Comments on new 3Q120 spare magnets

David Harding

21 March 2006

Given the importance of the neutrino program to Fermilab's future, it is
critical that we maintain a suitable set of spare magnets and consider
improvements to enhance the reliability of the operational magnets. The
NuMI beam line relies on 3Q120 quadrupole magnets for transport of the
primary proton beam. The magnets in the beam line were originally
constructed in the 1970's and 1980's for use in other fixed target beam
lines that have now been decommissioned. In preparation for installation
in the NuMI beam line, they were all tested for electrical integrity, as
well having the cooling water passages tested for leaks and flow rate.
In the course of that testing, so many magnets were found to have water
leaks that we had to scour the tunnels for additional magnets to
refurbish before we found enough good ones to complete the project. In
fact we were forced to use a few magnets with less cooling capacity than
optimal. While we now have a set of spare magnets, this history leaves
us concerned about the long-term viability of magnets and the adequacy
of the spares pool.

An additional concern is that some of the NuMI magnets are running at
RMS currents beyond their design level. Those magnets have been provided
with supplemental cooling plates that clamp onto the core of the magnet.
The RMS current is also being reduced by ramping the magnets, as the
required duty factor is rather low, but the high inductance of the
magnets limits this approach to reducing the power.

Over the years the original 3Q120 magnet design has evolved through
improved coils and cores, while maintaining the basic pole geometry
\[1\]. To systematically distinguish them, we now use three-letter
designators for the different styles. The two versions compared here are
called QQM and QQB. They have identical cores but differ dramatically in
the coils. The two big choices that will need to be made are 1) the
preferred style of coil and 2) whether to salvage old cores for use in
the new magnets.

The QQM, currently installed in NuMI, uses many turns of solid conductor
cooled indirectly by a few water passages connected to copper fins
between sections of coil. The QQB, installed in the Main Injector
transfer lines, uses fewer turns of hollow conductor directly cooled by
water. The table below compares a number of key parameters. The magnetic
properties of the two styles are identical for the same number of
Ampere-turns, but the QQB can run at higher excitations due to the
improved water cooling.

TD regards the hollow conductor coils as more robust than the indirectly
cooled coils. The drawings meet today's standards. Modern travelers are
ready to use. The tooling can be expected to be in good shape and take
minimal set-up time. None of the above is true for the solid conductor
cols. The labor for winding the hollow conductor coils and assembling
the magnets should be a bit less.

Recovering cores from old magnets would take a bit more labor than
stacking new cores. There appear to be enough failed 3Q120 magnets with
the larger cores so that if we reused the cores we could avoid the cost
of buying new laminations. The old magnets would be placed in the
debonding oven to have the epoxy oxidized. The tie plates that hold the
core together would be ground off. The old conductor would be removed.
(It is not salvageable.) The core would be grit-blasted to clean it up.
There may be rusting between laminations of the old cores that we would
need to seal in to reduce the danger to the new coil insulation. We
would need to try to discover what insulation was used on the old
magnets and whether it would stand up to the debonding temperature, and
if not, whether that would be acceptable for this application of the
magnets. The temperatures are controlled debonding adequately so that we
do not expect either a change to the magnetic properties of the steel or
mechanical deformation due to stress relief.

An additional choice is in the beam tube. The standard model beam tube
is round stainless steel, OD 2.950" to 2.960", wall 0.595"±0.001". In at
least one magnet built for the AP1 beam line, the round tube is replaced
by a "star shaped" tube, bumping the aperture in the horizontal and
vertical midplanes to about 4.23" ID, but with no increase on the
diagonal. Aside form the extra time and cost to procure the fancier beam
tubes, a disadvantage of the star tube is the displacement of small pole
piece stabilizers, leading to a possible slight degradation of the
magnetic field uniformity. The field quality beyond a radius of about an
inch is not known in any case, but it could be calculated.

In the mid 1990's the cost for constructing 17 QQB magnets for the Main
Injector transfer lines was \$41,156 each, exclusive of EDIA and
tooling. Broken down, it was \$20,006 for M&S, \$13,517 for SWF, and
\$7,633 for contract technicians. The M&S is likely more than double for
FY07. The prices of steel and copper, which dominate the M&S, have taken
dramatic jumps in the last few years. The price of raw copper is almost
three times what it was then. Most steel isn't up that much, but we got
an exceptionally good price on steel for the Main Injector, so the ratio
will probably be about that. The cost of labor has gone up, too. This is
less of a concern for you, unless we run into a conflict where the Lab
has to make a choice between our techs working on these quads and hiring
contract techs. Contract techs are less expensive per hour, but are also
far less productive initially.

Given the current technician level and other known projects, one year is
a rough estimate for the duration of fabrication. Assuming obligation
authority for the M&S were available at the start of FY07, work could
begin around February 2007. If, as is generally the case, the year opens
with uncertainty, fabrication work would begin later. Magnets could then
be installed during the 2008 shutdown without any extraordinary effort.

TD/Accelerator Support expects to be working on two other major projects
on the same time scale, new corrector packages for the Booster and spare
quadrupoles for the Main Injector. Production of the Booster correctors
is scheduled to begin around January 2007 with a deadline of completing
24 magnets in time for testing and installation during the (as yet
unscheduled) 2007 shutdown. That effort will take priority. 24 more
magnets plus spares will follow for the 2008 shutdown. The Main Injector
quadrupoles will be a continuation of work from FY06, building new spare
magnets and rebuilding magnets that have failed. This work should taper
off in the middle of 2007, but in any case will be lower priority once
the current spares pool is supplemented by even a few magnets. This
rough projection suggests that no additional technicians would be
needed.

Some engineering supervision will be needed whichever magnet style is
chosen. We expect that less would be needed in the case of the QQB,
since we are happy with that design. Any attempts to improve the QQM
performance would require an early investment of engineering time with
no assurance of a payoff. It is not practical to start that effort now,
but some exploration could begin later in FY06. Any changes would
involve drafting time, perhaps a couple of drafter-months, since all the
QQM drawings date from the pencil and paper era. Attempts at improvement
would introduce a delay in the whole schedule, but probably still allow
installation during a 2008 shutdown.

+--------------------------------+---------------+--------------+-----+
|                                | **QQM**       | **QQB**      | **U |
|                                |               |              | nit |
|                                |               |              | s** |
+--------------------------------+---------------+--------------+-----+
| **Turns per pole**             | 118           | 28           |     |
+--------------------------------+---------------+--------------+-----+
| **Resistance**                 | 1.6           | 0.16         | Ohm |
+--------------------------------+---------------+--------------+-----+
| **Inductance @ 100 Hz**        | 1.4           | 0.082        | H   |
+--------------------------------+---------------+--------------+-----+
| **Water flow @ 100 psi\        | 17            | 5.7          | gpm |
| (not including supplemental    |               |              |     |
| plates)**                      |               |              |     |
+--------------------------------+---------------+--------------+-----+
| **Core width**                 | 17            | 17           | Inc |
|                                |               |              | hes |
+--------------------------------+---------------+--------------+-----+
| **Core height**                | 15            | 15           | Inc |
|                                |               |              | hes |
+--------------------------------+---------------+--------------+-----+
| **Steel length**               | 120           | 120          | Inc |
|                                |               |              | hes |
+--------------------------------+---------------+--------------+-----+
| **Flange-to-flange length**    | 132.0         | 132.0        | Inc |
|                                |               |              | hes |
+--------------------------------+---------------+--------------+-----+
| **Core to lead end flange**    | 5.0           | 6.5          | Inc |
|                                |               |              | hes |
+--------------------------------+---------------+--------------+-----+
| **Core to bellows end flange** | 7.0           | 5.5          | Inc |
|                                |               |              | hes |
+--------------------------------+---------------+--------------+-----+
| **Assembly drawing**           | ME-388120     | ME-331805    |     |
|                                |               |              |     |
|                                | [Link to      | [Link to     |     |
|                                | TIF](ht       | T            |     |
|                                | tp://tdserver | IF](http://t |     |
|                                | 1/project/TDa | dserver1/pro |     |
|                                | rchivedDrawin | ject/TDarchi |     |
|                                | gs/drawings/3 | vedDrawings/ |     |
|                                | 88000-388999/ | drawings/331 |     |
|                                | 388120B1.TIF) | 000-331999/3 |     |
|                                |               | 31805E1.TIF) |     |
+--------------------------------+---------------+--------------+-----+
|                                |               |              |     |
+--------------------------------+---------------+--------------+-----+

References

1.  <http://tdserver1.fnal.gov/PBar-Magnets/Magnets/QQx/QQx.htm>

Subject: Spares for NuMI 3Q120\'s

From: Sam Childress \<childress@fnal.gov\>

Date: Fri, 17 Mar 2006 14:38:00 -0600

To: David Harding \<harding@fnal.gov\>

CC: Dave Pushka \<pushka@fnal.gov\>, wolff@fnal.gov, Bob Ducar
\<ducar@fnal.gov\>, \"George E. Krafczyk\" \<krafczyk@fnal.gov\>, Sam
Childress \<childress@fnal.gov\>, Craig Moore \<cmoore@fnal.gov\>, Bruce
Baller \<baller@fnal.gov\>

Hi David,

Per our discussions, I am inquiring as to requirements to
build/refurbish a number of quads suitable to provide an adequate 3Q120
NuMI spares inventory appropriate for the next decade of NuMI beam
operation.

In the process of refurbishing existing 3Q120\'s to use for the NuMI
beam, the existing lab inventory of magnets was exhausted in acquiring
the ones needed for NuMI initial operation. We have had good experience
during this first run with all of our magnets, but (based on historical
experience for the 3Q120\'s) there have to be concerns for long term
reliability of these quads, especially as we go to faster ramp rates
than for initial project design.

I consider a need for 6 (six) additional quads, with this number based
on the five current magnets which run at the highest currents \[from 71
to 83 amps at flattop\]. These are also the magnets for which we
currently use the supplemental external cooling.

Your recommendations along with approximate technical and resource
requirements are appreciated for two possible design considerations:

i\) Building/refurbishing new quads to match design of the existing
3Q120 units. There would be internal water cooling lines comparable (or
with some improvements as feasible) to the existing magnet design, but
-as currently exists - the cooling is by separate lines from the magnet
Cu coils.

ii\) Building new magnets similar to more recent era design quads
-higher current and with internal water cooled coils -- which maintain
the approximate external dimensions and B-dl capability as the 3Q120\'s.
The motivation here would be to build more robust magnets, but other
resource needs - power supplies, cables, water - would have to be
understood also.

Thanks much in advance for your inputs.

Regards,

Sam