Summary of the UK HARP Meeting held on Tuesday 2nd May 2000 in Sheffield

Present: Giles Barr, Chris Booth, Rob Edgecock, Alan Holmes, Richard Nicholson.
Apologies: Craig Buttar

Report from CERN Meeting
Rob had presented some of the concerns raised at the last HARP-UK meeting when he attended the HARP meeting at CERN on 11th April.
- He pointed out that we do not have funds to provide support for the last trigger & beam counter, so could not take this on. (This produced no reaction!)
- He presented our list of targets, including the two special ones (45° and varying thickness). It was agreed that 30 mm was a reasonable diameter. Our worries that the K2K target would be too large to fit were allayed as it was stated that this would be cut in a different place to ensure it should also fit through the hole.
- There were no objections to our plans for the support mechanism. Alan Grant is setting up a sub-group (beam, targets, support etc) to discuss this. Perhaps we should invite CERN people to the UK to discuss?
- TPC drawings are being produced by Mario Scandurra. Giles should visit on Monday if possible.
  ACTION: GB.
- 65 cm more space is available than we thought at our last meeting. This can be used for the beam chambers. (Distance from end of B-field in quad to focus (target) is 3.8 m, field ends 15 cm inside quad => 3.65 m available, rather than 3.02 m.)
  Jaap Panman supported moving the middle beam chamber upstream, so that it does not need displacing at each target change. This leaves 1.4 m available for insertion of target support.
- Rob presented the bar-code reader ideas. Lucie thought we had "more important things to worry about", but Jaap liked the idea! We should go ahead finding costs etc, but this has low priority.
  ACTION: RE.
- Friedrich suggested 2 thin targets, separated by 10 cm. After discussion, we decided that this was not a good idea, as we will be limited by TPC readout rate rather than beam intensity.
- GENERAL ACTION: GB, CB, RE to talk to people at CERN next week.
Target Support Tube
Alan had performed a stress analysis on support designs with a 2 kg target. An aluminium alloy tube, tapering from 7 mm wall thickness to 2 mm has a droop of only 0.7 mm. This would be cheaper and easier than a carbon fibre tube. Assuming the tube has the same final diameter as previously (to match target end-cap support) and is machined on the outside, the upstream end needs an external diameter of 64 mm. This requires a bigger hole in the TPC end-flange. Note: the old support tube for guide bearings inside the TPC is no longer needed and can be removed.
Alan also presented diagrams of a twin-rail sliding support outside the TPC, bolted to the end-flange. We need an accurately aligned collar at the TPC flange, to position the support tube when inside the TPC. 1.4 m appears to be adequate for changing thin targets, but we need a bit more for the thick ones.
A number of points were raised in discussion. The sliding support could also act as a support for the final beam counters, eliminating the need to displace them sideways. Alan will look at whether the support tube could taper down from 50 to 40 mm diameter instead, and we could have an end-cap fitting outside rather than inside. If both are aluminium, a bayonet fitting of end-cap to tube could bind up! Perhaps a flange fitting would be more reliable.
ACTIONS: AH & RN to discuss tube-endcap fittings. GB to discuss larger hole in TPC flange at CERN, with numbers from Alan by end of week.
Endcap Target Support
Richard showed us a support made with the same design as before but 0.2 mm wall thickness. This appears strong enough, and we were duly impressed! He suggested that instead of a cylindrical flange around the outside of the target, it could be held in place by nylon thread. (Eg 0.2 mm thickness, 2 horizontal and 2 vertical threads, both sides.) He will try it out.
ACTION: RN.

It was decided that the target should be outside the support tube, rather than centred on its end. It was also agreed that all targets should be weighed and measured before mounting. However, uniformity is more important - Richard will contact Goodfellows to check their tolerances for uniformity.
ACTION: RN.
Thick Target Support
The thickest target will be about 407 mm long. We need more thought about support mechanisms. Various possibilities were discussed. A thicker aluminium tube can be tolerated - say 0.4 mm. For these targets, we will have to centre the target on the end flange, or shorten the tube.
ACTIONS: RN to consider support possibilities. AH to think about Li, Hg, K2K and miniBoone target supports. GB to try (while at CERN) to arrange direct contact with miniBoone and K2K people.
Monte Carlo Input
Craig and Ian are starting to look at putting the target and support structures into FLUKA, which will enable studies of multiple scattering etc. to be started.
Next meeting: Provisionally arranged for Tuesday 6th June, in Oxford, prior to HARP meetings at CERN on 13th-14th June.

Chris Booth