Agenda

Minutes

Present: Vitaly, Eugene, Moskov, Hovanes, Pavel, Alex, Beni, Lubomir, Marshall, Richard, Sashi, Edy, Mikhail

Pavel simulated KLF beam using 20% CPS radiator. He uses 6cm OD beam pipe after KPT, but he used 4cm OD beampipe at the cryo-target. Pavel emphasized the importance of controlling the beam size of the diverging beam of CPS that contains particles other than kaons.

The beam spot at the KPT is wider, still fits in 6cm reasonably well. K-long rate at the cryo-target is consistent with factor of two increase. Statistics is still low due to CPU unavailability last week.

Eugene asked about radiation backsplash in front of CPS. Pavel says that neutron backsplash increased. Pavel expects that the temperature in the CPS will decrease. The magnet coil dose rate increased by about factor of four.

Pavel is already running higher statistics and also the low thresholds simulations.

Richard made the plots from GEANT4 simulations that allow us to compare the FDC and TOF rates for individual channels between KLF with 14cm W-plug and GlueX-II.

FDC rates per wire near the beam for KLF with 14cm tungsten plug are very close to what GlueX-II give with the same GEANT4 code.

Lubomir pointed out that with these rates the occupancies for these wires would be higher than 50%. Most likely, the thresholds for FDC in GEANT4 do not match the thresholds in reality. Lubomir thinks that FDC should be OK with 14cm tungsten plug.

Richard also studied the options of shielding to improve the rates of the detectors. One option was to shield the beam pipe between the target cart and the locations at 2m downstream of PS magnet exit, as was suggested by Pavel. The second option was to place a shielding wall in front of the target cart made of a single layer of lead bricks and tungsten collar around the beam pipe. In both scenarios, Richard still has another shielding wall after the PS magnet that interferes with KFM geometry.

The shielded pipe option reduces the rate in the start counter by about ~10%. Transverse shielding option reduces the rates in the start counter by more than a factor of x2. In both cases, the start counter is the cylindrical one (no nose cone).

The shielding pipe option reduces the rates in CDC by about ~40%. The shielding wall option reduces the CDC rates by about about factor of x5. Richard pointed out that factor of x5 reduction is what is needed for KLF 14cm plug setup to have rates similar to GlueX-II rates.

The shielding wall seems to be more effective for reducing detector rates. These options are not mutually exclusive, we can do both. We need to evaluate the weight of the wall and ask Tim how easy is to install it on the platform. Answering to Mikhail question about the wall location, Richard said that it is definitely better to have the wall close to the target. Hovanes pointed out that the shielding wall after the PS magnet that interferes with KFM needs to be removed from the GEANT4 simulations.

Note added later by Hovanes: Richard found that some jobs crashed that made the results shown at the meeting from the wall shielding incorrect. The slides posted on the meeting page show the corrected plots, not the ones shown at the meeting. The wall and the shielded pipe results provide very similar results. The improvement in the CDC by either shielding scheme is less than factor of x5.

Richard explained that plots shown in the previous meeting to determine the origin of the hits were "contaminated" by photons that undergo Compton scattering and change direction of the photon while the ID of the photons stays the same. This is because GEANT4 considers Compton scattering as continuous process and not a discrete one.

Pavel thinks that it would also be good to keep the shielded pipe (1cm walls) all the way to the target cell. This would have to be coordinated with the target group.

Beni showed pictures of the target cart with the refrigerator and the pipes around it. Putting a wall after the cart but in front of the refrigerator would require modification of the cart itself. But it would not be very difficult to modify the upstream flange to have a collimator mounted on it. Shielding the beam pipe all the way until refrigerator should not be a problem.

Eugene suggested that the shielded pipe configuration should not be made of a pipe with constant inner diameter but have a pipe with varying inner and outer diameter to reduce the detector rates coming from the interactions of the beam particles in the pipes. This could be realized by using a wider beam pipe but using collars and inserts to change the inner and outer diameters.