ECR Title: Implement beam centering servo for green wave front sensors	DCC No: E1400311-v2
Date: December 4, 2014
Requester: Sheila Dwyer	Impacted Subsystem(s): ISC, ALS
Description of Proposed Change(s): Replace/supplement picomotors for steering green beam on to wave front sensor heads with PZT mirrors, and implement a servo to maintain the centering.
Reason for Change(s): Both sites have had difficulty implementing green wave front sensors, partially due to a changing sensing matrix, partially due to poor beam quality. While Hanford has had success in closing three degrees of freedom repeatedly after improving beam quality, we have not been able to close all four degrees of freedom for any cavity. The sensing matrix changes when the beam moves off center on the WFS head. We currently use picomotors to center the beam, which generate enough noise when they are moved to unlock the arm cavities. We would like to test the use of PZT mirrors to servo the beam position, and see if this improves reliability of the WFS.
Estimated Cost: 13 bases for MCL PZTs 13 inch optic holders for mounting to Mad city labs PZTs 12+3 MCL PZTs and their controllers NANO-MTA2X, extended range +/-2.5 mrad (5 mrad full range) NANO-DRIVE with DC power supply (AR-10 option; factory set to ±10V) 6 Differential to single ended converter (four channels) Cables and feedthroughs Beckhoff Modules for sensor readbacks 12 EL3104, 12+3 Concentrator (similar to D1102045, PZT readback only)
Schedule Impact Estimate: minimal for testing during installation
Nature of Change (check all that apply): Safety Correct Hardware Correct Documentation	Improve Hardware Improve/Clarify Documentation Change Interface Change Requirement
Importance: Desirable for ease of use, maintenance, safety Desirable for improved performance, reliability Essential for performance, reliability Essential for function Essential for safety	Urgency: No urgency Desirable by date/event: __February 1st, 2015__________ Essential by date/event: ____________ Immediately (ASAP)
Impacted Hardware (select all that apply): Repair/Modify. List part & SNs: ______________________ Scrap & Replace. List part & SNs:_____________________ Installed units? List IFO, part & SNs: _________________ Future units to be built	Impacted Documentation (list all dwgs, design reports, test reports, specifications, etc.): D1400175, E140031, D1100683, E1300109, T1100472, D1001423, E1300151, D1201498, D1202497, D1201448, D1100607, D1101126, D1201495
Disposition of the proposed change(s): The disposition of this proposed engineering change request is to be completed by Systems Engineering and indicated in the “Notes and Changes” metadata field in the DCC entry for this ECR. The typical dispositions are as follows: Additional Information Required: in which case the additional information requested is defined. The ECR requester then re-submits the ECR with the new information using the same DCC number for the ECR but with the next version number. Rejected: in which case the reason(s) for the rejection are to be given Approved Approved with Caveat(s): in which case the caveat(s) are listed TRB: the ECR is referred to an ad-hoc Technical Review Board for further evaluation and recommendation. It is the System Engineer’s (or designee’s) responsibility to organize the TRB. The System Engineer (or designee) then makes a technical decision based on the TRB’s recommendation. Links to the TRB’s documentation (charge, memos, final report, etc.) are to be added to the “Related Documents” field for this ECR. CCB: a change request for approval of additional funds or schedule impact is to be submitted to the Configuration Control Board. Links to the CCB’s documentation (CR, etc.) are to be added to the “Related Documents” field for this ECR. Concurrence by Project Management: Acknowledgement/acceptance/approval of the disposition is to be indicated by the electronic “signature” feature in the DCC entry for this ECR, by one the following personnel: Systems Scientist Systems Engineer Deputy Systems Engineer