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Seismic attenuation chains concept, design and advancement status. Riccardo DeSalvo for the KAGRA Seismic group JGW -G1201259. KAGRA-SAS design philosophy. Use only well tested techniques, Take the best from both Virgo and LIGO examples: Virgo ’ s superattenuators/suspensions

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seismic attenuation chains concept design and advancement status

Seismic attenuation chains concept, design and advancement status

Riccardo DeSalvo

for the KAGRA Seismic group


JGW-G1201259 (LIGO-G1200939)

kagra sas design philosophy
KAGRA-SAS design philosophy
  • Use only well tested techniques,
  • Take the best from both Virgo and LIGO


    • 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

JGW-G1201259 (LIGO-G1200939)

type a type b

Modular design

Type A Type B

Filter zero

Standard filter

JGW-G1201259 (LIGO-G1200939)

dual tunnel solution
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!

JGW-G1201259 (LIGO-G1200939)

the top filter and ip table
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

JGW-G1201259 (LIGO-G1200939)

the type a kagra sas seismic attenuation system
The Type-A KAGRA-SAS Seismic Attenuation System
  • Amodern, simplified and improved version of the

Virgo Superattenuators

  • Guaranteed performance
  • Eliminate its main defects
    • GAS replaces MAS filters
    • damping stage added at top

JGW-G1201259 (LIGO-G1200939)

attenuation measurements

Thermal Noise

Measured Upper Limit

Attenuation measurements .


F. Frasconi

JGW-G1201259 (LIGO-G1200939)

improvements over virgo damping strategy
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.

JGW-G1201259 (LIGO-G1200939)

transversal mode damping
Transversal mode damping
  • seismic noise level of chain’s TM, 

with/without Eddy current damping

Chain modes

IP modes

JGW-G1201259 (LIGO-G1200939)

lowest mode damping
Lowest mode damping
  • RMS amplitude reduction

using shadowmeter on suspension wire

JGW-G1201259 (LIGO-G1200939)

backup damping
Backup damping
  • active seismic attenuation
  • Accelerometers onboard

similar to TAMA accelerometers.

Improved at AEI and NIKHEF

  • Or feed-forward from ground

JGW-G1201259 (LIGO-G1200939)

kagra pre isolator pedigree
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.

JGW-G1201259 (LIGO-G1200939)

secondary optics general concept
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

JGW-G1201259 (LIGO-G1200939)

attenuation chain
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 T1100450

and D1200818

JGW-G1201259 (LIGO-G1200939)

the four components of type b
The four components of type-B
  • External structure
  • Vacuum tank
  • Attenuation chain
  • Optical bench

Also see G1200806

JGW-G1201259 (LIGO-G1200939)

external structure
External structure
  • Mechanically Independent from noisy vacuum tank
  • Magnetic feet to satisfy relocation requirements
  • Also see T1100638

JGW-G1201259 (LIGO-G1200939)

sas project advancement
SAS Project advancement
  • Design/construction

(*) six out of eleven top filters to be completed within 2010/2012 budget

JGW-G1201259 (LIGO-G1200939)

kagra sas project status
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

JGW-G1201259 (LIGO-G1200939)