Physics Program at the Caltech LIGO 40m Prototype

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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

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Warped space-time Einsteins General Relativity
(1916)
We envision gravity as a curvature of space as a
massive body moves, the curvature changes with it.
Einsteins theory tells us that this information
will be carried by gravitational radiation at the
speed of light.
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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 arent very close to any black holes
  (fortunately!), and cant see them with light

But we can search for (weak-field) gravitational
waves as a signal of their presence and dynamics
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Why are we so confident? Hulse-Taylor binary
pulsar
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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 (?)

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Magnitude of GW strain

• Accelerating charge ? electromagnetic radiation
• Accelerating mass ? gravitational radiation
• Amplitude of the gravitational wave (dimensional
  analysis)
• 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

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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

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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
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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.

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Initial LIGO sensitivity
LIGO I
LIGO II
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Seismic isolation stacks
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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

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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)
• ETF, Stanford advanced IFO configs (Sagnac),
  lasers, etc

• 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, quick test at
  Glasgow 10m

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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.
• Wont 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)

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Arm cavity parameters and LIGO sensitivity
As rITM is increased, Garm is increased, fpol-arm
is decreased.
fpol-arm
We wish to control Garm and fpol-arm
independently to optimize shot noise curve
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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
with f kls 2pls(fcarrfsig)/c
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Tuning the signal response
By choosing the phase advance of the signal
(fcarrfsig) in the signal recycling cavity, can
get longer (SR) or shorter (RSE) storage of the
signal in the arms
f kls 2pls(fcarrfsig)/c
rCC
rITM
RSE
tuned (narrow band)
RSE
SR
SR
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Using DR to optimize sensitivity
Now we can independently tune hDC and fpolarm to
optimize sensitivity (eg, hug the thermal noise
curve)
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40m Lab Staff

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

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Building renovation

• Wall removed for added lab space
• New optical tables installed at vertex, south
  arm, ends

• Laser safety enclosure installed
• New control room added

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Vacuum envelope additions

• 12m suspended mode cleaner

• Output optics chamber

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Hardware and electronics

• New electronics racks, crates, cable trays
• Installation of vacuum ion pumps, control system

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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.

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Vacuum System Overview

• Expanded envelope -- MC, OOC chambers added
• Regenerated, reinstalled ion pumps
• Contaminant level unchanged opted for no
  bake-out

H2O
N2
O2
H2
Ar
CO2
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EPICS-based 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

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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 310-7
torr, and has a pressure of 1.310-6 torr in
low-vibration mode (ion pumps only).
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Pre-stabilized laser (PSL)
We use the same 10-watt NdYAG 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.
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Frequency stabilization servo (FSS)
By adjusting the lasers master oscillator to
keep a fixed cavity in resonance, the FSS reduces
frequency noise to 29
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
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PEM Weather Station
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PEM Particle Counter
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PEM Seismic Monitoring
4.2 earthquake in Westwood, CA (roughly 20 miles
SW of Caltech) at 5pm on September 9th, 2001
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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 has been acquiring cable prototypes,
which are tested with the apparatus shown here.
The cables are clamped to the MC end chamber
seismic stack, which is then vertically shaken.
Wilcoxon accelerometers are used to measure the
transfer function.
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Flexibility Testing Results
mechanical short
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Data acquisition system (DAQ)
Anti-aliasing filters
ADCU 64 analog-to-digital channels sampled at
up to 16 kHz
EDCU collects data 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 Fast
ethernet connection Serves data for
diagnostics Connection to CACR
Sun Ultra 60 Frame Builder Collects data
from DCUs Creates frame files Sends
files to RAID array
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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

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Optics Parameters (flat ITMs)
ETM
5.2422 57375
38250
3.0266 ?
ITM
Vacuum
MMT
MC
PSL
MMT
RF
ITM
ETM
RM
2646
173.7
BS
1000
149.3
1450.8
149.5
927.1
38250
2600
200
1145.4
12165
3.0266 ?
3.0408 -2.8103e5
3.0436 -2.5749e5
0.9854 1165.2
1.6288 4.5225e5
5.2422 57375
3.0674 -1.3929e5
1.6288 -4.5225e5
1500
0.371 ?
1.6435 58765
3.0448 -1.7481e5
3.0632 -1.776e5
1.6616 -40241
1.6285 ?
3.0219 17250
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Whats to come?Mode cleaner optics

• The suspensions are being baked at LLO, should
  be back next week
• The 3 diameter optics are scheduled to arrive
  in mid-February
• Must be carefully hanged and balanced before
  installation in the 40m

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Whats 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

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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?