Beam Loss Monitor activities at CTF3 and the Australian Synchrotron CLIC Workshop 18 January 2015 M. Kastriotou, E. Nebot del Busto M. Boland, E.B. Holzer, C. P. Welsch all CTF3 operators …

Outlook 1.The OBLM system 2.Test Beam Line (TBL) o Long pulses 3.Australian Synchrotron Light Source (ASLS) o Single bunch o Multi bunch 4.Two-Beam Module (TBM) o First beam loss crosstalk studies 5.Dogleg experiment o RF cavity induced background 6.Conclusions CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors2 Optical fibre BLM BLM Background Position resolution

Optical fibre Beam Loss Monitors (OBLMs) OBLM system is based on Cherenkov light Cost-effective, n,γ insensitive, covering long distances → ideal for linacs Optical fibre: o Pure Silica, high OH content, variable core Ø depending on application o Nylon jacket to protect against: humidity, ambient light CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors3 Photo sensor Photo sensor c 2c/3 beam pipebeam optical fibre γ Cherenkov

Optical fibre Beam Loss Monitors (OBLMs) OBLM system is based on Cherenkov light Cost-effective, n,γ insensitive, covering long distances → ideal for linacs Optical fibre: o Pure Silica, high OH content, variable core Ø depending on application o Nylon jacket to protect against: humidity, ambient light Development of custom made, shielded photon sensing modules o Silicon PhotoMultiplier (SiPM) (3x3 mm 2, default pixels, G = ) o Low pass filters (bias input) for noise filtering CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors4 Photon sensing module SiPM readout SiPM

Optical fibre Beam Loss Monitors (OBLMs) OBLM system is based on Cherenkov light Cost-effective, n,γ insensitive, covering long distances → ideal for linacs Optical fibre: o Pure Silica, high OH content, variable core Ø depending on application o Nylon jacket to protect against: humidity, ambient light Development of custom made, shielded photon sensing modules o Silicon PhotoMultiplier (SiPM) (3x3 mm 2, default pixels, G = ) o Low pass filters (bias input) for noise filtering Design of RF shielded chassis to include the modules High sampling (1-4 GS/s) and high bandwidth (250 MHz - 2 GHz) ADCs CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors5 Shielded crate Photon sensing module

OBLM at the TBL CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors6 Signal subtraction to account for showers from TBL only Optical fibre at the TBL Background fibre Signal fibre Real signal fibre 28 m Connecting fibre 25 m Connecting fibre 75 m 120 MeV 3 A (peak) 3 GHz µs

TBL: losses with long bunch trains Observing losses from a 1µs long pulse o Controlled losses generated by switching off quadrupoles o BPM signals to correlate CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors7 TBL

TBL: losses with long bunch trains Observing losses from a 1µs long pulse o Controlled losses generated by switching off quadrupoles o BPM signals to correlate CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors8 Nominal Q500 off Q550 off Q600 off Signal (V)

TBL: losses with long bunch trains Observing losses from a 1µs long pulse o Controlled losses generated by switching off quadrupoles o BPM signals to correlate CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors9 Nominal Q500 off Q550 off Q600 off Signal (V)

CTF3: losses with long bunch trains (II) CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors10 Determination of loss location from signal leading edge o Good qualitative agreement between oBLM and BPM profile loss measurements Localisation of loss down to (below) 2 m achieved! TBL Plans for 2016: Position resolution for long bunch trains, multi-loss location

Installation at the ASLS 216 m storage ring Many similarities to the CLIC Damping Rings 2 optical fibres covering the ring o 200 μm core Ø o 125 m Scraper fibre o Scraper o Injection point RF fibre o 2 In Vacuum Undulators (IVUs) o 2 RF cavities CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors11 Australian Synchrotron Light Source 3 GeV 200 mA 500 MHz 1-75 b inj. 100 MeV

AS: understanding beam losses, single - bunch M. Kastriotou - Beam Loss Monitors Scraper Fibre RF Fibre IVU3 IVU5 Injection Point Transfer Line Scrapers Storage Ring Scrapers Reflexion Scrapers 1 turn 1/10 turn IVU3 IVU5 Multi peaks observed due to losses in different positions CLIC Workshop

AS intrinsic time resolution Single bunch injection o Consecutive filling RF buckets 1-10 o Looking at raising edge of losses at scrappers (well defined location) One bucket (2 ns) shift disentangled shot by shot! CLIC Workshop 2016 M. Kastriotou - Beam Loss Monitors13 Position resolution <10 cm can be achieved !

AS: understanding beam losses, multi - bunch M. Kastriotou - Beam Loss Monitors Multi peaks observed due to losses in different positions o Rising edge still provides loss location information o Signal de-convolution required for losses in near positions Injection Point Transfer Line Scrapers ?? Storage Ring Scrapers Scraper Fibre RF Fibre 1 turn 1/10 turn IVU3 IVU5 CLIC Workshop Position resolution for multi-bunch and sensitivity for steady- state losses under investigation

BLMs at the TBM Installed detectors: o Little Ionisation Chambers (LIC) (CDR suggested) o OBLMs pixel SiPMs Motivation: measurement of BLM so-called beam loss “crosstalk” on the TBM o “Crosstalk”: losses of one beam line detected by the BLMs protecting the other → limitations in sensitivity of CLIC BLMs → study of the radiation on one beam line due to beam losses of the other CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors15 MB2 LICs 5 cm downstream of the AS7 m long Ø365 μm SiO 2 optical fibre, 4 m upstream the TBM DB 2 LICs 10 cm downstream of quads5 m long Ø200 μm SiO 2 optical fibre, 2 m upstream the TBM Photosensors at the downstream end of the fibre! SiPM

Measured crosstalk Average beam charge calculated from the BPMs Crosstalk calculated as: Crosstalk 1→2 = Q 2 /Q 1 3 types of measurements: 1. Main Beam (on) → Drive Beam (off), 1. Good MB transmission 2. Loss scenario: Insertion of OTR Screen in Califes 2. Drive Beam (on) → Main Beam (off) CLIC Workshop 2016 M. Kastriotou - Beam Loss Monitors 16 BLM integrated charge

Crosstalk during nominal Main Beam Califes good beam transmission o 100 shots acquired for increasing beam current o Losses detected by OBLMs only o High OBLM sensitivity → Dark current from electron gun monitored CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors17 Beam loss Dark current MB OBLM

Crosstalk during nominal Main Beam Califes good beam transmission o 100 shots acquired for increasing beam current o Losses detected by OBLMs only o High OBLM sensitivity → Dark current from electron gun monitored o Crosstalk measured at 3.4 % CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors18 Beam loss Dark current

Crosstalk during OTR screen insertion OTR screen insertion in Main Beam to induce losses o OBLM photodetector saturates o Losses detected by LICs o Crosstalk <1% CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors19

Drive Beam crosstalk to the Main Beam One set of measurements (100 shots), low Drive Beam current, 1.12 A o Bad beam transmission o OBLM photosensor saturates o Losses detected by the LICs o Crosstalk ~4 % CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors20 TBM Plans for 2016: Repeat with new setup (new pixel SiPMs) Cover the downstream side of the TBM “Read” the upstream of the fibre More conditions (good DB transmission, combined beam, TBM operation etc)

Installation at the dogleg – RF cavity background More than RF cavities in a 3 TeV CLIC o Background from electron field emission and RF breakdowns? Dark current sensitive system installed at the dogleg experiment (T24) o 900 μm OBLM pixel SiPM+ transimpedance amplifier CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors21 mA, accelerated 100 A, EM field collapses “Field emission and RF breakdown current measurements using optical fibre BLMs”, M. Kastriotou, Tue, Session 3

Measurements of RF cavity background Potential limitations due to RF cavity electron field emission CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors22 Sensitivity to RF breakdowns Sensitivity to field emitted electrons → RF cavity diagnostics tool ? Dogleg Plans for 2016: Continue with TD26 Loaded/unloaded comparison Diamond detector installed

Conclusions CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors23 First attempt at loss location reconstruction with long (1μs) pulses Resolution better than 1.4 m achieved for single loss location OBLM system was demonstrated suitable for the CLIC damping rings Position resolution below 10cm can be achieved for single bunch Sensitivity requirements previously verified (IBIC14) First measurement of beam loss crosstalk to BLMs at TBM Potential limitation of BLMs due to RF cavity dark current and RF breakdown Thank you for your attention!

Back up CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors24

CLIC BI review Most studies performed on losses generated in the first turn Sect 9 Upstr - Downstr v Q = c/n Q ~ 0.7 c 108 m Upstr - Downstr v Q = c/n Q ~ 0.7 c Sect 2 x = 0 m x = x 2 x = L FIB = 125 m L RING = 216m Beam in Storage Ring Beam in Transfer Line Injection point (t 0 ) Scrapers (t 0 + L/c) L = L RING - (x 1 - x 2 ) x = x 1 FIBRE GAP Two loss points on opposite sides of FIBRE GAP Two loss points on same side of FIBRE GAP Understanding Beam Losses

Calculations Mean value of the detected charge (C) Calculation of the Cherenkov photons that have given this signal o Readout circuit design o SiPM Gain Estimation of the number of electrons that, if crossing the fibre, would have resulted in this number of Cherenkov photons in the end of the fibre, taking into account o Light attenuation in the OF o Wavelength distribution of photon yield (~1/λ 2 ) o Angular dependency of photon yield and photon propagation o SiPM efficiency dependence on wavelength o Assumption 1 : β=1 o Assumption 2 : uniform angular distribution of e - ( 0 ◦ - 90 ◦ ) Jan 19, 2016M. Kastriotou CLIC Workshop26 θ e-e-

AS intrinsic time resolution & Booster phase shift Repetition with Booster RF phase shift by 180 ◦ o V oBLM (t = t photon ) = V thr o t photon → Photon arrival time (to upstream end) Time resolution study based on Δt = t photon – t mean t mean = t off + n bucket x T RF (central time of n th bucket) CLIC Workshop 2016 M. Kastriotou - Beam Loss Monitors27 σ t ≲ 300 ps σ x ≲ 4 cm

ASLS multi-bunch current CLIC Workshop 2016M. Kastriotou - Beam Loss Monitors28 Current profile of 75 bunch train