Wire Diameter Variation

Summary of problem During the gain mapping of a barrel module, some odd features in the gain variation along the straw length were observed The shape of gain variation did not match the typical expected shape from alignment problem or dirt on the wire surface. The problem was correlated to the Toshiba wire spool. With SEM, the diameter of suspected wires were measured and found that there was maximum of ~ 1 micron variation in the wire diameter. We do not know if the thickness variation is due the gold plating or the base tungsten wire or both. The gold plating quality is not affected by the wire diameter problem

DG/G (3.06)

Correlation with stringing

DG/G (3.06)

Correlation with spool #

‘bad’ and ’good’ wires

Due to misalignment

Correlation with SEM measurement The wire diameter was measured with SEM. We estimate that the relative accuracy between measurements is ~0.2-0.3 mm, which mainly depends on the cursor setting at the edge of the wire. From ‘bad’ wires, sections of high gain and low gain were chosen and wire segments (~1 cm long) were removed. From ‘good’ wires, random sections were chosen and wire segments were removed.

wire sections with different R

Correlation between wire diameter and gain

How to identify ‘bad’ wires from bad wires (bent straws) due to alignment problem ‘Bad’ wires should be kept while real off-set wires have to be pulled out. Study RMS( ~ADC width) .vs. DG/G distribution.

Good wire

Bent straws

‘Bad’ wire

RMS.vs. DG/G distribution

Conclusion The causes for gain variation Miss-aligned straws (out of spec) –> remove wire Wire caught by wire supports –> re-string wire Dirt on the wire surface –> re-stringing is not necessary Wire diameter variation –> re-stringing is not necessary The ‘bad’ wire can be identified by plotting ADC width. There is no problem with gold plating.