1. TCS Chiller Performance Review
Phil Willems
Nov. 17, 2004
LIGO R&D

2. Design Requirements Laser temperature: around room temperature, ±.5K
Flow rates:
Device
Max power dissipated
Flow requirement
Source of requirement
Carbon dioxide laser
80W
½ gpm
Access Laser Co.
Laser power supply
40W
‘cool to the touch’
AOM
30W
250 ml/min
IntraAction, Inc.
AOM driver
TBD
Noise: acoustic and EMI must be under ambient at nearest sensitive device (optical lever system)
Monitoring and control from control room using EPICS
Leak tight and robust
LIGO R&D

3. Commissioning Timeline
Device was installed on 2K Y arm Oct
Device was commissioned from Oct. 29 to Nov. 8.
Commissioning paused after overheating incident Nov. 6-7.
Forensics from Nov. 8 to today.
LIGO R&D

4. Installation
Site chilled water delivered to chiller from over 100 feet away through uninsulated copper pipe
This may account for some temperature issues and surges during control valve operation
Site chilled water and TCS table water pipes interlaid and touching
Insulation of TCS table supply pipe required for temperature stability
Prototype control electronics not plug and play
Control software implemented but not safety interlocks
LIGO R&D

5. Commissioning Submerged thermistor failed after 2 days (Nov. 1)
Thermistor was fine; problem later traced to bad solder joint outside chiller
Short term solution was to glue another thermistor to pipe leaving chiller
Laser power stabilized without AOM on (Nov. 3-5)
Laser power unstable with AOM on (Nov. 5)
Chiller noise performance verified (Nov. 6-7)
LIGO R&D

6. Overheating Incident
After noise test, chiller was switched on to run overnight
Apparently, one or both pumps failed to switch on
System ran at very high temperature for about 1-2 days
Much damage and corrosion to the chiller
Thermistors on TCS table showed no overheating, no flow to table- TCS table not affected
LIGO R&D

7. Why a Chiller Is Not a Boiler
LIGO R&D

8. Overheating Incident Analyzed
Without submerged thermistor operating, no way to monitor chiller reservoir temperature
Without software interlocks programmed, system could not power down safely had the submerged thermistor worked
Had system been fully operational before running unattended chiller would have safely shut itself down
Why did pump fail to start?
LHO reports that all Rio pumps studied failed to start 100% of the time
LIGO R&D

9. Forensics Chiller disassembled, analyzed, and rebuilt
Now it runs well even with the AOM on (for 30 minutes at least…)
Rio 1100 pumps tested for reliability
One pump tested by hand- 200 starts without failure
One pump tested by robot- robot itself not 100% reliable, but pump starts ~15,000 times without failure
Rio 2100 pump known to fail at LHO now under test
Coolant corrosion tests
Chloramine T not compatible with chiller components under accelerated aging test
Propylene glycol and sodium hydroxide are compatible
LIGO R&D

10. Chiller Performance After Rebuild
LIGO R&D

11. Final Results Compared to Requirements
Temperature of chiller and laser held to within .5K, as required
Flow rate is 1.3GPM, as required
Acoustic and electromagnetic noise is below ambient, as required
Operation fully controlled and monitored from the control room, as required
System is not yet robust to failure modes
Design not fully implemented, software interlocks missing when needed
New safeties can be added without change to conceptual design
LIGO R&D

12. Are the Design Requirements Good Enough?
The TCS laser stability is unverified even though the TCS chiller meets requirements. Laser power and coolant temperature fluctuations are frequently correlated.
Is .5K temperature stability sufficient?
Is 1.3GPM flow sufficient?
Recommend that no more TCS chillers be installed until reconditioned prototype performance is verified.
New chiller parts will replace boiled parts
Software interlocks will be fully implemented
Hardware interlocks under consideration
Plan new commissioning effort Nov. 29-Dec. 3.
LIGO R&D