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AdV-TCS (CO2 laser projector)
rocchi, berni - 14:54 Friday 07 July 2023 (60774) Print this report
WI CO2 laser instability

This morning, I received an e-mail from Francesco about a DMS red flag for the WI DAS Outer Ring power (see Fig. 1).

Indeed, looking at the data, it seemed that the laser had settled on a wierd working point. Thus, acting on the chiller set-point, I moved it to a better one (Fig. 2).

During this operation, I noticed that the chiller had a very low responsivity when decreasing the set-point (bottom-right plot of Fig. 2).

I think that a possible reason for this is that now the temperature inside the TCS Room and the Chiller Room are some degrees higher than few months ago (Fig. 3), even if the temperature in the central hall has not changed much. Considering that the Chiller Room is in direct contact with the external environment (indeed it is an "intercapedine"), we should think of strengthening the air conditioning (the fan-coil is already running at maximum speed and lowest temperature).

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nardecchia, menzione - 12:31 Monday 10 July 2023 (60790) Print this report

During the weekend, the temperature of the WI CO2 laser temperature fluctuated since the chiller was not able to stabilize it (see fig.1).

Waiting for the upgrade of the air conditioning in the 'intercapedine', this morning I asked to Nicola to increase the flux from 'medium' to 'high' in order to improve the laser stability.

Then, also the chiller step-point has been decreased multiple times to evaluate the effect on the temperature of the WI laser.

The increase of the chiller rotation pump speed allowed to decrease the temperature of the laser by 0.5 C but, the responsivity of the chiller changing set point was almost invisible  (see fig. 2).

As a further test, Nicola swapped the WI CO2 laser chiller with the  back up one.

The WI CO2 laser temperature started to decrease  immediately (see fig 3). 

At the end of the test, the standard system configuration has been recovered in order to preserve the cooling of the lasers even in case of failure of one of the two main chillers.

The result of this test is that the WI CO2 chiller no longer works well and should be replaced with the spare one.

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