Seismic attenuation chains concept, design and advancement status
Riccardo DeSalvo for the KAGRA Seismic group
JGW-G1201259
September 10, 2012 1JGW-G1201259 (LIGO-G1200939)
KAGRA-SAS design philosophy
• Use only well tested techniques,• Take the best from both Virgo and LIGO
examples:– Virgo’s superattenuators/suspensions– LIGO’s OSEMs
• Gain from the learned lessons:– Passive instead of inertial damping
• Designed for ease of use and fast lock acquisition
September 10, 2012 2JGW-G1201259 (LIGO-G1200939)
Type A Type B
Filter zero
Standard filter
Modular design
September 10, 2012 JGW-G1201259 (LIGO-G1200939) 3
Dual tunnel solution
• KAGRA SAS is mounted between two tunnels due to the restrictions of the space reserved for the cryostat
• Free and safe access to cryostat and seismic chain!
September 10, 2012 4JGW-G1201259 (LIGO-G1200939)
The top filter and IP table
• footed on solid rock• Inverted Pendulum
table with short legs• Large GAS filter• Easily accessible• No tall structures• Better safety
September 10, 2012 JGW-G1201259 (LIGO-G1200939) 5
The Type-A KAGRA-SAS Seismic Attenuation System
• A modern, simplified and improved version of the Virgo Superattenuators
• Guaranteed performance• Eliminate its main defects– GAS replaces MAS filters– damping stage added at top
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Thermal Noise
Measured Upper Limit
Attenuation measurements.
courtesy F. Frasconi JGW-G1201259 (LIGO-G1200939)
Improvements over Virgo:damping strategy
• Mode damping is vital for easy locking of the interferometer
• One extra filter is added at the beginning of the chain it is coupled with a suspended magnet ring to provide passive Eddy current damping for the attenuation chain yaw and other internal modes.
September 10, 2012 8JGW-G1201259 (LIGO-G1200939)
Transversal mode damping• seismic noise level of chain’s TM, with/without Eddy current damping
September 10, 2012 JGW-G1201259 (LIGO-G1200939) 9
IP modesChain modes
Lowest mode damping
• RMS amplitude reductionusing shadowmeter on suspension wire
September 10, 2012 10JGW-G1201259 (LIGO-G1200939)
Backup damping• active seismic attenuation• Accelerometers onboard
similar to TAMA accelerometers.Improved at AEI and NIKHEF
• Or feed-forward from ground
September 10, 2012 JGW-G1201259 (LIGO-G1200939) 11
KAGRA pre-isolator pedigree• The KAGRA SAS pre-isolator was
successfully tested in the a-LIGO HAM SAS, further improved at AEI SAS and Virgo-NIKHEF SAS
• • Performs passively the same
functions of all three a-LIGO active stages.
September 10, 2012 12JGW-G1201259 (LIGO-G1200939)
Secondary opticsgeneral concept
• Used for beam splitter and six recycler mirrors
• 1500 mm diameter tank• Easy access to optics
and optical bench from one port without entering
• Easily Relocatable
September 10, 2012 13JGW-G1201259 (LIGO-G1200939)
Attenuation chain
• Pre attenuator = inverted pendulum + top filter
• Standard filter with Eddy current damper
• Bottom filter• Intermediate mass and its recoil
mass• Mirror and its recoil mass
Design drawings T1100450and D1200818September 10, 2012 14JGW-G1201259 (LIGO-G1200939)
The four components of type-B
• External structure
• Vacuum tank
• Attenuation chain
• Optical bench
Also see G1200806September 10, 2012 15JGW-G1201259 (LIGO-G1200939)
External structure
• Mechanically Independent from noisy vacuum tank
• Magnetic feet to satisfy relocation requirements
• Also see T1100638
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Canned in 2 sub-units for travel and fast installation
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All 19 standard filters produced,
assembled & tested.Stored at Akeno
September 10, 2012 18JGW-G1201259 (LIGO-G1200939)
SAS Project advancement• Design/construction
(*) six out of eleven top filters to be completed within 2010/2012 budgetSeptember 10, 2012 JGW-G1201259 (LIGO-G1200939) 19
KAGRA- SAS Project status• 2010/2012 budget
• ( ~ 2 M$ including design and manpower)
– Completed design of all components– Completed prototypes of all critical components– Built all standard filters (UHV comp. and tested)
– Build 6 out of 11 Top filters
• 2013/2015 budget (t.b.d.)– Complete construction of all SAS and vacuum tanks
September 10, 2012 JGW-G1201259 (LIGO-G1200939) 20
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