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 56 6 56 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 88 8 78 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 44 4 45 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 12 2 13 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 1010 5 812 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.