IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 4 4“INSTANTANEOUS” LIFETIME MEASUREMENT IN STORAGE RING
WITH TOP-UP INJECTION*
Igor Pinayev†, Brookhaven National Laboratory, Upton, NY, USA
Abstract
Top-up operation becomes routine in the light sources.
The goal of the top-up operation is to keep the current ofthe circulating beam stable to avoid variations of the heatload on the beamline optics. It is also considered for theelectron-ion collider to maintain the polarization of theelectron beam. Frequent re-injection makes measurementof the beam lifetime very difficult if possible. Since, only
part of the bunch train is refreshed during the injection cycle then the distribution of the bunch charges in the train
has a characteristic saw-tooth distribution. The slope ofsaw tooth is defined by the lifetime and filling frequency
and can be used for the measurements. The data for processing can be obtained either from fast current transformer or from the raw ADC signal from beam position
monitor. In this paper we present the theoretical considerations as well as experimental data from NSLS-II storagering.

filters define the rising and falling of the induced train as
well as ringing down as one can see the in Fig. 2. After
amplification the signal is sampled with analog-to-digitalconverter [3]. The ADC sampling rate is chosen so that
there are 310 readings per turn. The clock is phased locked
to the RF frequency. The down sampling results in the500 MHz signal being converted into the 80 periods perturn. There is possibility to extract buffer of 100000 consecutive ADC readings per channel (more than 322 turns)
for the offline analysis.

TOP-UP OPERATION OF THE NSLS-II
To satisfy requirements of the beam stability NSLS-II
storage ring operates with top-up. Presently, around 1200
buckets out of 1320 are filled. The stored current is
400 mA, and lifetime is around 12 hours as shown in
Fig. 1. Each 200 seconds approximately 100 bunches are
injected into the ring to maintain current level [1, 2]. Therefore, top-up cycle takes 40 minutes. In the electron-ion collider being built at Brookhaven National Laboratory the refill is expected each two seconds making conventional lifetime measurement harder.

Figure 1: Screenshot of NSLS-II status showing stored
beam current and beam lifetime of 11.7 hours from theDCCT data between injections.

NSLS-II BEAM POSITION MONITORSNSLS-II BPMs are processing 500 MHz signal inducedby the circulating beam. The parameters of the bandpass___________________________________________* Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy† pinayev@bn.gov

Figure 2: Raw ADC signal from NSLS-II beam position
monitor. The visible modulation is due to the limited sampling rate (just below four readings per period).
To evaluate the signal level evolution along the train thesliding window was used. The user defined number of data
samples around the current ADC clock were used to perform sine wave fit and the amplitude of the wave was usedas signal strength. The 310 samples were padded with zeros on both sides for these calculations. The result is shownin Figs. 3 and 4. The sliding fit was using 11 points to smear
the modulation caused by artefacts in the NSLS-II injection
complex. The step down is clearly visible near ADC
clock 236. The amplitude of the step as well as average amplitude can be used for the evaluation of the beam lifetime(in assumption that injection is stable in time) from the period of the top-up:
𝜏𝑇

〈〉

(1)

The step was calculated as difference between two linear
fits on the left and on the right sides shown in Fig. 4. The
modulation of the intensity is caused by modulation ofcharge trains in the NSLS-II injection system.

MOP04407 Machine Parameter Measurements

125

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 4 4Figure 3: Amplitude of the BPM signal along the bunchtrain. Two red lines shows linear fit of the latest filled (left)and earliest filled (right) parts of the train. The estimatedlifetime is 10.6 hours.

Figure 5: Lifetime measurement from the slop of the amplitude. The region selected is just before the step down.

CONCLUSION
Preliminary analysis of the BPM data from NSLS-II
showed feasibility of using raw BPM data for an “instantaneous” measurement of the lifetime. The measurement accuracy can be adversely affected by modulation of injectedbeam amplitude as well as drifts in the delivered charge.

ACKNOWLEDGEMENTS
Author would like to thank Victor Smaluk from NSLSII for collecting and providing BPM data.

REFERENCES[1] R. Fliller, A.A. Derbenev, T. Shaftan, G-M. Wang, “Top Off
Algorithm Development and Commissioning at NSLS-II,” inProc. 7th Int. Particle Accelerator Conf. (IPAC’16), Busan,Korea, May 2017, pp. 2988-2990.

Figure 4: Zoomed in view on the step in the fill pattern.
As it was mentioned before the top-up operation causes
the saw-tooth modulation of the bunch charge since thetime from the injection into each bunch varies with its position in the train. Slope in the fill pattern can be used forlifetime measurements as well as it is shown in Fig. 5. The
slope is measured as growth rate of the amplitude per ADC
clock, time “span” is virtual fill time difference between
the first bunch and the last bunch in the sequence (it is not
actual time since the train of 100 bunches is injected). The
modulation of the fill pattern can affect the accuracy of themeasurement as well as stability of the injection system.
For example, if all data between ADC samples 20 and 230
is used the calculated lifetime will grow to 18 hours, most
likely due to the excessive charge injection into the region50-150 ADC clocks.

doi:10.18429/JACoW-IPAC2016-WEPOW060[2] R. P. Fliller, A.A. Derbenev, V. Smaluk, X. Yang, “Top Off ofNSLS-II with Inefficient Injector,” in Proc. 9th Int. Particle
Accelerator Conf. (IPAC’18), Vancouver, Canada, May 2018,
pp. 1327-1329.
doi:10.18429/JACoW-IPAC2018-TUPMF036[3] K. Vetter, J. Mead, B. Podobedov, Y. Tian, W. Cheng, “TheBNL EBPM Electronics, High Performance for Next Generation Storage Rings,” in Proc. of North American Particle Accelerator Conf. (NAPAC2016), Chicago, IL, USA, October
2016, pp. 1-5.
doi:10.18429/JACoW-NAPAC2016-MOA2IO02

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07 Machine Parameter Measurements