BTF microbunching structure with Micro-Channel Plate PMT Francesco Iacoangeli, Gianluca Cavoto INFN – Roma

Introduction A prototype for the Cherenkov detector for proton Flux Measurement (CpFM) of UA9 experiments was tested in October 2013 at the Frascati BTF. See M.Garattini’s talk. The aim of test beam was to measure the performance of optical coupling and the detection efficiency of a CpFM prototype. Some different setups were studied. The angular scan and intensity scan were run so as to find the best configuration for final CpFM of UA9. During system’s characterization the structure of microbunching appears on the waveforms

Detector The CpFM prototype is made up of a fused silica radiator and a Micro-Channel Plate photomultiplier (MCP) coupled together (directly or through a fiber bundle). Fibers/MCP adapter Fiber Bundle Cerenkov Radiator MCP hamamatsu R3809U Series Holder with thin window

Cerenkov radiator The used Cerenkov radiator has a geometrical coupling not optimized The Cerenkov detected light per electron depends on details of light reflection and diffusion in the radiator and at the radiator-PMT interface Radiator surface 21 mm MCP Area 11mm

Photo detector Micro Channel Plate Hamamatsu PMT with Fast Time response: Pros: -Typical Rise Time: 150ps -Typical Fall Time: 350ps FWHM < 50ps Low noise Cons: The effective photocathode area is a circle with diameter 11mm  Only a part of Cerenkov radiator is coupled (11mm x 21mm rectangular section)

Readout electronics Oscilloscope Lecroy WaveRunner 6 Zi : Bandwidth : 1Ghz Resolution: 8-bit Sample rate: 10 Gsample/s The bandwidth and the sample rate of oscilloscope isn’t optimal to see the microbunching structure

Hand Platform Rotation Stage Test Setup BTF Calo (Pb Glass Cerenkov) Čerenkov Radiator Oscilloscope MCP-PMT Signal Ethernet Beam window Control Room PC Hand Platform Rotation Stage

Typical Waveform 5 e- event Volt 5 e- event 100ps/div - Due to fast time response of MCP-PMT, Waveforms can show the peak of each micro bunch. - The measured charge of each peak should be proportional to number of electrons contained in the micro-bunch

Given the type of waveform the total charge of the signal is more significant than its amplitude Unfortunately in the tested configuration the charge of a single particle event is significantly fluctuating Nevertheless we tried to understand if it’s possible to use the CpFM to study the microbunching structure of BTF beam

Charge distribution Ne=1.5 Ne=1.5 Charge was calculated on a 40ns window centered on pulse minimum Events with zero electron was suppressed The plot of charge for nominal multiplicity of 1.5 e- shows the CpFM (MPC plot) isn’t good to discriminate single electron events

Charge resolution Ne=1,5 Ne=1,5 RMS/mean=0,16 RMS/mean=0,57 We considered the events selected by the first peak of CALO charge spectrum in order to estimate the resolution on single particle regime of CpFM RMS/mean ratio value shows a big variance for CpFM with single electron events.

Efficiency Efficiency=1- (MPC pedestal events) −(Calo pedestal events) Events –(Calo pedestal events) = 0,79 Ne=1,5 Ne=1,5 Overflow Events=1377 Overflow Events=3329 - pedestal values of charge for CALO and MPC were cut The ratio of efficiency of CpFM , normalized on CALO no-zero e- events is: 79%

Waveform persistence CpFM - Ne=35e- events CpFM zoomed - The persistence of waveform show that the CpFM prototype can discriminate the distribution of particles within the 10ns long bunch CALO - We found a two-peak shape of distribution that need to be explained (maybe due to gun RF ripple ?)

Time measurements MCP threshold CALO threshold Single Electron Event The thresholds to perform time measurements were selected depending on minimum observed signal in single particle regime but to reject background The values of threshold were fixed for all multiplicity of beam.

Time distribution The delay between Trigger (LINAC NIM trigger signal) point out the time distribution of particles on the 10 ns bunch. Ne=1,5 10 ns We don’t know the cause of the 2 distinct distributions on CALO delay histogram,. Ne=1,5 10 ns

Time resolution - Time resolution measurements were performed with multi-particles events (Ne=236) so as to have at least 1 particles in the first microbunch. RMS=266ps Ne=236 RMS=455ps 10 ns In this case too, we don’t know the cause of the 2 distinct distributions 20 ns We measure the delay from trigger edge (LINAC NIM Timing signal) of the first particle of each event The CpFM take out a distribution similar to the CALO’s one but by far less light

Conclusions The CpFM prototype was not optimized to perform time measurements and readout electronics bandwidth should be upgraded for fast timing signal, nevertheless we can recognize the microbunching beam structure Efficiency and resolution are quite affected by fluctuation on light detection: a suitable geometric coupling can decrease the ligth loss Performing a new data-taking, with a better geometrical match and fast timing readout electronics, will be good to improve the measurement the microbunching structure Eventually this system could be integrated as a BTF beam monitor detector.

SPARE

BTF Setup Diamond LAL Cerenkov INFN Cerenkov e- Beam BTF Remote Control Table BTF Calorimeter

Geometrical efficiency and optical coupling Bundle of fiber spot Lower light collection efficiency due to geometry: MCP-PMT area: π(11mm/2)2=95 mm2 Fibers cable area: 25π*(0.6mm/2)2=7.07mm2 Geometrical efficency ratio: 7/95 = ~7 % 10 mm 20 mm 75 mm ± 5 mm Electron’s beam Remaining efficiency losses due to optical coupling and fibers attenuation = 7/3.3 = ~ 50 %

Direct contact VS Fibers 47˚ (normalized to electron path length into the radiator) Charge per Electron Radiator/beam angle With fibers bundle the light detected per electron are 30 times less

Radiator with fibers bundle Charge per Electron (normalized to electron path length into the radiator) 47° Radiator/beam angle

Fiber’s bundles Bandle 1: Bandle 2: Fibers: Fibertech Type AS600/660 UVST Coating 780 μm Silicone Jacket 940 μm Tefzel 0.6 dB/m at 350 nm We tested 2 different bundles of same fibers Bandle 1: Homemade Fibers hand-cut by diamond wheel lapped with glass sand papers with increasingly grit (400 - 1200) Length: ~ 13 cm Bandle 2: Manufactured by Fibernet lapped with industrial lapping process Length: ~ 47cm 1 fiber cracked on manufacturing 

Time precision The separated plot of each distribution show a RMS of 266ps for the first and of 455ps for the second. This is promising to repeating the measure with more performing readout electronics

Time distribution 1e- Ne=1 10 ns measure window 10 ns