In Situ Measurements of Tevatron Dipole Kaiser Coil Signals

1. In Situ Measurements of Tevatron Dipole Kaiser Coil Signals • What is a Kaiser coil? • What have we done with them? • What are we doing (trying to do) with them this shutdown? • What have we learned so far? • Where do we go from here? ps

2. B the “Kaiser Coil” • a flux loop embedded in the yoke of a Tevatron dipole • orientation: parallel to the field • Sensitive to the orientation of the field (i.e. cryostated coil assembly) to the yoke • Voltage proportional to df/dt, f is the flux linking the loop • A perfectly aligned magnet produces no signal ps

3. Alignment lugs B Dipole alignment • dipole field angle measured in MTF • lugs adjusted so that the field was perfectly aligned w.r.t. lugs • lugs then used to place the magnet in the tunnel • Kaiser coil not involved in the alignment process ps

4. B Kaiser coil • says nothing about the placement of the magnet in the tunnel • provides • cross check on the field angle to lug transfer • position of the coil relative to the yoke • in situ monitoring ps

5. Kaiser coil readout • JDM was the first to try reading out the Kaiser coil in “modern” times • started reading the coil with SSW equipment during field angle measurements (see next slide) • used an AC excitation of the magnets and frequency analysis of the coil signal • effectively a lock in amplifier • good results ps

6. Kaiser coil readout • preparation for last year’s shutdown (JDM) • does the field angle change during reshimming? • does a magnet follow when it’s neighbor is rolled? • realization: in situ monitoring of field angle useful during the shutdown activities • use of SSW cart for this not desirable • proposal was to replicate SSW system on PC • cheap DAQ ($700) • write Labview applications to excite magnet, acquire and analyze data ps

7. Kaiser coil readout • Gen 1 tunnel system (fall shutdown 2003) • “GO – no GO” system • make an angle measurement • do an operation (roll, shim, etc.) • re-measure • if no change, go on • our good fortune was we never faced the other choice • measurements with an operation consistent with those with the null operation • we had done a calibration, off by ~/2 • system served it’s purpose • a handful of measurements were made • system big and clumsy • didn’t look at the data in a systematic way until much later ps

8. a segue • focus of interest (w.r.t. Kaiser coils) • last shutdown • effect of roll and shimming on magnet alignment • this shutdown • possibility of misalignment magnets due to breaking of the cryostat anchors ps

9. (possibly) broken cryostat anchors • lots of magnet lift data taken last shutdown during the re-shimming exercise • 10% had large changes from legacy measurements • cryostat anchors may have broken allowing the cryostat to rotate relative to the yoke • a criteria was developed to identify candidates • select the tail of the lift distribution • a handful of magnets above ground selected for study ps

10. broken anchor studies • field angles were measured w.r.t. lugs • candidates showed large differences relative to a sample of non-candidates • presumably changes since leaving MTF |difference| field angle w.r.t. lugs solid - “normal” dashed – b.a. cand. ps

11. broken anchor studies • if you don’t like histograms… • but I’m going to show more ps

12. Kaiser coil readout • Gen 2 tunnel system (fall shutdown 2004) • BD requested two systems for Kaiser coil measurements • survey all magnets cold early in the shutdown • quickly so houses to be warmed could be warmed • look for “outliers” • changes w.r.t. legacy measurements • also any anomalies • needed a real system • make an angle measurement • sign right this time! • easier to use systems ps

13. Gen 2 system • re-examination of the calibration of last year including sign • calibrate “my” K.c. readout w.r.t. SSW K.c. • during the course of other studies in MTF • warm, cold, dozen magnets • establish the sign of the SSW K.c. readout ps

14. Gen 2 system • ease of use • implement DAQ on a laptop • laptop comes out of the tunnel • data transfer (not on a floppy this time) • possible upgrades, etc. • package the power supply and cabling compactly and robustly • capable of leaping tall obstacles in a single bound • non-expert operation • show system here ps

15. kaiser coil alignment measurements in the tunnel♣ • ~1400 measurements to get the data for the 770 dipoles • you do the math • not particularly proud of that • on the other hand the data don't look that bad • problems • daq stopping for some reason • cables not connected right • operators caught on pretty quickly • cables breaking • it took 4.5 days to do all the magnets (no useful data on the 1st 0.5) • a significant amount of time spent plugging in the cable ♣assessment of 9/1 ps

16. tunnel data • quickly realized we need to reanalyze all the data • too little QC in the system • DAQ stoppages • cables not connected • needed pedestal subtraction (next slide) • I sent down the wrong calibration constant • it divides the signal instead of multiplying it • we got the sign right! • most of the time MeasurementsRu$ just in time just good enough ps

17. angle (mrad) - tunnel pedestal subtraction answer never 0! ps

18. polarity issues • signal cables misterminated • cable reterminated several times • 8/25 reterminated by BD EE support • 8/26 data are clearly flipped • reterminated 8/26, “correctly” • issue solved by providing “throwaway” pigtails • strings powered wrong • no way I can think of to protect against this • legacy data wrong? • changes in Kaiser coil connector polarity ps

19. polarity issues current state of the analysis♣ ♣8/26 data & 1 sector cleaned up still clearly data on the wrong diagonal ps

20. selected sectors polarity reversed tunnel data plotted by sector (selected sectors) ps

21. polarity issues • 31 magnets with distance from the diagonal > 2 mrad • they populate the tails of the distribution of differences between current and legacy data ps

22. issues • polarity issues must be resolved before making a list of “outliers” • look at magnets which were powered together • more or less equivalent to the sectors plot but not quite • look at measured currents • small differences in Rstring give different currents for the different groups powered • sequential measurements with the same current powered together • use “distance to diagonal” as a discriminator? • at least one case of “string powered backwards” and 1 magnet with the wrong polarity • messy! ps

23. Angle (mrad) - tunnel issues • pedestal subtraction not working right • doesn’t effect the tails much • needs work but doesn’t stop us from looking at outliers ps

24. issues • resolution • clearly the efficacy of pedestal subtraction effects the resolution • do we have enough signal? • there are a couple of things that would possibly help • they need study • we have multiple measurements of magnets in the tunnel data (~60) • some things can be studied in MTF • all take time ps

25. distance from positive diagonal resolution • initial impressions not always right • impression #1: warm data 2003 had a better correlation than cold data 2004 solid 2003 dash 2004 ps

26. Angle (mrad)  tunnel-legacy Angle (mrad) - tunnel a clear tail for examination (not all of them are polarity mistakes!) ps

27. plans • resolve polarity problems • to the extent possible • make a pass at identifying outliers for examination of lift data • identify magnets which have no measurements • if any • look at the S/N and other DAQ issues • system improvements • look at magnets in the warm houses • work on other issues and revisit #2 • remeasure all magnets cold ps

28. summary • this pass was focused on potential broken anchors • we have documented the as found state of all the magnets cold and a fraction warm • we ought to follow up and track this over time • Run II has barely begun • there’s a lot of data yet to take ps