1. Wire Diameter Variation

2. 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

3. DG/G (3.06)

4. Correlation with stringing

5. DG/G (3.06)

6. Correlation with spool #

7. ‘bad’ and ’good’ wires

8. Due to misalignment

9. Correlation with SEM measurement
The wire diameter was measured with SEM. We estimate that the relative accuracy between measurements is ~ 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.

11. wire sections with different R

12. Correlation between wire diameter and gain

13. 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.

14. Good wire

15. Bent straws

16. ‘Bad’ wire

17. RMS.vs. DG/G distribution

18. 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.