Summary of the reports from the TPC groups at the tracking sessions in Prague and Arlington ------------------------------------------------------------------ See the talks on the websites (where available) for more details. ********************************************************************** Prague 15-18.Nov.2002 --------------------- --------------------- See http://www-hep2.fzu.cz/ecfadesy/Talks/Tracking/ NB! Some of the talks (the ones without PS or PDF file) are not yet on the Prague website. I sent a mail to Vaclav asking that they be scanned and then posted. -RS See also Dean Karlen's summary: http://www-hep2.fzu.cz/ecfadesy/Talks/Detector_Plenary_Reports/ Karlen_Dean_prague02-tracking.pdf Aachen......................................................Sven Lotze Sven presented results of tests in a 2T magnet at Juelich. The currents at the Gem surfaces of their triple-Gem test chamber were measured at a function of the B field. The current at the anode showed a 15% increase between 0 and 2T, whereby a drop in the current was expected. This discrepancy can be understood by taking into account the fact that the current measured at the anode is the product primarycurrent*(collection*gain*extraction)**3 for the case that the 3 Gems contributes equally. Sven showed ideas for simulating the transfer coefficients by analyzing the electrostatic flux using the program Maxwell: preliminary comparisons with measurement look promising. Further improvements in the setup are being implemented for tests in the 5T magnet at Desy. Another point: longterm variation in the anode current could be understood via changes in atmospheric pressure. Finally the wire TPC will be replaced by a Gem version that can fit in both the NA35 fieldcage or the 5T magnet in Desy (see Felix Sefkow's Arlington talk below). Future studies will include minimization of ion feedback and optimization of Gem running in a 4T field. Desy/Hamburg................................................Markus Hamann Markus showed further studies of our track resolution by Thorsten Kuhl and himself. Since the last report (meeting on 15.Oct.02: see alephwww.mppmu.mpg.de/~settles/tpc/video151002.txt) the pad response function (PRF) has been implemented in the code of MarkusSchmacher/ThorstenKuhl. The PRF describes the charge sharing between pads and depends on gas diffusion and pad shape. Ideally a linear PRF would be best and a step-function PRF worst. Markus showed several cases which were calculated using a linear pad response function for the TDR gas and Ar2%CF2 for different drift lengths, pad shapes and induction gaps. (They agree fairly well with calculations by Dean Karlen, see below, but there are quantative differences due to different assumptions; by and large it seems that < 100mum should be achievable -- RS). Experimental measurements using the test TPC at Desy and 14mm pads, to account for the lack of B field compared to Tesla, show the expected qualitative behavior. The measurements will be continued in future. Desy/U.Hamburg/U.Rostock.....................................Thorsten Lux Thorsten reviewed the large TPC setup with trigger on cosmics. There had been problems with sparking destroying Gems, and the hypothesis was developed that it was due to the large capacitance from decoupling the pads from the HV. The HV arrangement was changed so that the pads are at ground potential, and this solved the problem. Thorsten then described the prototype being built and the tests in foreseen in the 5T magnet. (At the meeting the comment was made that the fieldcage design shown may be susceptable to charge buildup.) The status of the 5T magnet is that safety tests are finished, quench protection ready and cool-down in progress for first magnetic field in December to be followed by testing with the Aachen, Desy, Karlsruhe and Munich prototypes (see Felix Sefkow's talk at Arlington below for the continuation). Orsay/Saclay/LBL.........................................Vincent Lepeltier Vincent described ion-feed measurements in a 2T B field using a Micromegas TPC and a small-gap wire chamber (1cm drift in both cases). Sources were Fe55 for the wire chamber (gain 100000) and Sr90 for the Micromegas (gain 100). The total current measured in the wire version is reasonably constant with increasing B, while there is a factor 2 increase for the Micromegas. The latter may be due to better beta-ray collection at higher B field from the Sr90 source. The ion feedback does not depend on B for either Micromegas or wires and the dependence on the ratio drift to amplification fields E_D/E_A agrees with expectations in both cases (an effective E_A in the case of wires). Gas properties were simulated: Maximum gain for Micromegas occurs at 25mum gap for Argon with little dependence on quencher. This maximun is larger for heavier main gases, but the dE/dx expectation is already quite good for Argon. Ar2%CF4 has attractive properties: 8cm/mus drift speed at around 200 V/cm, sigma_transv.diffusion = 0.04 cm/sqrt{cm}, omeg*tau = 19, e- attachment maximum of 15/cm at 3kV/cm should be small since the amplification region is very thin for Micromegas and ageing tests show no ageing. The ion feedback modeling gives the result that the optimum should (= E_D/E_A) should occur for > 1000 l.p.i.meshes. Measurements show the expected behavior. Vincent showed the test TPC being built for cosmics and the 2T magnet. Finally ideas or improving the r-phi resolution for short drift distances are being tested: diffusion-after-multiplication or a resistive layer for spreading the charge (see Madhu Dixit's talk below). Munich........................................................Ron Settles This talk is not yet on the Prague website. The commissioning of the Star electronics is described below by Jochen Kaminski. A prototype TPC for the Desy 5T magnet being built was shown: it will have 2mm X 6 mm pads and be able to accomodate wire, Gem or Micromegas technologies (wires to start with). Finally calculations of the momentum resolution, together with Mike Ronan using Bruce Schumm's LCDTRK program, with and without a silicon external tracker, were shown: the improvement at high momenta due to SET is smaller the better the TPC resolution is, being 5-6 % for the TPC resolution goal of 100mum. The resolution with SET is worse for low momenta due to the additional multiple scattering introduced. These results contradict some of the SET results, and this must be understood. Carleton/Montreal(/Victoria).................................Madhu Dixit Madhu described the advantages of a MPGD compared to wires. They are studying the Gem technique and charge spreading for MPGD using a resisitive layer on the pads. The test TPC with Gems which is being used with cosmics was described, as well as some of the measurements with ArCO2 and P10 gases: the drift velocity and diffusion agree with expectations. The resolution is expected to be insensitive to the pad width as long as the pad width is smaller than 4 X the charge cloud size. For P10 2mm and 3mm pads are o.k., and for ArCO2 2mm is o.k. but 3mm is too wide. Madhu showed measurements of a track-angle effect which is possibly due to an oversimplified track fit. The resolution improves with electron statistics, except at very large numbers of electrons where delta rays start to worsen the resolution. The Carleton group is working hard on understanding charge spreading using a resistive anode. The telegraph equation is used in simulations to describe the time dependence of the spreading. The test setup has a double Gem with 4.4mm induction gap and a 33kOhm/sq resistive anode foil 50mum in front of the pad plane. Madhu showed how signals look and how the measurements agree with simulation. For 33kOhm/sq the PRF is too wide (sigma about 3mm), so a design for sigma = 700mum (2.5MOhm/sq) was tried for which the 1.5mm strips turned out to be too wide. Systematic resolution measurements with a collimated x-ray source were shown, and after correction for the bias in the center-of-gravity method, resolutions of 61-78mum were found, depending on the position along the pad. The results are promising and further tests of a mini-TPC are planned with cosmics and beams. Victoria(/Carleton/Montreal).................................Dean Karlen Dean reviewed the ingrediants for his Gem-TPC resolution studies, which have been discussed at earlier TPC meetings and were updated here. The track fit takes into account position, angle and electron cloud size; the gas used is Ar2%CF4; the pad size is 2mm X 6mm. The idea is that the transverse diffusion in a 1cm transfer region between Gems and pads should spread the charge enough to avoid single-pad hits. The expected resolution from the naive calculation averaging over 5 padrows is 23mum. The result from simulation is a bit bigger, by about 25%, and for this case (the Gem case) there is no improvement due to chevrons. Without defocussing (the micromegas case) the resolution is about 60mum for 5 padrows and chevrons can help. The padwidth in the defocussing case is optimum for a width around 4 X the sigma of the electron cloud. Also the simulations show that staggering the pads is better than not for wider pads, although for a width of 2mm there is hardly any difference. The Dean described the data analysis from the test TPC using ArCO2 and P10. The pad layout has 8 padrows where the 6 outer rows are used to define a cosmic track and the inner 2 to measure the resolution. The measured transverse diffusion is 190(500)mum/sqrt{cm} for ArCO2(P10), the x_0 resolution is 140mum for ArCO2, the functional dependence on drift distance is as expected (the absolute value is larger than the naive calcuation) and the padwidth of 2mm is better than 3mm. The analysis of a new large data set has begun, and the goal is to attain a resolution of much better than 130mum for 2mm X 6mm pads. Nikhef..................................................Jan Timmermans This talk has not yet been posted on the Prague website. Jan gave an update to the work he reported at our video meeting on 15.10.02, so here is the status at that time, and as soon as his Prague talk is posted, I (RS) shall update this summary. Harry van der Graaf and Jan concentrated on getting their hardware into operation, to study the feasibility of reading out a TPC with a pixel Si detector (Medipix). A test TPC just constructed at Nikhef has, for a start, 2 Gem planes followed by a wire plane where the signals were read out; the total gas gain was about 10^3. P10 gas, a drift field of 200V/cm and an Fe55 source were used. It was possible to measure pulse heights and the noise was reasonable (ca.100 e-). Jan and Harry hoped to have the Medipix2 chip running soon. Rostock.................................................Alexander Kaukher Alexander reported on investigating whether the TPC can be read out by digital TDCs. In principle this should be possible since only time and charge have to be read out for each pad. TDCs could give reduced power, be cheaper and easier. The charge is proportional to the the signal width above some threshold, so in principle only deltaT and T need to be measured. This technique is being used by CDF for the Central Outer Tracker, using the ASDQ preamplifier. The idea was tested with a FADC at Desy. Alexander showed the open questions for a TDC readout being addressed: amplifier type, charge-measurement technique, occupancy, "common stop" for the TCD signal, architecture, DAQ interface. Plans are to test 2 existing TDC-chips, from the Hera-B and Opera experiments, and to combine the Hera-B TDC with the AASDQ preamps. Karlsruhe/Cern..........................................Jochen Kaminski Jochen showed the test TPC that has been built; it will later be used in the 5T magnet at Desy. Cosmic rays are being measured in P10 using a double-Gem setup. The 1.27mm X 12.5mm pads are engraved on a double-layer PCB, and 256 will be readout using a Star-electronics testrig sent from Berkeley by Mike Ronan and Fred Biser. The track reconstruction GRTP package by Stefan Kappler was commissioned; it can be visualized at http://www-hep2.fzu.cz/ecfadesy/Talks/Tracking/TPC.gif. Jochen explained the analysis of the first cosmic-ray data. After cuts on the track angles, cluster charge, signal/noise and width were measured. Track residuals of 178mum in x and 149mum in z, for example, with this first data. Further optimizaton of the electronics is needed after which tests in beam and B field will be carried out. LBNL.........................................................Mike Ronan Mike's talk is not yet on the Prague website, so see his talk at Arlington below. He described the commissioning of the Star electronics for Germany (see Jochen Kaminski above), as well as tracking studies (see Ron Settles above) and work in Saclay/Orsay (see Vincent Lepeltier above). ************************************************************************ Arlington 9-11.Jan.2003 ----------------------- ----------------------- See http://alcworkshop.uta.edu/workgroups.php and click on Trk 1, or http://scipp.ucsc.edu/~schumm/lctrack/national_meetings/arlington_agenda.html NB! Some of the talks (the ones without PS or PDF file) are not yet on the Arlington website -RS. Summary of European TPC R&D Issues.........................Ron Settles This talk is not posted on the Arlington website, but it is at http://alephwww.mppmu.mpg.de/~settles/talks/ronfoilarlington.pdf This talk is a summary of our LC Note, so it is not necessary to repeat that here. TPC R&D News from DESY.....................................Felix Sefkow Felix described studies of the space resolution (see Markus Hamann and Thorsten Lux above). The large test TPC with double-Gem was shown, and measurement of space resolution described. This test TPC will also be used for studies of TDC readout (see Alexander Kaukher's talk above). The prototype being built at Desy for the 5T magnet should be ready soon. Finally the 5T magnet has now been commissioned, and measurements with the Aachen group and Gem setup described by Sven Lotze above were continued up to 5T. Very good agreement was found below 2T and from 2T to 5T the trends continued for the anode current, extraction and collection efficiencies. Next steps include ion feedback measurements, trying out Gems from Novosibirsk, finishing preparing the Desy, Munich, Karlsruhe and Carleton/Victoria chambers for tests in the 5T magnet. TPC readout with charge dispersion using a resistive anode ...............Madhu Dixit This has is not yet posted on the Arlington website. Meanwhile, see the summary of Madhu's Prague talk above. TPC tracking studies.......................................Dean Karlen Also this is still not on the Arlington website, so see the summary of Dean's Prague talk above. New TPC R&D Results and Plans (LBNL, Saclay/Orsay).........Mike Ronan This talk is on the web. Mike described the collaborative work between Berkeley and Saclay/Orsay. All technologies, Gem Micromegas, and MWPC will be studied. Gem and Micromegas have similar advantages, in that the electrons are collected directly after the gas gain so that the intrinsic resolution and granularity can be improved over wires in principle. The Micromegas work was covered by Mike in this talk. The principle of operation, the gain stability as a function of HV-pad gap, the funnel effect which reduces ion feedback and gas studies using CF4 quencher were reviewed. Sketches of the small-gap wire TPC and the Micormegas TPC built at Saclay were shown and well as feedback results in the 2T Saclay magnet. The large test chamber for that magnet, the star RO test bench and the 5T magnet were shown. The plans call for LBNL to continue vigorously in the work started on all three technologies.