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Simulations are still under way for beamline/shielding/lumi/plug optimization. We believe we have overcome the problem with the rates for the far forward scattering angles. The scattered ep elastic rate (only primary electrons) over all origin theta is greater than the incident rate, because for low angles, the cross section is so high the the probability of interacting in the target is greater than 1 (see previous report ).
When we integrate this from .0272° to 180°, we get 1 for elastic eps (and from .0523° to 180° for mollers). Mark's point target estimate for elastic eps yields the same low angle limit as the simulation for eps.
The prescription: generate mollers and eps from their respective minimum angles up to 3 degrees, with the correct radiative processes. This was done for the 2 plug case, histogramming the rates and energies at various detectors, with 1x107 triggered events. The results (see Table 1) are for an unoptimized beamline and shielding scheme - it is the same design presented before, but with what we believe to be the correct simulation parameters. If the powers in the plugs listed in the table are too high, then a plug solution may be infeasible.
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Table 1 - Plug powers and anode current results using the prescription described in the text. |
As you recall we have been attempting to beat down an oscillation that we see on the nanometrics amplifier/discriminator cards. We have been trying to run with as low a threshold as possible. We started out around 1V and are up to 2.5V now for stable operation. Juliette found an HKS "How To" document that quotes a value of 3V for the threshold on the Nanometrics cards. So maybe our situation isn't too bad.
With the threshold set at 2.5V we turned on the chamber HV to look for cosmics. The efficiency looks good on the scope but we don't have data or plots to report yet.
