Physics Program at the Caltech LIGO 40m Prototype

1
Physics Program at the Caltech LIGO 40m Prototype

• 40m objectives
• Progress to date
• Building rehab
• Vacuum envelope/controls
• PSL
• PEM
• DAQ
• Modeling
• Next step Input MC
• Long-term milestones

2
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.

3
We need Advanced LIGO!
4
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

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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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Advanced LIGO control scheme

• Chosen in Aug 2000, from best features of
  table-top prototypes
• Differences from Initial LIGO
• 5 cavity lengths DOFs
• (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

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Output mode cleaner,DC demodulation

• An output mode cleaner is desired to remove
  junk light from the asymmetric port GW signal
• Carrier light leaking out due to imperfect
  Michelson contrast
• Higher-order modes due to misalignment
• RF-modulated light for heterodyne GW detection
• Only carrier light and GW signal sidebands exit
  the output MC
• Can be a short, monolithic device like PSL
  pre-mode-cleaner
• Use DC (homodyne) demodulation to sense GW signal
  
• Offset-lock the arms by 510-12 m to allow a
  small, controlled amount of carrier light to
  reach the asymmetric port
• The light is filtered by the high-finesse arms,
  so low noise and pure TEM00
• Use carrier light as a local oscillator to beat
  against GW sidebands
• RF demodulation will also be present, used as
  control signal

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Advanced LIGO innovations to be tested at 40m

• A seventh mirror for signal recycling
• length control goes from 4x4 to 5x5 MIMO
• Detuned signal cavity (carrier off resonance)
• Pair of phase-modulated RF sidebands
• frequencies made as low and as high as is
  practically possible
• unbalanced only one sideband in a pair is used
• double demodulation to produce error signals
• Short output mode cleaner
• filter out all RF sidebands and higher-order
  transverse modes
• Offset-locked arms
• controlled amount of arm-filtered carrier light
  exits asym port of BS
• DC readout of the gravitational wave signal

Much effort to ensure high fidelity between 40m
and Adv.LIGO!
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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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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, Mike
  Smith, Peter King, Jay Heefner, Garilynn
  Billingsley, Janeen Romie, Rich Abbott, Dennis
  Coyne, Bob Taylor, Lee Cardenas, etc.
• Collaborating institutions (TAMA, CSUDH)
• Summer 2000-2001 eleven SURF undergraduates

14
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

15
Vacuum envelope additions

• 12m suspended mode cleaner

• Output optics chamber

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Hardware and electronics

• Acquired and installed new electronics racks,
  crates, power conditioners, 12 cable trays, etc.
• 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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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
• L. Jones designing removable covers for all ISC
  tables
• M. Smith has made layouts of all ISC tables, with
  detailed parts lists

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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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Frequency stabilization servo (FSS)
Cavity Visibility 93 Transmitted Power 5 mW
(losses due to mode mismatch at AOM)
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Pre-mode cleaner (PMC)
PZT resonance
Notch filter
Cavity Visibility 83 Transmitted Power 6.1 W
(8.7 W incident) Losses due to mode-mismatch, end
mirror
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Future PSL Effort

• Align, characterize new NPRO
• Revise table layout
• Relocate low-power pickoff
• New cyl. lenses for better circularity
• New mode-matching scheme
• Electrically isolate PSL table
• Install EOMs, QPDs, shutters, Tropel, etc.
• Final refinements
• Anodized beam tubes in both paths
• Heating jacket for reference cavity
• Higher reflectivity PMC
• PSL ready for commissioning of input mode cleaner

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Environmental Monitoring (PEM)

• 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

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Data acquisition system (DAQ)
Anti-aliasing filters
ADCU 64 analog-to-digital channels sampled at
up to 16 kHz (24 in use)
EDCU collects data from EPICS databases (77
channels in use)
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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Modeling of AdvLIGO and 40m

• Specification of all optical parameters
• Cavity lengths, RF sideband frequencies and
  resonance conditions
• mirror trans., dimensions, ROC, optical quality,
  tolerances
• Detailed length-control model scheme using
  Twiddle
• Adv.LIGO and 40m following parallel paths
• Alignment sensing control modeled using
  ModalModel (SURF student)
• Suspensions for 5" test masses modeled using
  Simulink (SURF student)
• Noise in GW channel modeled in Matlab (BENCH)
• Model of IFO DC response with imperfect optics
  using FFT program (CSUDH group) (in progress)
• Model of lock acquisition dynamics using E2E (in
  progress)
• Thermal effects modeled with Melody (in progress)

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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

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Input Mode Cleaner Optics

• The 3 diameter optics have been polished,
  tested, and sent for coating
• The suspensions are cleaned, baked, and ready
  for assembly
• B. Taylor is readying ovens for baking curing
  of assembled optics
• Experts in April will teach us how to hang and
  balance the optics

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Input Mode CleanerHardware 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

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Installation of Mode Cleaner End Chamber Seismic
Stack
Side view of end chamber
Steve Vass and Larry Jones prepare the stack for
installation
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Seismic Stack Cabling
To prevent seismic shorting, our in-vacuum
cables have a lot of slack!
The installation is nearly complete
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Input Mode CleanerCommissioning Schedule

• Suspensions arrive
• Optics tested, sent for coating
• Electronics acquired and installed
• In-vacuum cabling installed
• MC end chamber seismic stack installed
• Electronics cabling, cross-connects installed
• Optics return from coating, tested
• Optics prepared for hanging (magnets, bake)
• Hanging and balancing optics
• Optics installed in IFO
• Begin exercising mode cleaner

February March April May
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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, some LSC/ASC
• Glasgow 10m experiment informs 40m program
• 4Q 2002
• Hang and install core optics
• Complete LSC, ASC
• 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?

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Outstanding Development Tasks

• Careful review of IFO design
• 180 MHz photodiodes
• Needed for WFS, LSC
• Double demodulation (166x33 for 40m, 180x9 for
  AdvLIGO)
• Output mode cleaner design
• Arm offset-locking software
• DC photodiode
• In-vacuum? Suspended?
• Noise analysis
• Lock acquisition studies with E2E
• Report from Glasgow 10m

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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