Letters to the Editor
Clarifying the truss survey
It was a pleasure to read your article "The BIG Picture" (FERMINEWS, Vol. 23, No. 4, Feb. 25, 2000), which gave welcome recognition to the lab's Alignment and Metrology group. I would like to correct a couple of oversights. As the group's Alignment Task Manager for the DZero experiment, I performed the analysis of the survey data given to the physicist in charge, Al Ito, who was not mentioned in the story but should also be recognized.
I would also like to report that the second EMC Truss was surveyed using the same V-Star digital photogrammetric system on Monday night, February 28 in much better environmental conditions. The temperature was 45 degrees Fahrenheit with wind speed less than 10 miles per hour. The digital photographs were taken inside the bucket of a Cherry Picker supplied and operated by Roads and Grounds. I took the photographs and was assisted by Craig Bradford of the Alignment and Metrology group. Manuel Garcia and Jorge Hernandez Sr. of Roads and Grounds operated the Cherry Picker. Al Ito was present and assisted during the survey. In this picture, Garcia and I are inside the Cherry Picker bucket attaching a scale bar and retro-reflective targets to the truss.
Alignment and Metrology group
Cold facts on the truss
One small question is niggling me after reading the account of the survey of the End Muon System truss. What account was taken of possible expansion-contraction effects in the massive steel truss structure when it was surveyed by ėV-Star' camera? John Greenwood explained that the survey was done outdoors in a temperature of 12 degrees. I presume this is degrees Fahrenheit, rather than Celsius, and therefore cold enough to count as ģbrass monkeyī weather here in Britain. But what will be the ambient operating temperature of the truss? The software may resolve the targets to an accuracy of 1/100 of an inch, but does that accuracy of the target array still stand if there has been even a small expansion of truss components once the structure has been installed in a warmer working environment? Do you apply some kind of temperature correction within the software, or is the expansion effect negligible or even irrelevant?
BBC South West Plymouth, UK
BBC South West Plymouth, UK
(Tom Diehl, overseeing design and construction of the truss, responds:):
Good question. The coefficient of thermal expansion of steel is close to 6.3 x 10-6/degrees F. That is, it will expand by about 6 parts per million per degree F increase in temperature.
We carefully measured the temperature in several places in the truss frame as we took the survey. We will be using the frame indoors. The difference in the temperature between the time we took the survey and the indoor temperature is about 60 degrees F. The truss frame will be about 170 mils (1000ths of an inch) larger than when it was surveyed. This is an important enough difference to require that we make a correction.
Our plan is to scale the distance between the survey points to account for the change in temperature. Because the frame is a complicated construction that procedure will be an approximation. But it's good enough.
Thanks for your interest.
An alternative scheduling view
According to the Feb. 25th issue of FERMINEWS ("Feedback,"FERMINEWS, Vol. 23, No. 4, Feb. 25, 2000), lab management is inclined against alternative work schedules for lab employees, based on fairness. While it may be less than completely fair to ask some employees to work nonstandard weeks (four 10-hour days for example), we believe in some cases the benefit to the laboratory would justify the action, just as swing shifts and 12-hour shifts benefit certain groups at the lab. In our group we have proposed an alternative work schedule which increases the presence of technicians during the week and reduces overtime. No doubt there are other groups which also will feel the strain of Run II and could better serve the lab by offering alternative work schedules.
A few years back the Government was pushing for mandatory car-pooling to reduce congestion and emissions. A four day-work week could help in addressing these issues. It would also reduce the parking burden and vehicular traffic at the lab. By viewing the alternative work schedule in terms of its benefit to the laboratory, we hope the management will reconsider its stance and continue to investigate, and ultimately implement, this concept where appropriate.
Joel Fuerst and Ken Olesen,
Beams Division/Cryogenic Dept.
Beams Division/Cryogenic Dept.
Credit for a photo--and for Wilson
Regarding the photo of Bob Wilson together with Ned Goldwasser at the control console ("Robert Rathbun Wilson: Fermilab's founding director dies at 85," FERMINEWS, Vol. 23, No.2, Jan. 28, 2000)--actually, I took that picture with my own camera on one of my midnight shifts during some of the most challenging times in Fermilab's history.
In 1971, under Wilson's direction, we were rushing to finish the construction of the Main Ring, and achieve a 200 GeV beam, in less than 5 years. Many outside the lab regarded it as an impossible task. When we started testing magnets in the tunnel, we hit snag after snag. There was relentless shorting of magnet after magnet. Magnetized shavings of stainless steel stopped the beam.
All available physicists were mobilized. And we worked hard to bring the Main Ring into operation. We did not have any sophisticated computer system, which Bob hated, nor any elegant software, which engulfs us these days.
We were driving by car from one service building to the next service building in a car, carrying a Tektronics Scope 454 by hand and setting it up on a turned-over garbage can, chasing the beam around the ring, communicating with the control room with a telephone (there were no cellular phones yet). This kind of primitive operation went on for several months, mostly during overnight shifts, because the Main Ring magnets had to be replaced or fixed during the daytime. Sometimes the operation was so intense, we had a nurse on duty in the control room.
During those days, Bob used to visit us in the control room once a week or so. Some days he came to the control room with an old book. While we were tuning the beam, he read verse aloud to us in French about how perilously an Egyptian obelisk was being raised with a mighty group and an ingenious leader.
On such a night we finally led the beam all way around the six-kilometer ring, and we continued to try to send the beam around the ring for a second turn. We saw some good signs. Bob got excited and he volunteered to tune the beam by himself. He had never before asked us to let him do tuning. That is when I took his picture at the control console.
Another midnight shift produced a break-through of a dozen turns of circulating beam. By the end of March 1972 we had the 200 GeV beam circulating within the promised five-year period, thanks to everyone's coordinated effort under the direction of Bob Wilson.
|last modified 3/24/2000 email Fermilab|