From settles@mppmu.mpg.de Thu Aug 30 10:29:45 2007 Date: Thu, 30 Aug 2007 10:28:45 +0200 (CEST) From: Ronald Dean Settles To: lctpc@desy.de Subject: Revised summary of LP WP#37 phonemeeting 22.08.2007 Dear lctpc friends, There are three changes to the summary of last week's LP phonemeeting: =>Dean (who couldn't attend the meeting but replied to the summary-email) made suggestions as to the use of SiLC detectors for the cosmic running. =>Dan pointed out my typos w.r.t. the size of the bolts being discussed for the LP fieldcage. =>Dean points out that the a 20micron bowing of the LP endplate cannot be dismissed. The modifications are marked by => in the new version below... Cheers, Ron WP#37 22/08/2007 -------------------------------------------- Wednesday 8 August 2007 West Coast East Coast W.Europe Japan 07.00 10.00 16.00 23.00 Present: --Klaus Dehmelt --Ralf Diener --Michael Hauschild --Katsumasa Ikematsu --Dean Karlen (by email) --Sasha Kaukher --Leif Joensson --Martin Killenberg --Vincent Lepeltier --Takeshi Matsuda --Dan Peterson --Peter Schade --Oliver Schaefer --Ron Settles --anybody forgotten? Summary ----------------------- 1. Cosmic-trigger news --Takeshi summarized his first proposal calling for 14 counter slabs altogether above and below the TPC based on discussions with Klaus, Dean and others during the last few weeks. A basic question was, do we need counters of length different from t2k (210mm x 870mm). Klaus suggested that placing some of the counters perpendicular to the r\phi direction should make it possible to match the length to the TPC. Several scenarios were discussed: it was decided that we don't have to decide the exact arrangement at this point in time, but only the total number of counters to order to have flexibility in setting up the trigger early next year. Klaus added that PCMAG will be placed on a lifting, so that there will be additional flexibility for r\phi triggering arrangement (simulating tracks from the IP e.g.). We can also add Pb bricks if we want (comment by Michael); a platform for them would have to be made of course. Klaus said that SiLC is not planning to be part of the cosmic running during the first half of next year; their Si counters cover 4cm x 4cm, which is fine for beam tests of time-stamping, etc, but maybe not so important for cosmics (if someone has an important test for SiLC+cosmics, please let us know). =>Dean: Si+cosmics - two reasons for this: 1) High energy muons (distributed over broad range of phi and tan lambda) will be more useful for studying electric and magnetic field distortions than the 6 GeV electrons from the test beam. Having some of the cosmics tracks with precise silicon information will be useful anchor points. 2)I suggested a mode to study the effect of positive ion feedback was to operate the cosmic trigger while in the test beam... if a high intensity electron beam can be produced, then it would produce a source of positive ions and we could look for distortions in the muon tracks. Again, having some anchor points will be useful. This doesn't have to be in place from day 1, but it would be nice to have the capability. =>end It was decided that the total number of slabs we need is 15, and that we don't need slabs of a different lengths. Further it was agreed that Takeshi should order, as he suggested, 40 MPPCs with 100-400 pixels (30 `a 2/slab + 10 spares). The CDC group can handle the MPPCs financially, but the collaboration may have to help out for the counter slabs (we don't know the price yet: Takeshi will find it out next week). 2. LP1 fieldcage/endplate/electronics news. a. Dan's explained the new info on his webpage http://w4.lns.cornell.edu/~dpp/linear_collider/LargePrototype.html . 2007-08-21 - Gas seal test: by improving the shape of o-ring grove and using 4-surface contact (see the webpage for details) the background leaks were eliminated. After installing a flat plate for the "endplate+module", Dan measured a leak rate of 0.13cc/h/module, therefore about 1cc/h for the whole LP endplace. (Since the volume of the LP is about 3 x 10^5 cc, this seems to be quite acceptable.) Dan pointed out that if the LP o-ring grouve is in fibreglass material, surface treatment will be needed to ensure tightness. Peter and Dan have been exchanging info about endplane/fieldcage things: Dan suggested using a 4-surfact contact for the o-rings on the LP, while Peter said in Desy the engineers are thinking of a 2-surfact contact. The Desy technical people want to increase the radius of the o-ring, and Dan agreed that this is o.k. =>Dan: Desy is proposing 5mm bolts, rather than 6mm bolts, to allow space for inserting the "Ensat self-tapping threaded insert" rather than Helicoils. Dan is concerned if it will be possible to apply enough torque to compress the o-rings with either 5mm or 6mm bolts. Tests with these bolts must be performed. =>end Further, Dan is looking into a flat endplate-flange (in contrast to a flange with a "step" as discussed at the meeting on 08.08.2007); he will add a stiffening rib if necessary. After designing that, the decision between step and no-step can be made. [Note added by RS. For the Aleph TPC we had a 2-surface contact between the Stesalit fibre glass o-ring grouve and the aluminuim "wheel" frame. A thin coat of vacuum grease--which had been tested for outgassing properties (high-vacuum grease shouldn't outgas, right?)--was applied to the o-rings for the 36 sectors; the grease filled any pores that were in the fibre glass.] 2007-08-17 - Stress relief test plates: hanging weights from an endplate mockup of 30cm x 50cm area simulated 2.6mbar overpressure. The largest mullion deflection was 7 microns. This translates to about 20 microns (to be checked) for the LP. Peter thinks (to be checked) that this corresponds to an E-field distortion which is negligible. =>Dean: I think you cannot dismiss 20 micron deflections of the endplate. A rule of thumb is that a 20 micron displacement in the drift direction can produce a 20 micron deflection in the transverse direction for electron drift paths. The deflection is reduced by operating with a strong uniform magnetic field. However, if we want to effectively "measure" the magnetic field with tracking and photo-electron data, I think we need to understand the TPC without the magnetic field first - and so we should work hard to keep electric field distortions as small as reasonably possible. =>end [Note added by RS. This must be further discussed at the next meeting(s).] 2007-08-03 : A drawing for a Micromegas module (without gate) has been made (see the website). (Paul and Franck should cross-check.) b. JAE connectors. Leif has found a European supplier that is not too expensive; he will order connectors for 2000 channels from them to make sure we have enough on time to get started assembling the electronics. Takeshi will be in contact with the company at Kek on 28 August and see if we can get the remaining 8000 channels at their cheaper price. Martin said he would like to have 20 connectors for Bonn, and Sasha said he will buy 50 for his tests. 3. AOB --Info from Takeshi on PCMAG: To make the cryogenic operation of PCMAG safer and easier, a discussion with with Joachim last week at KEK led to the agreement that Takeshi et al would write a proposal to EUDET for the improvement, so that Joachim could include it in his budget (of 10-15k Euro) --Next meeting: 05.09.2007