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REVIEW 4 major objections 4 minor 2 references

A Fiber Optic Based High Voltage System for Stellar Intensity Interferometry Observations

T0 review · 4 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read A battery-powered, fiber-optically controlled high-voltage supply for photomultiplier tubes kept its output stable to 0.015% over four hours, implying PMT gain stability better than 0.01%.

desk verdict Useful engineering note on a battery-powered, fiber-isolated PMT HV supply, but the headline gain-stability numbers are off by a factor of ten because the paper multiplies 0.015% by 7 and calls the result 0.01%. read the letter →

arxiv 1908.03157 v1 pith:FHHJGFLB submitted 2019-08-08 astro-ph.IM

Rylee Cardon , Nolan Matthews , A. Udara Abeysekara , David Kieda This is my paper · ORCID
classification astro-ph.IM
keywords stellarintensityinterferometryphotomultipliertubeshigh-voltagepowersupplyfiber-opticcontrolpulse-widthmodulationgainstabilityradio-frequencyinterferencebatteryisolation
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper reports the design and laboratory performance of a battery-powered, fiber-optically controlled high-voltage supply for the photomultiplier tubes (PMTs) used in stellar intensity interferometry at a four-telescope gamma-ray observatory. The central result is that the high-voltage output stayed within 0.015% ($\mathrm{d}V/V$) over a four-hour test while the battery voltage fell at about 25 mV/hour; because the PMT's gain scales as $V^7$, this implies less than 0.01% PMT gain drift over four hours and less than 0.03% over a 12-hour observing night. The fiber-optic PWM control and floating battery are meant to eliminate ground loops and radio-frequency pickup, which would otherwise create spurious correlations between telescopes. This matters because intensity interferometry measures stellar angular structure from the cross-correlation of fast PMT signals, so both noise and gain drift directly degrade the science.

What carries the argument

The load-bearing chain is the receiver at the telescope focal plane: an optical PWM signal is converted by an inverting buffer and a low-pass filter made of an 8.2 kΩ resistor and 22 µF capacitor into a 0–5 V DC set-point, which drives a DC-to-DC converter module supplying the PMT bleeder chain. The transmitter side uses a microcontroller-generated PWM signal fed through a fiber-optic transceiver, and the whole receiver is powered by a floating Li-Ion battery, so there is no conductive path between the HV output and any ground. The identity that carries the stability argument is $G \propto V^7$ for the eight-dynode PMT: a fractional voltage change $\mathrm{d}V/V$ is multiplied by 7 to obtain the fractional gain change, translating the measured 0.015% voltage stability into the claimed 0.01% gain stability.

What would settle it

Log the HV output with a voltmeter of 0.001 V or better alongside the battery voltage for four hours: if the output shows a drift above 0.015% ($\mathrm{d}V/V$) correlated with the battery drain, the stability claim falls. Separately, measure the PMT's single-photoelectron peak position versus applied voltage; an exponent measurably different from 7 would rescale the claimed 0.01% gain stability proportionally.

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Extended reading notes

Core claim

On its own terms, the paper establishes that a custom, remotely programmable high-voltage supply can power a PMT in an intensity-interferometry camera without introducing measurable drift or conducted noise. In a four-hour laboratory run, the output voltage varied by less than 0.015% even as the 15 V Li-Ion battery drained at roughly 25 mV/hour; the voltage was also reproducible to within one volt for a fixed PWM duty cycle. Using the eight-dynode PMT's gain law $G \propto V^7$, the authors convert this into a gain stability of better than 0.01% over four hours and less than 0.03% over a full night. The design isolates the PMT from the control electronics by sending the PWM set-point and on/off commands over plastic optical fiber, leaving the battery-powered HV receiver as the only conductive connection to the tube. The paper further reports that four such systems are operating in regular on-sky stellar intensity interferometry observations, with stable gain over nightly timescales.

Load-bearing premise

The gain-stability estimate rests on the assumption that the photomultiplier's gain scales exactly as the seventh power of the applied voltage; if the true exponent differs, the estimated gain drift changes in proportion.

Editorial extensions

If this is right

  • Four copies of the HV system are already used in regular on-sky stellar intensity interferometry observations, so the claimed stability has field operation behind it.
  • Over a 12-hour night, PMT gain drift from battery drain stays below 0.03%, smaller than the reported few-tenths-of-a-percent gain effects from sky-brightness or temperature changes.
  • Because the control path is optical and the supply is battery powered, ground loops are broken, reducing the radio-frequency pickup that would create spurious cross-correlations between telescopes.
  • The design is low-cost and general enough to be reused for other PMT-based, low-noise detectors that need isolated remote high-voltage control.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The quoted stability bound is set by the measurement resolution (<0.1 V), so the true HV drift may be even smaller; a higher-resolution voltmeter would tighten the 0.015% and 0.01% numbers rather than loosen them.
  • The $V^7$ gain law is assumed from the dynode count; a direct single-photoelectron calibration of gain versus voltage for the actual tube would turn the estimated gain stability into a measured quantity and would show whether the exponent has any voltage dependence.
  • If the HV drift is as small as reported, gain calibration for stellar intensity interferometry observations could be performed rarely, making systematic errors from gain drift subdominant to atmospheric and background fluctuations.
  • The same fiber-isolated, battery-floating architecture could be applied to other high-speed photon-counting instruments, where common-mode noise through ground loops is a limiting noise source.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 4 minor

Summary. This conference proceedings paper describes the design, construction, and laboratory testing of a battery-powered, fiber-optically isolated high-voltage (HV) supply for the photomultiplier tubes (PMTs) used in the VERITAS stellar intensity interferometry (SII) system. The HV level is programmed remotely via a PWM signal transmitted over a plastic optical fiber, with a separate fiber link for on/off control. The authors report that the HV output is stable with respect to battery voltage variations, with a measured variation of less than 0.015% (dV/V) over a four-hour interval, and they use an assumed V^7 PMT gain scaling to estimate a gain stability of better than 0.01% over four hours and less than 0.03% over a 12-hour night. The system is stated to be in regular use for SII observations at VERITAS.

Significance. The engineering contribution is practical: the design is low-cost, electrically isolated, and deployed at the VERITAS telescopes, which is a useful step for SII instrumentation. The laboratory data are direct measurements rather than fits to a model, but the central quantitative claim is undermined by an arithmetic error in converting HV stability to gain stability, and the measurement is resolution-limited without reported uncertainties. If corrected, the paper would still provide a useful description of the system, but the present version's headline numbers do not follow from its own data.

major comments (4)
  1. [Section 3, Figure 4] The text states that a fractional HV change of 0.015% leads, via the V^7 gain law, to a PMT gain variation of less than ~0.01% over 4 hours. This is arithmetically inconsistent: 7 x 0.015% = 0.105%, and 7 x (0.0038% per hour) x 12 hours = 0.32%. The gain-stability values in Section 3 and the Conclusion are therefore off by roughly an order of magnitude. This is an internal error in applying the stated scaling, and it directly affects the comparison with other gain-drift sources, which are said to be 'on the order of a fraction of a percent.' Please correct the arithmetic and adjust the claims accordingly.
  2. [Section 3, Figure 4 caption] The caption states that the output HV 'did not fluctuate at a level that was observable by the resolution of the measurement apparatus (<0.1 V).' The quoted stability of '<0.015%' is therefore an upper limit set by the measurement resolution, and no error bars or absolute HV set point are reported. A gain-stability claim based on this null result should be presented as an upper bound, with the resolution propagated through the V^7 conversion.
  3. [Abstract] The abstract states that the HV level 'is reproducible to within one volt for a given duty cycle of the PWM signal,' but no data, figure, or test procedure supporting this reproducibility claim appears in the body of the paper. Please either include the measurement or remove/qualify the claim.
  4. [Section 3] The assumed V^7 dependence of PMT gain is asserted without a citation to the Hamamatsu R10560 data sheet or a measurement for the specific tube. Because the claimed gain stability scales linearly with the exponent, a deviation in the exponent would proportionally change the result. Please provide a reference or discuss the expected range of the exponent.
minor comments (4)
  1. [Section 2] The text says the block diagram is 'presented in Figure 3,' but the block diagram is labeled Figure 1; please correct the cross-reference.
  2. [Section 4] The sentence beginning 'His corresponds to a relative gain stability...' contains a typo; 'His' should be 'This.'
  3. [Section 3] The statement that sky brightness and temperature effects are 'on the order of a fraction of a percent' is vague; please give quantitative values or a reference so the comparison is meaningful.
  4. [Figure 4] The linear fit to the battery voltage data is shown as a dotted line, but the fit parameters and residuals are not provided; reporting them would allow the reader to assess the drift rate.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the HV stability claim is a direct measurement and the PMT gain scaling is an externally supplied relation, not a fitted or self-cited input.

full rationale

The paper's central claim is an instrumental stability measurement: the high-voltage output was observed directly over four hours and varied by less than 0.015% in dV/V (Section 3, Figure 4). This is a laboratory observation, not a prediction derived from a fitted parameter or from the claim itself. The conversion from HV stability to PMT gain stability uses the stated relation that gain varies as V^7 for an eight-dynode Hamamatsu R10560 PMT, attributed to reference [2] (the VERITAS PMT upgrade paper). That scaling law is an external input, not something constructed within this paper, and it is not fitted to the same data used to assert stability. The paper also cites its own prior work [3,4] for the on-sky SII system, but that citation is contextual and not load-bearing for the quantitative stability claim. The skeptical observation that 7 x 0.015% = 0.105%, not ~0.01%, is a potential arithmetic inconsistency in the paper's own numbers, but it is a correctness concern, not circularity: the measurement and scaling law are independent of the conclusion, and the error does not arise from defining the output in terms of the input. Therefore the paper exhibits no significant circularity.

Assumptions & free parameters 0 free parameters · 4 assumptions · 0 invented entities

The paper introduces no new physical entities and fits no model parameters to make a scientific claim. It relies on standard PMT and electronics behavior as axioms. The absence of direct noise measurements and detailed calibration means several domain assumptions remain unverified.

assumptions (4)
  • domain assumption PMT gain varies as V^7 with eight dynode stages
    Stated in Section 3 without a citation or derivation; used to convert HV stability into gain stability.
  • domain assumption Fiber optic transmission and battery power eliminate ground-loop RF pickup
    Design premise in Section 1 and 2; no direct measurement of noise pickup is provided.
  • domain assumption The PWM-to-DC low-pass filter produces a stable control voltage linear with duty cycle
    Implicit in the design (Figure 3); the linearity is not explicitly verified but is standard for such circuits.
  • domain assumption The EMCO CA-12N DC-to-DC converter outputs an HV proportional to the control voltage
    Relied on for setting the PMT HV; manufacturer's behavior is assumed, and no calibration curve is shown.

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Cite this review

Pith. "Pith review of A Fiber Optic Based High Voltage System for Stellar Intensity Interferometry Observations." pith.science (2026). https://pith.science/paper/FHHJGFLB

@misc{pith2026190803157,
  author       = {Pith},
  title        = {Pith review of: A Fiber Optic Based High Voltage System for Stellar Intensity Interferometry Observations},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/FHHJGFLB}},
  note         = {Machine review of arXiv:1908.03157}
}
read the original abstract

Beginning in Fall 2018, the VERITAS high energy gamma-ray observatory (Amado, AZ) was upgraded to enable Stellar Intensity Interferometry (SII) observations during bright moon conditions. The system potentially allows VERITAS to spatially characterize stellar objects at visible wavelengths with sub-milliarcsecond angular resolution. This research project was on the construction of a high voltage power supply for the photomultiplier tubes (PMTs) used in the SII camera. The high voltage supply was designed to be electrically isolated from all other electronics (except for the PMT) to reduce noise pickup. The HV supply operates on a Li-Ion battery, and the high voltage level is remotely programmed using a pulse width modulation (PWM) signal that is generated by an Arduino Yun microcontroller and distributed through a fiber optic cable. The electrical isolation of the fiber optic control system suppresses the pickup of radio frequency interference through ground loops. A separate fiber optic transceiver pair is used for the on-off control of the high voltage power supply. Tests were performed that show the high voltage level is reproducible to within one volt for a given duty cycle of the PWM signal. Furthermore, the high voltage output level was shown to be stable with respect to variations in the input battery voltage used to power the high voltage supply. The high voltage system is currently being used in regular SII observations at VERITAS. This poster will describe the detailed design and performance of the system.

Figures

Figures reproduced from arXiv: 1908.03157 by the authors.

Figure 1
Figure 1. Block diagram of the SII-HV system. The HV control GUI is hosted on a server computer which communicates to the four high voltage systems (T1, T2, T3, T4) via Ethernet. Inside the HV system at each telescope (e.g., T1 HV), server commands are received by an Arduino Yun microcontroller (Tx) which generates a PWM signal and On/Off signal which is transmitted to the HV control system (Rx) and battery at the camera foca… view at source ↗
Figure 2
Figure 2. Left: PMT setup at camera focal plane with 45o mirror and remotely controlled HV supply (bottom left corner). Middle: PWM HV control transmitter box, including Arduino Yun, two fiber optic on-off controls, and two PWM outputs in each control box (blue connectors). Right: The ESKA GHCP 4002 2.2mm core plastic fiber optic cable that transmits the PWM signal from the telescope trailer to the HV supply at the camera Foc… view at source ↗
Figure 3
Figure 3. Circuit diagram for the SII-HV receiver located in the camera of the telescope. The low pass filter for converting the PWM to the DC signal is comprised of the 8.2 kOhm resistor and the 22 uF capacitor output of the LS04 inverter and feeding into pin 2 of the CA-12N DC-to-DC HV converter [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: The above plot shows the results of tests on the SII-HV supply system demonstrating the stability of the system over time. The top panel shows the loss in battery voltage over time for the supply used to power the SII-HV receiver. A linear trend is fit to the data and …

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Works this paper leans on

2 extracted references · 2 canonical work pages

  1. [1]

    http://pos.sissa.it/ A Fiber Optic Based High Voltage System for Stellar Intensity Interferometry Observations Rylee Cardon, Nolan Matthews*, A

    PoS(ICRC2019)643 ã Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). http://pos.sissa.it/ A Fiber Optic Based High Voltage System for Stellar Intensity Interferometry Observations Rylee Cardon, Nolan Matthews*, A. Udara Abeysekara and David Kieda De...

    work page 2018

  2. [2]

    Holder et al., The first VERITAS telescope, Astroparticle Physics, 25, (6), 391-401, 2006

    work page 2006

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