J. Oberling, P. King, J. Bartlett, R. Savage
Following on from yesterday's plumbing work, today we concentrated on recovering the 35W FE, the 70W amplifier, and completing the remaining items from FRS 10753.
This morning, Peter recovered the 35W FE without much fuss and also installed the new solid block base for the 70W amplifier. He and I recovered the 70W amplifier, also without much trouble; we tweaked beam alignment for a compromise of power and beam quality and were able to return the beam very close to what it was before the new base installation. We then proceeded to take a beam propagation measurement to use in PMC mode matching. This was necessary as the installation of the new amplifier base resulted in the 70W amp moving closer to the PMC by ~1/2", which in turn will have an effect on PMC mode matching. At this point we broke for lunch.
The final part we needed to complete the chiller work (an adapter for installation of a throttling valve on the supply line out of the chiller) arrived today, so this afternoon Jeff and I installed the valve. After leak checking and leak fixing, we fired the chillers up and all was well.
Rick and I then balanced the flows and pressures out of the crystal chiller. To do this we completely opened the new external bypass Jeff installed a couple months ago and completely closed the chiller's internal bypass; this internal bypass being open was what was causing the very high operating pressure (70 psi!) for the system. In this configuration the chiller had a flow of 38 lpm. We then used the throttling valve to reduce the overall chiller flow to 18.7 lpm (keep in mind that the external bypass was still completely open, so almost all of that water was flowing through the bypass, not the PSL manifold). We then slowly closed down the external bypass to provide a pressure drop for the PSL manifold, therefore letting water flow through the various cooling circuits. As it stands right now, the flows and pressures of the PSL cooling system are:
Please keep in mind that most of that chiller flow is still going through the external bypass. This is an absolutely huge improvement as prior to this work we were running with a manifold inlet pressure of 70 psi (!!!). At this point I returned to the enclosure to return it to "Science Mode" so Robert can assess if all of this plumbing work made a difference in PSL table vibration. Tomorrow we will begin mode matching the PMC, with our goal being >50W transmitted power with the ISS ON.
One small, but important, clarification.
The high supply- and return-side pressures observed earlier were not due to the internal bypass being open. They were due to the 50 psi pressure drop across the heat exchanger due to the high total flow (internally bypassed, externally bypassed, and through the laser circuits) going through the heat exchanger (on order 30 lpm) inside the chiller on the return path to the open reservoir.
Similar pressures were observed with the internal bypass closed but the external bypass open, also giving about 30 lpm through the heat exchanger.
Closing the internal bypass valve, reducing the pump output flow by about a factor of two using the throttling valve, and adjusting the flow through the laser circuits using the external bypass valve allowed us to set the desired flows through the laser circuits while reducing the overall system pressure.
This scheme was developed in consultation with J. Riebock, an engineer at TechnoTrans, US rep for the chiller manufacturer.