Subject: last version of TPG RF/X-ray test plans Date: Tue, 01 Jul 2003 11:45:05 +0200 From: Emilio Radicioni To: Marco Apollonio CC: Edda Gschwendtner , giulio.saracino@na.infn.it, marco.apollonio@ts.infn.it, gastaldi , Alain Blondel , Gabriella Catanesi dear All, the last version of what we believe it is reasonable to do, in order to assess potential problems related to RF and X-ray backgrounds, is included in this email. Comments, please. cheers marco, emilio --------------------------------------------------------------------- Photon and RF background related issues for the TPG: ============================================ POTENTIAL PROBLEMS: P0) RF noise pickup from RF cavity. P1) occupancy in the detector due to X-rays conversions in the gas and in the detector structure. P2) response of the "ionization charge amplification" part, i.e. the 3-GEM structure, to X-rays: P2.1) (low-energy) X-ray induced photo-electric extraction of e- on the surface of the first GEM foil P2.2) (high-energy) X-ray conversion in the first GEM foil producing electrons which are further amplified by the 2 subsequent GEMs. It is likely this issue is NOT particularly hazardous for detector peroformances, since amplification due to 2 GEMS is 1/100 of the amplification by 3 GEMs, unless the primary photon source is VERY intense. TENTATIVE SOLUTIONS S0) As already declared during the MICE collaboration meeting in Berkeley (October 2002) we plan to measure noise pickup figures near an RF cavity at CERN. There are two possibilities: one is the 88MHz cavity built in the framework of cooling channel design; the second option is using a 200MHz, thus providing an RF noise spectrum as close as possible to the one in the final MICE setup. A survey of possible test areas will be done during July, in the aim of having a prototype chamber operational near a cavity during September. Depending on the availability of time and manpower, a staged approach will be adopted in the following order: - RF pickup on the chamber itself; study grouding techniques - RF pickup when the chamber is under HV - Comparison of ionization signals in RF ON and RF OFF modes. - Shipping of the chamber and relevant equipment to Lab-G for further tests at 800MHz S1) we learnt from 26/6/03 meeting that a photon spectrum taken at LabG exists. We consider this as a starting point to address issue P1. We can use this spectrum as an input for a GEANT4 simulation, shoot X-rays according to this sepctrum in our detector and study the occupancy due to Compton and Photoelectric e- using different detector configurations, e.g. Ar or He based mix. S2.a) Another level of understanding is how the GEM are "efficient to X-rays"; an ideal detector should be transparent to X-rays, which is not. We should understand what happens to electrons generated in the conductive film of the first GEM stage, namely: how many conversions we get and how much amplified the relevant signals are. Once more a Geant4 simulation will be used to generate X rays while drift and amplification of ionization electrons will be carried out by other codes (presumably GARFIELD/MagBoltz). We consider this as a way to address issue P2. S2.b)In parallel to this software program we plan to expose the detector prototype to radioactive sources: 54Mn produces 5.5 keV X-rays (25%) and 800 keV gammas (100%). Gammas can be used as a trigger tag while X-ray absorption in the medium can be studied, covering therefore the lower part of the spectrum. 60Co produces a pair of gammas (1.17 + 1.3 MeV) in principle easy to trigger but we introduce the complication of pair production effect. Again, as a general comment, these data taken with sources can be compared to a proper simulation. Software issues. A decision on the options of having the simulation initially performed in G4MICE or in a standalone G4 program will be taken soon. Nevertheless, algorithms eventually developed in a standalone program will lately be ported to G4MICE. The reconstruction issues have already been discussed in several meetings. The approach is the following: - for comparison purposes, the simulation of the trackers is done in G4MICE - since a common MC output format has been chosen, we will use such an output as input to reconstruction algorithms implemented in a HARP-derived software framework. - The source of TPG specific algorithms will be made public. Possibility to run the TPG reconstruction on MC data will be given to any interested person participating to the software project. - Depending on availability of time and manpower, the TPG reconstruction algorithms will eventually be included in the MICE software architecture.