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

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V. Scarpine†, B. Fellenz, A. Semenov, D. Slimmer
Fermi National Accelerator Laboratory, Batavia, IL, USA
Abstract
The Mu2E experiment will measure the ratio of the rateof the neutrinoless, coherent conversion of muons intoelectrons as a measure of Charged Lepton Flavor Violation.
As part of the Mu2E experiment, a proton storage ring,called the Delivery Ring, will utilize resonant extraction toslow-spill protons to the experiment. To regulate and optimize the Delivery Ring resonant extraction process, a fasttune measurement scheme will be required. This Mu2E
tune meter will measure the average tune and the tune spectrum, in multiple time slices, through the entire resonant
extraction cycle of nominally 43 msec. The Mu2E tune
meter system utilizes vertical and horizontal 21.4 MHz
Schottky detector resonant pickups, taken from the decommissioned Tevatron, high-gain amplifiers and digitaldown-conversion FPGA logic for its signal processing.
This paper will present the design of this Schottky tune meter as well as tune measurements from the Mu2E deliveryring.

low noise RF amplifiers, bandpass filters and a high-speed
FPGA-based DAQ board.

Figure 1: Mu2E delivery ring beam parameters.

MU2E SLOW SPILL
The Mu2E experiment will search for the charged-lepton
flavor violating process μ−N → e−N [1]. Mu2E proposes tomeasure the ratio of the rate of the neutrino-less, coherent
conversion of muons into electrons in the field of a nucleus,
relative to the rate of ordinary muon capture on the nucleus.
This requires the resonant extraction of a stream of pulsed
beam, comprised of short micro-bunches (pulses) from theDelivery Ring (DR) to the Mu2e target [2].
Mu2e uses 8 kW of 8 GeV protons extracted from theFermilab Booster. Figure 1 show a table of key DR beam
parameters. Once 1e12 protons are injected into the DR,
beam is then slow extracted to the Muon proton target atthe DR revolution frequency of 590.08 kHz over a nominally 43 ms spill period. Between each spill period, thereis 5 ms reset period, in which there is no extraction. Afterthe 8th spill, there is no beam in DR for 1.02 s. Figure 2
shows the Mu2E DR intensity timeline for eight slow
spills.
By exciting two families of the harmonic sextupoles inthe DR, the third integer slow-spill resonant extraction condition is established [3]. Figure 3 shows the modelledchange in the DR tune along a single slow spill along withexpected data points from this tune meter system.

Figure 2: Mu2E slow spill beam timeline.

Figure 3: Expected tune along slow spill.

MU2E TUNE METER SYSTEM
The Mu2E tune meter system, shown in figure 4, consists of 21.4 MHz inductively resonated stripline pickups,___________________________________________* This work was supported by the U.S. Department of Energy undercontract No. DE-AC02-07CH11359.
† Scarpine@fnal.gov

Figure 4: Mu2E tune meter system.

WEP03307 Machine Parameter Measurements

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A Schottky Tune Meter for the Fermilab Mu2E Delivery Ring*

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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3IBIC2023, Saskatoon, CanadaJACoW Publishing
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The system requires low noise RF amplifiers with +80db
gain. Crystal bandpass filters are used to suppress the revolution harmonics of the DR. A high-speed FPGA-based
DAQ board to use for the digital signal processing.

21.4 MHz Schottky Pickups
Inductively resonated, balanced stripline pickups wereused to observe tunes in the now decommissioned Tevatronaccelerator [4]. These 21.4 MHz Schottky resonant pickups
are now being reused for the Mu2E DR. The Schottky detectors are 1 m striplines consisting of two copper bars
which can be moved by stepper motors to change the sensitivity. Its resonant frequency can also be tuned by using
the variable capacitor Cv. Presently these detectors aretuned to resonate around 21.4 MHz with a loaded QL =370 [5]. Two of the Schottky detectors, one vertical andone horizontal, were installed in the Mu2E DR. Figure 5
shows photos of the vertical Schottky pickup.
The DR revolution frequency is 590.018 kHz.
The 21.4 MHz resonate frequency of these Schottky detectors then requires us to look for the DR tune lines between
the 36th and 37th harmonics of the DR revolution frequency. Figure 6 shows the vertical and horizontal tunes
lines between the 36th and 37th harmonics. This figure also
shows the frequency responses of both vertical and horizontal Schottky detectors, tuned to optimized sensitivity totheir respective tune lines, as well as the bandpass filter
widths.

consists of four 16-bit, 250MSPS ADCs, four 16-bit250MSPS DACs and a Cyclone V FPGA. The present tune
meter system utilizes two of the ADC channels for the vertical and horizontal Schottky signals. The FPGA logic digitally down converts the tunes at the 36th harmonic down tobaseband. The down converted data is then either analyzed
in the FPGA to generate FFT spectrums or else is offloaded
to a local computer to further analysis. Figure 7 shows ablock diagram of the FPGA logic for down conversion.
The signal processing analysis can time slice the down
converted data to generate FFTs along the slow spill. Thesystem can select the number of time slices and whether toaverage the time sliced FFT across many slow spills to help
reduce noise fluctuations in the FFT spectrum.

Figure 7: Block diagram of tune digital signal processing.

INITIAL RESULTS
The Mu2E tune meter system has been tested during initial commissioning of the Mu2E DR. Initial tune measurements were made with a spectrum analyzer in place of ourFPGA board. This allowed for us to confirm the analog
portion of the tune meter with a slower system. Figure 8
show the vertical tune line, along with the bandpass filter
width, for ~5e10 protons coasting in the DR.

Figure 5: 21.4 MHz resonant Schottky pickups.

Figure 6: Schottky pickup response and tune spectrum at
21.4 MHz.

Digital Signal Processing
The Mu2E tune meter systems uses a high-speed FPGA
VME board that was originally designed as part of a digital
damper system for proton storage rings. This board

Figure 8: Coasting DR tune taken with spectrum analyzer.
After initial measurements, the spectrum analyzer wasreplaced with our digital FPGA board. We tested the board
operation with millisecond time slices. Figure 9 shows aWEP033
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07 Machine Parameter Measurements

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preliminary measure of the tune spectrum at injectionof ~1e11 protons into the DR. This shows the potential ofmeasuring the tune along the slow spill at a few millisecond resolution.

ACKNOWLEDGEMENTS
We would like to acknowledge the Fermilab Mu2E accelerator team, Jerry Annala, Dean Still, George Deinlein,
Dave Vander Meulen, Brian Drendel and Steve Werkema
for their knowledge and beam studies support.

REFERENCES[1] R. Bernstein, The Mu2e Experiment, Frontiers in Physics,
vol. 7, 2019 7 doi:10.3389/fphy.2019.00001

Figure 9: Preliminary DR tune measurements withMu2E tune meter at beam injection.

[2] A. Ibrahim et al., “Preliminary Design of Mu2E Spill Regulation System (SRS)”, in Proc. IBIC’19, Malmo, Sweden,
Sep. 2019, paper MOPP033[3] V. Nagaslaev et al. The Mu2e Experiment, Phys. Rev. Accelerators and Beams, vol. 22, p. 043501, 2019.
[4] D. Martin et al., “A Schottky Receiver for Non-Perturbative
Tune Monitoring in the Tevatron”, in Proc. 13th Particle Accelerator Conf. (PAC'89), Chicago, IL, USA, Mar. 1989, pp.
1483-1486.
[5] C.Y. Tan, P. Lebrun, and X. L. Zhang, “Tune Measurement
Methods of the Tevatron”, in Proc. 20th Particle Accelerator
Conf. (PAC'03), Portland, OR, USA, May 2003, paper
WPPG052, pp. xx-xx.

CONCLUSION
A Schottky digital tune monitor system, based on 21.4
MHz resonant stripline pickups, has been design, installed
and tested in the MU2E DR. Initial tune measurements
show that beam tunes can be measured during the proposed
Mu2E slow spill time at the time resolution of a few milliseconds. Future beam measurements will focus on measuring these tunes during a slow spill over the full dynamic
intensity range in the DR.

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427

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12th Int. Beam Instrum. Conf.
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