Present: Chris Allgower, Andy Bacher, Hermann Nann, Tom Rinckel, Paul Pancella, Ed Stephenson
Meeting came to order at 3:10 pm.
No meeting was held last week.
NOTE that many beliefs held during the meeting and recorded below are changed by the coil failure in the septum which occurred hours after the meeting adjourned.
SEPTUM MAGNET
Rinckel reported that the septum magnet appears to work, and that mapping is finally underway. (See earlier email broadcast from Tom for details.) A current of 1300A seems to be comfortably below the maximum, indicating no problem achieving the desired field strength. It might even work without the booster water pump, depend- ing on the final field value, but the booster is used during mapping. Only one end of the magnet has been measured, and only in the mid- plane, but one out-of-midplane map is planned before turning the magnet around. Mapping may be completed by this time next week.
Pancella presented the first crude estimate of the upstream effective edge of the field based on data taken so far. It appears to be parallel to the yoke at the point where the reference trajec- tory enters, but also displays substantial curvature. This can be accounted for in TRANSPORT, but revised calculations will wait until the other end has been mapped.
Initial measurements of the field inside the shielding for the cooler beam indicate that this shielding should be extended farther upstream. These measurements can continue simultaneously with mapping.
CHANNEL DESIGN
Now that a bit more is understood about the source and effects of sextupole strength in the quadrupoles, a logical change to make would be to rotate one of the first two quads by 90 degrees about the beam axis. If done properly, this would cause the designed-in sextupole moments to nearly cancel eachother, and TRANSPORT predicts a substantially smaller spot at channel end would result. Pancella presented calculations and drawings showing his proposal to put the K300 first in line, in its normal orientation, followed by the K600 on its side. This clearly would fit with a 21.5 degree channel bend (13.3 kG in the septum if the effective length is not too far off). A detailed look at the pole profiles and vacuum chambers (in consul- tation with Kinser and Fox) indicates that the calculated cone envelope fits in the vacuum chambers with a clearance of nearly 1 cm all around, and no changes are required to the vacuum chambers now being constructed.
There seemed to be general agreement that this change should be made. Given the uncertainty in the multiple scattering calcula- tions, it seems important not to spread the cone too much by other effects. Related to this is the question of the diameter of the vacuum chamber between the quads and the final detectors. It will be considerably easier to design and build a chamber based on 12-inch pipe than it would with 14-inch pipe. Current TRANSPORT calculations indicate that the smaller pipe is quite adequate, but the method of including multiple scattering makes it impossible to determine the exact shape of the distribution of rays at channel end. One attempt to model the channel with GEANT some time ago led to about an 12 inch predicted width, but that was a one-shot calculation with quite different quadrupole configurations (by Pickar) and then clearance was added to arrive at a final detector width of 14 inches. Tom will check on how the available flanges might influence this decision, while Ed and Paul will try to push the reliability of the multiple scattering predictions.
Pancella has also done the TRANSPORT calculations now for the first test run. Using the same magnet configuration as appears optimum for alphas, he puts in the kinematics relevant to pd -> 3He and the _current_ gas jet target location. Since the 3He momentum for the same cone angle is considerably lower than for alphas, two effects combine to make the acceptance smaller: less vertical focussing in the septum and larger multiple scattering. Pancella predicts that 1.7 degrees may not fit in the quads, but 1.6 probably would. This is fairly inconsequential, since the goal is simply to see how the channel works, and we will be free to vary the beam energy (and thus the cone angle) to actually determine the acceptance behavior of the channel.
As an aside, with the GJT in its current location, the 1.7 deg. 3He cone nearly fits through the existing "snout" for the exit of the 6 degree magnet chamber, and 1.6 deg. would clear nicely. Thus a new "snout" is not needed until we move the target upstream to its final location.
SCHEDULING
Rinckel presented a subsection of a GANTT chart which shows it should be possible to have our channel ready to test by the end of February, although it will be tight. This of course depends on everything happening as planned.
The very benign running schedule for the Tagger experiment which was presented to the visiting committee last week appears to be slipping again. Testing of the LH2 target in the Cooler during February now appears very unlikely. Our best strategy is still to be ready for a channel test as soon as possible. It looks like all detectors will be ready on schedule, although Stephenson will check on possible conflicts in the scintillator shop. Our group will have to be responsible for mounting of the detectors and testing in place.
TARGET BOX
Pancella worked with Doskow over the past week to make some progress on the target chamber design. There is no problem with mounting the field clamp on the 6 deg. magnet without changing the target position, and still accomodating all pumps. It should soon be possible to specify the main chamber welded assembly for outside bids. Dimensions are settled, and details of construction and means of mounting the thin side windows are now being worked out. Jack is also working on a test fixture for overpressuring these large windows.
The meeting adjourned at about 4:50 pm.