Status Report of the Tevatron Alignment Task Force

and a

Report on Magnet Survey Activities During the

2003 Summer-Fall Shutdown

by the

Tevatron Alignment Task Force

Introduction:

The Tevatron Alignment Task Force was established in May 2003 to
coordinate various tasks in the Tevatron dealing with magnet survey and
alignment. The roles and responsibilities of the membership of the Task
Force is given in Table 1.

Table 1: Roles and Responsibilities of the Tevatron Alignment Task Force

  ---------------------------------- ------------------------------------
  We report to Roger Dixon, head of  Recommendations are reviewed and
  the Accelerator Division.          approved by Peter Garbincius, Craig
                                     Moore, and Vladimir Shiltsev.

  The task force leader is Ray       The shutdown coordinator is Jim
  Stefanski                          Volk.

  The Run II project leader is Jeff  Mike Syphers represents the
  Spalding                           Accelerator Integration Department.

  PPD and TD Management is           Bob Bernstein, John Greenwood, Terry
  represented by John Cooper and Bob Sager, and George Wojcik represent
  Kephardt.                          the AMG

  The Technical Division             The Accelerator Division
  Representatives are Ray Hanft,     representatives are Keith
  Dave Harding, Jamie Blowers, Fred  Gollwitzer, Norm Gelgand, Bruce
  Nobrega, and John Tompkins.        Hanna, Todd Johnson, Mike McGee,
                                     Duane Plant, and Aimin Xiao

  The PPD representatives are Alvin  Consultants are Gerry Annala, Don
  Tollestrup, Hans Jostlein and      Edwards, Al Russell, and Jean
  Jesse Guerra.                      Slaughter

  Rob Roser and Rich Smith represent Outside Consultants are: Andrei
  CDF and D0.                        Seryi (SLAC) and Andrey Chupyra
                                     (BINP)
  ---------------------------------- ------------------------------------

The work of the Task Force is given in the mission statement:

> I. The Task Force has two primary tasks to deal with:

1.  Measure the Tevatron: Locate the Magnets relative to each other;
    Locate the cold mass relative to the magnet yokes for dipoles,

2.  Monitor motion in the Tevatron.

> II\. The alignment work has the following components:

1.  Develop a horizontal survey network for the Tevatron, to tie the
    tunnel into a global network. The network is called TevNet. Its
    installation was a primary goal of the 2003 summer shutdown.

2.  Shorten the time it takes to make roll measurements so that these
    could be done in a few days and repeated periodically.

3.  Set up a systematic study of Tevatron corrector magnet settings and
    BPM readings to monitor the occurrence of changes in the Tevatron.

> III\. The installation of motion detectors has the following
> components:

1.  Continue to install inclinometers around the ring to locate any
    movement that might explain the fact that the Tevatron must be
    retuned every 10 days or so. In addition to the inclinometers,
    install hydrostatic level sensors (HLS) positioned in strategic
    parts of the tunnel to look for irregular motion.

2.  Collect the HLS from MI-8, and the Aurora mine, and install them in
    Tevatron sector B to see how well they might work as long term
    elevation and tilt monitors.

3.  Develop a modified HLS at BINP for simultaneous measurements of
    elevation and tilt. Andrey Chupyra has a rough idea of what we're
    looking for, and may be able to deliver a prototype this year.

In preparation for the summer shutdown the Task Force concentrated on
completion of the issues outlined in the mission statement. This
document represents a report on the status of meeting the goals given in
the mission statement and providing an outline of work to be done.

The bulk of the work done in the summer and fall of 2003 came during the
scheduled shutdown that took place between September 8 and November 15,
2003. However, two unscheduled shutdowns of significant duration
occurred that gave us additional time to complete roll corrections,
realignment and surveys[^1]. These occurred between December 8 to
December 15, caused by a conning tower failure, and December 19 and
December 29 initiated by a six house quench.

In addition to the issues addressed in the mission statement, alignment
tasks at CDF (to bring the IR into the detector's acceptance) D0 (to
correct an aperture restriction) A0 kickers (to correct an aperture
restriction) and F0 Lambertson magnets (to study the interface between
beam transfer from the Main Injector to the Tevatron) were addressed and
are reported in this document.

![](media/image1.png){width="4.95in" height="3.688888888888889in"}

> **Figure 1: TevNet as it is laid out on the surface of the site.**

**Physical Alignment of the Tevatron:**

***TevNet***

The physical alignment of the Tevatron was the main task undertaken by
the Alignment and Metrology Group (AMG) during the summer shutdown. It
consisted of installation of an alignment network in the Tevatron
tunnel, and simultaneously measuring horizontal and vertical positions
of Tevatron magnets. Combining these tasks provided the most efficient
way to measure magnet positions, while installing TevNet. Most of the
effort comes in setting up the instruments. The actual measurements take
little time. As a result the AMG was able to provide a complete
measurement of horizontal magnet offsets from the Murphy line, and a set
of relative vertical data for all of the yoke magnets in the Tevatron,
during the installation of TevNet. The results of these measurements are
discussed in later sections.

TevNet is a system of alignment monuments located on the surface of the
site, and within the accelerator tunnels. The surface configuration of
TevNet is shown in Figure 1. The Main Injector and Tevatron rings are
clearly visible. TevNet consists of 1,736 stations in the control
network. 28,612 observations using GPS, Mekometers, laser trackers, and
traverse were used to make measurement (observations) of station
positions. A Least Squares fitting method was used to find the optimal
positions that minimized the overall errors.. For example, the distance
between stations directly across the Tevatron ring, which has a one
kilometer radius, was determined to a precision of about 2.5 mm; or
about one part in a million, using the surface stations. For
measurements in the tunnel, which will be more tightly constrained,
relative measurements across the ring are good to about 1 mm.

The TevNet is also part of the National Geodetic Survey (NGS). This
property isn't used in our work in the Tevatron, but is important for
NuMI and other potential long baseline neutrino experiments.

The survey stations in the Tevatron tunnel are related to the site
risers in TevNet with a precision of about 0.25 mm. Because the
installation of TevNet involved tying this surface network into
alignment stations within the tunnel, vertical site-risers were needed
to provide an optical connection between the surface and tunnel. We were
fortunate to find air ventilation ducts located around the ring that
could be used as site risers. Twelve of these ducts, plus two other
existing site risers, were used to install TevNet.

Figure 2 shows the ducts and towers used for this work:

a)  A photograph of an air duct that is not in use. These are found at
    all of the 2 and 3 numbered houses around the ring.

b)  A photograph of a ventilation unit sitting atop an air-duct. These
    are seen at the 1 and 4 numbered houses around the ring.

c)  At the bottom of each of the 24 air ducts sits a cable tray that
    obstruct a clear view into the alcove. A special device was designed
    by Mike McGee to bring the line-of-sight around the cable tray.

d)  A photo of the alcove at the bottom of the air ducts, showing also a
    cable tray. The AMG used twelve air ducts for the installation of
    TevNet. Those used were located at the 1 and 3 houses.

e)  A photograph of one of twelve towers constructed above the
    air-shafts, this one at C3. From the top of the tower, which extends
    above the surrounding structures, readings taken at the surface can
    be transmitted down the sight-riser, nee air-duct.

As an example of the work already done, measurements made in the tunnel
by a Laser Tracker can be evaluated for quality by considering the
precision achieved in redundant distance measurements. Over 69,000
measurements were made in the Tevatron using the 1,688 measuring
stations. Over 63,000 of these measurements were redundant, so that the
precision of the observations could be calculated. The precision
measurements are used as weights in the Least Squares fitting process.
Figure 3 shows the results of these measurements. The vast majority have
a standard error smaller than 50 microns. Measurements that have a
standard error greater than 1/2 mm are considered erroneous, and are
studied to determine the cause of the error. These are ultimately
eliminated from the data set, because they might severely distort the
network.

In Figure 4a, the set of error ellipses is shown based on the
observations made in the tunnel, and tied into TevNet. If the location
of one station is fixed, the position of all of the remaining stations
in the tunnel can be computed with an associated error ellipse. The
largest error would be associated with the station directly across the
ring from the fixed station, and would have a transverse error of 18 mm.
When all 14 stations are used the largest transverse error is about 3.8
mm and this is an error at the 95% confidence level. Figure 4b shows the
comparable plot.

The work involved in understanding the network is continuing. When
complete, an independent confirmation of the location of the Murphy line
will be possible. The horizontal positions of elements in the Tevatron
tunnel will have been measured better then ever before. Magnet
elevations and rolls will also be available at better precision.
Repeated measurements will be done more quickly than would be possible
with traditional methods. Being able to locate the position of elements
in the tunnel and to periodically check for changes is an important part
of establishing a system of configuration control for the Tevatron.

![](media/image2.jpeg){width="2.6251968503937007in"
height="1.6307086614173227in"}![](media/image3.jpeg){width="1.8751968503937009in"
height="1.6307086614173227in"}![](media/image4.jpeg){width="2.8751968503937007in"
height="1.3692913385826773in"}![](media/image5.jpeg){width="2.75in"
height="1.8751968503937009in"}![](media/image6.jpeg){width="2.160236220472441in"
height="2.8751968503937007in"}

> **Figure 2: Photographs of air ducts, and towers used during the
> installation of TevNet.**

![](media/image7.wmf){width="5.2in" height="2.3868055555555556in"}

**Figure 3: A laser tracker evaluation chart.**

![](media/image8.png){width="3.5in" height="2.875in"}

**Figure 4a: From the secondary traverse observations taken in the
tunnel, an error ellipse can be formed for the location of any station
relative to any other station. In this Figure, we plot the error
ellipses of each station relative to station A12. The largest error is
on the opposite side of the ring at D13, where the ellipse has a
two-sigma semi-major axis of 18mm. This is analogous to the situation
before the installation of the network if the best current practices
were used. This is the best we could hope for using the Murphy--line.**

![](media/image9.png){width="3.0in" height="3.097916666666667in"}

**Figure 4b: By using TevNet, and the 14 constraints represented by the
site risers, the situation around the ring is much improved. The largest
two-sigma error, represented by the semi-major axis of an error ellipse
is 3.8 mm. This should be compared to the two-sigma error in Figure 4a
of 18mm. This is an improvement of roughly a factor of 25: We quantify
the improvement by taking the ratio of the areas of the error
ellipses.**

***Magnet Roll Measurements and Corrections***

In addition to the survey measurements done by the AMG, an independent
effort took place to measure magnet rolls along the entire Tevatron. In
particular, a substantial effort was made to shorten the time involved
in making these measurements, by improving the measurement fixture used,
and incorporating direct readout of the measurements into a laptop. Two
fixtures were actually used: The first was similar to the fixture used
in the January shutdown. This fixture proved problematic, in that
calibration issues arose during its use. We finally settled on a less
precise, off-the-shelf protractor that was much easier to use.
Measurements from both fixtures were read directly into a laptop.
Experimenters from CDF and D0 took the measurements of magnets in the
tunnel, and Keith Gollwitzer analyzed the data.

![](media/image10.wmf){width="5.0in" height="2.716666666666667in"}

> ![](media/image11.png){width="4.245275590551181in"
> height="2.663779527559055in"}**Figure 5a: Comparison of magnet rolls
> (Dipoles and Quadrupoles) around the entire Tevatron before and after
> the summer shutdown and the two December shutdowns. Current rolls are
> in purple, the corrected Oct-03 rolls are in dark blue and are seen
> only for measurements that changed during the shutdown. The origin is
> at A0.**

Improvements in magnet roll during the shutdowns were striking. Figures
5a and 5b show a comparison of roll measurements before and after
adjustment during the shutdown and the beam-off periods that followed.
Many of the most troubling sections were corrected. A comparison of
magnets with substantial rolls before the shutdowns and after is given
in Table 2. In particular, all of the magnet rolls greater than 4 mrad
have been eliminated. There are now 51 magnets with rolls greater than
one mrad that should be corrected, compared to 141 before the shutdowns.
(Our present threshold for roll correction is 1 mrad.) The biggest
remaining rolls are in A and E Sector. This work had an immediate impact
on vertical corrector magnet settings, which had previously run close to
capacity. Corrector currents are now running at much more reasonable
levels as can be seen in Figures 6a and 6b.

Table 2: Comparison of magnet rolls before and after the summer
shutdown. (#before, #after)

  ---------- ---------- --------- -------- -------- -------- -------- --------
  House      Roll Angle \>N mrad                                      

             \>1        \>2       \>3      \>4      \>5      \>6      \>7

  A-1        (3,3)                                                    

  A-2        (20,2)     (10,0)    (8,0)    (8,0)    (4,0)    (2,0)    (2,0)

  A-3        (4,4)                                                    

  A-4        (2,2)      (1,1)                                         

  B-1        (20,0)     (9,0)     (3,0)                               

  B-2        (19,0)     (7,0)     (2,0)    (1,0)                      

  B-3        (2,2)                                                    

  B-4                                                                 

  C-1        (11,0)     (1,0)     (1,0)    (1,0)    (1,0)             

  C-2        (5,4)      (3,3)     (2,2)                               

  C-3                                                                 

  C-4                                                                 

  D-1        (1,1)                                                    

  D-2        (4,4)                                                    

  D-3                                                                 

  D-4        (2,1)      (1,0)     (1,0)    (1,0)    (1,0)             

  E-1        (1,1)                                                    

  E-2        (17,4)     (10,0)    (3,0)                               

  E-3        (23,17)    (13,8)    (5,3)                               

  E-4        (2,2)                                                    

  F-1        (1,1)                                                    

  F-2        (2,2)                                                    

  F-3        (1,1)                                                    

  F-4                                                                 

                                                                      

  Total\>N   (141,51)   (55,12)   (25,5)   (11,0)   (6,0)    (2,0)    (2,0)
  ---------- ---------- --------- -------- -------- -------- -------- --------

![](media/image13.jpeg){width="3.05in" height="2.572047244094488in"}

![](media/image14.jpeg){width="2.75in" height="2.4138888888888888in"}

**Figure 6a: Comparison of vertical corrector magnet currents before and
after the shutdowns. The origin is at C0. The vertical scale changes
from (-6 to 13 amp) before to (-5 to 6 amps) after.**

![](media/image15.jpeg){width="3.106299212598425in"
height="2.7318897637795274in"}![](media/image16.jpeg){width="2.89251968503937in"
height="2.7251968503937007in"}

**Figure 6b: Comparison of horizontal corrector magnet currents before
and after the shutdowns. The origin is at C0. The vertical scale changes
from (-13 to 6.5 amp) before to (-6 to 6.5 amps) after.**

***Horizontal Offsets***

![](media/image17.wmf){width="4.5in" height="3.239763779527559in"}As
part of the TevNet installation process, the AMG made measurements of
horizontal offsets to the Murphy line for quadrupole and dipole magnets.
This took relatively little added time, since most of the effort was
involved in setting up the instrumentation for the TevNet installation.
Relative magnet elevations were also measured; these will be discussed
in the next section.

The results of the measurements are given in Figure 7. These data
represent the first comprehensive measurements of horizontal offsets in
the Tevatron since the initial installation. The results indicate that
the magnets were relatively stable horizontally over the years. Only two
quadrupoles were sufficiently out-of tolerance that a specific effort
was made to correct their offsets. The improvement in horizontal offsets
evident in Figure 7 came about by systematically correcting the
horizontals whenever any other work was done on a magnet, such as a roll
correction or magnet stand replacement.

***Elevations***

![](media/image18.wmf){width="3.959722222222222in"
height="2.8743055555555554in"}Part of the process of correcting magnet
rolls, installing new magnet stands, or correcting horizontal offsets
includes local corrections to magnet elevations. These corrections were
aimed at smoothing local variations, so that magnets sit on a common
line within several Tevatron magnet cells. A before-after comparison is
shown in Figure 8. Some improvement in global variations around the ring
is seen in this plot, but because the corrections are local, the curves
appear very similar.

Global elevation corrections will not be carried out until the TevNet
results are available and orbit simulations are done to determine the
sensitivity of the Tevatron orbit to variations in magnet elevations.
Based on operating experience since the shutdown, we might suspect that
magnet elevations have a large tolerance and that more effort should be
devoted to roll corrections and spool piece alignment.

***Where do we go from here?***

"The original specification for horizontal and vertical alignment of the
Tevatron was 10 mils for quads and 30 mils for dipoles with respect to
the monument system. The total error budget also included measuring the
magnetic center of the elements, setting the reference lugs on the
outside with respect to the magnetic center, and the error on analyzing
and installing the monument system. We will shoot for nothing less 20
years later, especially since TevNet will give us better information
about the monument system[^2]."

The experience of the summer shutdown pointed to the importance of spool
piece alignment. These were not considered in this year's plan.
Measurements made during the shutdown have shown that the spools may be
significantly out of alignment in some parts of the ring.

##### Correction to the skew-quadrupole component in Tevatron dipoles 

The horizontal and vertical betatron oscillations in the Tevatron were
strongly coupled, requiring the skew-quadrupole correction circuits to
run at about 60% of the maximum current. Don Edwards and Mike Syphers
reported beam measurements that showed the source of the coupling to be
distributed fairly uniformly around the ring, rather than concentrated
in one or a few locations. Their analysis of several different
measurements concluded that the strength of the coupling was consistent
with a skew-quadrupole component in each dipole of approximately one
"unit" (parts in 10^4^ at one inch). A measurement that was also
confirmed by the Technical Division, in that one unit of skew-quadrupole
component could be attributed to a settling of the cryostat over time.

![](media/image19.jpeg){width="3.8846456692913387in"
height="2.7700787401574805in"}

**Figure 9: A cross-sectional view of a Tevatron dipole. The smart bolts
are located at the upper corners and are spring loaded. Dumb bolts are
located at the lower corners and are not spring-loaded. Three mil shims
were placed at the dumb bolt ends to correct for the vertical settling
of the cryostat**

The coupling is corrected globally, but the removal in 1991 of spools
with skew-quad correctors on each side of each IR, to make room for new
low-beta insertion components, left the coupling uncorrected locally
through these two sensitive regions. Tracking studies done by Norman
Gelfand showed that the skew-quad component in the dipoles leads to,
among other things, a vertical dispersion of 0.5 meters, with the
majority coming from the intersection regions. To correct for the
skew-quad component in the dipoles, the cryostats had to be shimmed to
raise them to the original positions. Figure 9 illustrates how the
process took place. This Figure shows a cross-sectional view of a
Tevatron dipole and the location of the bolts that hold the cryostat in
place; the so-called smart and dumb bolts. For each of the 106 magnets
that were corrected in the Tevatron, three mils shims were added at the
dumb bolt ends on each of the nine locations along the magnet length.
Figure 10 shows some of the cold lift measurements made during the
January shutdown, the first indication of a problem in cryostat
elevation within the dipole yoke.

![](media/image20.wmf){width="4.699212598425197in"
height="3.313779527559055in"}

During the shutdown, 106 dipoles were re-shimmed to remove the skew-quad
component of magnetic field. The corrected dipoles corrected are
distributed on either side of the intersection regions, namely from
A44‑2 through B19‑5 and from A44‑2 through D19‑5. The end points on
these lists are half way between the last remaining skew quad corrector
and the first missing skew quad-corrector. By Norman Gelfand\'s
calculation, this would reduce the vertical dispersion from 0.5 m to
0.15 m, and Tevatron operation since the shutdown seems to confirm that
the machine is now much more easily tuned.

In addition, measurements made during the shutdown by technicians from
the Technical Division suggest that there may be a problem with the
cryostat anchor inside the yoke of many dipoles in the ring. The extent
to which this defect is present in the Tevatron is being studied. The
effect on magnetic field quality and stability is also under study by
the Technical Division.

**Installation of Real-Time Motion-Sensors:**

Beam properties in the change on a time scale of roughly ten days. These
changes are sufficient to require a complete retune of the machine.
Magnet motion or tunnel movement may be the cause of some of these
periodic. Tilt monitors have been used in the Tevatron to detect magnet
motion at the IR's and some of the arcs. Based on the data available,
significant changes may be taking place. The estimates, given in Table
3, are based on observation taken over five to seven month periods.
Extrapolating the data to one year time periods suggests that magnet
rolls of about ½ mrad per year may be taking place. We'll continue to
make these observations to try to confirm these results.

Figure 11b shows two measurements made by tilt monitors set on top of
quadrupoles in the arcs. After a quench, one magnet is seen to recover
back to its original position, while the other does not. Such changes
may account, at least in part, for changes that occur in machine
operation after a quench. We need to understand the cause of magnet
motion during a quench.

During the shutdown, twenty-six hydrostatic level sensors (HLS) were
installed in the tunnel, primarily in B-Sector. These were previously
used in MI-8 and the Aurora mine for liner-collider ground-motion
studies. They were placed in Sector-B, because this sector seems to be
one of the most troublesome in the ring. Tilt monitors were also placed
in sector B to cross-calibrate with the HLS. Figures 11a shows a some of
the data available from the HLS in B-sector.

![](media/image21.jpeg){width="2.7854330708661417in"
height="2.457086614173228in"}![](media/image22.jpeg){width="3.1244094488188976in"
height="2.461023622047244in"}

**Figure 11a (left) and 11b (right): Examples of HLS and tilt-meter data
taken after installation of these devices in the summer shutdown. Figure
11a shows the response of the HLS in different parts of B-Sector in a
one-week period Figure 11b shows one of the tilt monitors responding to
a local disturbance probably a magnet-quench.**

![](media/image23.png){width="3.0in" height="2.4in"}In Figure 12 we
shows two graphs of recent data taken with an geometer at B0. The
vibrations caused by the passage nearby of a 25T tractor/trailer were
easily measured, as were also the increase in losses in the Tevatron. In
the Figure on the right the passage of a fire-truck nearby causes spikes
to occur in a loss monitor. The operational significance of this
\"fire-truck effect\" is shown by the spikes on T:LE012: This is one of
the loss monitors used for feedback by the collimator system. If these
disturbances were to occur during halo removal, the collimators would
stop prematurely. Additional geophones may be placed on the low betas at
CDF during coming shutdowns to further track down the mechanism for this
effect.

**Figure 12: Recent measurements made with an accelerometer at B0. The
figure on the left shows the effect of a 25 T tractor/trailer passing
nearby. The figure on the right shows spikes that occur on loss monitor
readout when a fire-truck passes nearby.**

The work on real-time motion detection is in its infant stages. These
are sufficient devices of different kinds now in the tunnel to give us
experience with their use and applicability. Additional HLS and
tilt-monitors placed around the ring would also provide a more complete
picture of changes that take place. Questions such as, "Do seasonal
variations take place in parts of the ring, but not others? How do
variations in mounting fixtures affect the way that magnets respond to
quenches and other disturbances? What affects can be attributed to the
magnet ramp, and are the effects uniform around the ring?" Our goal is
to measure real time motion in the entire ring to look for these
correlations, and to compare them to accelerator simulations. Perhaps
we'll be able to eliminate the short term changes that occur in the
Tevatron and the subsequent the need to retune the Tevatron even after
only brief periods of operation.

**Magnet Stand Replacement:**

![](media/image25.jpeg){width="2.5in"
height="1.449212598425197in"}Magnet stands have suffered corrosion in
areas where water accumulated during floods, or because of seepage
through cracks in the tunnel concrete. The occurrence of the water in
the tunnel has since been greatly reduced, but the affected stands are
still in place. An example of a corroded stand is shown in Figure 13.

Sixty-one dipoles had new stands installed during the shutdown, in areas
where the greatest damage was observed. A summary of magnet stand
replacement by Tevatron location is given in Table 4. During the next
shutdown, additional dipoles stands will be replaced, as well as
affected quadrupole and spool-piece stands.

**Changes at B0 and D0:**

An accident that occurred several years ago involving the D0 LBQ girder
caused a 0.25 inch horizontal displacement at one end of the girder.
Recent aperture scans revealed a serious restriction at D0, making it
imperative to correct the situation. In Figure14a, we show the survey
data of the LBQ before the shutdown (as-found) and after (as-set). It
may be that this single ¼ inch correction did the most to open up the
Tevatron aperture for this run. Craig Moore led the effort for this
work.

The month of December had many machine down days. We took the
opportunity to adjust the vertical position of the IR at B0. The IR was
about 6mm high at CDF, nearly falling off the edge of the detector
acceptance. The solution was developed by a team lead by Vladimir
Shiltsev, including Mike Syphers, Valery Lebedev, Norm Gelfand and Mike
Martens. The correction involved moving the LBQ down by about 50 mils,
which satisfied CDF requirements. The alignment changes are shown in
Figure 14b.

![](media/image26.png){width="4.320078740157481in"
height="3.056299212598425in"}

**Figure 14a: A ¼ inch horizontal correction was carried out at D0 on
the upstream side of Q4. Initial (as-found) positions are shown compared
to the corrected (as-set) positions.**

![](media/image28.wmf)

**Figure 14b: Vertical changes carried out at B0 to shift the IR down by
about 5 mm, and back within the CDF acceptance.**

####### Tevatron Lambertson Liners

![](media/image29.wmf)Head-tail instabilities, caused by the interaction
between the proton and p-bar beams, were observed and studied prior to
the summer shutdown. This instability arose because the iron in the
injection Lambertson magnets sustained long-latency for beam images. The
impedance of the iron causes the latency. To reduce the impedance, and
thereby reduce the head-tail instability, low resistivity liners were
fabricated and installed in the field free region of the four Lambertson
magnets at F0. Petr Ivanov of the Tevatron Department developed the
concept, and Alex Chen of the Mechanical Support Department did the
mechanical design.

> The design constraints required that the liner be thin (1mm) to retain
> as much aperture as possible, have low resistance to dissipate charge,
> and be ridged to allow for insertion in the field free region. In

addition, the liner required perforations so that trapped gas did not
spoil the vacuum. A 98% copper 2% beryllium alloy was chosen as the
fabrication material. The basic shape chosen was a five sided "dog
house" shape. The circulating beam resides near the peak in the liner.
The base of the liner was designed to provide spring loading, forcing
the peak into the field free region. This spring action forces the
magnet aperture to be as large as possible.

To install the liners the center two of the four F0 Lambertson magnets
were removed from the beam line. The liners were then inserted into each
of the four 3 meter long magnets. A spring loaded pull through target
was developed as a tool to help AMG measure the fit of the liner in the
magnet aperture. The measurement provided a check that the liner was
pushed against the peak of the aperture as much as possible, and that
there were no obstructions in the field free region to degrade the
circulating beam. The target carried a corner reflector that was used by
the Laser Tracker system. The target was both pulled and pushed through
the Lambertson magnets before and after liner insertion. These data were
compared to assure that there was no restriction in the aperture. Figure
14 shows a typical aperture scan with before and after data.

After completing the liner insertion, the two central Lambertsons were
replaced on the movable stands and optically surveyed back to the
as-found position. In addition to new liner insertions, improvements
were made to the vacuum and instrumentation on both the upstream and
downstream ends of the magnets. Improved stands and mountings were
installed for the BPMs and strip line detectors. Differential pumping
was added to improve the vacuum in this region of the Tevatron. In the
process of reassembly a mismatch or misalignment of about 6mm (0.25
inch) was discovered between the Tevatron and Main Injector. Given the
size of the beam pipe, the aperture of the magnets and that the history
of successful beam transport in this part of the Tevatron, no attempt
was made to correct this misalignment during the summer shutdown. More
work will be needed to understand the source of the misalignment,
further beam studies will be done, with the goal of correcting this
problem at the next opportunity.

####### A0 Kicker Realignment

During the first part of Run II, aperture scans near A0 showed a
restriction in the vicinity of the anti proton kickers. An optical
survey revealed that the anti proton kickers were misaligned in the
horizontal plane at the upstream end by 15 mm (0.6 inches). Figure 16
shows the deviation of the kicker alignment form an ideal horizontal
line.

A study of survey data taken in 2000 and 2001 did not reveal this large
discrepancy. All five kickers are mounted on a bedplate that was
designed to move during the change from 800 GeV fixed target operations
to colliding beam operations. Adjacent and to the radial inside were the
bedplates for the fixed target extraction Lambertson magnets. Both
systems were designed for easy movement during change over between these
two running modes. It appears that sometime between March 2001 and
October 2003 the bedplates for the Lambertson magnets were pushed into
the bedplate for the kickers causing the offset.

The bed plates for the Lambertson magnets were jacked up and placed on
cribbing to immobilize them. The kicker girder was pushed back into the
proper alignment and optical survey was used to realign each kicker on
the correct position. Aperture scans in A0 indicate that the restriction
has been successfully removed.

![](media/image30.wmf)

> **Figure 16: Deviation of A0 kickers relative to an ideal horizontal
> line.**

**Conclusion**

A great deal was accomplished during 2003. Complete measurements of
magnet roll, horizontal offsets, and relative elevations were completed
in the Tevatron tunnel. Most of the bad rolls were corrected, and
further corrections will be done as access to the tunnel becomes
available. TevNet was installed, and data processing is currently taking
place. When complete, these measurements will provide a guide to future
realignment in the Tevatron. A set of motion detectors was installed in
B-sector an in B0 and D0. These provide a test-bed for discovery of what
moves in the Tevatron tunnel, and provides an opportunity to measure
long term stability and reliability of these devices. The effects of the
smart bolt corrections require some dedicated beam study time, but early
indications are that coupling is greatly improved in the Tevatron, and
that vertical dispersion is reduced. Work in measuring magnet rolls will
continue in the future. We will soon eliminate all major magnet rolls,
and future measurements will be made on a regular basis to check magnet
stability.

In 2004, TevNet information will become available. A proposal will be
prepared to align the Tevatron to within original specifications: As
Tevatron beam intensity increases, the need to minimize beam losses
requires maximum aperture, which can only be achieved with good magnet
alignment. Furthermore, an inventory of all elements in the Tevatron
will be done to make certain that the alignment standard is met. In the
recent past, many of the biggest alignment errors were discovered in
elements that were forgotten, or not often used. There will also be an
effort to understand short term motion in the Tevatron tunnel. The
effects of magnet quenches, and ground motion have been seen at the 100
micron level. Whether the effects are cumulative, and whether they
constitute an issue for Tevatron optics is to be understood.
Considerable effort will also be given to better coordinate data
available from instrumentation with alignment information. Efforts to
develop an appropriate database are in process. Studies of cryostat
changes in Tevatron magnets will continue in the Technical Division,
hoping to address potential problems before they occur.

[^1]: *Falstaff.* What wind blew you hither, Pistol?

    *Pistol.* Not the ill wind which blows no man to good.

    [William Shakespeare](http://www.bartleby.com/100/138.html): *Henry
    IV. act v. sc. 3.* 

[^2]: Quote from Craig Moore.