Simulations Guided Efforts to Understand MCP Performance

Transcription

1 University of Chicago Simulations Guided Efforts to Understand MCP Performance M. Wetstein, B. Adams, M. Chollet, A. Elagin, A. Vostrikov, R. Obaid, B. Hayhurst V. Ivanov, Z. Insepov, Q. Peng, A. Mane, J. Elam S. Jokela, I. Veryovkin, A. Zinovev LAPPD Collaboration Meeting Dec 9 211

2 An opportunity ALD gives us the unique ability to vary electrical, secondary electron yield (SEY) and geometric properties of MCPs independently. Compared with commercial MCPs, which are typically made from a single material (lead-glass), we can produce MCPs with much wider variety of properties, other properties held fixed. Can explore limiting cases and place stronger constraints on MCP models. 2

3 MCP characterization - Experimental Method 6. Our main focus: 2 samples: 2 nm Al2O3 2 nm MgO Two materials demonstrate similar secondary electron yield for striking energies below 1 ev... Nsecondaries nm MgO 2 nm Al2O3 S. Jokela, I. Veryovkin, A. Zinovev The curves start to diverge at high energies striking energy (ev) 2 nm MgO SEY data 6 Is the MCP avalanche driven by the smaller fraction of high energy strikes? What is the role of backscattering? SEY, [1/electron] Z. Insepov Data: tilt= Fit: tilt= Fit: tilt=1 Fit: tilt=2 Fit: tilt=3 Fit: tilt=4 Fit: tilt=5 Fit: tilt=6 Fit: tilt=7 Fit: tilt= Primary electron energy, ev 3

4 Friday, November 25, 211 MCP characterization - Experimental Method true secondaries are typically low energy and isotropic back-scattered electrons keep most of the original energy and remain at grazing incidence. Friday, November 25, 211 BS probabilities are calculated form a theoretical model. Overall normalization is left to tune... 4

5 Details in Simulations: The LAPPD Simulations Program Goal to develop a predictive, pseudo-physical MCP model to help guide MCP design. Help improve understanding of what is going on inside the pores. Takes experimental materials characterization as input. Two components: true secondary electron yield (SEY) specular reflection of incident primary electron, eg backscattering or BS SEY at normal incidence is measured. SEY at grazing incidence is extrapolated using a theoretical material model quasi-elastic reflection of the primary electron is derived from a theory. Normalization of the BS probability is a tunable parameter (controls the fraction of highly energetic electrons in the pore). 5

6 Facilities and Resources: ANL MCP Characterization Lab: A fast (sub-psec), pulsed laser with precision optics 8 nm Ti:Sapph laser pulse durations O(1) femtoseconds 1 Hz repetition rate non-linear optics to produce UV(266 nm) and blue light (4nm) average power ~8 mwatt optics capable of micron-level translations and potential to focus on single pores Vacuum systems for testing 33 mm photocathode-mcp-anode stacks approximating a complete device Capable of holding variable stacks of 1-3 MCPs and simple photocathode able to accommodate multiple readout designs capable of 1-7 torr 2 complete systems with parts for a third 8 MCP testing system (now commissioning) Fixtures for testing sealed-tube detectors (now commissioning) multi-ghz RF electronics several oscilloscopes with 3-1 Gz analog bandwidth high gain, low noise RF amplifiers high-frequency splitters, filters, etc 6

7 The APS-Team 7

8 Method Control the number of photoelectrons (PEs) by attenuating the laser to the point where only a small fraction of pulses produce signal. Trigger on laser pulses to achieve very precise measurements of transit time Control size and position of beam to isolate individual spots on the MCP Record each pulse separately to produce statistical distributions. Integrate and fit the pulses to determine arrival time and gain. Able to discriminate between signal pulses and dark-current (random firing of the MCP) Single plate testing allows us to study gainvoltage behavior without saturation. Single plate is coupled to a low-noise amplifier fraction of pulses with MCP signal / ndf / 4 p ±.2996 p ± average laser intensity (nanowatts) time from trigger = MCP transit time + known optical and electronic delays... Mean Pulse Shape, MCP 72/78 at 2.6 kv UV intensity (nw) 1V anode gap 8V anode gap 5V anode gap 2V anode gap Area of pulse = total charge. When divided by incident charge, this gives the gain time (seconds) x 1 9 8

9 MCP characterization - Results 19 MgO 14 Al2O3 average measured charge per pulse (>8) MCP at 1.36 kv MCP at 1.44 kv MCP at 1.5 kv measured charge per pulse from MgO MCP MCP at 1.36 kv MCP at 1.44 kv MCP at 1.5 kv PC Voltage, kv PC V = 2 Volts PC V = 14 Volts PC V = 3 Volts PC Voltage, kv x 1 6 9

10 MCP characterization - Results 19 MgO 14 Al2O3 average measured charge per pulse (>8) MCP at 1.36 kv MCP at 1.44 kv MCP at 1.5 kv measured charge per pulse from MgO MCP MCP at 1.36 kv MCP at 1.44 kv MCP at 1.5 kv PC Voltage, kv PC Voltage, kv MgO MCP is more sensitive to photocathode voltage (first strike energy) MgO MCP is more sensitive to MCP voltage over the range: kv Slope (not just offset) of the pulse height versus photocathode voltage curves seem to depend on MCP voltage in the MgO. Slope of these curves should be identical if each strike is statistically independent of the next. Could be pointing to BS! 1

11 MCP characterization - Results average predicted charge per pulse (>8) <Gain> MgO PC Voltage, kv MgO 2 nm; Average gain above 8, vs. PC voltage [V]; Lambda=6.5 MCP at 1.36kV MCP at1.5kv MCP at1.44kv measured charge per pulse from MgO MCP Al2O3 PC Voltage, kv MCP at 1.5 kv MCP at 1.44 kv MCP at 1.36 kv We observe similar dependences in the Monte Carlo... 11

12 MCP characterization - Results &"%$ &"$! &"#$ +&1,2+3/4 +&1,5*637/ &"!!!"%$!"$!!"#$ *+,-./123*+,-.45#1)2 +6 &"$ 789 :,;<5+6,=- *+,-./123*+,-.45#1)2 +6 &")( 789 :,;<5+6,=- *+,-./123*+,-.45#1)2 +6 &"$ 789 >+6+ *+,-./123*+,-.45#1)2 +6 &")( 789 >+6+!! '' &%$ #() )$!!"#$#%&$"#'( )#*$&+(,-#*$./ Systematic uncertainties cancel out in the ratio of the gains for MgO and Al2O3. Predictions made by simulations match well with the data. 12

13 MCP characterization - Timing Questions Timing sensitivity driven by signal to noise. For single plate operation, this is small. We are not yet sensitive to the fewpicosecond resolutions predicted by simulations. Will repeat these TTS studies with MCP pairs in near future. TTS (picoseconds) nm MgO 2 nm Al2O toy study intrinsic TTS pure signal to noise Pulse Height (N electrons) x Pulse Height ( N electrons ) x

14 Summarizing Our Progress 14

15 Summarizing Our Progress 15

16 Summarizing Our Progress 15

17 Year 2 achievements: Developed operational experience performing current-based, average gain measurements. Demonstrated > 15 amplification on Argonne-made, 33mm ALD functionalized glass plates. Demonstrated better than 2 psec time resolutions for single photoelectons in ALD MCPs Developed protocol for pulsed, single-photoelectron characterization. Close work with simulations and material characterization to improve fundamental understanding of MCP performance. Relative shift in mean arrival time of signal VS anode-gap voltage Average pulse shape for single MgO MCP at 1.5 kv, different photocathode voltages Relative Shift in Mean Arrival Time of Signal Vs Voltge on Anode Gap Relative Arrival Time of Signal (psec) Completion of laser characterization lab for systematic MCP testing in the time domain time (seconds) Voltage Across the Anode Gap (Volts) Gain curves for mock tile MCPs Comparison of ALD-MCP gains with Comparison of ALD MCP Gains w Commercial MCP commercial MCP Designed system for characterization of 8 MCPs, sealed tubes and lifetime testing x1-9 1 Gain MCP 122 Avg Mock Tile MCP Commercial MCP 1 1 voltage (volts) field strength (Volts/mm) 16

18 MCP characterization - Next steps and publication plan Complete draft of a paper on MgO/Al2O3 comparison together and ready for godparent review. Plans to write a paper on our experimental setup in Review of Scientific Instrumentation Sequel papers hopefully soon to follow. This is a major focus of the project... 17

19 Medium to Long Term Planning for the 33mm Program Wrapping up version 1. measurements Finishing current measurements with set up as is...approximately 2-3 more months Planning version 2. Modifications for single pore illumination... Double pulsing studies months Some transitional measurements inbetween Life time studies, batch uniformity studies... 18