Beam Instrumentation performance duringcommissioning of the ESS Normal Conducting linac
Irena Dolenc Kittelmann (presenter),R. Baron, E. Bergman, E. Donegani, V. Grishin, H. Hassanzadegan,
H. Kočevar, N. Milas, R. Miyamoto, M. Mohammednezhad, F. Nilen,
D. Noll, K. Rosengren, T. Shea, R. Tarkeshian, C. Thomas

IBIC’23, 12th September 2023 - TU1I02

Outline• ESS facility• ESS linac – overview and commissioning plan• ESS linac Beam Instrumentation– Deployed for the Normal Conducting Linac (NCL) commissioning phase– Key features and contributions for selected systems• Summary2

ESS – European Spallation source• ESS – research facility under construction– Provide neutron beams for neutron basedresearch.
– Neutron production based on bombardmentof a tungsten target with a proton beam
generated by a pulsed linac• Location– ESS currently under construction in Lund,
Sweden– DMSC (Data Management Software Centre)
based in Copenhagen, Denmark• ESS – European project– 13 founding countries– Over 40 European partner institutions– Over 130 collaborating institutions
worldwide– Collaborating under in-kind model3Acknowledgments
We wish to thank all current and former colleagues from ESS and external institutes
for their essential contribution in making the ESS linac project possible
In particular, for help received during the design, development, manufacturing,
installation and testing of the BI systems:• Bergoz (BCM)• CAENels (ICBLM)• CEA (nBLM, IPM)
• CERN (ICBML, Fast WS)• DESY-Hamburg (BCM, BPM)
• Elettra-Sincrotrone (WS)
• ESS Bilbao (EMU, WS, BPM, BCM)
• INFN-Legnaro (BCM, BPM)

• LUT (nBLM, ICBLM)• Pantechnik (LEBT and MEBT FC)• Radiabeam (DTL4 FC)• STFC-UK (BCM, BPM)
• University of Oslo (Target Imaging)• University West (Luminescent coating)• WUT (installation, BCM)
4ESS linac
Overview• NCL - Normal Conducting Linac– Ion Source, LEBT, RFQ, MEBT, DTL (5)• SCL – Superconducting Linac– Spoke (13), MBL (9), HBL (21/5/0)• Beam Delivery and Transport Line– HEBT (contingency, upgrade; up to 16 additional
cryomodules)– Dump line
– dogleg (4o, 4.5m elevation), A2T

ParameterValueAverage beam power – design

5 MWBeam energy – design

2 GeV

Average beam power – initial op.

2 MW

Beam energy – initial op.

800 MeV

Average beam power – 1st beam on Target

1.4 MW

Beam energy – 1st beam on Target

570 MeVPeak current

62.5 mA

Beam pulse length

2.86 ms

Beam pulse repetition rate

14 Hz5

ESS linac

Commissioning• ESS linac commissioning performed in phases.
• First 4 phases– In parallel to commissioning, installation downstreamof the end destination– Completed• Focus here: 4th phase, DTL4 commissioning run

Commissioning
phase end destination

Start - EndEnergy
[MeV]

LEBT

2018/09/19 – 2019/07/03

0.075

MEBT (3 phases)

2021/11/10 – 2022/05/23

3.6

DTL1

2022/05/30 – 2022/07/22

21

DTL4

2023/04/19 – 2023/07/13

74

Dump

2024

570

Target2025

570

Start of user program

2026

800
6

Beam Instrumentation for ESS linac
DTL4 commissioning phase

Systems critical for commissioning andagreed to be operational for certain phase• Formal verification workflow:– Verified in the lab before installation.
– Tested with other systems in the accelerator
environment.
– Verified beam → operational.

• Faraday Cups (FCs)• Beam Current Monitors (BCMs) - TUP038• Beam Position Monitor (BPMs)

Systems deployed for beam studies• At intermediate stage of development• To gain early experience with beam
• Collected valuable data for system development andbeam characterisation– Neutron sensitive Beam Loss Monitors (nBLMs)– MEBT Emittance Measurement Unit horizontal station (EMU-H)• Limited beam studies and offline analysis achieved.

– Wire Scanners (WSs)– Ionisation Chamber based Beam Loss Monitors (ICBLMs) TUP004– MEBT EMU vertical (EMU-V).
– Results not covered here.

7Faraday Cups
3 FCs used during DTL4 commissioning run• Beam end-destination• Measure transported beam current at the destination• 6 MHz BW• 125 MHz sampling rate, typically decimated to 10 MHz

LEBT FC• Designed to withstand full power at the IS exit (74keV)– Beam current 100 mA– Beam pulse length up to 6 ms
– Rep. rate 14 Hz

MEBT FC• Absorption of 3.6MeV beam with current up
to 62.5mA andDTL4 FC• Supported commission activities with:
Beam mode
Probe
Fast com.
RF testSlow com.
Slow tuning

Current[mA]
66662.5
62.5Pulse
length [μs]5150550Rep. rate
[Hz]114110.2 (dose lim.)

Restriction
Total pulses at 21MeV≥39MeV74MeV≥39MeV74MeV• In a dedicated shielding after the DTL4 tank
• The residual dose rate measured to be 1.1 mSv/h after 4
weeks of decay since the end of the DTL4 commissioning.

– pulse length ≤ 5 μs at rep. rate of 14 Hz– Pulse length ≤ 50 μs and rep rate of 1 Hz

8BCMFeatures• 9 BCMs used during DTL4 commissioning phase• Sensors: ACCTs mostly custom-designed by
BergozMeasurements• Beam current measurement

Bergoz ACCT

BE unit– noise level <50μA peak-to-peak,– 0.1 mA accuracy,– 1 MHz BW• Beam current waveform– 88 MHz sampling (raw), configurable for processedsampling• Average beam current over region of interest(ROI), pulse charge• Beam pulse width, pulse repetition rate, arrival
time of beam trigger• Beam loss – differential measurement between
BCM pairs

A high current beam pulse as measured by theDTL4 FC and five BCMs from the ISrc to DTL49BCMFeatures
Machine protection functions• Interlocks– to detect if beam current, pulse width, pulse repetition
rate outside allowed limits;– to detect if beam pulse outside the allowed time window;– on differential measurement with several BCM pairs.

• Thresholds configured automatically based on selectedbeam destination and envelope (“beam mode”(*))• In few cases thresholds adjusted following beam
damage assessment– Mostly to address beam availability issues due to RF
breakdowns and other disturbances [TUP038]• Post-Mortem buffer implemented on FW level tocapture detailed BCM data on beam trip events• Overall reaction time of the BCM system measured tobe ~1 μs

BCM processed waveform (blue) and allowed beam
window (green), recorded with ~3μs, ~2mA beam(*) Beam mode is defined by• max. beam pulse length,• max current and• max rep. rate.
10

BCM

DTL4 commissioning run experience

MEBT chopper leakage• Beam pulse before (RFQ BCM) and after (MEBT BCM) MEBTchopper dump.
• Non-zero floor inside the pulse on MEBT BCM• Observed only on the BCM located just after the chopper dump
(MEBT BCM).
• Leakage due to beam scattered on the chopper dump.
• Effect not observed on BPMs and FC further downstream due togeometrical constraints.

Environment• RFQ BCM:

– Negative spikes at the edges of RF pulse.
– Assumed to be due to multipacting.

• DTL1 BCM, DTL2 BCM– Small baseline changes during the RFpulse.
– Assumed to be due to field emission.
11

BPM

Features
21 BPMs operational during DTL4 commissioning phase• RF systems in NCL operates at 1st harmonic (352.21 MHz)
• BPMs in NCL designed to operate at 2nd harmonic(704.4MHz) to minimize interference• RF processing chain of the signals and data standardised
for all BPMs
MEBT BPMs (8)• Matched stripline sensors• Placed in quads

DTL1-4 BPMs (13):• Shorted stripline sensors• Placed in drift tubes• Stronger interference with RF system observed DTL1
• Strong 1st and 2nd harmonics coupling of RF system atlocations in DTL where drift tubes closer to the RF ports– Leaking to BPM sensors nearby, interfering with the signal– Additional high-pass filters introduced on the BPM inputs tofilter out 1st harmonic that couples into BPM sensors.
– 2nd harmonic spectral leak from RF system is to be improved

12

BPM

Data and DTL4 commissioning experience
FPGA-processed data streams• Raw data from the 4 individualantennas– ~20MHz BW, 88MSa/s• Near-IQ waveforms for positions,magnitudes and beam phases– ~2 MHz BW, 5.8 MHz sampling• Averaged data for positions,magnitudes and phases– available at a rate of 1 per beam pulse,– calculated in a ROI set through timing
system triggers.

DTL4 commissioning experience• BPMs extensively used to characterise thebeam properties.
• Beam studies exploiting BPM data
included– trajectory correction,– phase scans,– longitudinal pulse shape tuning,– beam timing characterisation.

• BPM waveforms crucial for– adjusting machine parameters to optimize
uniformity in pulse characteristics within apulse and– timing characterisations of the beam.
13

BPM

DTL4 commissioning – examples of BPM data
BPM measurements reported during a phase scan
(MEBT buncher 3):• BPM phase difference and BPM amplitude as afunction of cavity set phase for different cavity setvoltages• Optimal cavity set phase– 90o from max. acceleration– BPM phase difference curves crossing– BPM amplitude peak

Stability run - data collected with a BPM in MEBT• Top: 2D histogram, distribution of BPM averagephase and amplitude per pulse• Collected over 4 hours of operation with 6 mA
and 5 μs beam
• Bottom: projection on x-axis– average phase distribution during the run– stability of machine and the BPM together

14Bunch-by-bunch characterisations
FBCM and FBPM

Fast BPM (FBPM) and Fast BCM (FBCM)• Provide high bandwidth and high sampling rate
(20 GSa/s) measurements• For bunch-by-bunch characterisation of the beam
– To verify MEBT and LEBT chopper rise and fall times– Precise timing alignment of the two choppers.

FBCM:• Confirm Rise/fall time of the beam after MEBT chopper• Measuring individual bunches• Both in MEBTFBCM• Based on Bergoz Fast Current Transformer (FCT)• 700 MHz BW
FBPM• 2 regular stripline BPMs, 30.1 cm apart• 3 GHz analogue FEE with matched propagation
delay between channels (±50ps)• Able to measure beam energy with with accuracyof ~ ±20keV and precision ~ ±100keV15

Bunch-by-bunch characterisations
Interlock reaction timeReaction time of the complete interlock chain• Characterised with FBPM
• Controlled interlock induced on BCM
located just after MEBT chopper dump bylowering the threshold on maximum current• Full chain reaction time consist of– Reaction time of BCM– signal transmission to FBIS, FBIS processing time,– signal transmission to systems acting to stop thebeam production (LEBT, MEBT chopper),– time for systems to dump the beam

Fast Beam Interlock System (FBIS) at ESS:
• A detection system (BCM, BLM, etc) detects
unacceptable beam conditions - request to stop
the beam send to FBIS
• FBIS utilises several systems to inhibit beam
production – LEBT and MEBT chopper to dump
the beam propagating through the front end of thelinac• Reaction time measured– With MEBT and LEBT chopper: ~2.3 μs– With only LEBT chopper: ~3.2 μs– Difference due to the beam stored in the machine
between MEBT and LEBT chopper at the time ofthe interlock.
– MPS requirement: 3 μs
16EMUDesign• MEBT EMU: slit-grid type• Slit– 368 mm upstream of grid– 2 graphite plates to collimate the beam reaching thegrid– 0.1 mm aperture– Select a slice of beam phase space and project it on thegrid.

pitch• Grid– 24 tungsten wires, 0.5 mm pitch– Grid PCB (A) surrounded by bias plates (B)• Biased up to ±1.2kV.
• To control the electric field experienced by the secondaryelectrons.

– Additional tungsten wires (F) mounted on the bias
plates to enhance the field created by the plates.

• DAQ– Signals acquired through configurable gain stages– Followed by 5MSa/s digitiser

F17

EMU

DTL4 commissioning run - results
Activities during DTL4 run:• Signal quality investigations.
• Initial beam studies.

Observations:• Bias 0V:

Scanning result for horizontal plane (at 1kV)
• Multiple slit scans• Bias >500V:– grid position shifted by 0/3, 1/3 and 2/3 ofwire pitch– To improve angular resolution → 167 μmresolution– Significant contribution from SEE (neg. signal) picked
up on wires adjacent to those exposed to beam
– Negative signals supressed– Positive signal enhanced by factor ~4• Signal measured with 30 μs beam pulse– Integrated over final 15 μs– First 15 μs: evolution in emittance (likely fromSC compensation in LEBT)• Background over entire range of measured x’– Assumed to be due to beam scattering– Found to follow Gaussian shape– Preliminary analysis indicates RMS emittanceclose to the value expected from beam physics
model18

BLMSystems
2 types, differing in detector technology• ICBLM – Ionisation Chamber based BLM– 266 parallel plate ionisation chambers (based on LHC BLM chambers),
almost exclusively in high energy parts of the linac [TUP004]– Real-time (FPGA) data processing of the raw detector signals providing
induced current measurements at 1MHz rate on the FW level• nBLM – neutron sensitive BLM– 82 neutron detectors (Micromegas, CEA), mostly lower
energy part of the linac– nBLM-F (fast) – for fast losses with high particle fluxes– nBLM-S (slow) – for losses with low particle fluxes– Raw signals sampled at 250 MHz (~140 MHz BW) for further processing(FPGA)– Discriminate fast neutrons from background (RF photons, slow neutrons)on event-by event basis – neutron rates at 1MHz on the FW level• Available FPGA processed data:– For monitoring and machine protection purposes– Detailed data from various stages of processing (on demand)
19

nBLM

DTL4 commissioning run• 36 nBLMs– MEBT: 2 × 2– DTL1 - DTL4: 4 × 8• Collected data
– To study system performance, background,procedure for setting system configuration.
– Continuously collecting detailed partiallyprocessed and monitoring data during lastfew weeks of the DTL 4 commissioning run.
– Dedicated experiments .

nBLM installation in DTL

DTL nBLM• Different set of beam parameters constant during
30min – 1h time window.
• Controlled loss.

– Offline analysis ongoing.
MEBT nBLMs
20

nBLM

DTL4 commissioning run - resultsnBLM-F, close to end of DTL4:• Neutron event (single, pileup) distribution overtime in machine cycle (~2-2.5h time window)• Demonstrate pulse width and its location inside
the machine cycle consistent with expected values.
~5 μs
beam pulse

Average neutron events (single, pileup) per beam pulse - preliminary:• nBLM-F:– Peaks at the end of DTL3 and DTL4 consistent with observations fromactivation surveys– Peak at end of DTL1: majority of particles outside of the DTL1 acceptanceare expected to be lost at the end of DTL1.

• nBLM-S:– Pileup: event rate defers from actual neutron rate
– Ongoing analysis to account for that, input to neutron detection algorithmnBLM-F~50 μsbeam pulse

nBLM-S21

Summary
Example of interesting developmentwork at ESS on Luminescent coating(C. Thomas) of the Target wheel for
the Target Imaging• NCL commissioning phase completed.
• Required beam instrumentation successfully
supported the NCL commissioning phase.
• Continued to install SCL and transport line
instrumentation in parallel with the NCL
commissioning activities.
• Upcoming commissioning phases:– 2024: initial commissioning of the entire SCL andtransport line to the Dump
– 2025: first beam on Target by transporting beamthrough dogleg and A2T.

• Additional instrumentation downstream ofDTL4:– 10 BCMs - TUP038– 77 BPMs– 46 nBLMs, 262 ICBLMs - TUP004,– 5 Ionisation Profile Monitors - TUPD36 and 11 WSs– 4 Aperture Monitors systems,– 3 Target Imaging – to monitor uniformity of beamraster on the target.

Target Wheel
Coating

Downstream of DTL–
before spoke installation start.
Spoke installation
ongoing22