Deliverable of NA5: Gravitational Wave Antenna (GWA)

Deliverable of NA5: Gravitational Wave Antenna (GWA)

WP 1: Antennas commissioning and characterization

Annual Report (1/4/2004 – 31/3/2005)

M.Barsuglia1, A.Freise2, H.Grote3, S.Hild3, P.LaPenna2,

G.Losurdo4, H.Luck3, J.Smith3, L.Taffarello5, M.Visco6

1 Laboratoire de l’Accellerateur Lineaire, Orsay, France

2 European Gravitational Observatory, Cascina, Italy

3 Max-Planck-Institut für Gravitationsphysik, AEI, Hannover, Germany

4 INFN and Universita di Firenze/Urbino, Firenze, Italy

5 INFN and Universita di Padova, Padova, Italy

6 CNR, Roma, Italy

1. Objectives

The WG1 has been setup to achieve the following goals:

To speed up the commissioning and the characterization of Virgo and GEO by means of a deeper collaboration between the two teams;

to develop common methods of characterization of interferometric GW detectors to be applied to Virgo and GEO;

To provide inputs for establishing priorities for short term improvements of the existing interferometric detectors on the base of the Virgo and GEO characterization.

1. Milestones and deliverables

In the first year the group is due to start the activity, set up a web page, start the comparison of the noise sources for Virgo and GEO. All the milestones have been reached:

the activity has been started and proceeds regularly. Three meetings have already been performed and the fourth one has been scheduled at the beginning of April 2005;

the web page has been setup ( and is currently used as a tool to plan and follow the group activity;

the comparison of noise sources has been the main task of each meeting. In the following sections we describe how we proceed.

This report is the only deliverable required for the first year.

1. Appointed people

Ten people have been appointed as members of the WG1 by the executive board. They have been chosen among the people who partecipate actively at the commissioning of Virgo, GEO and the resonant detectors. The appointees are:

M.Barsuglia (Virgo)

A.Freise (Virgo)

H.Grote (GEO, co-chairman)

S.Hild (GEO)

P.La Penna (Virgo)

G.Losurdo (Virgo, co-chairman)

H.Lück (GEO)

J.Smith (GEO)

L.Taffarello (AURIGA)

M.Visco (Nautilus/Explorer)

The WG1 is chaired by G.Losurdo (Virgo) and H.Grote (GEO).

Despite the fact that the mission of the group deals with the commissioning of interferometric detectors, the long experience with noise analysis of the people working on bars is helpful. It should be remarked that all the WG1 meetings are open to all interested people.

1. Activities performed

- The first WG1 meeting was held at the Virgo site on July 7-8, 2004;

-the second meeting was held at the University of Hannover / GEO site on September 23-24, 2004;

-the third meeting was held at the Virgo site on January 22-24, 2005;

-the fourth meeting has been scheduled: it will be held at Hannover on April 7-8, 2005.

The work on noise comparison has been started and will be continued along three parallel paths:

comparison of the detectors subsystems and operation procedures;

comparison of tools for data handling;

comparison of technical noise sources and methods for noise investigations.

The meetings have been organized keeping in mind the final goal of reaching methods of noise characterizationcommon to GEO and Virgo. This requires, as intermediate step, the reciprocal knowledge of the experiment structures and operations. Therefore, in each meeting talks on the status of the detectors, talks on the different subsystems, talks on tools used for data handling, on site demonstrations on the interferometer operation have been scheduled.

1. First meeting, Cascina, July 7-8 2004

All the appointees attended the first meeting. B.Willke (GEO) and R.Flaminio (Virgo) attended the first meeting as guests.

The plan of the meeting was the following:

-an introductory talk about the objectives of ILIAS-N5 and especially of WG1, given by one of the chairmen;

-three talks on the status of the detectors (GEO, Virgo, bars);

-talks on specific commissioning topics (Locking, noise characterization).

Presentations and discussion

G.Losurdo reminded the objectives of ILIAS-N5, the objectives of WG1 and the recommendations of the executive board.

H.Lück presented the GEO status. The main topics of discussion were: the use of Faraday isolator, the GEO MC topology, the fused silica fibers used to suspend he test masses (load, coating, violin modes), the mirror curvature thermal compensation, the stationarity of noise.

A.Freise presented the Virgo status. Main topics of discussion: the injection bench resonances (visible in the Virgo sensitivity curve), the control of the output modecleaner, the data acquisition system.

M.Visco and L.Taffarello presented the status of the resonant detectors (Explorer, Nautilus, Auriga, Minigrail). Main topics of discussion: the efforts done to widen the bandwidth, the spurious peaks in the Auriga sensitivity curve, cryogenics issues.

H.Grote presented the GEO locking and control strategy. Main topics of discussion:

The GEO electrostatic actuators, the control design for split actuation, the power recycling and its role in the lock acquisition process, the signal recycling, the tunable optical gain.

Matteo Barsuglia presented the Virgo locking and control strategy. Main topics of discussion:

the use of only one phase modulation frequency in Virgo, the locking of output modecleaner, the control loop simulations with SIESTA.

J.Smith gave a talk on noise analysis issues in GEO, describing how noise projections are performed and how the contribution of single noise sources to the sensitivity can be investigated.

The drawbacks of simpler coherence studies with respect to noise projections were discussed.

Paolo La Penna presented the noise analysis in Virgo. Main topics of discussion: the main methodologies used in Virgo to estimate the contribution of known noise sources, the frequency noise caused by the input modecleaner optical bench, the noise of the actuators.

Because of long and detailed discussions developing we scheduled talks by G.Losurdo (suspension control) and M.Visco/L.Taffarello (noise in bar detectors) were postponed to next meeting.

In the final discussion of the meeting the following points were risen and decisions made:

- since everybody was really satisfied with the vivacity and the deep level of the discussion, it was agreed that the style of the meeting should be maintained in the sense of as open discussions as possible, taking place during presentations. Therefore the allocated time for each topic should be rather long.

- It is proposed (for the next meetings) to support the discussion of technical topics by providing documentation (internal reports, papers).

- For the next meeting, people giving talks are requested to submit the slides in advance (if possible), or at least to circulate an abstract of their presentation.

1. Second meeting, Hannover, September 23-24, 2004;

The second working group meeting was held at the University of Hannover and the GEO site on September 23-24, 2004. All the working group appointees attended the meeting. In addition to those, B.Willke (GEO) and I.S.Heng (GEO) attended as guests.

Similar to the first meeting, the objectives were directed towards the analysis and comparison of main sources of noise, limiting the Virgo and GEO sensitivities.

In this early state of the collaboration this included presentations and discussion on experimental structures and operation of the detectors. Therefore, talks on the status of the detectors, on different subsystems, and an on-site demonstration of the interferometer operation were the main objectives of the meeting. Having the further future in mind, the group also discussed about how we can prepare the exchange of data.

Presentations and discussion

P. La Penna gave a talk on the progress of Virgo commissioning since the first working group meeting in July. The discussion included the progress in auto-alignment and control noise reduction, the reduction of the laser input power by 90%, and the plans for a new injection bench.

The talk about progress of GEO commissioning was given by H.Lück, with the discussion comprizing the progress in sensitivity, the output optics in a vacuum system, an upgrade of Michelson loop electronics, and the effects of different sizes of the signal-recycling modulation index.

G. Losurdo gave a presentation on the hierarchical control of the Virgo Superattenuator.

Discussion topics included digital control systems, the control strategy to reach Virgo sensitivity at low frequencies, and the principal similarity of the hierarchical control of Virgo and GEO (with implementation details varying a lot though).

A presentation on the GEO interferometer operation was given by H.Grote. The procedure of optics manual alignment and the locking of the various optical cavities of GEO was discussed, followed by a practical demonstration.

M.Visco reported on noise sources in resonant-mass detectors (bars). Topics of dicussion were the effects of thermal noise, electronic noise, cosmic rays, and latest sensitivity improvements.

The noise analysis in GEO was presented by J.Smith, with a discussion about the coupling

of noise sources to the detector in dependence of the 'demodulation phase'. Examples of noise identification and reduction were discussed, along with non-linearities in the electrostatic actuators.

S. Hild presented the GEO data tools, with discussion taking place about the data acquisition and collection, the file format, data-acquisition web interface, data tools (Matlab, Triana), and monitor software. Here a discussion about the requirements of exchanging data between the collaborating projects was started. It was agreed to exchange a data file in the so called 'frame format', which is the standard format for data storage of the gravitational-wave research community. Testing of the readability of such files is to be done by the respective other group.

(At the time of the third meeting, the reading of a GEO framefile by the VIRGO data-viewer was successfully implemented.)

Since the Virgo and GEO detectors are in different states of the commissioning, it was agreed that it was not yet the right time to start a common noise analysis, which is foreseen in the working group task list for a later time anyway.

1. Third meeting, Cascina, January 22-24, 2005;

The WG1 of the ILIAS-N5 convened for its third meeting at Cascina. All the appointed people were present, except P.La Penna (at Caltech). Several non appointed people attended the meeting: B.Willke, R.Flaminio, M.Punturo, L.Barsotti, E.Tournefier, R.Gouaty, H.Heitmann and others. Some of them were invited to give talks. In fact, we believe that the participation in the WG1 activites could be very positive for all the people involved in the commissioning, especially the PhD students and the Post-Docs, and we plan to invite non-appointees also at the next meetings.

Presentations and discussion

L.Taffarello presented the status of the AURIGA detector. Main topics: spurious peaks in the sensitivity curve, non-linearities in the system, improved seismic isolation of the antenna

J. Smith presented the status of GEO. Main topics: improvement of sensitivity in several steps, after dominant noise source of scattered light was removed. Increase of IMC-injected power by about factor of 2. Dark port power noise, reduction of modulation index to stabilize RF power. Signal recycling modulation.

L.Barsotti (Virgo PhD student, invited) presented the status of Virgo and the locking of the recycled interferometer. Main topics: locking of full Virgo, full hierarchical control of suspension. Problems with a traditional lock acquisition strategy. The variable Finesse approach for the lock acquisition.

Open problems: 'jumps' of power observed, occuring within 20ms.

R.Flaminio (Virgo, invited) presented a talk on the problem of sidebands transmission at Virgo input modecleaner.

Main points: the coupling of MC length noise to modulation sidebands and to sensitivity. The possible solutions being studied: control IMC length or modulation frequency by servo.

H.Grote presented the strategy for input modecleaner locking and alignment at GEO. This talk was requested by the Virgo people since Virgo is currently designing a new input bench. Main topics:

the differences between GEO and Virgo for what concerns the sidebands transmission problem and the absolute length drift of the input modecleaner. Automatic alignment setup of modecleaners. Scanners with 1kHz bandwidth used to center beam on quadrants.

S.Hild presented a study of the scattered light in GEO interferometer. Main remarks: care (and thought) must be taken when placing optical components close to beam waists. In these cases, scattered light is easily focused back to main interferometer paths. Differential Michelson paths (e.g. scattering into one arm) are much more critical in this respect as common Michelson paths (e.g. scattering into PR cavity).

E.Tournefier (Virgo, invited) presented the work of optical characterization of the Virgo interferometer. Main points: measurements of losses, radii of curvature of the mirrors, finesse of the cavities, contrast defects, absolute lengths.

A.Freise gave a demonstration (in the Virgo control room) on the use of dataDisplay, the custom software used in Virgo to display the detector data and make some analysis.

The Virgo team gave a demonstration (in the Virgo control room) of the interferometer locking procedure. The current level of automation and the plans for improving it were also discussed.

A whole session was dedicated to discuss the next steps of the group activity:

-organization of the next meetings:

the basics of the detectors have now been learned. The next meetings will focus more to “open problems” met during the commissioning, to be discussed in a kind of brainstorming way. We plan to include concluding remarks on these discussions within the meeting minutes;

-software/data exchange:

Virgo reading of GEO frame is established, GEO reading of Virgo frame is planned. Test installation of GEO frameserver at Virgo has been planned, along with exchange of Matlab-based tools for frame access and data-handling;

-student exchange:

both groups agree on the opportunity to exchange students for short periods within the WG1 framework. A clear topic on which the exchange could be focused should be identified;

-frequency of meetings:

the group agreed to slowly develop towards more frequent meetings and/or additional tele/phone-meetings. The latter ones may be scheduled upon request of one team to discuss actual subjects.

1. Fourth meeting, Hannover, April 7-8 2005

The fourth working group meeting is scheduled for the 7.-8. April 2005 and will be held in Hannover.

Besides updates of the current detector status from Virgo, GEO, and the bars, we plan to have talks on a few subsystems and hold a discussion session about an actual commissioning problem.

The topic of this discussion will be chosen close to the meeting, such that the discussion has the possibility to actually contribute to commissioning progress.

1. Plans for the next 18 months

Year 2, 1st semester:

The analysis and comparison of main sources of noise, limiting the Virgo and GEO sensitivities is the main goal of this period. The basis for this has been laid by the presentations and discussions of the former meetings. We will continue to to have talks about various detector subsystems to enhance the understanding of detectors, but we also plan to have dedicated sessions, discussing

a particular actual problem, which in most cases will be related to a specific noise source.

Another task of this period will be the comparison of characterization methodologies and tools,

which can go naturally along with investigating noise sources.

Preparation of recommendation for short term improvements is a third topic of this period.

Year 2, 2nd semester:

Continuing the tasks of the 1st semester, we plan to exchange software tools between the groups,

and develop common algorithms for data characterization.

Year 3, 1st semester:

Maintaining the work on noise sources and comparison of characterization methodologies, we will try to implement common algorithms for data characterization and noise analysis.

Other topics:

The path towards common noise characterization requires the creation of a common language, since the names and the acronyms used by the two experiments to identify similar parts of the detectors or similar data channels can be quite different. Speakers have been asked to make the effort of contributing to the creation of a common “dictionary”, probably to be located at the website.

We also plan to continue to invite non-appointed people who are experts on some aspects of the detector and its data-characterization, to give talks on relevant topics.

1. Conclusive remarks

We remark that the experience done up to know in the WG1 group has been extremely positive for many reasons:

-all the group members are very knowledgeable about commissioning problems: the resulting discussion has always been useful. Ideas to improve the detectors are continuously exchanged;

-among the appointees a good spirit of collaboration has been established, which is very helpful to the fulfilling of one of the main objectives of the group: a joint effort on the detectors noise characterization;

-the first four meetings have been organized at the Virgo and GEO sites. Convening at the sites allowed precious “control room sessions”, showing everybody how the detector is actually operated, what can be the difficulties, what are the differences between the two interferferometers, what are the problems that have been solved at one detector but not yet at the other one;

-the steering committees of Virgo and GEO agreed to give the WG1 group the privililege to exchange the technical data of the two detectors. We intend to exploit this privilege in the next months and years to perform joint analysis on some specific problems. A first test of data exchange has been performed: a GEO data file has been succesfully read using Virgo custom software.

FIGURES

Figure 1: the evolution of the Virgo sensitivity during the first year of the ILIAS-N5 activity.

Figure 2: the evolution of the GEO sensitivity during the first year of the ILIAS-N5 activity.