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					              Physics Program at the Caltech
                   LIGO 40m Prototype

   Intro to gravity waves
   The LIGO experiment
   Purpose of the 40m
   Progress
    »   Building renovation
    »   Vacuum system & controls
    »   Pre-stabilized laser
    »   Environmental monitoring
    »   Data acquisition
    »   System modeling
 Coming soon

                         D. Ugolini, UCSD Colloquium, 2/12/01
           Warped space-time: Einstein’s
             General Relativity (1916)

We envision gravity as a
curvature of space; as a
massive body moves, the
curvature changes with it.



                                             Einstein’s theory tells us that
                                             this information will be
                                             carried by gravitational
                                             radiation at the speed of light.

                     D. Ugolini, UCSD Colloquium, 2/12/01
                                      Strong-field GR
•Most tests of GR focus on small deviations
from Newtonian dynamics
(post-Newtonian weak-field approximation)
•Space-time curvature is a tiny effect
everywhere except:
     The universe in the early moments of
     the big bang
     Near/in the horizon of black holes
•This is where GR gets non-linear and
interesting!
•We aren’t very close to any black holes           But we can search for (weak-field)
(fortunately!), and can’t see them with light      gravitational waves as a signal of their
                                                   presence and dynamics

                                 D. Ugolini, UCSD Colloquium, 2/12/01
Why are we so confident?
Hulse-Taylor binary pulsar


                           Neutron Binary System
                PSR 1913 + 16 -- Timing of pulsars


                                          17 / sec
                          

                     ~ 8 hr
                                               
   D. Ugolini, UCSD Colloquium, 2/12/01
                Nature of Gravitational Radiation
General Relativity predicts :
• transverse space-time distortions,
freely propagating at speed of light
• expressed as a strain (h = L/L)
• Conservation laws:
     •conservation of energy 
          no monopole radiation
     •conservation of momentum 
          no dipole radiation
     •quadrupole wave (spin 2) 
          two polarizations
 plus () and cross ()

                              D. Ugolini, UCSD Colloquium, 2/12/01
                     Magnitude of GW strain
   Accelerating charge  electromagnetic radiation
   Accelerating mass  gravitational radiation
   Amplitude of the gravitational wave (dimensional analysis):
             2G            4 2GMR 2 forb
                                         2
       h  4 I   h 
             cr                    c4r
      
       I = second derivative
    of mass quadrupole moment
    (non-spherical part of
     kinetic energy)
   G is a small number!
   Need huge mass, relativistic
    velocities, nearby.
   For a binary neutron star pair,
     10m light-years away, solar masses
      moving at 15% of speed of light:
                         D. Ugolini, UCSD Colloquium, 2/12/01
                                       The LIGO Project
LIGO: Laser Interferometer Gravitational-Wave Observatory
 US project to build observatories for gravitational
   waves (GWs)
 to enable an initial detection, then an astronomy of
   GWs
 collaboration by MIT, Caltech; other institutions
   participating
    »   (LIGO Scientific Collaboration, LSC)
    »   Funded by the US National Science Foundation (NSF)
Observatory characteristics
 Two sites separated by 3000 km
 each site carries 4km vacuum system, infrastructure
 each site capable of multiple interferometers (IFOs)
Evolution of interferometers in LIGO
 establishment of a network with other interferometers
 A facility for a variety of GW searches
 lifetime of >20 years
 goal: best technology, to achieve fundamental noise
   limits for terrestrial IFOs
                                    D. Ugolini, UCSD Colloquium, 2/12/01
                 International network
       Simultaneously detect signal (within msec)
               GEO           Virgo
LIGO                                             TAMA
                                                          detection confidence
                                                          locate the sources
                                                          verify light speed
                                                         propagation

                                                          decompose the
                                                         polarization of
                                                         gravitational waves
                                    AIGO
                  D. Ugolini, UCSD Colloquium, 2/12/01
                                How does the LIGO
                               interferometer work?
   The concept is to
    compare the time it takes
    light to travel in two
    orthogonal directions
    transverse to the
    gravitational waves.
   The gravitational wave
    causes the time difference
    to vary by stretching one
    arm and compressing the
    other.
   The interference pattern is
    measured (or the fringe is
    split) to one part in 1010, in
    order to obtain the
    required sensitivity.


                                D. Ugolini, UCSD Colloquium, 2/12/01
Initial LIGO sensitivity




                      LIGO I            AdvLIGO

 D. Ugolini, UCSD Colloquium, 2/12/01
We need Advanced LIGO!

                         X10 in sensitivity = x1000
                          volume searched

                         LIGO: 0.3-3 inspirals/year

                         Adv. LIGO: 300-3000
                          inspirals/year

                         Factor of ten improvement
                          needed at all frequencies


  D. Ugolini, UCSD Colloquium, 2/12/01
                      40m Laboratory Upgrade -
                            Objectives
 Key elements of Advanced LIGO to be
prototyped elsewhere:
   » LASTI, MIT: full-scale prototyping of
   Adv.LIGO SEI, SUS (low-f)
   » TNI, Caltech : measure thermal noise in
   Adv.LIGO test masses (mid-f)
   » AIGO, Gingin : high powered laser,
   thermal effects, control stability
   » ETF, Stanford: advanced IFO configs
   (Sagnac), lasers, etc



    40m Primary objective: full engineering prototype of optics control
     scheme for a dual recycling suspended mass IFO (high-f)
       » Minimize transition time to Advanced LIGO at main sites
       » Control scheme set by LSC/AIC, first test at Glasgow 10m

                             D. Ugolini, UCSD Colloquium, 2/12/01
The signal recycling mirror

                   We add a signal recycling mirror
                   (SM) at the asymmetric output port.
                   This forms a compound mirror with
                   the input test masses (ITMs) with
                   reflectivity:

                                                tITM rSM e i
                                                 2
                               rcm  rITM   
                                              1  rITM rSM e i
                          with  = kls = 2ls(fcarr+fsig)/c


   D. Ugolini, UCSD Colloquium, 2/12/01
                Advanced LIGO control scheme
 Chosen in Aug 2000, from best features of table-top prototypes
 Differences from Initial LIGO
   » 5 cavity lengths DOF’s
     (LCM, LDM, lPRC, lSRC, lmich)
   » SRC does not see carrier light
 AdvLIGO will use two pairs of
  RF sidebands (~9/180 MHz)
   » Applied before input MC
   » 9 MHz to symm. port, sensing PRM
   » 180 MHz to asym. port, sensing SRM
   » Demod at 171/189 MHz to sense
     lPRC, lSRC, lmich, insensitive to arms
   » Because of detuned SRC, only one sideband in a pair is resonant in SRC/PRC


                             D. Ugolini, UCSD Colloquium, 2/12/01
                      40m Laboratory Upgrade –
                          More Objectives

 Expose shot noise curve, dip at tuned frequency
 Multiple pendulum suspensions
    » may need to use Adv. LIGO suspensions to fully test control system
    » Not full scale. Insufficient head room in chambers.
    » Won’t replace full-scale LASTI tests.
 Thermal noise measurements
    »   Mirror Brownian noise will dominate above 100 Hz.
 Facility for testing small LIGO innovations
 Hands-on training of new IFO physicists!
 Public tours (students, DNC media,
  the Duke of York, etc)


                              D. Ugolini, UCSD Colloquium, 2/12/01
                              40m Lab Staff

 Alan Weinstein, project leader
 Dennis Ugolini, postdoc
 Steve Vass, master tech and lab manager
 Ben Abbott, electrical engineer
 AdvLIGO engineers/physicists: Larry Jones, Jay Heefner, Garilynn
  Billingsley, Janeen Romie, Mike Smith, Fred Asiri, Dennis Coyne,
  Peter King, Rich Abbott, Bob Taylor, etc.
 Collaborating institutions (TAMA, CSUDH)
 Guillaume Michel, visiting grad student (winter/spring 2001)
 Summer 2000-2001: eleven SURF undergraduates



                       D. Ugolini, UCSD Colloquium, 2/12/01
                         Building renovation
                                          Old IFO dismantled, surplus
                                           distributed to LIGO, LSC
                                          Wall removed for added lab space
                                          New optical tables installed at
                                           vertex, south arm, ends




 Roof repaired, cranes retouched
 Laser safety enclosure installed
 New control room, entrance
  changing area added
                        D. Ugolini, UCSD Colloquium, 2/12/01
             Vacuum envelope additions




12m suspended mode cleaner                     Output optics chamber

                   D. Ugolini, UCSD Colloquium, 2/12/01
Hardware and electronics
               Acquired and installed new
                electronics racks, crates, power
                conditioners, 12” cable trays, etc.
               Installation of vacuum ion pumps,
                control system




  D. Ugolini, UCSD Colloquium, 2/12/01
STACIS Active seismic isolation



     One set of 3 for each of 4 test chambers
     6-dof stiff PZT stack
     Active bandwidth of 0.3-100 Hz,
     20-30dB of isolation
     passive isolation above 15 Hz.




       D. Ugolini, UCSD Colloquium, 2/12/01
                                   Optical Layout

        All suspended optics (other than
         MC) have optical levers
        Almost all of 9 output beams come
         out in this area
        12m input mode cleaner
        short monolithic output MC
        baffling, shutters, scattered light
         control
        Currently designing removable
         covers for all ISC tables
        Have made layouts of all ISC tables,
         with detailed parts lists

D. Ugolini, UCSD Colloquium, 2/12/01
                 EPICS Vacuum control system

• Reads out valve
status, pump status,
and pressures

• Provides operator
and monitor screens

• Has code for slow
safety interlocking

• Communicates
directly with data
acquisition system

                       D. Ugolini, UCSD Colloquium, 2/12/01
             Residual Gas Noise Requirement
                                           The plot at left includes the residual gas
                                           noise for a vacuum of 10-6 torr, dominated
                                           by water and nitrogen. At higher pressures
                                           the noise becomes significant at the tuned
                                           frequency.




The 40m vacuum system can run as
low as 3*10-7 torr, and has a pressure
of 1.3*10-6 torr in low-vibration
mode (ion pumps only).

                           D. Ugolini, UCSD Colloquium, 2/12/01
               Pre-stabilized laser (PSL)




We use the same 10-watt Nd:YAG solid-state infrared laser as
the main LIGO sites. The goal of the PSL system is to provide
frequency and intensity stabilization, with minimal power loss.
                    D. Ugolini, UCSD Colloquium, 2/12/01
             Frequency stabilization servo (FSS)




By adjusting the laser’s master oscillator
to keep a fixed cavity in resonance, the
FSS reduces frequency noise to < 1 Hz.
                             D. Ugolini, UCSD Colloquium, 2/12/01
                       Pre-mode cleaner (PMC)




The PMC uses the concept of Guoy phase to
remove all non-TEM00 modes from the main
beam, without reflecting it back to the PSL

                            D. Ugolini, UCSD Colloquium, 2/12/01
  Environment Monitoring

 Several seismic sensors
   » 2 3-axis Wilcoxon accelerometers
   » 1-axis Ranger seismometer
 MetOne particle counter
 Davis Instr. weather station
 Still adding more
   »   Magnetometer
   »   Microphones
   »   Line monitor
   »   STACIS readout


       D. Ugolini, UCSD Colloquium, 2/12/01
                 Data acquisition system (DAQ)
Anti-aliasing filters                                               ADCU – 64 analog-to-
                                                                    digital channels sampled
EDCU – collects data                                                at up to 16 kHz
from EPICS databases
                                                                    512 GB RAID array
                                                                     • Full data for 48 hours
                                                                     • Second trends for 1 month
                                                                     • Longer trends “forever”
Sun Ultra 10 “Frame
Broadcaster”                                                        Sun Ultra 60 “Frame Builder”
 • Fast ethernet connection                                          • Collects data from DCUs
 • Serves data for diagnostics                                       • Creates frame files
 • Connection to CACR                                                • Sends files to RAID array


                             D. Ugolini, UCSD Colloquium, 2/12/01
               Interferometer modeling efforts
   Specification of all optical parameters
     »   Cavity lengths, RF sideband frequencies and resonance conditions
     »   mirror trans., dimensions, ROC, optical quality, tolerances…
   Length and alignment control with Twiddle, ModalModel
   Suspensions for 5" test masses modeled using Simulink
   Model of IFO DC response with imperfect optics in progress using FFT
    program (CSUDH group)
   Model of lock acquisition dynamics using E2E in progress




                            D. Ugolini, UCSD Colloquium, 2/12/01
                  Length sensing signals from
                           Twiddle




• Twiddle is a Mathematica program to numerically calculate response of RF
demodulation of IFO signals in response to motion of mirrors away from
locked configuration.
• Can construct MIMO length sensing and control matrix.
• AdvLIGO control matrix much more diagonal than LIGO I!
• Mainly due to the availability of 2 pairs of RF sidebands
• Use double demodulation at asym port for the Michelson ( l- ) signal
                         D. Ugolini, UCSD Colloquium, 2/12/01
 What’s to come?
Mode cleaner optics

             • The 3” diameter optics have been
             polished, tested, and sent for coating

             • The suspensions are cleaned,
             baked, and ready for assembly

             • Readying ovens for baking &
             curing of assembled optics

             • Experts in April will teach us how
             to hang and balance the optics
D. Ugolini, UCSD Colloquium, 2/12/01
                    What’s to come?
            Length sensing and control (LSC)

 Each optic has five OSEMs (magnet
  and coil assemblies), four on the back,
  one on the side



                                                The magnet occludes light
                                                 from the LED, giving position

                                                Current through the coil
                                                 creates a magnetic field,
                                                 allowing mirror control


                        D. Ugolini, UCSD Colloquium, 2/12/01
                         Input Mode Cleaner
                       Hardware and Electronics

 Wiring drawings are complete
    » LSC/ASC for mode cleaner
    » Digital suspension controllers for full IFO
    » All electronics should be in-hand by end of
      February
    » Cabling, cross-connects underway

 In-vacuum cabling finished, needs to
  be cleaned and baked

 MC end chamber seismic stack ready
  for installation when cabling is finished



                             D. Ugolini, UCSD Colloquium, 2/12/01
             Input Mode Cleaner
           Commissioning Schedule

             Suspensions arrive
February     Optics tested, sent for coating
             Electronics acquired and installed

             In-vacuum cabling installed
             MC end chamber seismic stack installed
 March
             Electronics cabling, cross-connects installed
             Optics return from coating, tested

             Optics prepared for hanging (magnets, bake)
 April       Hanging and balancing optics
             Optics installed in IFO

 May         Begin exercising mode cleaner

             D. Ugolini, UCSD Colloquium, 2/12/01
                    Milestones through 2004
 2Q 2002:
   »   Install cables and seismic stacks in mode cleaner, output optics chamber
   »   Hang and install mode cleaner optics
   »   Install suspension controllers, LSC, some ASC
   »   Glasgow 10m experiment informs 40m program
 4Q 2002:
   » Hang and install core optics
   » Complete ASC, ISC
   » Control system finalized
 3Q 2003: Core subsystems commissioned, begin experiments
   » Lock acquisition with all 5 length dof's, 2x6 angular dof's
   » Measure transfer functions, noise
   » Inform CDS of required modifications
 3Q 2004: Next round of experiments.
   » DC readout. Multiple pendulum suspensions?

                          D. Ugolini, UCSD Colloquium, 2/12/01
                                  Summary

 The 40-meter is on schedule to serve as an RSE
  controls/engineering prototype for Advanced LIGO

 Significant progress has been made in several
  subsystems:
   » Vacuum controls, PEM, DAQ up and running
   » PSL ready pending new table layout
   » Digital suspension controls, some LSC/ASC in next 2-3 months


 Expect to exercise mode cleaner in summer 2002
  and full IFO in summer 2003

                     D. Ugolini, UCSD Colloquium, 2/12/01
Seismic isolation stacks




  D. Ugolini, UCSD Colloquium, 2/12/01
                    Cable Flexibility Testing

There has been concern that the
in-vacuum cables used at the sites
are too stiff, and would short out
the 40m seismic stacks.




Larry Jones acquired several cable prototypes,
which were tested by measuring the transfer
function of the MC end chamber seismic stack,
shown here.



                        D. Ugolini, UCSD Colloquium, 2/12/01
Flexibility Testing Results

                              mechanical short




   D. Ugolini, UCSD Colloquium, 2/12/01

				
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