Design considerations
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Transcript of Design considerations
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22nd March 2005 LIGO-G050178-00-R
Passive attenuation for the LIGO Output mode cleaner;
HAM SAS
R. DeSalvo, S. Marka, V. Sannibale, A. Takamori,
C. Torrie , A. Bertolini
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22nd March 2005 LIGO-G050178-00-R
Design considerations• Simplest possible seismic attenuation system.
– One single stage of passive attenuation– Fully UHV compatible– Suitable for all conceivable options of OMC – Satisfying LIGO and Adv-LIGO requirements for all HAMS– Broadband attenuation performance 50~60 dB– Tidal correction and < rad alignment incorporated– Earthquake protection incorporated – Upgradeable to active attenuation as reserve of att. power– As inexpensive as possible
• Can replace stacks even without replacing optical tables
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Results• Expected performance compatible to cumulative
performance of all three layers of ad-LIGO active attenuation
• Cost of one single layer• Less control complexity than a single layer (passive)
– equal complexity, if upgraded, to active attenuation
• Suitable to instrument any HAM for any load
www.LIGO.caltech.edu/~desalvo/HAM-SAS
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Notable characteristic
• Horizontal and vertical degree of freedom decoupled
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Horizontal attenuation
Base platform
Flex joints
Inverted Pendula
Intermediate(GAS) platform
X Y
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Earthquake generator shaking tower
Illustrating An IP performance
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Typical IP performance
To 10 mHzresonance
60 dB
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HAM IP first tests• Preliminary test results• 60 dB achieved without CounterWeight• 1/8 payload (8 times better at full payload)• Further improvement with CW• 80 Hz resonance, reducing attenuation performance,
moved above 100 Hz and dampable with eddy currents
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A similar IP leg
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22nd March 2005 LIGO-G050178-00-R
Dynamic micro-positioning• LVDT for nanometer positioning memory
• Voice coil actuator
• Tidal corrections from global controls
• milli Watt in-vacuum power
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Dynamic micro-positioning
• Co-located LVDT actuator units
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Static micro-positioning
• Remotely actuated springs in all d.o.f.– No standing currents in actuators
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Vertical direction, the GAS springs
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Vertical direction, the GAS springs
Optical bench
Intermediate platform GAS springs
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Vertical direction, the GAS springs
Optical bench
Equivalent LVDT/actuator unit implemented
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Illustrating a GAS spring performance
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Typical GAS Passive vertical attenuation performance
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•attenuation factors as large as one thousand for frequencies above 3 Hertz for LF-GW-ID
• Sizeable attenuation at the micro seismic peak at 150 mHz
Low frequency performance
-50
-40
-30
-20
-10
0
10
0.1 1
Frequency [Hz]
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Bellow equivalent springs(neutralized by GAS)
Two CantileverGAS springs
350 Kg Payload
Load capabilities, DFBS prototype
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Complete SAS design for HAMs
Existing Optical bench
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Transition from LIGO-I to Adv-LIGO
• The transition between
LIGO and Advanced LIGO is obtained by simply eliminating a number of spacers
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SAS design for BSCs
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BSC SAS
• The HAM-SAS design fits in the BSC and is capable to offload the entire weight
• An additional pendulum stage, needed to reach the (lower) level required by the quad suspensions, gives a redundant safety factor in horizontal isolation
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HAM and BSC SAS features
• SAS is a viable and inexpensive in-vacuum seismic attenuation candidate for Adv-LIGO (60 dB broadband)
• One passive layer can potentially replace all three stages of stiff SEI
• Upgradeable to active attenuation as reserve of attenuation power
• Fully compatible with the SUS system
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22nd March 2005 LIGO-G050178-00-R
HAM SAS design status
• HAM SAS design for OMC or any other HAM bench is ready for productionhttp://www.ligo.caltech.edu/~desalvo/HAM-SAS and
http://www.ligo.caltech.edu/~desalvo/HAM-SAS.doc
• Preliminary bidding indicate a cost of ~ 150K$ and production times of the order of three months
• Prototyping in LASTI, to validate the design should be considered
• Scaling of the design is possible for BSC