Present: Chris Allgower, Andy Bacher, Jack Doskow, Paul Pancella, Tom Rinckel, and Ed Stephenson
Meeting came to order at 3:08 pm.
TARGET BOX
Jack Doskow updated us on the status of the target box design. Not much has been done in the last month, due to other obligations. The discussion turned to the logistics of switching between Tagger and CE78. It was agreed once again that such switches should not happen very often, but that where possible, we should design with that possibility in mind. We will have a totally different box with its own internal baffles. We would share pumps, cold head and nozzle with its support, and possibly catcher tube. Thus the changeover will require removal of pumps, nozzle and catcher, lifting out the old box, dropping in the new, alignment of apertures, installing nozzle and catcher, reattaching pumps, and leak checking. The open sides of the CE78 box probably make alignment easier than for the current box. It is probably easier to switch to CE78 than to switch back. Tom is concerned, however, about the weight of the current box, and how difficult it might be to get it out. Jack will try to calculate this.
Doskow and Pancella will sit together next week to try and advance this design some more, with a particular effort to evaluate the magnitude of any machine shop work. We are reminded that Walt Fox has calculated 1/8" of aluminum would be thick enough for the side walls, but that rupture/seal tests may still be necessary, requiring in turn the fabrication of some sort of test fixture, which may also require some machine shop work.
CHANNEL DESIGN
Pancella presented results of his detailed study of the magnetic channel optics using the program Transport. Earlier Transport results reported by Berg have largely been superceded as more details have been added to the input parameters and the calculation has been extended to second order.
In particular, the septum will probably give us much less vertical focussing than originally predicted. The sextupole components of the first two quadrupole magnets lead to significant aberrations, partly because it seems they are additive in the current configuration. These two effects, along with the predicted multiple scattering, make it appear that the envelope of alpha particles will only be marginally contained, ie., we will be filling the apertures of all of the quadrupole magnets, and the alphas will be very spread out at the end of the channel. (This latter confirms Pickar's estimates from GEANT.)
Two options were raised which might improve the situation. First, there are a couple of ways the net sextupole contribution might be reduced. One would be to turn one of the first two quads on its side. It is thought that this would make alignment difficult, since we had planned to align the quads without their vacuum cans first, then split the tops off to install the vacuum chambers without moving the magnets. Another possibility is to reduce the sextupole in Q1 (the K600) by increasing its vertical aperture (which is currently smaller than the horizontal). The disadvantage here would be loss of calibration of the field from earlier maps. This will have to be considered further.
The second improvement might be to increase the bend in the septum to restore some of the lost vertical focussing. This is a question of the actual limit on power/cooling of the assembled magnet, and it is not known at this time what the maximum field will be. Tom says it will be early January before we have this data point in hand.
Allgower reported that the number of lead glass detectors that have failed but might be fixable has been reduced to three, bringing the total number of working ANL detectors to 96.
Our meeting next week will be rescheduled for 4:00 pm on next Tuesday!
The meeting adjourned at about 4:25 pm.