## Report on the Roll Tests of Connected Tevatron Dipoles 

## At the Magnet Test Facility 

Tom Peterson

Updated August 13, 2003

INTRODUCTION

Technical Division was asked by Beams Division to assess whether
realignment of magnets in the tunnel can be done safely without warming
up the magnets and disconnecting them from each other. Realignment
involves both transverse movement and roll, but concerns mostly involved
rolls and included the following:

-   the coil might not move with the iron due to end constraints on the
    cryostat

-   a leak from air to insulating vacuum could develop

-   the cryostat (as opposed to interconnect) might be twisted

-   the beam tube bellows might be damaged

-   a leak from helium or nitrogen to vacuum could develop

-   adjacent magnets could move

Also, perhaps a test would reveal some surprises

TEST PROCEDURE

Location.

Stand 6 at MTF. In addition to cryogenic supply, it has an existing
vacuum system for pump down, access to a helium purge for continuous
leak checking during rolling, and access to magnet bus via current leads
for warm or cold powering. Stand 6 required some preparatory work, as
did the magnet supports.

Preparations.

A few more MTF-style Tevatron magnet supports were fabricated and
installed. The Stand 6 extension was aligned and bolted in place. In
order to help us understand Kaiser coil measurements, changes in a
Kaiser coil signal were compared with mechanical and stretched wire
measurements of actual cryostat/coil rotations in a yoke assembly, using
partially disassembled TB0334 in IB2.

Procedure.

1.  We placed 66" quad TQ223F, and dipoles TC0443 and TC0504 in that
    order on test stand 6 at MTF. The quad was connected to the test
    stand power leads; dipoles were electrically isolated and powered
    via the voltage taps.

> ![](media/image1.wmf){width="5.999305555555556in"
> height="0.9423611111111111in"}

Figure 1. Magnet arrangement on Stand 6 in Industrial Building 1.

2.  Each dipole was supported at four points using MTF dipole supports,
    but in a manner identical to the tunnel 4-point supports. (The quad
    was supported like the dipoles, thus not as firmly locked in
    position as in the tunnel.)

3.  The magnets were mechanically aligned and leveled. Connections were
    made using tunnel-style seals by a BD technician. A tilt meter and
    dial indicators were used to measure roll and offsets. Dial
    indicators were set in position on each magnet and zeroed. A dial
    indicator also measured cryostat box to yoke motion. We set the tilt
    meter on TC0443 above the supports nearest TC-0504. The photos below
    show the interconnect (open in the first photo, then closed) with
    dial indicators.

> ![](media/image2.png){width="5.4944444444444445in"
> height="2.752083333333333in"}
>
> Figure 2. TC0443-to TC0504 interconnect open, showing dial indicators
> including one on top to check for cryostat-to-yoke motion.
>
> ![](media/image3.png){width="5.995833333333334in"
> height="3.9972222222222222in"}
>
> Figure 3. TC0443-to TC0504 interconnect closed, showing dial
> indicators.

4.  We zeroed the tilt meter and checked that all dial indicators were
    zeroed.

5.  A pen mark across the vacuum flanges at the gap between clamp
    sections served to check for slip of vacuum flanges relative to one
    another.

6.  Baseline (before rolling) stretched wire and Kaiser coil
    measurements were made. Smart bolt depths were measured and
    recorded.

7.  We rolled TC0443 four milliradians by means of the 1" vertical
    support nuts. Four milliradians = 14 arc-minutes = 0.23 degrees. The
    vertical jacks are 4.5" off center, so 18 mils vertical motion is
    required, about 1/8 of a turn. We lowered the two jacks on the east
    (Stand 4) side by approximately equal amounts, to get 4 mr roll
    toward Stand 4. There was some lateral motion as a result of these
    adjustments which we did not try to correct.

8.  Dial indicators at each end of the magnet were used to confirm
    approximately the same amount of motion at each end, but we were
    concerned primarily with the dipole-dipole interconnect and did not
    try to perfectly match the position changes at the two ends.

9.  We recorded all dial indicator readings, including dial indicators
    on the magnets looking at cryostat end box position relative to the
    iron yoke, and we recorded tilt meter readings.

10. We took stretched wire readings to measure magnetic field roll. (We
    powered each dipole separately via the voltage taps and powered the
    quad via the test stand power leads.)

11. We took Kaiser coil readings. (We powered each dipole separately via
    the voltage taps.) The Kaiser coil allowed us to monitor potential
    rotation of a dipole\'s collared coil relative to its yoke.

After the first set of roll data were taken:

12. Repeated steps 4 through 11 for another 4 mr roll in the same
    direction another set of readings. (Yes, first rezeroed the dial
    indicators and tilt meter.)

Cold roll test after we finished with stretched wire tests:

13. We did a 4 milliradian cold roll test to check mechanical integrity
    (leak tightness) of joints between rolled magnets. Kaiser coil
    provided indication of coil positional change. (Stretched wire had
    to be done only with magnets warm and open to air, since we have no
    warm bore for a string of Tevatron magnets.)

![](media/image4.png){width="5.992361111111111in"
height="3.9944444444444445in"}

Figure 5. View from feedbox end.

![](media/image5.png){width="5.997916666666667in"
height="3.997916666666667in"}

Figure 6. View from turnaround box end.

RESULTS

The following three figures were created by Joe DiMarco from magnetic
measurement data.

![](media/image6.wmf){width="5.99375in" height="5.451388888888889in"}

Figure 7. Warm roll tests to 8 mr and back show (by means of single
stretched wire) that the coil of TC0443 followed the yoke to less than
0.2 mr in one test. (We do not know why the coil seemed to move more
than the yoke in the other test, but we suspect that the measurement of
the mechanical roll of the yoke was slightly in error.)

![](media/image7.wmf){width="5.99375in" height="5.451388888888889in"}

Figure 8. The coil of TB0334 was rolled relative to its yoke by a known
amount in a test in IB2 in order to obtain a set of calibration data for
a Kaiser Coil. Two more dipoles will be similarly tested in IB2 to
confirm that the Kaiser coil calibration is representative.

![](media/image8.wmf){width="5.99375in" height="5.451388888888889in"}

Figure 9. Kaiser coil follows the yoke to less than 0.2 mr. We do not
understand the change in initial offset in TC0443 from trial 1 to trial
2, but the initial offset does not change our conclusion that the coil
follows the yoke.

Mechanical measurement results.

-   A pen mark on the vacuum flanges indicated varying amounts of
    relative slip during both warm rolling and cold rolling.

-   A dial indicator on the cryostat box showed less than 1 mil movement
    relative to yoke even at 8 mr of roll

-   A leak detector on the assembly showed no increase of vacuum
    pressure or helium background during cold rolling.

-   Following cold roll tests, inspection of the beam tube bellows
    indicated some permanent deformation.

-   Follow-up warm roll tests with only the internal lines (cryo lines
    and beam vacuum) connected showed the nature of the beam tube
    bellows deformation. (See photos below.)

-   Other internal bellows showed less apparent strain, as one would
    expect since they are longer and smaller in diameter.

![](media/image9.png){width="5.677083333333333in"
height="3.7888888888888888in"}

Figure 10. Beam tube bellows strained due to 8 mr of twist

![](media/image10.png){width="5.679166666666666in"
height="3.785416666666667in"}

Figure 11. Beam tube bellows following tests, back at zero roll
position.

Answers to the list of initial concerns.

-   Coil might not move with the iron due to end constraints on the
    cryostat.

Test result\--not a problem; the coil moved with the yoke.

-   A leak from air to insulating vacuum could open up.

Test result\--no leaks with this test.

-   The cryostat (as opposed to interconnect) might be twisted.

Test result\--not a problem; the cryostat was not twisted.

-   The beam tube bellows might be damaged.

Test result\--it was, but not catastrophically. It is a matter of amount
of roll and deformation.

-   A leak from helium or nitrogen to vacuum could open up.

Test result\--no leaks in this test.

-   Adjacent magnets could move.

Test result\--no significant motion.

We thought that perhaps a test would reveal some surprises. Yes, the
vacuum flanges slipped! This was a key mechanical result.

Summary of results.

-   In warm roll tests, the collared coil does track the motion of the
    yoke. The yoke of TC0443 was rolled in steps of 4 milliradians to 8
    mrad and back to zero. Stretched wire measurements indicated that
    the coil followed the yoke to within the accuracy of the
    measurements, about +/- 0.1 mrad. Kaiser coil measurements and smart
    bolt depth measurements confirm little coil-to-yoke relative motion.

-   The magnets connected on either end, TC0504 and TQ223 (note: quad
    not supported like in the tunnel), moved a little, but less than 0.4
    mrad with TC0443 at 8 mrad.

-   The system remained leak tight. However, a line across the vacuum
    flange joint showed that the pairs of vacuum flanges slipped
    relative to one another in a similar way at each end of the magnet,
    about 30 mils, or about 5 milliradians. Thus, there is some risk of
    opening an insulating vacuum-to-air leak with the roll.

Comments and recommendations.

-   On the positive side

    -   The coil followed the iron yoke.

    -   The system remained leak tight during a cold roll up to 4 mr.

    -   The adjacent dipole was not too much affected by the roll.

-   Reservations

    -   Vacuum flanges slipping (for example, at an old joint where the
        o-ring has dried or sticks to the flanges) could produce an
        air-to-cryostat vacuum leak. Vacuum flanges not slipping could
        result in relative coil motion.

    -   Beam tube bellows look permanently deformed.

    -   This was a sample of one, and the issue may be more statistical
        in nature. Maybe not all magnets behave like these have on the
        MTF test stand in terms of vacuum flange slip or even coil-yoke
        motion.

    -   Initial roll conditions in the tunnel may not be neutral.

-   Recommendation based on these tests (as of July 23)

    -   Cold rolling carries definite risks, but so does a thermal
        cycle. Tests at MTF indicate that small cold rolls (\< 2 mr) may
        work.

    -   The above conclusion is extremely conservative, based on the
        limitations and uncertainties in the studies so far. Tests will
        be done to clarify the twist limits of the beam tube bellows and
        also to explore the issue to vacuum flanges slipping with a dry
        O-ring.