Detecting single electrons in IOTA Giulio Stancari for the FAST/IOTA group Fermi National Accelerator Laboratory Workshop on Single-Electron Experiments in IOTA Fermilab, November 9, 2018 This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. https://indico.fnal.gov/event/18395
Contributors J. Jarvis, N. Kuklev, I. Lobach, A. Romanov, J. Ruan, J. Santucci, A. Valishev The SRF Group in the Mechanical Support Department The FAST Facility Department The Accelerator Research Department � 2 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Motivation Detect synchrotron-light signal and characterize backgrounds in IOTA for 1. Beam diagnostics : turn-by-turn intensity monitor with wide dynamic range , from nominal intensities (~10 9 particles) down to single electrons 2. Scientific experiments in IOTA • what is the time structure of radiation emission from a single electron in a storage ring? Is it random, regular, chaotic? • is there correlation between the emission from different dipoles? • many other ideas… (this workshop) Stancari et al., FERMILAB-FN-1043-AD-APC � 3 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Experimental layout linac dipole (D600) 50-250 MeV e - from injector M1R M1L IOTA dipoles M2L M2R M3L M3R IOTA M4L M4R • Main dipoles instrumented with vacuum windows, light-transport periscopes, and light-tight boxes • Synchrotron light is detected with photomultipliers and on cameras � 4 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Experimental layout in IOTA injection line light-tight box M4L 30-degree dipole M3L 60-degree dipole IOTA ring on July 27, 2018 � 5 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Experimental layout in IOTA photomultiplier shutter photomultiplier mirror 2 synchrotron radiation lens electron beam camera M3L 60-degree mirror 1 dipole vacuum translation window stage N. Kuklev � 6 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Choice of photodetectors Currently, we have available • cameras • conventional photomultipliers (PMT): • current mode or pulse mode to cover the full range of IOTA beam intensities • microchannel-plate photomultipliers (MCP-PMT): • < 100 ps transit-time spread for timing measurements • can be gated • multi-pixel photon counters (MPPC, SiPM): • pulse height allows to resolve individual photoelectrons • very compact • higher dark counts, sensitive to radiation � 7 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Signal processing and data acquisition schematic PICOAMMETER SYNCHROTRON LIGHT PMT AMP FAN-OUT WAVEFORM SHUTTER DIGITIZER HV DISCRIMINATOR EVENT TIMER DELAY BEAM SYNC COINCIDENCE COUNTERS REFERENCE OSC. � 8 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Expected signal Wavelength [nm] 1100 650 450 350 300 250 200 150 5 ⋅ 10 − 3 D600 300 MeV D600 250 MeV photon flux D600 150 MeV Spectral flux density [photons/pass/eV] D600 100 MeV 2 ⋅ 10 − 3 IOTA 150 MeV IOTA 100 MeV 10 − 3 IOTA at 5 ⋅ 10 − 4 150 MeV 2 ⋅ 10 − 4 IOTA at 10 − 4 100 MeV Typical photoelectron yield 5 ⋅ 10 − 5 is ~ 2 × 10 -4 / e - 100 Window Mirrors Light transmission [%] Coated lens 80 Total 60 40 light transport 20 0 14 MCP − PMT Q.E. [%] R5916U − 50 mod. 2 12 R3809U − 51 10 8 6 4 detector response Stancari et al., FERMILAB-FN-1043-AD-APC 2 0 (assumes full cone acceptance) 2 4 6 8 Photon energy [eV] � 9 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Expected angular distribution of synchrotron radiation in IOTA Energy density per electron per pass in (2.17, 2.75) eV band 30-degree dipoles show 60-degree dipoles are preferred some edge radiation SRW calculation by J. Jarvis � 10 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Some IOTA experiments with synchrotron radiation Measurements carried out during the past few weeks of commissioning: Interval between pulses, revolution period Intensity vs. time, beam lifetime How to achieve a known low number of stored electrons • Wait. Test machine stability over many hours, with natural beam decay • RF scraping: induce losses by lowering and restoring cavity voltage • Dark linac current and detuned injection (see Romanov’s talk) � 11 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Beam-based measurement of revolution period (IOTA @ 100 MeV) 0 − 10 PMT signal [mV] − 20 − 30 − 40 − 50 100 200 300 400 500 600 700 Time [ns] Over 598 turns, with PMT, avg. rev. period = 133172.6 ± 2.8 (stat.) ps (which agrees with rf cavity oscillator) We plan to measure turn-by-turn revolution times and synchrotron oscillations , down to single electrons � 12 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Beam lifetimes over the course of a long store Electrons stored in IOTA from 14:00 till 22:41 on Oct. 31 PMT sensitivity study started at 17:00 Used rf voltage to partially scrape the beam, then observed natural decay ● 200 50 very low beam intensity 150 IOTA M3L PMT counting rate [kHz] (50-80 e - in IOTA) Beam lifetime [min] exponential model 40 ● 100 ● of counting rate 30 50 ● ● reduced lifetime due to lower rf voltage 20 (260 V vs. nominal 560 V) 17.6 17.7 17.8 17.9 18.0 ● ● Time [h] − 5 − 4 − 3 − 2 − 1 Time to end of store [h] Lifetime improves with decreasing beam intensity � 13 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Decay of photon counting rate Towards the end of the store, one observes discrete steps in counting rate… 450 650 400 IOTA M3L PMT counting rate [kHz] IOTA M3L PMT counting rate [kHz] 600 350 300 550 250 500 beam extinction 200 450 18.1 18.2 18.3 18.4 18.5 20 21 22 23 Time [h] Time [h] � 14 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Observation of discrete steps in pulse counting rates IOTA beam experiment of Oct. 31, 2018. Last 12 circulating electrons. 460 Discrete steps are multiples of 3.0 kHz, which corresponds to a single electron 12 electrons 450 IOTA M3L PMT counting rate [kHz] Last electron circulated for 4 minutes (2 billion turns) 440 Single-electron experiments are possible in IOTA 430 1 electron We have an absolute calibration of low beam currents: 420 (1.203083 pA) × N e background level First observation of steps at 100 MeV 410 and without undulator? 21.5 22.0 22.5 23.0 Time [h] � 15 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Light from single electrons on camera Integrating over 1 s, the cameras can see individual electrons, too! Camera intensity identifies number of stored electrons from intentionally detuned injection of dark linac current A. Romanov � 16 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Conclusions After only 2 months of commissioning, we have sensitive diagnostics in IOTA to detect single electrons with both cameras and photomultipliers A few electrons can be stored in IOTA by rf scraping (slow and coarse) and by detuned dark-current injection (faster and more reliable) Experiments with single electrons in IOTA are definitely feasible and some have already started Ideas and collaborations are welcome! Thank you for your attention � 17 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Backup slides
Experimental apparatus at D600 microchannel-plate photomultiplier lead-brick shielding optional filters synchrotron 8% radiation 92% beam camera splitter light-tight box shutter � 19 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
Microchannel-plate photomultiplier (MCP-PMT) features Excellent timing (sub-ns) and high gain (10 3 -10 7 ). Can be gated. Limited current at high rate. Hamamatsu R5916U-50 mod. 2 reused from Tevatron Synclite. PHOTONS � 20 Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018
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