At approximately 15:30 UTC (8:30 PDT) on Saturday, 7/8/2017, the flow through the HPO laser heads dropped by ~0.12 lpm; see the first attachment.  This is worrying as the trip point for the laser head flow is set to 0.4 lpm; the flow through heads 2 and 3 is sitting at ~0.45 lpm, just 0.05 lpm above the trip point.  Looking at the other channels in the cooling system the picture becomes a little clearer (maybe).

The 2nd attachment shows the pressures in the PSL cooling manifold; H1:PSL-OSC_PRESS1 is the pressure at the manifold input, H1:PSL-OSC_PRESS2 is the pressure at the manifold output.  As seen in the attachment, the pressure at the inlet increased slightly, and the pressure at the outlet dropped slightly.  The third attachment shows the flow through the HPO power meter circuit (H1:PSL-OSC_PWRMETERFLOW), the 35W FE laser circuit (H1:PSL-AMP_FLOW), and the overall flow out of the PSL crystal chiller (H1:PSL-OSC_XCHILFLOW); the flow out of the chiller dropped slightly (~0.1 lpm) while the flow through the HPO power meter and 35W FE circuits both increased very slightly (interestingly, the signal from the FE flow sensor cleaned up after the event, and the frequency of drops in the power meter flow sensor signal also decreased).  The most likely cause of this behavior is some kind of flow restriction, probably somewhere in the laser head cooling circuit (although it is possible there could be a blockage in the filters under the PSL table).

The 4th attachment shows the temperature of the individual laser heads.  All saw an increase of ~0.2 °C, which indicates that this is a real drop in the flow through the HPO laser heads.  Fortunately this was not enough to effect the output power of the laser (5th attachment), and the temperatures have remained steady since the loss of flow on Saturday.

In the short term, we can try increasing the overall flow at the crystal chiller to see if it clears whatever is restricting the flow; at the very least we can increase the flow so we are a bit further from the trip point.  We will also inspect the filters beneath the PSL table when we are in the enclosure during tomorrow's maintenance window.  Any further investigation will require opening up the cooling system, which is highly invasive.