written by H. Ogren,
Indiana University
Sept.15, 1996
The 1.5 meter module prototyping will aid us in several areas:
The 1.5 meter prototype design will be based on "standard" inner layer profile of module as defined in ITA1-95-12 by H. Danielson et. al. These is detailed in mddd301.dwg on Craig Kline's page. (which is a translation of E. David's drawing to a full 1.5 meter module).
This module profile has been used to manufacture the mold to form the 1.5 meter shells, and for the three-part punch that will form the individual polypropylene sheets used at transition radiator. Within this standard profile we can change or modify many design details, such as Kapton divider position and makeup, alignment tabs on kapton, electrical layout on HV plate, design of tension plate, gas feeds and flushing feeds, and alignment pins.
Both of the 1.5 meter modules do not need to be identical. A comparison of the performance and the assembly ease of several endcap designs may be desirable.
The 1.5 meter module will be made with a 400 micron thick carbon fiber shell. A short section development part has already been finished by Composite Horizons, Inc. This tool mold will be used to determine the correct profile to compensate for spring-back. It will also be used as a test point for dimensional specifications. Machine work is progressing on long tool mold for the 1.5 meter module and carbon fiber pre-preg for three shells has been ordered.
Outstanding questions:
What is the variation in wall thickness (400 microns +-?)
What is the profile variation, and what do we require?
Should all shells have kapton or Mylar film on inside? (gluing?,HV?)Depending on delivery time for the prepreg, it appears that we could have out first long shell by October. We anticipate having 3 long shells and one short module constructed this year.
The type of radiator to use in the 1.5 meter module has not been determined. The earlier decision to purchase the full barrel quota of oriented radiator has been called into question by the latest beam tests.
What ever radiator we use the position of the holes and the gas cooling tubes has already been fixed by the punching tool. The present tool, also produces a somewhat larger passage for the straws than was used for the CERN 50 cm test module. The hole sizes were specified at 4.8 mm but seem to measure about 4.9mm, this is probably due to the thickness of material that is punched. We will try to keep it closer to 4.8 mm if possible.
We have arranged to have it punched by a company near Indianapolis, Breiner, Inc. They are prepared to punch it when the material arrives. We believe that it will take several weeks to punch the 10,000 or so pieces that will be required.
We will need about 1000 1.5 meter long straws for the two modules and for individual straw tests. Hampton/Nolfolk State/ TJNAF will assist.
October
2 full length shells received, 1 additional, available for testing
Fiber, radiator sheets punched, toling for staking complete
Kapton dividers constructed
Shell machining and cutting tooling complete
Shells machined
Alignment tooling complete
November
Assemble module, insert radiator, align kapton dividers
Align and glue dividers
Receive HV plate and hardware
Receive straws
Complete end plate alignment tooling
December
Insert and glue straws
gas
test, HV tests
Receive Tension plates, hardware
Complete tooling for wire stringing
January
Complete gas tests and HV tests
string wires
HV and gas tests
Spring
Receive electronics
test with cosmic rays and sources
Summer
Beam test in august
There were a number of changes planned, based on this construction experience.
1) The HV plate needs to be made out of insulating material.
2) With an insulating plate, the straw sockets are not needed for insulation, so the
straws could contact the ends of the HV plate.
3) HV foil had problems with broken petals- replace?
4) HV foil to capacitor sleeve had a weak gas seal.
Can these be corrected for the new HV plate, required in November?
A substantial variation on the HV plate design has been suggested by Duke.
In this design, the HV connection to the straw is made with conducting glue. A newly designed insulating cap pushes into the straw. It has a top section that surrounds the straw end and contains the conducting glue. The twister or wire centering V fits inside the cap. One advantage is that both the inside and the outside of the straw is electrically connected to the HV traces on the board. A HV foil is not used.
This will require:
New HV board layout for HV traces.
Production of new caps.
New Capacitor sockets
New HV connection strip for external connection.
The principle source of gas leaks in the 50 cm module were through the side walls of the shell in the gas volume between the HV and Tension plates. The new shell appears to be much tighter construction.
One variation on the design is a continuous collar that holds both the tension plate and the HV plate. It will eliminate the gas leak thorough the shell. It also has the advantage that the alignment of this collar now directly is attached to the HV plate and the straws. If this collar is insulating, then the problems of break down or shorting of signal to the collar is also eliminated.
This will require an insulating collar and a small change in the dimensions of the Tension plate. The remainder of the tension plate can remain the same, perhaps a small increase in the capacitor sleeve hole will be required.
One other concern is the soldering of the tension plate. The wire bushings are soldered at their bases to signal strips on the inside of the tension plate. This is easily broken when the wire connection is soldered. One suggestion has been to simply glue the crimping pin into the connection and not to solder. Perhaps this should be tried on the 1.5 meter modules.
The cooling pathways will remain in the obtuse angle corners of the module. We will create a via along the module with thin walled material. At the endplate this will transition into an aluminum tube that penetrates the HV and Tension plates and is glued there for a gas tight seal. A separate cooling tube of plastic or aluminum can be inserted though this via.
For the 1.5 meter modules the flushing will be done through the side openings in the shell. We will learn from these tests the extent of the leakage problem and can plan on closed flushing if there is a problem.