Jim Clarke, Duncan Scott (ASTeC), wellcome to the collaboration! Aerogel, Kirk McDonald ---------------------- - Background of ~1000 p.e. per bunch seen. Expected signal is 1000 to 10000 p.e./BX Cerenkov thereshold at ~4 MeV - Background probably comes from the e- beam undneath the table. Rotate counters by 90 degree to move them away from e- beam This needs preparation (fixtures). - Shorten the channel. Flexible design. Can be done within a few days, if needed. - Dieter pointed out that there is a large neutron background in this area, but the device is probably not sensitive to neutrons. - Do we need to calibrate the counters? If so, how? - How are we going to determine the background? Is data with undulator off, okay for that? - There will be a common stand for SiW and Aerogel: Who will take responsability? Undulator, Alexander Michailichenkov ------------------------------------ - 3D drawings of the whole setup available. - Alexander is preparing two undulators. Second undulator with opposite helicity? - Alexander shows photographs of the two undulators. Mechanical frame is already produced. - The two undulators will be mounted on a precision gig-plate. It will be kept for the experiment. - Power supply for 1 undulator existing and tested. Alexander wants to build one that can power both undulators at the same time. - New idea presented: Undulators could be cooled with ferro fluid, i.e. coloidal suspension of micro ferrits in oil. This increases the magentic field (field calculations shown). - 25000$ approved to order 2.5 l of the fluid (CBN 04-3). - General agreement to start with the ferrofluid cooling. But keep regular oil cooling as backup. - Discussion on inner diameter of the beam tube. Original ID is 42 mil. With the ferro fluid, we would get a higher photon yield for this ID or we can increase the ID to 50 mil and would still have the original photon yield. Alexander will produce two windings and tubes with 42 and 50 mil. (Identical or opposite helicity?) They can be exchanged within a few days. We will need two different collimators for the different IDs. - Tests of the undulator will be done at Cornell (including the ferro fluid). Some tests at SLAC before installation. Machine Equipment, John Sheppard, Dieter Waltz ---------------------------------------------- - John presented a complete list of all necessary beam instrumentation. - We need to install a 7th bending magnet to bend the 50 GeV beam down to the dump. - For the initial steering of the beam through the undulator (or the empty tube) some problems with the beam containment system are expected. - A target station for the positron target is foreseen that can handle 3 or 4 insertions: a blank target and targets of different thickness. - The sliding table will be adjusted to fit Alexanders 3 3/4" rig plate. - The machine vacuum will end in front of the collimator at the entrance to the positron diagnostics section. Behind the shielding wall, just before the positron production target, the photons will enter the poorer experimental vaccum. Positron Spectrometer: Kirk McDonald ------------------------------------ - Several options discussed. We will have a focusing solenoid after the target. Other options will not persued further. - Offset between gamma-beam-line and positron polarimeter axis. In the current design this is 18". We could inprove our yield by shortening the the offset. We are limited by the space needed for the CsI and its shielding. Min. distance 12 cm for detector + 10 cm lead shielding + 5 cm borenated poly shielding + 5 cm stay clear of gamma beam ==> minimum offset 14" - Vacuum: 8" x 2" box channel with 1 mil stainless steel windows in the spectrometer. Simple vacuum of 1 mbar, is sufficient. We can use Wilson joints (rubber O-rings) between solenoid and spectrometer. - Proposal to add a faraday cup at the spectrometer exit for flux meausrment. Is there enough space? - Gradient of Edge-Focusing? Yuri proposes edge-focusing. We would need a 16 degree angle of the endfaces to achive optimal transmission. Alexander proposes gradient-focusing (pole shoes that create a gap between the poles of varying thickness). Question: To which extent does the iron of the nearby analyzing magnet affect the fringe fields that make the edge-focusing. - Target material: Ti was choosen for its stress resistance. For the real project this is mandatory, but not for E166. Roman will simulate W versus Ti target for E166 and we'll decide afterwards. - Roman shows simulations with a yield substantially smaller than the value from the proposal. He has a relatively large distance between spectrometer exit and reconversion target. Is this the reason for the small yield? ==> Monte Carlo simulations for a few setups. Analyzing Magnet, Peter Schueler -------------------------------- - Peter shows B-field maps with a number of configurations of the magent core. - What is the maximum current density for the coil. Peter assumes 2 A / mm^2 Alexander says we can go to 10 A / mm^2. Background Sources ------------------ Here is a list of potential background sources - Myons from beam - cosmics - Neutrons from dump and elsewhere - synchrotron radiation from bending magnet - lost electrons from beam - backscatters from walls, floor, ceiling - electrons and photons from production target - background from scattering/annihilation in the spectrometer - photon beam line and gamma-dump - RF pickup - Vinod showed Fluka simulations, optimizing the Pb/poly sandwiches for shielding. Front |--------|--|--|--|--| Pb Po Pb Po Pb material 20 5 5 5 5 cm Back |--|--|--|--| Po Pb Po Pb material 5 5 5 5 cm - Neutrons from our gammas are probably not a problem. Most are below neutron production threshold anyhow. - The collimator under the gamma-dump (PC8) is a potent neutron source. - We'll add poly to the shielding there. - We'll take delayed measurements to determine the neutron background. - Dieter will do an inventory of the neutron shielding upstream and check for holes. - Shileding task force: Carsten, Bill, Morri, Achim, Dieter, Vinod. Will produce a concept for the shielding of the positron and gamma diagnositcs sections. - Synchrotron radiation: (From a memo from John) critical energy 740 keV, 10^5 to 10^7 photons on target total power 0.35 mW on target, compared to 87mW from undulator. Probably not a problem. - Yuri, talk on background from the beam halo. Largest background comes from halo particles hitting the undulator tube inside the undulator. Background from collimator is small. Background from scattering on residual gas in the tube is 1 e- / bunch. Dieter will measure the vacuum in the tube. - RF pickup Airgap at the dump entrance will be moved to inside the dump. Airgap at E164 can be closed with Al-foil That should reduce RF pickup substantially. Systematics ----------- Task force: Bill, Peter, Kirk, Achim Rough Schedule -------------- 15.6. Pre-installation 1.8. Installation of equipment 15.9. Completion of installation 4.to 8.10. Linac operation begins 8. to 31.10. E166 run 3. to 31.1.05 2nd E166 run 1.2. Deinstallation Running Plan for October ----------------------- week 1: Tune beams week 2: detector checkout week 3+4: polarisation Person power for October: ------------------------- Kirk Mc Donald John Sheppard Peter Schueler Vinod Bharadwaj Roman Poeschl Gary Bower Achim Stahl Rainer Pitthan Bill Bugg Dieter Walz Jim Clarke Carsten Hast Duncan Scott Zen Szalata Thomas Schweizer Yuri Batygin Hermann Kolanoski Achim Weidemann ? Steve Berridge Rick Iverson Alexander Michailichenkov Jim Turner Franz-Josef ... That is more than we need.