Present: Allgower, Bacher, Gardestig, Olmsted, Rinckel, Stephenson
SUMMARY OF THE RUN:
The first purpose was to bring the magnetic channel back into operation using the parameters available at the end of the previous commissioning run. This was accomplished is a small amount of time. The realignment of the third quadrupole resulted in a beam spot centered on the delta-E(2) scintillator. No adjustments were needed to the channel magnets. Changes in the position of the delta-E(2) scintillator caused most of the protons to be out of time in the trigger, so that most of the events represented p+d -> 3He+pi0. The cone angle was measured to be 1.55 degrees, and was partially cut by the edge of the first wire chamber. Later the cone angle was reduced to 0.95 degrees, which fit with room to spare. For both energies, the RF frequency was used to obtain the Cooler circumference; the results overlap within errors the answer obtained last May.
A new segmented delta-E(1) detector was tested. The four segments were held in place with a frame that clamped the light guides, and a mount of unistrut that held the PMT bases and bore the weight of the whole assembly. In putting this detector together, it was found that the original configuration would not work because the scintillator was not mounted flush to the edge of the light guide, and this interference caused the assembly to have large gaps. So the directions of the scintillator were changed, resulting is a less sturdy mount. As a result, gaps appeared from places where scintillator was missing or overlapping. Some of this was corrected during the run. The detector was hard to mount. In the end, it was about 1 inch low.
The Pb-glass were read out using only the channel trigger so as not to miss any information on the response to gammas from pi0 decay. Pulses were seen with twice the height of the cosmic signal, but the spectrum sloped gently down from low pulse height. Typically 2-3 detectors fired on a single side above the discriminator threshold. Events with only one side were not as numerous compared to double side hits as expected. Some effort was invested to get as many detectors working as possible; in the end only two failed to produce some signal. A large amount of data was taken to observe pi0 decays. Cosmic data was taken simultaneously. Time signals were observed, but the sortware to remove the multiplexing was not implemented online.
Some data was taken below threshold, and some data taken without target above threshold. In both cases, high energy events resembling pi0 gammas were seen in the Pb-glass with correct timing. Further investigation is needed to determine the origin and character of this background, since we may encounter it again with the deuteron beam.
The new luminosity system, consisting of two forward plastic scintillators and a position sensitive silicon detector, failed to produce any coincident signals. For some time, the luminosity system was included in the data stream using only the forward detectors. It was later determined that the beam spot was shadowed by the nozzle and cold head, the cold head being larger than what was drawn on earlier plans.
Difficulty was also encountered with the nozzle. It clogged after 1-2 days of operation to the point that only about 10% of the beam was consumed during a flattop that lasted nearly a minute. Once it was warmed to room temperature; then on later cycles to only about 150 K. This cycling helped temporarily.
SHORT TERM CHORES WHILE THE COOLER REMAINS OPEN:
The Cooler is available for about 1.5 weeks while the change is made from proton to deuteron beam. During this time a number of items are being addressed.
Measurements of the silicon position are being made so that drawings of the target box can be brought up to date. Then the silicon was removed, along with the exit window. A second window will be made an tested for leaks.
The gas lines in the target system were checked for leaks. The line from the gas control panel to valve V1 was replaced. This may have been a source of air leaking into the D2 on its way to the nozzle.
A large effort was made to identify changes to the luminosity system. A second set of scintillation detectors will be set up outside the side windows of the target box to observe d+d elastic scattering near 45 degrees on either side of the beam. The scintillators will be split into two wedge-shaped sections so that position along the beam direction will lead to varying pulse heights in the two sections. It is hoped that this will replace the profile given by the position-sensitive silicon. In addition, the two sections will be oppositely displaced vertically to allow a diagnostic on the vertical position of the beam. A design for the scintillators was prepared and sent to the shops for construction. The calibration will require two additional scintillators that observe protons at 45 degrees and deuterons near 25 degrees. At the same time, a new, higher position will be developed for the silicon detector, and both systems tested during the next run. Chris Allgower has assembled electronics for the new system.
More deuterium target gas has been ordered.
An inventory was taken of all the materials, thicknesses, and distances along the particle flight path through the channel. The plan is to make a new model of the energy loss and particle timing that can be used to predict the changes needed in going from 3-He to 4-He operation. Also the calibration of the channel time measurements was repeated, with the result that the timing is 21.0 channels/ns. A pulse system is build and running that simulates the event timing for 3-He. This can be changed in a controlled way to check the timing for 4-He.
FEBRUARY PROJECTS
During the next month, several key issues will be addressed: