Microchannel Plate Devices Research Articles

Development of scalable electronics for the TORCH time-of-flight detector

The TORCH detector is proposed for the low-momentum particle identification upgrade of the LHCb experiment. It combines Time-Of-Flight and Cherenkov techniques to achieve charged particle separation up to 10 GeV/c. This requires a time resolution of 70 ps for single photons. Existing electronics has already demonstrated a 26 ps intrinsic time resolution; however the channel count and density need improvements for future micro-channel plate devices. This paper will report on a scalable design using custom ASICs (NINO-32 and HPTDC). The system provides up to 8 × 64 channels for a single micro-channel plate device. It is also designed to read out micro-channel plate tubes with charge-sharing technique.

Improved time response for large area microchannel plate photomultiplier tubes in fusion diagnostics.

Fusion diagnostics that utilise high speed scintillators often need to capture a large area of light with a high degree of time accuracy. Microchannel plate (MCP) photomultiplier tubes (PMTs) are recognised as the leading device for capturing fast optical signals. However, when manufactured in their traditional proximity focused construction, the time response performance is reduced as the active area increases. This is due to two main factors: the capacitance of a large anode and the difficulty of obtaining small pore MCPs with a large area. Collaboration between Photek and AWE has produced prototype devices that combine the excellent time response of small area MCP-PMTs with a large active area by replacing the traditional proximity-gap front section with an electro-optically focused photocathode to MCP. We present results from both single and double MCP devices with a 40 mm diameter active area and show simulations for the 100 mm device being built this year.

Plastic microchannel plates with nano-engineered films

Since their invention decades ago, microchannel plate (MCP) performance has been defined by the properties of the substrate material, which defines both mechanical structure and electron amplification within the device. Specific glass compositions have been developed to provide the conduction and electron emission layer at the surface of the pores. Alternative technologies using quartz and alumina substrates have not matured enough to become a viable substitute to lead–glass-based MCPs. In this paper we report on the development of new MCP devices from plastic substrates. The plastic substrate serves only as a mechanical structure: the electron amplification properties are provided by nano-engineered conduction and emission layers. The film deposition procedures were optimized for low temperatures compatible with the polymethyl methacrylate (PMMA) plastic chosen for this work. The gain of the PMMA MCP with aspect ratio of ∼27:1 and pore diameter ∼50 μm spaced on 70 μm hexagonal grid exceeded 200 at 470 V accelerating bias. Development of hydrogen-rich plastic MCPs should enable direct detection of fast neutrons through proton recoil reaction. Recoil protons with escape ranges comparable to the wall thickness will initiate an electron avalanche upon collision with the pore walls. The electron signal is then amplified within the MCP pore allowing high spatial and temporal resolution for each detected fast neutron. We expect to achieve ∼1% detection efficiency for 1–15 MeV neutrons with temporal resolution <10 ns, spatial resolution of <200 μm and very low background noise.

Position Sensing Using Pico-Second Timing With Micro-Channel Plate Devices and Waveform Sampling

Micro-Channel Plate devices (MCP) provide fast signals with rise-times in the 100 ps regime. The coupling of the MCP anode plane to 50 ¿ transmission lines allows both a precise time measurement and additionally the potential for a position measurement with an accuracy of a few hundred microns for large-area devices. We present position measurement results obtained with MCPs from Photonis, 10-cm long transmission lines, and a calibrated laser source, using waveform processing after digitization. A detailed simulation of the transmission lines is also presented, including simulation results for transmission lines up to 1-m in length. We compare the measured position resolution for two identical setups but with MCPs of different pore diameters: 25 and 10 microns.

Microfabricated capillary array electrophoresis DNA analysis systems

Microfabricated “laboratory-on-a-chip” systems are revolutionizing all aspects of genetic analysis. The development of capillary array electrophoresis (CAE) microchannel plate devices makes possible the performance of 96 or more high-speed separations in parallel on a single wafer-scale device. The fluorescently labeled DNA samples are detected within the microchannels with a novel four-color rotary confocal fluorescence scanner. The capabilities of this system for genotyping are demonstrated through multiplex separations of short tandem repeat and hereditary haemochromatosis allele-specific amplicons. Furthermore, with newly developed folded channel designs that maintain high resolution, these CAE microplate systems are used to perform 96 high-quality DNA sequencing separations in parallel to ∼500 bases per capillary in less than 30 min. These densely packed microfabricated device technologies will facilitate the even more rapid collection of vast amounts of genetic data in the future.

RF-plasma treatments of surface-conductive alkali-lead silicate glass and microchannel plate devices

RF-plasma treatments of surface-conductive alkali-lead silicate glasses and microchannel plate devices were performed using argon, ammonia and nitrogen gas mixtures. The effects of the different plasma-treatments on the composition of the glass surface were studied using Secondary Ion Mass Spectroscopy (SIMS) and X-ray Photoelectron Spectroscopy (XPS). A surface depletion of rubidium and cesium due to migration into the bulk of the glass and due to sputtering/vaporization of alkali ions from the glass surface was observed after the plasma treatments. The use of N 2 and NH 3 in the plasma gas resulted in the incorporation of nitrogen into the glass surface up to a depth of ∼100 Å. The effect of the plasma treatments on the water adsorptivity of actual microchannel plates was studied using Temperature Programmed Desorption (TPD). The TPD results showed that the argon plasma treatments helped in improving the short-term water adsorptivity properties of the microchannel plate devices, but long-term (>6 months in air) benefits were lost.

Simple analytical model of gain saturation in microchannel plate devices

We derive, discuss, and test against experimental data an analytical model of the gain saturation in microchannel plate (MCP) devices. By introducing a simple recharging circuit for each dynode, we extend the well-known, unsaturated gain model of Eberhardt to a microchannel operating in condition of gain saturation and show that the amplification of a current pulse and the voltage drop along the channel can be described by a pair of coupled differential equations. Solutions of these equations are given in various conditions, including an approximate solution, valid in the case of weak saturation and a general solution in implicit form. The behavior of a microchannel operating in current mode is studied by finding the transient and steady-state solutions obtained with an input step current wave form. Exact solutions are given for the charge gain of pulses with a short duration, compared to the dynode recharging time, and for the gain recovery of a microchannel after the amplification of a short pulse. The single channel saturation model is then extended to multistage MCP assemblies by taking into account the statistical distribution of the photoelectrons at the input and the spread of the multiplied electron cloud in the interplate gaps. The expressions found in this way are used for the best fit of experimental data from a Z-stack MCP photomultiplier operated in single and double pulse mode. Satisfactory agreement between the model and experimental data is obtained in the case of single pulse measurements, finding a reduced chi squared χ2=4.67. Less satisfactory agreement is found for double pulse data, giving χ2=7.46 and a clear indication that the model may be significantly improved by taking into account the charge redistribution among the dynodes during the recharging process, neglected in the present formulation.

Formation and behavior of surface layers on electron emission glasses

The thermochemical reduction of thin surface layers on multicomponent lead-silicate glasses is fundamental to their use in electron multiplier and microchannel plate devices. These surface layers can exhibit a specific conductivity as high as 10 −2 (Ω cm) −1 and secondary electron yields up to 3.5. However, due to the complex processing used in the fabrication of the devices, a basic understanding of the chemical and structural surface characteristics responsible for these properties has not been established. Moreover, the effects of prolonged electron bombardment upon the chemical characteristics of the surface have not been extensively investigated, nor related to any associated degradation of the electron emission properties. In this study, the clean fracture surfaces of these glasses were investigated. The effects of hydrogen reduction, chemical etching, and prolonged electron bombardment were determined. Ion-scattering spectroscopy (ISS) was used for its monolayer sensitivity, especially to alkali species, while secondary ion mass spectroscopy (SIMS) provided depth profiles. The hydrogen profile created by the reduction could also be obtained with SIMS. X-ray photoelectron spectroscopy (XPS) was employed selectively to examine changes in the oxidation state of the surface species. It was found that the hydrogen reduction of these glasses creates a thin 20–50 nm silica-rich surface layer. The layer of reduced lead atoms is beneath this zone, and is visible to depths of the order 5 μm, but the hydrogen profiles which are found in these surfaces extend only 0.5 μm in depth. The electron bombardment of these surfaces leads to a decrease in concentration of alkali and lead in the surface monolayer, and to a change in the hydrogen profile. The cross-section for this bombardment-induced change in the surface composition correlates with the reported gain degradation in microchannel plate devices.

Effects of perturbing magnetic fields on the performance of photoelectronic sensors

Photoelectronic sensors are all susceptible, to a greater or lesser degree, to the influence of perturbing ambient magnetic fields. Theoretical and experimental results are presented for the effects of axial and transverse magnetic fields on the various types of image intensifiers (including microchannel plate devices), TV camera tubes, and photomultipliers. The most immediately apparent effects are image displacement and loss of focus; additionally, changes in gain and certain other more subtle effects may be encountered. Numerical and graphical or nomographic methods for determining the magnitudes of the major effects in the different electron-optical systems at various voltages are provided, and electrode supply tolerances may be obtained therefrom. The nomographs can also be used to derive the focus conditions for magnetically focused systems. Interpretations of previously unexplained phenomena in the behavior of microchannel plates are also presented.