Attached plot shows rate of pressure increase in ~2l volume upstream of TUDA with Ni window #2 installed on reentrant flange. Comparison between

a)pumping out TUDA and 2l volume, and

b) filling TUDA with ~340mbar of He and pumping out 2l volume.

In both cases, 2l volume isolated from pumps at start.

Gradients are comparible, hence no detectable He leak through window.

Will repeat with other windows and blank flange tomorrow.