Detecting single electrons in IOTA Giulio Stancari for the FAST/IOTA - - PowerPoint PPT Presentation

Giulio Stancari for the FAST/IOTA group

Fermi National Accelerator Laboratory

Workshop on Single-Electron Experiments in IOTA
 Fermilab, November 9, 2018

Detecting single electrons in IOTA

https://indico.fnal.gov/event/18395

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.

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Contributors

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• 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

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Motivation

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Stancari et al., FERMILAB-FN-1043-AD-APC

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 (~109 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)

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Experimental layout

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50-250 MeV e- from injector

IOTA linac dipole
 (D600) IOTA dipoles

• Main dipoles instrumented with vacuum windows, light-transport periscopes, and

light-tight boxes

• Synchrotron light is detected with photomultipliers and on cameras

M1R M2R M3R M4R M4L M3L M2L M1L

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Experimental layout in IOTA

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injection line M3L 60-degree dipole M4L 30-degree dipole light-tight box

IOTA ring on July 27, 2018

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Experimental layout in IOTA

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vacuum
 window mirror 1 mirror 2 synchrotron
 radiation M3L 60-degree dipole electron
 beam lens photomultiplier photomultiplier shutter camera translation stage

• N. Kuklev

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Choice of photodetectors

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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

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Signal processing and data acquisition schematic

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SYNCHROTRON LIGHT PICOAMMETER WAVEFORM DIGITIZER COUNTERS PMT SHUTTER HV AMP FAN-OUT BEAM SYNC DISCRIMINATOR COINCIDENCE DELAY EVENT TIMER REFERENCE OSC.

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Expected signal

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Spectral flux density [photons/pass/eV] D600 300 MeV D600 250 MeV D600 150 MeV D600 100 MeV IOTA 150 MeV IOTA 100 MeV 5 ⋅ 10−5 10−4 2 ⋅ 10−4 5 ⋅ 10−4 10−3 2 ⋅ 10−3 5 ⋅ 10−3 1100 650 450 350 300 250 200 150

Wavelength [nm]

Light transmission [%] 20 40 60 80 100

Window Mirrors Coated lens Total

2 4 6 8 2 4 6 8 10 12 14 MCP−PMT Q.E. [%]

R5916U−50 mod. 2 R3809U−51

Photon energy [eV]

photon flux light transport detector response

IOTA at 150 MeV

Stancari et al., FERMILAB-FN-1043-AD-APC (assumes full cone acceptance)

Typical photoelectron yield is ~ 2×10-4 / e- IOTA at 100 MeV

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

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SRW calculation by J. Jarvis

Energy density per electron per pass in (2.17, 2.75) eV band 60-degree dipoles are preferred 30-degree dipoles show some edge radiation

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Some IOTA experiments with synchrotron radiation

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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)

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)

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100 200 300 400 500 600 700 −50 −40 −30 −20 −10 Time [ns] PMT signal [mV]

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

• scillations, down to single electrons

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

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17.6 17.7 17.8 17.9 18.0 50 100 150 200 Time [h] IOTA M3L PMT counting rate [kHz]

−5 −4 −3 −2 −1 20 30 40 50 Time to end of store [h] Beam lifetime [min]

• 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

Lifetime improves with decreasing beam intensity

reduced lifetime due to lower rf voltage (260 V vs. nominal 560 V) very low beam intensity (50-80 e- in IOTA) exponential model

• f counting rate

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Decay of photon counting rate

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18.1 18.2 18.3 18.4 18.5 200 250 300 350 400 450 Time [h] IOTA M3L PMT counting rate [kHz] 20 21 22 23 450 500 550 600 650 Time [h] IOTA M3L PMT counting rate [kHz]

Towards the end of the store, one observes discrete steps in counting rate…

beam extinction

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

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21.5 22.0 22.5 23.0 410 420 430 440 450 460 Time [h] IOTA M3L PMT counting rate [kHz]

background level 1 electron 12 electrons

Discrete steps are multiples of 3.0 kHz, which corresponds to a single electron Last electron circulated for 4 minutes (2 billion turns) Single-electron experiments are possible in IOTA We have an absolute calibration of low beam currents: (1.203083 pA) × Ne First observation of steps at 100 MeV and without undulator?

IOTA beam experiment of Oct. 31, 2018. Last 12 circulating electrons.

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Light from single electrons on camera

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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

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Conclusions

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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

Backup slides

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Experimental apparatus at D600

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light-tight box shutter synchrotron
 radiation beam
 splitter

8% 92%

camera

• ptional


filters microchannel-plate
 photomultiplier lead-brick
 shielding

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Microchannel-plate photomultiplier (MCP-PMT) features

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Excellent timing (sub-ns) and high gain (103-107). Can be gated. Limited current at high rate. Hamamatsu R5916U-50 mod. 2 reused from Tevatron Synclite.

PHOTONS

Giulio Stancari | Detecting single electrons in IOTA Workshop on single-electron experiments in IOTA | Fermilab, 9 Nov 2018

Previous observations of discrete steps in photon flux

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Riehle et al., NIMA 268, 262 (1988) BESSY storage ring Pinayev et al., NIMA 341, 17 (1994) VEPP-3 storage ring