Date: Fri, 31 Mar 2000 10:15:03 +0100 (BST) From: "k.strain" To: "Gary H. Sanders" cc: ouimette_d@ligo.caltech.edu, Seiji Kawamura , Keith Riles , Mike Zucker , Eric Gustafson , worden@ligo.caltech.edu, ajw@hep.caltech.edu, "k.strain" , excomm@ligo.caltech.edu Subject: 40m AG meeting at LSC: minutes. Dear Alan and committee, sorry for the delay in these minutes but I got ill after the STAIC meeting. I would be very happy for any comment or correction to what appears below. The meeting was quite busy and I may have missed some points or wrongly attributed remarks. Summary of the current position:- Most of the questions raised by Alan and AG members have at least been touched on in our two meetings. Several of the more important points have either been resolved, or are likely to be soon (concerning vacuum/baking/stacks/contamination etc.). The two major points outstanding seem to be: 1) pre-isolation. This has been suggested by a few people as a good idea. Alan has confirmed that he is now looking into the options - including STACIS type mounts. 2) configuration. This is a big one, with lots of consequences. Unfortunately the AIC WG is not yet able to pin down some of the options for the LIGO II configuration (although this is a high priority). That makes it hard to finalise the configuration of the 40m experiments. Minutes of the meeting. Please tell me what I got wrong here! 40m Advisory Group Please see Alan Weinstein's overview talk which formed the core of the meeting. Contributing audience: Gary Sanders, David Shoemaker, Mike Zucker, Seiji Kawamura, Eric Gustafson, Guido Mueller, Jordan Camp, Dennis Coyne, and James Mason. [who have I missed, who was there but did not contribute?] SK asked about division between the science prototype/engineering prototype. GS: The engineering prototype should be very close to a LIGO II first article test. It is not possible to free up CDS effort as early as it is posisble to start experimenting on the 10m at Glasgow. DS: Teams developing LIGO II subsystems should be physically co-located. GS: Most likely people developing this system would copme from the CDS group. MZ: Why not upgrade electronics at Glasgow after the first stage? AW: It is not necessary to minimise the number of test interferometers as they are good for training. GS: The 40m will be rebuilt, the question is what is the best use for it. MZ: The 40m has a wide range of capabilities, are there other jobs for it? Some points arising on Slide 3: secondary 40m goals GS: The stiff suspension option is likely to be easier to adapt/fit than the soft one given the small tanks. MZ: Suggests that it is best to concentrate on the primary objectives, not suspension tests. EG: Suggests testing a complete PSL, using the 40m to do at least part of the testing appropriate to a phase noise interferometer experiment AW: The main objective is to build an electronics/engineering prototype, something that was lacking in LIGO I Discussion of points on slide 40m Interferometer Upgrade (modecleaner and modulation) MZ: &DS: Compare cost and performance differences between 3" and 4" optics. (SQL probably not important.) GM: points out that all of the proposed control schemes place some restrictions on the various path lengths, such as requiring the short MI to be at a bright fringe for the modulation. AW: The existing photodiodes are inappropriate DS: The noise demands may not have to be quite as stringent for 100 MHZ, easing photodiode design. MZ: Points out that the 1m modecleaner would need 150 MHz modulation to pass at the FSR AW: Baseline is post modecleaner modulation at 30 & 90 MHz Some points raised on slide about RSE JC: Points out that the sensing scheme has many new features over LIGO I and that a re-evaluation of the noise is needed. GM: notes that detuning is important here too. JC: We must have a test of the noise couplings. MZ: The interferometer has to be parametrised in terms of fluctuating modulation frequencies and lengths. Some points raised about seismic noise and isolation MZ: Are there really vertical modes at ~35 Hz? AW: The transfer functions were obtained from a simple model. DS: How much Viton is in the seats compared to that in the old stacks? - the volume is comparable, the surface less, but the main point is that the seats are new, clean material SK: There is too much residual vibration in the 1-10 Hz range, this should be reduced by a factor of 10. AW: That needs pre-isolation. MZ: Suggests (comercial) external isolators under the stacks. Some questions were raised about the real significance of Viton based contamination in mirrors used with green light. What are the results? DC: should be clarified with JC. DS asked for clarification of the flow of effort to and from the 40m. KS: there will be 1 FTE from GLA to 40m at start of RSE experiments there should be similar support from UF in the same time frame. Before then GLA are happy to accomodate visitors to work on the RSE experiments (Oct 00 to Oct 02). Discussions arising from the Schedule MZ: Is there a PSL by 2nd quarter 01? Would it then be wise to have a runup/intermediate optical layout for first tests, e.g. a suspended cavity. Discussions about multiple pendulums and related control issues DS: Multiple pendulums may be needed to give similarity of control between the 40m and LIGO II. Would they ease locking or otherwise? MZ: To what extent are lock acquisition studies part of the plan? JM: How applicable would they be to 4km system? MZ: Model validation would be possible, need scaling laws to full size. DS: Suggests increasing storage time to simulate longer system. KS: Suggests double pendulumd are relatively easy and yet contain most of the new dynamics. MZ: Suggests a serial approach: 1) use LIGO SOS 2) swap out end mirrors (etc.) for double pendulums MZ: Is wavefront sensing needed? Yes, must check all the matrix elements that need to be known for LIGO II. Discussion of longer modecleaner options MZ: 12m or 40m modecleaner options? AW: not for beam quality, but perhaps for passing modulations and eliminating noise MZ: Worry very much about location of modulation. Next meeting: TBD. END OF MEETING ******************** Dr Kenneth A. Strain Physics & Astronomy University of Glasgow Glasgow G12 8QQ tel +44 141 330 5884 fax +44 141 330 5881 *********************