Tom McCarville Oct 30, 2007 HOMS/SOM Design Status 30 Oct 2007 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA SM1 HM1HM2 SM2 SM3/4

Tom McCarville Oct 30, m Preliminary design/test of HOMS & SOMS integrated mirror systems is nearly complete High risk areas receiving special attention are the subject of this talk Risk levels: Well established solutions & practices Moderate effort to demonstrate Significant effort to demonstrate

Tom McCarville Oct 30, 2007 The HOMS design incorporates additional features to achieve - higher pointing resolution - tighter figure control HOMS & SOMS share the same basic design Rotation spindle & drive cam Mirror mount assembly Vacuum Chamber Translation slide 6-axis strut assembly Support Pedestal Z X Y (vert.) Tunable Z force 3 fixed Y forces & constraints 2 fixed X forces & constraints Y constraint flexure Z constraint B 4 C chin guard

Tom McCarville Oct 30, 2007 Mirror figure error must limit the beam divergence change to < 10% Figure requirements and allocation to contributing factors are expressed in nm, peak/valley < requirement > requirement << requirement 50 mm 30 mm 250 mm 175 x 10 mm 2 50 mm 30 mm 450 mm 430 x 15 mm 2 SOMSHOMS Tangential axis Sagittal axis

Tom McCarville Oct 30, 2007 Figure error budgets were established by finite element analysis of the mirror and mount Conclusions from finite element calculations of assembled mirror & mount: - Coating stress + fabrication errors dominate the figure error - Net curvature is primarily sphere - Spherical errors can be corrected by bending the mirror HOMS Contribution Coating Mounting Thermal Gravity Total (convex) Changes since HOMS PDR: - Mirror holes relocated to better balance gravity load - Refined modeling boundary conditions

Tom McCarville Oct 30, 2007 HOMS tangential figure will be adjusted during operation by bending the mirror An axial force & constraint are applied near the back of the mirror 200 nm concave pre-figure will unbent during assembly on an interferometer - bending will be applied before securing vertical hold down springs - the model shows aspheric curvature near free corners 4.4 lb 3.7 lb Mirror bonded to mounting pads Unbonded (vertical springs loose)

Tom McCarville Oct 30, 2007 Motorized micrometer Shaft & bellows Manual Pre-load Adjustment Anvil Adjustment spring Concave pre-figure removed by applying force to the anvil while observing with an interferometer Mirror assembly is installed into the vacuum chamber & adjustment spring is attached Figure is remotely adjusted by pull/push on the adjustment spring - spring travel range provides high resolution, high thermal stability The HOMS mirror assembly accommodates real-time figure control

Tom McCarville Oct 30, 2007 Measured deflection is in reasonable agreement with the finite-element model Aspheric residual from bending is within our measurement noise floor Bender performance is being validated on the HOM prototype: a silica mirror on Invar mount Vibration scale Calculated: 2.7 lb FOV 5nm 0 15mm 0270mm 450 mm Measured area: 270 x 15 mm 2 Turbulence scale +/- 1.5 nm uncertainty Measured on 12” interferometer

Tom McCarville Oct 30, 2007 HOMS mirror pointing stability requirements are very challenging FEH Z X (hor.) Y (vert.) NEH SM1 HM1 SM2 SM3/4 HM2 Plan view (not to scale) Rotation increments must in step the beam within 10% of its diameter at the experiment stations - long term stability should be even less  30 m  300 m

Tom McCarville Oct 30, 2007 Rotation spindle - flexure type Stepper motor step/rev Pusher - 2 axis flexure The HOMS rotation resolution requirement has been demonstrated Two capacitance sensors with 0.5 nm resolution measure angle change - they are fast enough (5 kHz) to demonstrate natural frequencies are  o >>100 Hz Harmonic drive :1 for HOMS Cam assembly mm offset Data for a 1 mm offset cam, 2500:1 harmonic drive, in 10 nr increments

Tom McCarville Oct 30, st tier: Eliminate thermal jitter with periods < 1 hr - any air tight enclosure will suffice - long period temperature oscillations penetrate easily - rotation jitter closely follows temperature - a long period oscillation remains, but is it rotation or sensor drift? A tiered approach is taken to evaluate pointing stability Outside air Inside air Insulation No Insulation All carbon steel components

Tom McCarville Oct 30, 2007 Sensor drift makes it difficult to trust long term measured trends Sensor calibration block 60 mV drift Sensors are placed in a static gage block to measure temperature correction Uncorrelated drift is also observed, corrupting long term data. Presently investigating how to improve this Zero Drift in nrad

Tom McCarville Oct 30, 2007 Additional measures being investigated to control rotation drift: 2 nd tier: add a thermally compensating material to the rotation linkage - requires accurate long term rotation measurements 3 rd tier: use water tempered to limit excursions inside the enclosure < +/- 0.1 C - compact air cooled chillers are readily available 4 th tier: adjust rotation real time by measuring x-ray beam drift Another alternative: make everything out of Invar instead of stainless steel – not presently being pursued

Tom McCarville Oct 30, 2007 Summary of key opto-mechanical design issues – figure and pointing corrections are both metrology limited The contributing factors to figure error are becoming well understood - mounting, thermal, and gravity induced errors are small: coating & fabrication errors dominate - errors < nm are not easily measured for off-line correction - real time correction during operation is advisable for HOMS Long term pointing stability is under investigation - insulation eliminates rotation fluctuations with < 1 hr period - passive compensation requires nm resolution sensors with long term stability: not yet identified - tempered water will limit enclosure variations < +/- 0.1 C - real time pointing corrections are always an option (last resort)