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

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


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!


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


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


September 10, 2012 7

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.


Transversal mode damping• seismic noise level of chain’s TM, with/without Eddy current damping


IP modesChain modes

Lowest mode damping

• RMS amplitude reductionusing shadowmeter on suspension wire


Backup damping• active seismic attenuation• Accelerometers onboard

similar to TAMA accelerometers.Improved at AEI and NIKHEF

• Or feed-forward from ground


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.


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


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)

http://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/DocDB/ShowDocument?docid=450


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



Canned in 2 sub-units for travel and fast installation


All 19 standard filters produced,

assembled & tested.Stored at Akeno


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


Documents

Seismic attenuation chains concept, design and advancement status