Carnarvon was offline due to a shutter motor failure, and a computer failure. The shutter motor and reduction gearbox was replaced with the spare from the on-site shipping container. A new computer was installed. Further work was completed on the Jabba fibre conversion to resolve some ongoing issues and return the instrument performance and data quality to expected levels

Hale, Steven J.

University of Birmingham Research Archive, E-papers Repository

BiSONBirminghamSolar-OscillationsNetworkTECHNICAL REPORT NO. 393Shutter repairs and updated fibre conversion at Carnarvon in2019 FebruarySteven J. HaleThe University of Birmingham, Edgbaston, Birmingham B15 2TT2019 March 27This technical report series is published by:SLHigh-Resolution Optical-Spectroscopy GroupSchool of Physics and AstronomyThe University of BirminghamEdgbaston, Birmingham B15 2TT, United KingdomTelephone: +44-121-414-4551Shutter repairs and updated fibre conversion atCarnarvon in 2019 FebruarySteven J. HaleThe University of Birmingham, Edgbaston, Birmingham B15 2TT2019 March 27AbstractCarnarvon was oﬄine due to a shutter motor failure, and a computer failure. Theshutter motor and reduction gearbox was replaced with the spare from the on-site shippingcontainer. A new computer was installed. Further work was completed on the Jabba fibre-conversion to resolve some ongoing issues and return the instrument performance and dataquality to expected levels.Contents1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 12 Site Maintenance . . . . . . . . . . . . . . . . . . . . . . 23 Jabba Optimisation . . . . . . . . . . . . . . . . . . . . . 31 IntroductionJabba was converted from direct sunlight to fibre-feed in 2018 April [1], but the weather towardsthe end of that visit was poor meaning that little testing could be completed. Following the con-version, several issues with the data quality were identified including low frequency drifts/stepsand increased high frequency noise. Additionally, less than a month after the visit the shuttermotor failed, shortly followed by the computer, taking the whole site oﬄine.Steven Hale visited Carnarvon from 2019 January 31 to February 11. The purpose of thisvisit was to replace the shutter motor and the computer, and to make additional modificationsto the Jabba fibre-conversion to improve the data quality. Section 2 first discusses the repairsto the shutter motor and the computer, and some general maintenance required to bring thesite back online. Section 3 then discusses the further changes to Jabba and the configurationupdates that were required to restore the data quality to that of previous years.12 Site Maintenance2.1 Shutter MotorShortly after the previous site visit, the shutter motor failed on 2018 May 3. The spare shuttermotor and reduction gearbox were installed during this visit on 2019 February 1 and confirmedoperational. There is no longer any stock of spare motors or gearboxes at Carnarvon or Birm-ingham.2.2 Rain DetectorThe rain detector was tested and confirmed positive reaction to water. The weather module stilloccasionally suffers from false rain trips, and the cause of these remain under investigation.2.3 ComputerShortly after the previous site visit, the computer failed on 2018 July 16. A new power supplywas installed on 2018 October 2 but the computer would no longer boot. It was suspected thatone or both of the hard disks had been damaged during the power supply failure.On arrival during this site visit it was confirmed on 2019 February 1 that the computer didnot boot, it halted at the Dracut emergency shell with the error that it was unable to mount/mnt/sysimage. The problem was a corrupt XFS filesystem. After running XFS repair on allfilesystems the issues were resolved and the system would boot. This problem rarely, if ever,happened during power failures when using the ext4 filesystem and so it is recommended toreturn to using ext4 on future site PCs rather than the new RHEL/CentOS/Fedora default ofXFS. One of the hard disks could not be detected by the BIOS and would eventually timeout,but this was related to a partially dislodged SATA connector.Despite the original computer returning to normal operation, a new PC was installed on2019 February 2. The existing DIO and RS232 cards were transferred over from the old system.The new PC is configured with CentOS release 7.6.1810 and kernel 3.10.0-957.1.3. The DIOcard device driver (the gnat) is confirmed to work with this kernel release, but has not yet beentested on anything newer.2.4 UPSOn the previous site visit, it was found that the UPS provided zero seconds of backup power. Anew Upsonic Power ESAT-15 UPS was ordered, but it did not arrive before the end of the visit.On arrival during this visit, the new UPS was found unpacked and powered but with none ofthe outputs connected. The ESAT-15 was installed on 2019 February 2, and tested to ensure itcould close the dome from fully open at least once with the utility supply disconnected.2.5 RCDsThe three RCDs on the dome three-phase incoming supply were tested via their built-in testbuttons on 2019 February 2 and confirmed operational.23 Jabba Optimisation3.1 OpticsThe original Jabba double-field spectrometer optical configuration is shown in Figure 1. Thelenses, labelled L1 through L6, are defined in Table 1. During the site visit in 2018 April [1],both L1, L2, and the filters were removed, and the fibre output mounted at the shared focalplane between the original L1 and L2 lenses. The new L2 fibre collimating lens is a ThorlabsAC254-030-B-ML with focal length of 30mm and diameter 25.4mm, the same lens as used atthe input of the fibre.Lens L3 originally produced a solar image on L4 immediately before the first magnet assembly.L4 is a Fabry lens intended to change the imaging of the system such that the image formed in thevapour cell is of the objective aperture rather than the Sun. The Fabry lens partially scramblesthe solar image and reduces the effect of so-called Doppler Imaging inside the vapour cell. Whilstthe image scrambling effect is no longer required when using an image-scrambling optical fibre,these two lenses were maintained as originally installed in order to minimise the changes tothe instrument. Unfortunately it was later found that the data quality had deteriorated dueto a lower signal-to-noise (i.e., cell hot-to-cold) ratio, and this was believed to be caused by anincrease in the non-resonantly scattered light from within the cell ovens. The change in initialcollimation optics produces a beam that has a slightly larger diameter than the original design,and this may have been causing the increased illumination of the inside of the ovens.On this visit, both L3 and L4 were removed. Lens L4 was replaced by a Thorlabs AC254-100-B-ML lens with focal length of 100mm and diameter 25.4mm, which focuses the collimatedbeam into the vapour cell and ensures that the beam is sufficiently converged to clear the magnetentrance aperture. The effect of the Fabry lens is no longer required since image scrambling isachieved via the optical fibre. Only lens L5 between the two ovens is now original to the design ofJabba. Lens L6 is no longer present since the transmission monitor was not reinstalled followingthe 2009 spectrometer refit [2]. The beam collimation, focus, and alignment was checked byremoving the 1.5 nm interference filter and both the ovens. A 770 nm fibre-coupled LED wasused to provide a beam through the instrument, which could be viewed and optimised. This sameoptical configuration is in use successfully with the fibre-conversion of Klaus at Mount Wilson [3],and so no further issues are expected with the optical design.3.2 Oven TemperatureThe oven temperatures and hot-to-cold ratios were checked both before and after installation ofthe new optics. When using a fibre-coupled 770 nm LED as a light source, the initial hot-to-coldratios were 4.1 and 4.5 for forward starboard and forward port, and 1.5 and 2.3 for aft starboardand aft port. These are higher ratios than produced from sunlight, since the LED does not havethe 770 nm absorption line present and so the results are similar to what would be achieved ifmeasuring the solar continuum. As expected, the aft cell is poor due to high cold counts.After replacing lenses L3 and L4, the hot-to-cold ratios changed to 4.2 and 4.7 for forwardstarboard and forward port, and 1.6 and 2.2 for aft starboard and aft port. These results show aslight improvement for the forward cell, and little change for the aft cell which still suffers fromhigh cold counts. It is not clear what is causing the ongoing problems with the aft cell, or whythe values show such a large difference between starboard and port detectors.3Figure 1: The Jabba double-field spectrometer optical configuration. Dimensions are in mil-limetres. The spectral intensity and polarisation state in the vicinity of the incident Fraunhoferline is shown at various locations along the optical path. The lenses are defined in Table 1.Reproduced from Lewis (1996) [4].Table 1: The Jabba double-field spectrometer lenses. Reproduced from Lewis (1996) [4].Lens f (mm) φ (mm) Manufacturer Part Number1 150 63 Spindler & Hoyer 32 22282 50.8 25.4 Newport PAC0403 250 31.5 Spindler & Hoyer 32 22724 50 18 Spindler & Hoyer 32 22655 40 31.5 Spindler & Hoyer 31 13396 50 40 Spindler & Hoyer 31 1340Detectors 20 21 Comar 20AF21A heating curve to optimise the temperature set-point for both cells was produced on Febru-ary 9. The results are shown in Figure 2. The optimum cell stem temperature was selectedas 98 ◦C. The cell cube/top temperature was defined at the standard 20 ◦C above the stemtemperature, resulting in a set-point of 118 ◦C. At these temperatures the hot-to-cold ratiosachieved with sunlight were 2.5 and 2.8 for forward starboard and forward port, and 1.6 and2.2 for aft starboard and aft port. The values from the forward cell have decreased to 60% ofthat when using the LED, and this is about the reduction expected due to the depth of thesolar absorption line. Both the cells show low hot-to-cold ratios suggesting that there is littlepotassium remaining in the cells, and they will likely need to be replaced soon. The cells werenot replaced on this visit since very few spares are available in HiROS stock, and so replacementsare restricted to only when absolutely necessary.When Jabba was reinstalled in 2009 September, BTR323 shows the hot-to-cold ratios were3.8 and 3.4 for forward starboard and forward port, and 2.3 and 2.9 for aft starboard and aftport [5]. The hot-to-cold ratios from Jabba have never been as high as some instruments at other490 92 94 96 98 100 102Cell stem temperature (C)80000100000120000Sum(counts)Fore star Fore port Aft star Aft portFigure 2: Oven stem temperature scan for both forward and aft cells. The optimum set-pointwas selected as 98 ◦C for the stem, and 118 ◦C for the cube/top.sites even when the vapour cells were new. Recent work at Las Campanas where a new vapourcell was installed in Hannibal resulted in a hot-to-cold ratio of 14, which is predominantly dueto the style of oven in that instrument having exceptionally good control of the non-resonantlyscattered light.3.3 GuidingThe guiding performance was measured during a site visit in 2016 August and found to have aFWHM of about ±8′′ [6], which is more than sufficient to maintain an image of the Sun on theend of the fibre. The guiding showed a drift of about a third of a degree between sunrise andsunset, which was believed to be due to flexure of the mount itself between the guider telescopeand Jabba where the camera was attached. However on this visit it was noticed that the fibrealignment does appear to show a variable offset throughout the day, even though Jabba and itsheavy magnets are no longer on the mount, and this movement could be contributing to the lowfrequency issues if the drift is large enough to cause vignetting at the edge of the fibre.The fibre input was aligned on the mount during the initial installation in 2018 April [1].On this visit, some mechanical adjustments were made and another guider scan completed. Theresults are shown in Figures 3 and 4. These results are not as clean as from the last visit dueto slight haze and occasional cloud. The final micrometer values were selected as 9.0mm inRA and 3.25mm in declination. The scan was performed near solar noon to ensure that anyguiding drift should be symmetric about the centre of the fibre core and so minimise the chanceof vignetting towards the edge. It is interesting to note in Figure 3 that the ratio begins toincrease again as the solar image drifts far off the edge of the fibre, below a micrometer settingof 5.0mm, and this could be another cause of low frequency offsets in the ratio. Perhaps a lenshood should be installed to limit the off-axis field-of-view.3.4 Magnetic Pockels CellJabba has two Pockels cells. The magnetic Pockels cell is L13, and the velocity Pockels cell is L14.During diagnostic work in 2016 August, L14 was removed and L13 moved from the magnetic54 5 6 7 8 9 10RA micrometer (mm)050000100000Sum(counts)Fore star Fore port Aft star Aft port4 5 6 7 8 9 10RA micrometer (mm)0.00.10.2RatioFore star Fore port Aft star Aft portFigure 3: RA guider micrometer scan. 1mm of micrometer travel is approximately 0.3° changein angle. The final setting was selected as 9.0mm.position to the velocity position [6]. Later, in 2018 April, Jabba was converted to fibre-feed andthe two Pockels cells restored to their original positions [1]. However, this was a mistake sincethe fibre-feed does not maintain solar polarisation information and so any solar mean magneticfield data is lost. On this visit, L13 was removed again and returned to Birmingham. Jabba nolonger captures solar magnetic data. The last magnetic data available from Jabba was prior tothe site visit in 2016 August.3.5 Polarisation MixingThe existing counter configuration is causing mixing between each polarisation phase. WhenJabba was returned to Carnarvon in 2009 [5], new digital counters were also commissioned forthe first time. A default configuration was used which was believed to be similar to the originalcounters [7, 8], with a “front porch” of 0.5ms (the time delay between commanding a polarisationstate switch and counting recommencing), and a data acquisition time per phase of 5ms. Thesevalues produce a switching rate for the velocity Pockels cell of 90.9Hz and for the magneticPockels cell of 45.45Hz. The total acquisition time (i.e., actual counting time) in each 4 s periodis 3.4 s resulting in 15% dead-time in each sample.60 1 2 3 4 5 6Dec micrometer (mm)050000100000Sum(counts)Fore star Fore port Aft star Aft port0 1 2 3 4 5 6Dec micrometer (mm)0.10.2RatioFore star Fore port Aft star Aft portFigure 4: Declination guider micrometer scan. 1mm of micrometer travel is approximately 0.27°change in angle. The final setting was selected as 3.25mm.Recent simulations of the Jabba scattering detector performance has shown that due to thehigh-gain / low-bandwidth of the circuit it takes about 2ms to 4ms to pass a transient signal(i.e., during a polarisation state change) depending on what is considered to be “complete”. Fora 10% to 90% transition the switching time is about 2.5ms. When using a 0.5ms front porchthe polarisation states become mixed since the detectors are barely halfway towards seeing thenew polarisation state at the time when counting restarts. This polarisation mixing could be thecause of low-frequency issues in the data, and the gain/offset differences in sensitivity betweenport and starboard detectors. On February 8 the front porch was briefly increased to 2ms andthe ratios from the forward port and starboard detectors did indeed move closer together.Before making a permanent change to the counter configuration, other issues need to beconsidered. If the front porch is increased to 2.5ms, then the data acquisition time per phasemust be reduced to 3ms if we wish to maintain the same 90.9Hz switching rate. However, thisincreases the dead-time to 49% and so reduces the statistical precision of the mean measuredin each 4 s sample. If we allow the acquisition time to increase to 8ms per phase then thedead-time rises to only 25.6% at the expense of reducing the velocity switching rate to 47.6Hzand the magnetic switching rate to 23.8Hz. Noise from atmospheric scintillation reaches −3 dBat about 5Hz and −10 dB at about 25Hz, and so this reduction in switching rate should haveno detrimental effects on atmospheric noise level.7Carnarvon/Jabba - 2019 February 28-5051015202530050,000100,000150,000200,000-2 0 2 4 6 8 1005001,0001,5002,0002,5003,0000 2 4 6 8 10FOM high: 100.2, FOM low: 22.7InvSens: 5672 m/s  Oﬀset: 716 m/s-4-3-2-1012341 2 3 4 5 6 7 8 9 10Figure 5: Data from Jabba with the counters reconfigured to use a 2.5ms front porch and 47.6Hzswitching rate. The low frequency drifts have been almost completely removed, and the whitenoise visible at high frequency also shows a noticeable improvement.Shortly after this site visit, the above changes were made to the counter configuration onFebruary 27. Figure 5 shows data from February 28. The weather is rather hazy/dusty andso the results are not ideal, but the low frequency issues have been almost completely resolvedand there is a noticeable improvement at high frequency. The ratios from the forward port andstarboard detectors now show similar sensitivity, and so this resolves a problem that has beenobserved since 2009 [5]. However, the calibration inverse sensitivity is still low at 5.6 km s−1rather than the typical expected 3 km s−1, and the reason for this is still under investigation.The weather in Carnarvon following this configuration change has been poor, however thedata so far do at least now appear as good as before the fibre conversion. The polarisation mixingissue will have existed since Jabba was reinstalled in 2009. It is not clear why the problem ismore pronounced with the fibre feed than with direct sunlight, or what impact the problem hashad on the historic data.References[1] Hale, S. J. and Ross, E. Jabba fibre conversion at Carnarvon in 2018 April. BiSON Tech-nical Report Series, Number 389, High-Resolution Optical-Spectroscopy Group, Universityof Birmingham, UK, 2018. URL http://epapers.bham.ac.uk/3139/. [page 1, 3, 5, 6][2] Hale, S. J. and Miller, B. A. The Installation of a Digital Autoguider in Carnarvonin 2011 September. BiSON Technical Report Series, Number 348, High-Resolution Optical-8Spectroscopy Group, University of Birmingham, UK, 2012. URL http://epapers.bham.ac.uk/2051/. [page 3][3] Hale, S. J. Klaus fibre conversion at Mount Wilson in 2018 June. BiSON Technical ReportSeries, Number 390, High-Resolution Optical-Spectroscopy Group, University of Birming-ham, UK, 2018. URL http://epapers.bham.ac.uk/3140/. [page 3][4] Lewis, D. J. A Dual Optical, Resonance-Scattering Spectrometer and the Probing of theSolar Atmosphere. Ph.D. thesis, School of Physics and Space Research, University of Birm-ingham, UK, 1996. [page 4][5] Barnes, I. and Miller, B. A. Jabba is Returned to Carnarvon in 2009 July. BiSON Tech-nical Report Series, Number 323, High-Resolution Optical-Spectroscopy Group, Universityof Birmingham, UK, 2009. URL http://epapers.bham.ac.uk/2043/. [page 4, 6, 8][6] Hale, S. J. Repairs to Jabba at Carnarvon in 2016 August. BiSON Technical Report Series,Number 381, High-Resolution Optical-Spectroscopy Group, University of Birmingham, UK,2016. URL http://epapers.bham.ac.uk/3133/. [page 5, 6][7] McLeod, C. P. BiSON Scaler System Notes. BiSON Technical Report Series, Number 23,High-Resolution Optical-Spectroscopy Group, University of Birmingham, UK, 1994. [page 6][8] McLeod, C. P. Replacement of DVM by Scalers at Carnarvon in 1994. BiSON Techni-cal Report Series, Number 33, High-Resolution Optical-Spectroscopy Group, University ofBirmingham, UK, 1995. [page 6]9

Shutter repairs and updated fibre conversion at Carnarvon in 2019 February

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Shutter repairs and updated fibre conversion at Carnarvon in 2019 February

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