# Comments on a review of Primary Beam Instrumentation

# and Multiwire Conceptual Design

**October 14, 2002**

## Update on NuMI Instrumentation

## Presenter: S. Childress

1.  ([Reviewer: J. Crisp]{.underline}) OTR profile monitors should be
    seriously considered. It\'s a powerful statement that one of the
    chief consultants at CERN does not build multi-wire profile monitors
    any longer in preference to OTR\'s. Marc Ross at SLAC claims the
    foils can be made much thinner.

2.  ([Reviewer: J. Crisp]{.underline}) One advantage given to the foils
    is that they are thin enough that some could be left in the beam and
    used by an auto-tune program. They would be substantially easier to
    build if they did not have to move out of the beam.

3.  ([Reviewer: J. Crisp]{.underline}) The biggest problem we have with
    multi-wires is proper mounting and tensioning of the wires. The
    wires are built by winding the wire onto a frame by machine. The
    machine precisely controls the spacing as well as the tension. The
    frame is used to hold the wires while they are soldered into the
    grid. It is a delicate process that requires attention. The titanium
    foils are going to be more difficult and serious thought should be
    given to this procedure.

4.  ([Reviewer: R. Ford]{.underline}) The Beams Division (specifically
    the inst. and mechanical depts.) must maintain and operate these
    things after they are built and should be a willing participant in
    the design and operation of them. I am particularly concerned about
    the handling and baking procedures every time the devices are
    exposed to air. Miniboone has exposed its multiwires to air several
    times since installation and it would have been a pain to rebake
    them each time.

5.  ([Reviewer: B. Kramper]{.underline}) In the Tevatron we found that
    the noise on the LVDT signals from the tunnel was too great to use
    them for any accurate measurement of collimator or target
    positioning. Even with signal conditioning and software averaging we
    could only get +/- 4%. We are presently using them only to determine
    direction of movement and are actually counting (in the front end)
    the number of steps moved. This has been reproducible to 1 mil in 2
    inches.

6.  ([Reviewer: V. Scarpine]{.underline}) In general, I feel that the
    design is very sensitive to the mechanical handling and long term
    stability of the foils. It may be a very difficult mechanical
    assembly.

7.  ([Reviewer: V. Scarpine]{.underline}) Also, it wasn\'t clear why OTR
    detectors are not being considered. A simple OTR system could be
    assembled quite cheaply.

8.  ([Reviewer: B. Webber]{.underline}) I highly recommend contacting
    Mike Plum (scientist) [mailto:plum@lanl.gov](mailto:plum@lanl.gov)
    and/or Ross Meyer (mechanical engineer) at Los Alamos to get
    information on the wire scanner mechanical acutators they are
    developing with Huntington for the SNS project. I know they have
    done quite a lot of work and have looked at positioning
    repeatability, etc. There is assorted material on the Web at
    http://www.sns.gov/diagnostics/diaghome.html. The mechanical
    actuator can be expensive in terms of development time if you start
    fresh.

9.  ([Reviewer: B. Webber]{.underline}) I don\'t know the details of
    applying OTR in the NUMI case, but I think you may be cheating
    yourself if you don\'t have someone take it seriously. It would seem
    to offer tremendous advantages over secondary emission devices, if
    there is enough light over the dynamic range of your beam. It is not
    at all obvious to me, if the physics is right, that it would require
    more engineering development time or pose more technical risk than
    the proposed foil sem. One contact person for OTR would be Alex
    Lumpkin at the Argonne APS, mailto:lumpkin@aps.anl.gov, phone
    630-252-4879.

## Conceptual Design for NuMI Multi-Wire SEMs

## Presenter: S. Kopp

10. ([Reviewer: T. Anderson]{.underline}) If foil is used, what is it\'s
    sensitivity to shock. i.e.: mechanical shock as in installation and
    pressure shocks from pumpdown and letting the system up with N2.
    During let-up or a system failure there could be a significant
    pressure wave moving through the beam pipe.

11. ([Reviewer: T. Anderson]{.underline}) What is the sensitivity of the
    foil to cleaning processes? The foil could be exposed to various
    chemicals and contaminants during fabrication and must be able to be
    cleaned and baked.

12. ([Reviewer: T. Anderson]{.underline}) There was concern about the
    material used for guide clamps, this could be a stainless steel
    bearing assembly (dry no grease). Synthetic materialsmay not hold up
    under a bake and typically have high out-gassing rates.

13. ([Reviewer: T. Anderson]{.underline}) Out-gassing tests should be
    done on the materials. To the first order this could be done by
    putting an equivalent amount (samples that have equivalent surface
    areas or volumes to the parts that will be used) of the non standard
    materials (those that are not stainless steel or that have potential
    trapped spaces) in a vessel of sufficient size that the samples
    would dominate the gas load. The out-gassing should be measured at
    steady state (not rate of rise) and an RGA analysis should be
    included.

14. ([Reviewer: J. Crisp]{.underline}) It was not clear how the signal
    wires are connected to the strips. As Dan Shoo indicated, you may
    want to look at how multi-wire grids are connected.

15. ([Reviewer: J. Crisp]{.underline}) The LVDT should work over the
    full range of motion. A second, high resolution LVDT could be added
    to work only near the in position.

16. ([Reviewer: J. Crisp]{.underline}) The tunnel environment can be
    very humid. Although environmental controls will attempt to keep the
    tunnel above the dew point, this system will fail eventually. These
    devices must be designed to handle that eventuality. An enclosure
    surrounding the device with a small heater could insure the delicate
    mechanisms and electrical connections remain dry.

17. ([Reviewer: J. Crisp]{.underline}) Fiducials that are accessible
    from the outside after the device is installed are required. The
    accuracy of wire position with respect to these should be clearly
    understood. The survey group should be asked to comment on the
    design.

18. ([Reviewer: J. Crisp]{.underline}) The 50% variation in titanium
    thickness is a concern for both mechanical strength and signal
    accuracy.

19. ([Reviewer: J. Crisp]{.underline}) Some information suggests a
    clearing field is required based on changes in profile with beam
    intensity. The magnitude of these changes was not known.
    Approximations were used to suggest a round hole in the clearing
    field plane for the beam to pass through would be ok. These ideas
    should be more concrete before they are designed into the system.
    The effect has not been seen at Fermilab, without clearing fields,
    in spite of a large dynamic range in beam intensities. The effect
    may simply be attributed to a reduced signal to noise ratio?

20. ([Reviewer: J. Crisp]{.underline}) Stepper motors are certainly
    adequate but the cost of the motor and the controls are significant.

21. ([Reviewer: J. Crisp]{.underline}) Linear motion slide bearings need
    to be made to withstand baking.

22. ([Reviewer: J. Crisp]{.underline}) Signal cables between the tunnel
    and equipment gallery are an important topic that was not discussed.

23. ([Reviewer: R. Ford]{.underline}) It does not appear that all the
    beam heating and tension issues are understood.

24. ([Reviewer: R. Ford]{.underline}) The fiducialization and alignment
    of the proposed devices could be much better than the current
    multiwire design if done properly.

25. ([Reviewer: R. Ford]{.underline}) A better understanding of cost
    should be made relative to the current multiwire design. While these
    devices would be nice to have, I don\'t think they are necessarily
    worth twice or three times the cost. It only takes us about 5
    minutes to manually mask off miniboone loss monitors from the beam
    permit system for studies and it only takes seconds with the beam
    off to put the MWs in the beam.

26. ([Reviewer: R. Ford]{.underline}) Having a backup plan to use wires
    if the foils become a problem would be useful.

27. ([Reviewer: R. Ford]{.underline}) For reference, the KTeV/NuTeV
    SEEDs had a 4% SEE and the KTeV tgt SEED experienced a 20% loss in
    SEE for a fluence of \~5e20 p/cm^2^. We had reasonable signal
    strength above 1e12 protons delivered over a 20 sec spill length.

28. ([Reviewer: J. Krider]{.underline}) The spring tensioning mechanism
    for the strips should be analyzed more carefully. It appears to me
    to be something that could work in the 1 gram range of tension, but
    not 90 grams.

29. ([Reviewer: J. Krider]{.underline}) There is a related question of
    how much tension is needed on a 7 inch long strip to keep it
    straight enough under transverse stresses of gravity or asymmetric
    heating across the width. Also, what happens to the strips during
    baking or during pumping down or letting up the vacuum, when there
    is significant gas pressure on the strips?

30. ([Reviewer: J. Krider]{.underline}) How are electrical connections
    made to the strips? I have seen spot welded joints on CERN strips,
    and the first generation Pbar target SEM had spot welded wires that
    worked well but required significant practice.

31. ([Reviewer: D. Pushka]{.underline}) Concerns expressed about the
    connector and the humid environment may have a simple solution. The
    ceramaseal feed thru connected to a D connector and coat the D
    connector with a little di-electric grease. If it is necessary to be
    really over careful, put all of this into a gasketed electrical box
    and place a small bag of dessicant in the box with the connector
    before tightening down the cover.

32. ([Reviewer: D. Pushka]{.underline}) I would advocate summing the
    surface areas of all of the components (Ti foils, rails, vacuum box,
    kapton inuslated wires, bellows, PEEK rail guides, etc.), apply
    outgassing rates to each material surface, and sum the results to
    estimate the total gas load. Then compare this to 20 feet of beam
    pipe for a sanity check. Is this gas load from this instrument equal
    to 200 or 2 feet of beam pipe? Terry also said that Teflon in the
    vacuum was okay (temperature range of 350 to 500 F), Teflon melts at
    about 620 F, PEEK at 480 F. Vespel, another high performance
    polyimide, can be used at temperatures of 550 F continuously, 900 F
    intermitantly. Your bearings are a solvable problem w/o resorting to
    ceramic, which I would be concerned about the abrasiveness
    generating particulate and wearing the shafts.

33. ([Reviewer: V. Scarpine]{.underline}) What is the long term
    mechanical stability of the foils? Since the foils will be crimped,
    how uniform will the tension remain? What are the foils mechanical
    vibration response? Will repeated motion cause a change in foil
    position over time?

34. ([Reviewer: V. Scarpine]{.underline}) Since the foils will be used
    to calibrate the BPM\'s, what will be used to calibrate the foils
    after assembly in the beamline? What cross-check will be used to
    insure that the foils have maintained position from assembly until
    insertion into the beamline?

35. ([Reviewer: D. Schoo]{.underline}) I suggest that the signal cable
    bundle be an \"adhesiveless\" Kapton ribbon. We have had excellent
    results with these on the multiwire detectors. They are radiation
    tolerant, vacuum compatible and provide a sturdy mounting for the
    signal wires especially since the end connections will need to have
    a good mechanical support and minimal pull stress for terminating to
    the foil ribbons. They can be made in almost any shape to match the
    physical dimensions of the interface and they flex easily for
    connection to things that move.

36. ([Reviewer: D. Schoo]{.underline}) I might also suggest a hermetic
    vacuum feedthrough connector for the signals. Before we used the 50
    pin D-sub connectors on the multiwire detectors, we used a 55 pin
    circular vacuum feedthrough connector with a small shell. We
    converted to the D-sub because it was far easier to mount and to
    terminate the flat-to-round cable into the mating connector. The
    mating D-sub is not hermetic which would not be advisable in the
    damp environment. We have samples of a Sealtron #MS27470Y17E35P and
    mating Aero #MS27467T17B35S that may be evaluated. The feedthrough
    connector is a solder cup type on the vacuum side but others are
    available with long pins that a flat cable can be easily soldered
    to. PC layouts already exist for this footprint.