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Systems-Level Characterization of ALD-Functionalized MCPs Gap spacing voltages Gap 1: “first strike” Impacts on variability of transit time and amplification Gap 2: Impact on saturation of MCP pair, spatial spread of signal Gap 3:spatial and temporal spreading of the charge cloud. Space charge effects. Interface with anode. Determine optimal operational voltages. How do these optimal voltages depend on particular choice of MCPs? Explore tradeoffs between gain, timing, saturation. Geometry (pore size, L/D) Chemistry (SEE, resistive layer) Plate quality Uniformity Noise Stability Resistivity Saturation Relaxation time Anode Structure, Signal Processing The new laser lab was recently built at the APS Sector 7 to perform various characterization tests on MCPs, using a femtosecond Ti:sapphire laser. This system can deliver 50-femtosecond pulses at a fundamental wavelength of 800 nm and at a repetition rate of 1 KHz. Non-linear crystals (BBO) are used to generate blue (400nm) and UV light (266nm). The laser-beam spot size can be adjusted down to a few microns to address single pores and can be translated across the MCP surface with micron resolution to measure the uniformity of the MCP gain and timing properties. A custom-made flange was developed to hold variable stacks of 1-3 MCPs, a photocathode, and accommodate the signal output from the anode board and the high voltage inputs. The data are recorded on high-bandwidth oscilloscopes, and scans for various operational voltages of the MCP stack are fully automated. Once the LAPPD-designed PSEC-chip is available, it could also be integrated into our data acquisition system. FACILITIES AND RESOURCES EARLY ACHIEVEMENTS AVERAGE GAIN MEASUREMENTS 1.0000 10.0000 100.0000 1000.0000 10000.0000 100000.0000 700.0000 850.0000 1000.0000 1150.0000 1300.0000 Comparison of ALD MCP Gains with Commercial MCP MCP 122 Avg Mock Tile MCP Commercial PULSED MEASUREMENTS 0 10000.0000 20000.0000 30000.0000 40000.0000 0 75 150 225 300 1.5 kV Trend 1 Trend 2 Trend 3 0 50 100 150 200 0 37500 75000 112500 150000 # Occurences MgO; Umcp=1.5kV; En=300eV COMPLETE DATA-MC CYCLE Demountable Tile Testing: In parallel with the testing of sealed tubes, we have constructed a system for testing stacks of 8” plates in a large vacuum chamber. We performed tests on a stack consisting of a single 33mm MCP on top of our first 8” x 8” MCP and observed the first pulses from a microchannel plate of this size. These tests also represented a working demonstration of our delay- line anode design. The oscilloscope screenshot on the right shows a representative MCP signal from the 8” plate (green and yellow traces for the two ends of a stripline), referenced to the triggering laser pulse (purple). The timing depends on the operating conditions (applied voltages, location of laser focus, etc.). We now have our first pair of 8” plates in the chamber ready for testing. 8” MCP Testing: The Microchannel Plate (MCP) Characterization Lab at Argonne represents a unique collaboration between the High Energy Physics (HEP) Division and the Advanced Photon Source (APS). Both divisions have a vested interest in the development of photo-detectors with precision timing and high spatial resolution. While other characterization facilities at Argonne focus on testing microscopic and material properties for the Large Area Picosecond Photodetector (LAPPD) effort, the MCP Characterization Lab is designed to study photocathodes, MCPs, and anodes in assemblies approximating a complete device. Leveraging the APS's ultra-fast laser installations and high- speed electronic expertise, this effort measures the optical and electronic characteristics of MCP assemblies simultaneously with precision timing and gain under realistic operating conditions. AREAS OF INTEREST MCP parameters ALD gives us the unique ability to vary electrical, secondary electron yield (SEY) and geometric properties of MCPs independently. What impact do each of these properties have on the overall timing, gain, and saturation of the MCP, all others held fixed? What is the best anode design for a particular application. How does one reduce channel counts and cost without sacrificing timing or spatial resolution? How to maintain multi-GHz analog bandwidth and 50 ohm impedance? The use of Atomic Layer Deposition (ALD) to functionalize MCPs provides a unique opportunity to further our fundamental understanding of MCP performance. By separating the resistive, geometric, and secondary emissive properties, we can control many parameters individually, all others held constant. This allows us to explore a larger space of possibilities in testing and constraining various models of MCP behavior. Early in this project, we developed significant operational experience working with MCPs, both commercial and ALD- functionalized. This experience informed our later design for the laser lab. In the process we achieved several notable successes: the first observation of a signal from an Argonne- fabricated MCP and improved gain on a commercial plate after the application of a secondary- electron emission (SEE) enhanced ALD layer. Once the laser lab was completed, we conducted a first series of “average gain” measurements, where we determined the ratio of DC input to output currents. These efforts provided useful feedback for the construction of an average- gain characterization system by the ALD group. As the right-hand plot illustrates, we were able to observe gains well-above 10 5 for single, ALD- functionalized MCPs. These are comparable to the gains observed in typical commercial plates. In this figure, “Avg Mock Tile MCP” refers to the average gain-voltage curve for the 8 MCPs used in our “mock tile” and “MCP 122” was the ALD- based channel plate with the highest previously observed gain. The “demountable tile” represents a major step in the LAPPD project. The device consists of vacuum assembly designed to the mechanical specifications of a final detector, except that the top window is removable, sealed by compression on a Viton gasket. The demountable tile will give us important feedback on the mechanical, electrical, and vacuum properties of a fully sealed tube, combined with rapid prototype turnover. We have successfully vacuum- tested this assembly, and soon plan to perform first laser tests with functional 8” MCPs. field strength (Volts/mm) The main strength of the ANL MCP lab is our ability to use fast laser pulses to study the timing and gain characteristics of MCPs. The laser provides us with an external trigger from which we can measure the arrival time of the MCP signal. We can adjust the intensity of the laser so as to statistically control the number of photoelectrons produced per pulse. We recently completed a series of measurements on single MCPs with identical resistances, but different compositions for the secondary electron emission layer (20nm Al 2 O 3 , 20nm MgO, 2nm MgO). The intensity of the laser in these tests was set to produce roughly 10 photoelectrons per pulse. The upper two figures show distributions of the integrated charge (left) and arrival time (right) of the MCP signal per laser pulse for the 20nm MgO plate. The lower two plots show the average integrated charge and arrival time of the signal, as a function of photocathode voltage. Corresponding test samples with the same emissive layers have been characterized by the materials-characterization group. These material properties were then used as inputs to our MCP model and the resulting simulations will be compared with the data. -1.3 -0.8 -0.3 0.2 0.7 1.2 1.7 x 10 -9 seconds Arrival Time Distribution, 20nm MgO Single Plate at 1.5 kV, , 300V on Photocathode Integrated Charge Per Pulse, 20nm MgO Single Plate at 1.5 kV, 300V on Photocathode Average Integrated Charge Per Pulse, 20nm MgO at Different PC and MCP Voltages Avg. Integrate Charge (n-electrons) Average Arrival Time Per Pulse, 20nm MgO at Different PC and MCP Voltages 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 The goal of our current characterization effort is to produce a complete data/modeling cycle where MCP simulations based on measured material properties can predict observations in real MCPs. B. Adams, M. Chollet, M. Wetstein - Argonne National Laboratory (ANL) We would like to thank our colleagues in the LAPPD collaboration for all of their contributions to this work. Argonne National Laboratory's work was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences and Office of High Energy Physics under contract DE-AC02-06CH11357. 0 1 2 3 4 5 6 0 200 400 600 800 20 nm MgO SEY data SEY, [1/electron] Primary electron energy, eV Data: tilt=0 Fit: tilt=0 Fit: tilt=10 Fit: tilt=20 Fit: tilt=30 Fit: tilt=40 Fit: tilt=50 Fit: tilt=60 Fit: tilt=70 Fit: tilt=80
