Outline ideas/status K.A. Strain GEO HF Outline ideas/status K.A. Strain

GEO HF Contents: goals; a walk through the various subsystems; project status. timescale 5 years cannot all be very advanced should have some groundbreaking technology cost envelope limited probably in region 15~20Meuro probably relies on support from other projects laser, ASI, digital control hardware …

GOAL: science in the kHz range Region of interest for GEO HF

LASER Ideas Implications of 200 W LZH developing 200W laser for Advanced LIGO natural choice for GEO HF timescale about right, price known Implications of 200 W require upgraded injection optics to handle probably require active thermal correction even in all-reflective scheme

Vacuum and infrastructure existing vacuum system just adequate with reduction of leak rate modest improvement of H2 pump speed site infrastructure mostly adequate move to digital control could allow/require housing most control hardware outside central building central building tank layout essentially fixed, apart from minor changes e.g. to mode cleaner

Optics arms probably require cavities, either FP or diffractively coupled moderate finesse (order 100) Sagnac (perhaps Dual recycled) or FP-RSE could both work to give maximum performance at 1~3 kHz (bandwidth varies among solutions, but this requires very detailed calculation)

Optics: mirrors and light power small, low absorption (<1ppm) low/moderate scatter (~30 ppm) - how clean can we keep them? hopefully small diameter (10~15 cm) helps power 200W/100ppm = 2MW for two arms should be OK for heavily thermal compensated FP or diffractive coupled system with some thermal compensation (heating per optic is < ~1W)

Seismic isolation Detection band (>500 Hz) suspensions adequate (if 3 stage) Control band (0.1 to 10 Hz approx) acquisition: want slow relative mirror velocities, short suspensions ease control and with 600m arms mean most isolation needed around 0.5 to 5 Hz Must be compact! single high gain stage active isolator in tank lid probably adequate (if payload is kept small) aim for “industrial strength” turnkey solution?

Suspensions: aims easy to control strong isolation of ground noise >500 Hz strong isolation of control noise >100 Hz assumed locking bandwidth <100 Hz as perturbations less than in GEO 600 where 100 Hz suffices passive filtering allows relatively simple implementation of (noisy) digital controllers small total mass (allow compact ASI) short total length cartridge installation to ASI (pre assembled, aligned)

Suspensions Optimum mirror mass/size depends on substrate choice, coatings etc. Outline design expect ~5 kg and 10~15cm dia. allows short final stage for easy control from one stage up (sus thermal noise not a big problem) two relatively short (15~20cm?) stages with 2~3 Hz vertical isolators (blades) to give 6 dof isolation whole thing held in frame, not too large or heavy for easy handling (60cm tall, ~25 kg) eddy current damping as local control (few small magnets adequate) electromagnetic actuation at top and middle stages

Control Likely to be very complex, due to optical configuration (esp. FP RSE), thermal problems Desire digital control to reduce commissioning time penalty (with finite money) is no fast control and limited dynamic range ASI important to reduce control burden suspension designed to make control easy (q.v.) control problem then tractable, but complex

DAQs GEO 600 system works to 6 kHz probably adequate possibly upgraded within GEO 600 lifetime

Injection optics main changes rebuild mode cleaner probably just 1 high-power modecleaner adequate at HF reconsider isolation (Advanced LIGO design OK) reconsider modulation (ditto) but need to look at whole scheme when configuration settled

Thermal compensation Probably need a design with low power (<<10 kW) at the BS. Ring heaters assume ring heaters fitted to cavity optics might be adequate for a diffractively-coupled configuration Scanning laser probably needed for FP-RSE, but depends on many unknowns (coating homogeneity for example)

Project status Outline design studies and tentative project scheduling (summer 2004) Notification of project to MPG and PPARC for initial evaluation (now) Proposals needed over the next ~year for funding start ASAP To avoid going “off-air” need much work done off site Partners welcome!