fast plastic scintillator (EJ-260), and the emitted light is collected using an optical imaging system coupled to a thermoelectrically cooled scientific complementary metal-oxide-semiconductor camera. This offers a robust solution for data acquisition at a high repetition rate, while avoiding the added complications and nonlinearities of micro-channel plate based systems. Different ion energy ranges can be probed using a modular magnet setup, a variable electric field, and a varying drift-distance. We have demonstrated operation and data collection with this system at up to 0.2Hz from plasmas created by irradiating a solid target, limited only by the targeting system. With the appropriate software, on-the-fly ion spectral analysis will be possible, enabling real-time experimental control at multi-Hz repetition rates.

Electron Capture by Proton Beam in Collisions with Water Vapor

In low energy ion-molecule collisions, electron capture is one of the most important channels. A new experimental setup was developed to study the electron capture process using low-energy ion beams extracted from an electron cyclotron resonance (ECR) plasma-based ion accelerator. Experiments were carried out with the proton beam colliding with water vapor in the energy range of 70–300 keV. Capture events were detected using a position-sensitive detection system comprising micro channel plates (MCPs) and a delay line detector (DLD). These e-capture events can be a result of pure capture reactions as well as transfer ionization. The capture cross section was found to decrease sharply with the beam energy and agreed well with previous measurements. The setup was also used to detect the events that gave rise to the single and multiple e-capture (integrated over all recoil-ion charge states) of C4+ ions. The capture cross-sections for one, two, three, and four electrons were measured for 100 keV C4+ ions. The ratio of multielectron capture yield to that for single e-capture decreased with the number of captured electrons.

A comprehensive analysis of electron emission from a-Si:H/Al2O3 at low energies

Recently developed microchannel plates (MCPs) based on amorphous silicon offer potential advantages with respect to glass based ones. In this context, secondary electron emission (SEE) at very low energies below 100 eV has been studied for relevant materials for these novel devices. The aim of this work was to quantify the low energy electron emission—secondary emission and elastic scattering—from amorphous silicon and alumina and the dependence of the emission energy distribution on the primary electron energy, which was previously unknown. Secondary emission and energy distribution were both modelled and measured using equipment particularly designed for this energy range. The effects of roughness, angle of incidence and surface composition were analysed. We show crossover energies as well as the angular dependence of electron emission from amorphous silicon and alumina, with a maximum experimental emission yield value of 2 and 2.8, respectively, at an incident angle of 75∘. A parameterization for the energy dependence of the emission energy spectrum at low energies was derived. This extensive analysis is fundamental for a comprehensive understanding of the performance of amorphous silicon-based MCP detectors. It provides a complete model for SEE for a detailed description of the detector operation. The present results thus set the basis for a simulation framework, which is an essential element to increase the performance of these detectors and enable further developments.

High performance cross strip imaging readout Planacon sealed tubes

Sealed tube microchannel plate (MCP) detectors have provided a valuable platform for high time resolution photon counting detectors. Specifically, electronic readout MCP based sensors have been used as photon counting, imaging, event time tagging detectors for astronomy, time resolved biological imaging, imaging LIDAR, Cherenkov (RICH), scintillation detection, and neutron imaging. For future initiatives we have been developing novel atomic layer deposited MCPs, UV photocathodes and cross strip (XS) readouts for sealed tube detectors. Novel, atomic layer deposited MCPs can replace standard MCPs, providing enhanced gain stability with reduced intrinsic background and lower gamma ray sensitivity. Additionally, XS readouts provide a compact package to achieve high resolution imaging of single photon positions at low MCP gain. The Photonis Planacon is a commercial sealed tube detector (∼50 mm area) which we have modified to incorporate these novel technologies and demonstrate their performance and robustness.

Upgraded Cherenkov time-of-flight detector for the AFP project.

We present the results of our performance studies of the upgraded Cherenkov time-of-flight (ToF) detector for the AFP (ATLAS Forward Proton) project. The latest version consists of solid L-shaped fused silica bars, new customized ALD-coated micro-channel plate photomultipliers (MCP-PMTs) miniPlanacon XPM85112-S-R2D2 with an extended lifetime which operate at low gains (order of 103), and an updated construction. The improvements were aimed to increase the efficiency, the lifetime as well as the radiation hardness of the detector which has been designed to operate in high radiation areas (above 400 kGy/year). The detector was finally tested at the CERN-SPS test-beam facility (120 GeV π+ particles) in August 2021 prior to its installation at the Large Hadron Collider (LHC) at CERN. Measurements proved the detector kept its inner timing resolution of 20 ps despite the rather low gain of its photodetector and reduced optical throughput caused by inevitable changes in the detector geometry.

The scaling law of cluster sizes revisited: Clusters formed via coexpansion of a molecular and a rare gas species

We report experimental measurements of cluster sizes formed from supersonic expansion of two different species based on the time-of-flight principle. Argon clusters containing aromatic molecules are ionized at 266 nm at a low laser intensity. A high voltage is used to accelerate the heavy cluster ions thereby increasing the sensitivity of a microchannel plate detector. Our measurements of argon clusters, neat molecular clusters, and molecular-Ar clusters, are all in qualitative agreement with results predicted from the scaling law, but the fitting exponents for the dependence of cluster sizes on both the stagnation pressure and temperature are different.

Microchannel Plate Detector Gain Decrease Through Storage Under Environmental Conditions

Open microchannel plate (MCP) detectors are widely used for detection of particles and photons with diverse instruments, including the space flight ones. Space missions preparation and flight instruments construction commonly takes long time during which it is difficult or impossible to ensure the recommended storage conditions (inert gas atmosphere or vacuum) for MCP detectors. We have estimated the gain decrease of a flight laser ionization time-of-flight mass spectrometer LASMA utilizing an MCP detector during its storage under normal conditions (1 atm. pressure, air atmosphere, room temperature, air humidity 40-60%) for almost 10 years. It was found that the detector sensitivity (i.e. gain) over observations period decreased by 2.4–2.8 times. Such decrease can be considered not critical for some instruments using non-position-sensitive MCP-based detectors. The data obtained can be applied to develop requirements for flight instruments constructions, storage, and service, which could simplify some space missions preparation.

Analysis and simulation of time-of-flight spectrum in Rb<sup>+</sup>-Rb hybrid trap

The time-of-flight mass spectrum of charged particles, which are created through two-step cw-laser photoionization of laser-cooled <sup>87</sup>Rb atoms in an ion-neutral hybrid trap, is quantitatively investigated to further facilitate the study of Rb<sup>+</sup>-Rb reactive collisions. A microchannel plate (MCP) is used to detect charged particles, and two spectral peaks corresponding to the <sup>87</sup>Rb<sup>+</sup> ions and the product <inline-formula><tex-math id="Z-20230423060254-1">\begin{document}$ \rm {}^{87}Rb_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.png"/></alternatives></inline-formula> of the Rb<sup>+</sup>-Rb reaction were observed in the time-of-flight spectrum, respectively. The two peaks overlapped with each other and both showed an asymmetric profile. The information about the intensity, position, and half-width of the peak for a specific ion species was derived by fitting the time-of-flight spectrum with the probability density function of the Gumbel distribution. Then the relative ion intensity was converted into absolute ion number through the following steps. The rate equation of the total number of ions, which includes the number of atoms, the calibration factor of MCP, and the effective decay rate of ions in the ion trap, was established by modeling the photoionization of atoms. Combined with the absolute number of atoms measured by absorption imaging, the calibration factor in converting the ion intensity into the ion number was derived and the relative ion intensity was converted into the absolute number of ions. This provides a method of calibrating the MCP. The reliability of our calibration method was proved by the fact that the calibration factor in converting the intensity measured by MCP into particle number is independent of the duration of photoionization, the intensity and wavelength of the ionizing laser. Moreover, in order to explain the relationship between the peak width and temperature of the corresponding ion species, the time-of-flight spectra of the ions trapped in the ion trap were simulated by using COMSOL Multiphysics. The simulation results demonstrated that the large ion kinetic energy results in a narrow spectral peak. In sum, we quantitatively analyze and simulate the time-of-flight spectrum of the photoionization of cold atoms in the Rb<sup>+</sup>-Rb hybrid trap. The absolute number of ions is obtained by the intensity of the spectral peak, and the width of the spectral peak is related to the temperature of the ions. These results lay a foundation for the in-depth analysis of the ion-atom reaction collision and charged particle temperature relaxation in the photoionization of cold atoms, and thus further elucidating the subsequent collisional dynamics of ultracold plasmas.

Determination of the Plasma Delay Time in PIPS detectors for fission fragments at the LOHENGRIN spectrometer

The VElocity foR Direct particle Identification spectrometer (VERDI) is a 2E-2v fission spectrometer that allows the measurement of the total mass distribution of secondary fission fragments with a resolving power of 1-2 u. It consists of two time-of-flight (ToF) arms, with one Micro Channel Plate (MCP) detector and up to 32 Silicon PIPS (Passive Implanted Planar Silicon) detectors per arm. The MCPs provide the start timing signals and the PIPS detectors provide both the energy and the stopping ToF signals. In real conditions, the PIPS signals are affected by the formation of plasma from the interaction between the heavy ions and the detector material. The plasma contributes to a reduction in signal amplitude, resulting in a Pulse Height Defect (PHD), and introduces a signal delay, known as Plasma Delay Time (PDT). An experiment to characterize the PDT and PHD was performed at the LOHENGRIN recoil separator of the Institut Laue Langevin (ILL). Characteristic fission fragments from the 239Pu(n,f) reaction were separated based on their A/Q and E/Q ratios, allowing the measurement of a wide range of energies from 21 to 110 MeV and masses between 80 and 149 u. Six PIPS detectors were characterized to study their individual responses to the PDT and PHD effects. The signals were recorded in a digital acquisition system to completely exploit the offline analysis capabilities. Achieved combined timing and energy resolutions for fission fragments varied between 72(2) ps and 100(4) ps and 1.4% - 2% (FWHM), respectively. Preliminary PHD and PDT data are presented from the masses A=85, 95, 130 and 143. The PHD trends are strongly correlated with both the ion energy and mass. The PDT, on the other hand, shows a strong variation as a function of the ion kinetic energy but a smaller dependence on the ion mass.

The cascade matrix electron flow amplifier based on an electron multiplier concentrator

The design and operation of a cascade matrix electron flow amplifier based on an electron concentrator multiplier is considered. Unlike classical microchannel plates, the proposed amplifier can provide a high density of output current, which also allows it to be used as a field cathode in vacuum microelectronics of giga and terahertz ranges. Keywords: Microchannel plate, secondary emission, screening, electron concentrator multiplier, field cathode.

Afterpulse measurement of JUNO 20-inch PMTs

In this study, we present the large photomultiplier tube (PMT) afterpulse measurement results obtained from the Jiangmen underground neutrino observatory (JUNO) experiment. A total of 11 dynode-PMTs (R12860) from the Hamamatsu company (Hamamatsu Photonics K.K. (HPK)) and 150 micro-channel plate PMTs (MCP-PMTs, GDB-6201) from the NNVT company (North Night Vision Technology Co., Ltd. (NNVT)) were tested. Subsequently, an afterpulse model was built according to the afterpulse time distribution and the probability of occurrence for these two types of PMTs. The average ratio of the total afterpulse charge with a delay between 0.5 \(\upmu\)s and 20 \(\upmu\)s to the primary pulse charge is \(\sim\) 5.7% (13.2%) for the tested MCP-PMTs (dynode-PMTs). The JUNO experiment will deploy 20,012 20-inch PMTs; this study will benefit detector simulation, event reconstruction, and data analysis regarding the JUNO experiment.

Каскадный матричный усилитель электронного потока на основе умножителя-концентратора электронов

The design and operation of a cascade matrix electron flow amplifier based on an electron concentrator multiplier is considered. Unlike classical microchannel plates, the proposed amplifier can provide a high density of output current, which also allows it to be used as a field cathode in vacuum microelectronics of giga and terahertz ranges.

Dynamics of many-body fragmentation of carbon dioxide dimer tetravalent ions produced by intense femtosecond laser fields

We study experimentally the three-body Coulomb explosion dynamics of carbon dioxide dimer <inline-formula><tex-math id="M5">\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M5.png"/></alternatives></inline-formula> ions produced by intense femtosecond laser field. The three-dimensional momentum vectors as well as kinetic energy are measured for the correlated fragmental ions in a cold-target recoil-ion momentum spectrometer (COLTRIMS). Carbon dioxide dimer is produced during the supersonic expansion of <inline-formula><tex-math id="M6">\begin{document}${\rm{(CO_2)_2}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M6.png"/></alternatives></inline-formula> gas from a 30 μm nozzle with 10 bar backing pressure. The linearly polarized laser pulses with a pulse duration (full width at half maximum of the peak intensity) of 25 fs, a central wavelength of 790 nm, a repetition rate of 10 kHz, and peak laser intensities on the order of <inline-formula><tex-math id="M8">\begin{document}${\rm{8 \times10^{14}}}\;{\rm{W/cm^2}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M8.png"/></alternatives></inline-formula> are produced by a femtosecond Ti:sapphire multipass amplification system. We concentrate on the three-particle breakup channel <inline-formula><tex-math id="M10">\begin{document}${\rm{(CO_2)_2^{4+}}} \rightarrow {\rm{CO}}_{2}^{2+}+{\rm{CO^+}}+ {\rm{O^+}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M10.png"/></alternatives></inline-formula>. The two-particle breakup channels, <inline-formula><tex-math id="M15">\begin{document}${\rm{(CO_2)_2^{4+}}} \rightarrow {\rm{CO}}_{2}^{2+}+ {\rm{CO_{2}}^{2+}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M15.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M19">\begin{document}${\rm{CO_2^{2+}}\rightarrow CO^++O^+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M19.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M19.png"/></alternatives></inline-formula>, are selected as well for reference. The fragmental ions are guided by a homogenous electric field of 60 V/cm toward microchannel plates position-sensitive detector. The time of flight (TOF) and position of the fragmental ions are recorded to reconstruct their three-dimensional momenta. By designing some constraints to filter the experimental data, we select the data from different dissociative channels. The results demonstrate that the three-body Coulomb explosion of <inline-formula><tex-math id="M20">\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M20.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M20.png"/></alternatives></inline-formula> ions break into <inline-formula><tex-math id="M21">\begin{document}${\rm{CO}}_{2}^{2+}+{\rm{CO}}^++{\rm{O}}^+$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M21.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M21.png"/></alternatives></inline-formula> through two mechanisms: sequential fragmentation and non-sequential fragmentation, in which the sequential fragmentation channel is dominant. These three fragmental ions are produced almost instantaneously in a single dynamic process for the non-sequential fragmentation channel but stepwise for the sequential fragmentation. In the first step, the weak van der Waals bond breaks, <inline-formula><tex-math id="M22">\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M22.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M22.png"/></alternatives></inline-formula> dissociates into two <inline-formula><tex-math id="M23">\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M23.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M23.png"/></alternatives></inline-formula> ions; and then one of the C=O covalent bonds of <inline-formula><tex-math id="M24">\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M24.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M24.png"/></alternatives></inline-formula> breaks up, the <inline-formula><tex-math id="M25">\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M25.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M25.png"/></alternatives></inline-formula> ion breaks into <inline-formula><tex-math id="M26">\begin{document}${\rm{CO^+}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M26.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M26.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M27">\begin{document}${\rm{O^+}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M27.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M27.png"/></alternatives></inline-formula>. The time interval between the two steps is longer than the rotational period of the intermediate <inline-formula><tex-math id="M28">\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M28.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M28.png"/></alternatives></inline-formula> ions, which is demonstrated by the circle structure exhibited in the Newton diagram. We find that the sequential fragmentation channel plays a dominant role in the three-body Coulomb explosion of <inline-formula><tex-math id="M29">\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M29.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M29.png"/></alternatives></inline-formula> ions in comparison of the event ratio of the two fragmentation channels.

Booster-microchannel plate (BMCP) detector for signal amplification in MALDI-TOF mass spectrometry for ions beyond m/z 50 000.

Top-down proteomics deals with the characterization of intact biomolecules, which reduces the sample complexity and facilitates the detection of modifications at the protein level. The combination of the matrix-assisted laser desorption/ionization (MALDI) technique with time-of-flight (TOF) mass analysis allows for the generation of gaseous ions in low charge states from high-mass biomolecules, followed by their mass-to-charge ratio (m/z) separation, as high-mass ions drift down the flight tube more slowly than lighter ones. However, the detection efficiency of conventional microchannel plate (MCP) detectors is strongly reduced with decreasing ion velocity-corresponding to an increase in ion mass-which impedes the reliable detection of high-mass biomolecules. Herein, we present a simple modification of the MCP detector that allows for the amplification of the signal from ionized proteins of up to m/z 150 000. Two circular electrodes were assembled in front of the conventional detector and set to negative electrical voltages to affect the positively charged ions directly before they impinge on the MCP, possibly through a combination of a velocity boost and ion optical effects. In the present study, three booster electrode configurations were experimentally tested to maximize the signal intensification. Compared to the conventional MCP assembly, the signal intensity was amplified in a proof-of-concept experiment by a factor of 24.3 and of 10.7 for the singly charged BSA ion (m/z 66 400) and for the singly charged IgG ion (m/z 150 000), respectively, by applying the booster-MCP (BMCP) detector.

Time-Resolved Imaging of High Mass Proteins and Metastable Fragments Using Matrix-Assisted Laser Desorption/Ionization, Axial Time-of-Flight Mass Spectrometry, and TPX3CAM.

The Timepix (TPX) is a position- and time-sensitive pixelated charge detector that can be coupled with time-of-flight mass spectrometry (TOF MS) in combination with microchannel plates (MCPs) for the spatially and temporally resolved detection of biomolecules. Earlier generation TPX detectors used in previous studies were limited by a moderate time resolution (at best 10 ns) and single-stop detection for each pixel that hampered the detection of ions with high mass-to-charge (m/z) values at high pixel occupancies. In this study, we have coupled an MCP-phosphor screen-TPX3CAM detection assembly that contains a silicon-coated TPX3 chip to a matrix-assisted laser desorption/ionization (MALDI)-axial TOF MS. A time resolution of 1.5625 ns, per-pixel multihit functionality, simultaneous measurement of TOF and time-over-threshold (TOT) values, and kHz readout rates of the TPX3 extended the m/z detection range of the TPX detector family. The detection of singly charged intact Immunoglobulin M ions of m/z value approaching 1 × 106 Da has been demonstrated. We also discuss the utilization of additional information on impact coordinates and TOT provided by the TPX3 compared to conventional MS detectors for the enhancement of the quality of the mass spectrum in terms of signal-to-noise (S/N) ratio. We show how the reduced dead time and event-based readout in TPX3 compared to the TPX improves the sensitivity of high m/z detection in both low and high mass measurements (m/z range: 757-970,000 Da). We further exploit the imaging capabilities of the TPX3 detector for the spatial and temporal separation of neutral fragments generated by metastable decay at different locations along the field-free flight region by simultaneous application of deflection and retarding fields.

Simulation on Secondary Electron Multiplication Behavior of the Microchannel Plate under DC Mode

In this study, a three-dimensional microchannel model of a single hollow-core glass fiber was constructed and the Finite Integral Technique and Monte Carlo method were combined to comprehensively simulate the electron multiplication process in a single channel under DC mode. The electron dynamic trajectory in DC electron emission mode was achieved. The effects of different structural parameters and applied bias voltage on the electron gain and the most probable exit energy at the output end of MCP were investigated. The results show that the electrons with a certain initial current can be continuously and stably multiplied in the channel under DC mode and eventually reach a stable value because of the space charge effect; additionally, the electron gain increases with the increase in the bias angle and DC bias voltage and decreases with the increase in the penetration depth of the MCP output electrode. The electron gain at the output end of the MCP increases with the length-to-diameter ratio under the normalized voltage but shows a maximum value under the constant voltage. The simulation results are consistent with the reported experimental trend and theoretical analyses. The method provides data support for the optimal structural design of the microchannel plate.

Beam Trajectory Analysis of Vertically Aligned Carbon Nanotube Emitters with a Microchannel Plate

Vertically aligned carbon nanotubes (CNTs) are essential to studying high current density, low dispersion, and high brightness. Vertically aligned 14 × 14 CNT emitters are fabricated as an island by sputter coating, photolithography, and the plasma-enhanced chemical vapor deposition process. Scanning electron microscopy is used to analyze the morphology structures with an average height of 40 µm. The field emission microscopy image is captured on the microchannel plate (MCP). The role of the microchannel plate is to determine how the high-density electron beam spot is measured under the variation of voltage and exposure time. The MCP enhances the field emission current near the threshold voltage and protects the CNT from irreversible damage during the vacuum arc. The high-density electron beam spot is measured with an FWHM of 2.71 mm under the variation of the applied voltage and the exposure time, respectively, which corresponds to the real beam spot. This configuration produces the beam trajectory with low dispersion under the proper field emission, which could be applicable to high-resolution multi-beam electron microscopy and high-resolution X-ray imaging technology.