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Preliminary Maxwell Calculations

Preliminary Maxwell Calculations. SB Tent Crew. Apr 15, 2008. “solid” mesh. GEM. solid pad plane. Maxwell Model. Single GEM. dV GEM = 500V To save computation time, Drift Gap (and dV drift ) was scaled by x6: drift gap = 280u ~1.5mm/6 dV drift = 1/6 * biasVoltage

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Preliminary Maxwell Calculations

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  1. Preliminary Maxwell Calculations SB Tent Crew Apr 15, 2008

  2. “solid” mesh GEM solid pad plane Maxwell Model • Single GEM. • dVGEM = 500V • To save computation time, Drift Gap (and dVdrift) was scaled by x6: • drift gap = 280u ~1.5mm/6 • dVdrift = 1/6 * biasVoltage • induction gap = 280u ~1.5mm/6 • dVinduction = 1/6 * 500V • P1=P2 • 2um x 2um x 2um resolution. • This is (slightly) wrong! • P1 should equal F1 • P2 = P1*cos(60°) • scaling V by same factor as gap (x6) assumes uniform E-Field in drift gap. • E-Field isn’t uniform P2 drift gap induction gap

  3. Ez vs z • Ez vs z is not constant (as we assume when we scale the mesh voltage by the reduction in distance of drift gap. • But the <Ez> in the drift gap IS what we expect!! (120V/1.5mm = 0.8 kV/cm) • So… Maxwell seems to be working. We just need to tweak a few parameters. Projection

  4. E-Field Lines DG: –30/6 Volts per 280um DG: 120/6 Volts per 280um • Slight differences… • Not what is expected. • at –30/6 Volts, some field lines should go to mesh. • Both these voltage configurations have forward bias properties. • Simulation needs to be rerun with more realistic gaps. • This has been started but isn’t yet finished.

  5. y x E-Field at GEM Surface Drift Gap: 120/6 Volts per 280um • Slice of Ez along red line: • ~flat Ez away from hole. • Near hole, large pe extraction field. • in hole, Ez drives e’s through hole. • <Ez> on GEM surface ~3kV/cm

  6. y x E-Field at GEM Surface Drift Gap: –30/6 Volts per 280um • Slice of Ez along red line: • ~flat Ez away from hole. • Near hole, large pe extraction field. • in hole, Ez drives e’s through hole. • <Ez> on GEM surface ~4kV/cm

  7. PE Collection Efficiency great news! Extraction Efficiency FB 120/6 V per 280um – Maxwell 3D Extraction Efficiency • Bob Azmoun measured • PE collection efficiency vs GEM surface extraction field. • 3 kV/cm should be well on the plateau of PE extraction efficiency. • Even better news… • –30/6 V per 280um seems to have higher extraction efficiency than 120/6 V per 280um.

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