measurements of several parameters of plasma panels october 2011
TRANSCRIPT
Measurements of several parameters of plasma panels
October 2011
Parameters of interest
• Effective capacitance in panel– Gas gap– Electrode width
Motivation
• We are directly measuring voltage drop on the readout side of the system
• α current α ∆Q• ∆Q α (C)() • Therefore the effective
capacitance of the panel is an important parameter
Methods
• Capacitance measurement– Used standard capacitance meter– Split each panel into 9 approximately equal areas
• Effective capacitance could be a function of position on panel
– Took many measurements across electrodes in each area
• Gas gap measurement– Used standard calipers to measure plate and panel
thicknesses
Sample gas gap calculation and uncertainty
For Xe filled panel:
∆ = = = .0447 mm = = x = 0.08 mmGas Gap = 6.57 – (3.10 + 3.08) = 0.39 mm ± 0.08 mm
Measurement Plate 1 (mm) Plate 2 (mm) Whole panel (mm)
1 3.10 3.08 6.48
2 3.12 3.07 6.50
3 3.08 3.12 6.60
4 3.10 3.05 6.63
5 3.08 3.07 6.63
Average 3.10 ± .0447 3.08 ± .0447 6.57 ± .0447
Large Vishay
All values in pF, with uncertainty ± 1 pF
Gas gap: 0.38 ± .08 mmElectrode width: 1.23 ± .01 mm
5 5 5
6 6 5
6 6 5
Large Babcock
All values in pF, with uncertainty ± 1 pF
Gas gap: 0.39 ± .08 mmElectrode width: 1.22 ± .01 mm
8 8 8
8 8 7
8 7 7
• Coming soon
VF - mini
All values in pF, with uncertainty ± 1 pF
Gas gap: 0.29 ± .08 mmElectrode width: 0.88 ± .01 mm
4 4 4
4 4 4
5 5 5
Xe filled panel
All values in pF, with uncertainty ± 1 pF
Gas gap: 0.16 ± .08 mmElectrode width: 0.34 ± .01 mm
2 1 1
2 2 1
3 2 2
Big Panel 1
All values in pF, with uncertainty ± 1 pF
Gas gap: 0.17 ± .08 mmElectrode width: 1.20 ± .01 mm
13 7 10
10 5 8
12 8 10
Capacitance vs gas gap and electrode width
We would like to investigate the relationship between the values I measured and the panel’s capacitance. The geometry of the panel, specifically gas gap and electrode width, should determine the effective capacitance across electrodes. However, the contributions from other strips in the panel constitute the majority of the effective capacitance. So then capacitance at any point is really a function of panel electrode width, electrode spacing, panel dimensions, and gas gap, in addition to irregularities within the panel (i.e. degradation of electrodes).
ConclusionCapacitance vs position on panel: We expect effective capacitance to be greatest near the middle of the panel, where all other electrodes can contribute to effective capacitance. This seems to be the case within my error values.Capacitance of BP 1: The performance of BP 1 has been decreasing over time. The current of heavy ions generated during discharge degrades the electrode through repeated collisions. We know that the signal generated is proportional to the charge deposited on the electrode, which is proportional to the gap’s effective capacitance. Measuring greatly reduced capacitance where the panel has been in use is a measurement of decrease of panel performance.