TUP038

BCM System Optimization for ESS Beam Commissioning through the DTL Tank4
H. Hassanzadegan1, R. A. Baron1, K. Czuba2 , S. Gabourin1, P. K. Jatczak2 , H. Kocevar1, M. Mohammednezhad1, J. F. Murari1, S. Pavinato1, K. Rosengren1, T. Shea1, R. Zeng1
1European Spallation Source ESS ERIC, Lund, Sweden
2Warsaw University of Technology, Warsaw, Poland

Introduction
The ESS BCM system is not only used for beam measurement but it also plays an important role for machine protection particularly in the normal-conducting part of the linac.
During the previous beam commissionings to the MEBT and DTL1 FCs and before the cavities were fully conditioned, RF breakdowns and other types of discharges in the cavities
had a major impact on beam availability due to the Fast machine protection functions of the BCM. Following an investigation on the root cause of the beam trips, the configurationof the machine protection functions was modified to improve beam availability in the more recent beam commissioning to the DTL4 FC. In addition to this, some optimizations
were made in the BCM system to improve beam measurement, and a few more functions were added based on new requirements. Here, we report on these improvements andthe results obtained during the beam commissioning through the DTL4.

BCM System Overview

BCM Machine Protection Suite- 19 Bergoz ACCTs: 9 in the normal-conducting and 10 in the superconducting part ofthe linac.
- One Fast BCM in the MEBT.
- Wall-mount FE unit including Bergoz ACCT-E.
- Rack-mount BE unit including customized electronics for signal filtering, fanout,
voltage/impedance matching, ACCT auto calibration, network connection etc.
- uTCA crate including:Beam-mode-dependant thresholds on:- Pulse amplitude- Pulse length- Trigger length- Trigger frequencyoooooo

NAT Power supply
NAT MCH
Concurrent Technologies CPU
Struck SIS8900/SIS8300-KU
MRF Timing
AMC for RS485/optical interface- Customized BCM FW for beam measurement and machine protection.
- EPICS IOC

Absolut (above) and differential (below)
beams with the RFQ-MEBT1 differential pairBeam-mode-independent thresholds on:- Errant beams- Beam exist- Differential beams:
o Fasto Medium-speedo Slow

Beam expected and errant mask windows

Beam Availability Issues/Solutions
Spike/disturbance summary:- EMI in the ISRC:-BCM Measurements-Measurement noise: < 50 μA peak-peakAccuracy: < 0.1 mA
Bandwidth = 1 MHz
Per-pulse measurements:
oooooo HVPSo High power contactors
o Safety (i.e. ground) relay

An RF breakdown in the DTL2 causing ringing with theother BCMs (with cal. windings being connected)

RF breakdowns in the DTL
RF/vacuum breakdowns in the MEBT buncher 3 cavity
Broken insulator around the LEBT repeller ring causing sparks
Induced current in the series-connected ACCT calibration windings due to DTL RF
breakdowns

Action items for fixing the beam availability issues:

Average beam current over a ROI
Pulse charge
Pulse width
Pulse frequency
Beam pulse presence with the ISrc, LEBT and MEBT BCMs

- The ISrc EMI issues were resolved through:- Voltage of the ISrc platform (using a voltage divider).
- Supplied current to the ISrc (ACCT on the HVPS cable to the platform)

oooo

Grounding of the ISrc cage and the electronics racks was improved.
Additional shielding (i.e. flexible conduits) was installed on the ACCT cables to the ISrc/LEBT ACCT FEs.
EMI filters were added to the input power of the ACCT-E power supplies.
Surge protectors and filters were installed on the cable from the ISrc voltage divider.

- The Fast upper/errant interlocks in the DTL were replaced by Medium-speed
differential interlocks.
- Calibration windings of the DTL ACCTs were disconnected after the in-site
tests/verifications were completed and before starting with beam.

Summary and outlook
A low current beam pulse measured by 8BCMs from the LEBT to the DTL4

A high current beam pulse measured by 9 BCMs fromthe ISrc to the DTL4, and a FC at the end of DTL4.

Other improvements- A Fast BCM (i.e. FCT) with BW=700 MHz at the MEBT end measures:o 10 ns rise/fall time of the beam pulseo Individual proton bunches- New RS485/optical AMC (collaboration with WUT-Poland) for improving the BCMFBIS interface.
- A special BCM channel with sub-μA accuracy was tested and verified with beam.

FCT signal measured by a fast oscilloscope

LVDS to RS485/opticalconverter AMC

20-h history of the charge-per-pulse and the 1hour average beam current

During the ESS beam commissioning through the DTL tank 4, nine BCM channels weresuccessfully used for beam measurement, machine protection and timing
synchronizations. At the start of the commissioning, the beam availability was impacted
by a large number of beam trips due to spikes on the BCM readouts. An investigation
then showed that the spikes were partly due to EMI and other types of external
disturbances, and partly due to RF / vacuum breakdowns particularly in the DTL section.
The issue was then resolved by addressing the EMI issues and reconfiguring part of theBCM protection functions to make them less sensitive to the spikes but sensitive enoughto beam losses that pose a damage potential. During the same commissioning run, a Fast
BCM, a Medium-speed differential interlock and a special BCM channel with sub-μA
measurement accuracy were successfully tested and verified with beam as well. It isplanned to continue with the BCM activities in 2023-2024 by installing in total ten newBCMs in the DTL tank 5 and the superconducting part of the linac as well as three BCMs
in a new ISrc-LEBT Test Stand that is under construction. It is also planned to make theBCM-FBIS interface more robust by deploying a newly developed RS-485/optical interface
module. The other parts of the system including the electronics, FPGA firmware,
software and the operator interfaces have already become mature following a few
rounds of improvements, hence no major changes are planned in the near future.

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