New DCM for spectroscopy an engineering challenge review

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2 New DCM for spectroscopy an engineering challenge review Y. Dabin, R. Baker, L. Zhang, H. Gonzalez, R. Barrett, Ph. Marion, O. Mathon, R. Tucoulou Page 2

3 DRIVERS FOR A NEW DCM: GENERAL OUTLINES Page 3

4 THE CRYSTALS CONFIGURATIONS 1 st /2 nd Xtal On axis Crystals stroke Axis offset Page 4

5 CRYSTAL POSITIONING: PLACING THE CENTRE OF ROTATION 1 st Xtal fixed white T CoR d White beam spot, moving or fixed on the First crystal: Fixed: thermal time constant better averaged BUT: L Bragg radial stroke T = d 2 cosθ B 1 st Xtal moving L Bragg longitudinal stroke L = d 2 sinθ B T Independent of configuration white d Monochromatic beam fixed on 2 nd Xtal: 2 nd Xtal Bragg angle better defined CoR 1 st crystal moving: High flow LN2 set Page 5

6 CRYSTAL POSITIONING CENTRE OF ROTATION LOCATION Centre of rotation θ B min b + h = a tan( ) L x1 white Tricky thermal Conditions At max Bragg Placing the white beam out of the axis white h b a Page 6

7 A LOT OF CRYSTALS COMBINATIONS POSSIBLE White beam at CoR CoR on the crystal surface Hot spot constant location Better thermal conditions P area =maximum See L. Zhang s talk Possibility of making hot spot moving Reducing the minimum Bragg T = L = d 2 cosθ d 2 sinθ B B ~ Xtal length unchanged Page 7

8 THE CRYSTAL PARALLELISM : THE FUNDAMENTAL ISSUE Cryo mount Angular Correction control Gonios & tables Crystal parallelism is the fundamental performance of any DCM Page 8

9 CRYSTALS PARALLELISM DRIVERS Drivers items characteristic cure Studies drivers Geometric Cryo-field from crystal set Thermal field from scattering Crystals at different temp. Dynamics Moving stages ~ repeat Metrologylookup table Plate ~ repeat Piezos deformation Stage shrinkage instability Stages and holders Crystal Cryobox Moving stages Flexures instability Lack of cooling power rate. Response time Fast events Thermal break heater (TTF) Radiation shield Heater (TTF) LN2 on 2 nd crystal Push dynamic studies-high frequency track Static studies Thermal studies & Simulating Thermal transfer Function Vibration analysis Page 9

10 CRYSTAL CAGE PARALLELISM : THE ROTATING PLATE AND TRAVEL CASES Rotating plate Drives angular errors Angular deviation From a lack of Stiffness (Bragg dependent) 20 Kg Depends on Ball track straightness Best figures are: 25 µrd/200mm Probably then : 0.1 µrd/mm (locally?) kohzu situation: Lower cam removes the weight (not the angular deviation) Two parallelisms: Bragg plane Cross plane Page 10

11 BM23 PARALLELISM ERROR INVESTIGATIONS Courtesy J. Borrel, O. Mathon Parallelism error (arcsec.) initial setup with setup of the translation with setup of the translation and pre loading (without load) with setup of the translation and pre loading (with load) 27/09/2010 Kohzu reference Before upgrade Final performance Autocollimator Measurements Room temp. As delivered several year before tetab (deg) data 2011 data 2003 before Kohzu intervention data 2007 after Kohzu intervention In situ Piezo correction Seems to be a consequence of the weight added on the Kohzu mechanism 3 crystals set instead of 2 Piezo Controller values piezo PI controler value (A.U.) At present KoHzu tuning angle (deg.) Page 11

12 REMARK: RADIAL MOVE MAY BE OF LESS IMPORTANCE Beam moves Remark: Radial stroke ensure fixed exit But Fixed exit is not mandatory for energy scanning E ~1000 ev 2 nd Radial stroke θ Β Pseudo-Fixed exit operation Sample slit Or seg. slit Used when experiment Requires large size beam (rather seldom) Slit distance should remain small Angular aperture Should 100 µrd Page 12

13 CRYSTAL PARALLELISM DURING ENERGY SCANS Parallelism error 100 nrd during scans The error is lower than the limit Strategy when the error is above the limit ( 100 nrd) Metrology in situ possible. watch Probably Probe system No correction (ideal case!) Recent mono May be there Error is repeatable (RT + cryo) Corrected within Mono Fine stages Probes (Look-up table+ Piezo strain gauges) Corrected externally probes but no feedback at the sample (vert. + Horz. Positioning) Minimum requirements With still a simple system Error is not repeatable Corrected in real time Probe system (straight edge+ capacitor) Dynamic TF with piezos Complex system Would require developments Page 13

14 CRYSTAL PARALLELISM : AVOID MECHANISM THERMAL SHRINKAGE Exp: A. Chumakov, K. Martel (ESRF ID18 ID20) Solid ceramic isolator (very low conductivity) High stiffness modulus (no vibrations) Limited conductive contact areas (no thermal leaks) Then crystal travel stages Exp at ESRF with EUROTHERM temperature PID controller At ID20 ± 1 m K for post mono Courtesy C. Henriquet Passive support structure ESRF wish Corrective stages Page 14

15 THE BRAGG AXIS MOTOR CASE Motor operation Motor scans Page 15

16 LN2 FEEDER BOX: A HEAVY INFLUENCE, MAY BE AWAY FROM SUPPLIER S External flexible line Moving LN2 feeder box Seems quite strongly Influencing the Mass inertia Page 16

17 BRAGG AXIS DYNAMICS Bragg axis motor should move an optimized set More Tricky winding LN2 feeders Fixed box Moving box Here: 40 I kg.m2 90 LN2 feed box With flexible windings 85% 8% 5% Fraction of mass inertia sharing Page 17

18 BRAGG AXIS DYNAMICS Mass centroid Far from axis Adding a counterweight improves Unpowered reaction but magnifies The dynamic considerations Typically from 40 to 60 Kg.m 2 Added external Counterweight: mm Page 18

19 MOTOR DYNAMIC OPERATION Motor torque = Dynamic load + Permanent load Everything Connected with acceleration Friction Off axis masses Hand out forces Everything at constant velocity C + 2 d θ ( t) = J 2 dt C i J is the total mass inertia of the Bragg axis C i is anything constant ( ) := J m i C a t, β, i, I dθ2( t, β) Everything dynamic + 1 i η ( I dθ2( t, β) + C o + C f ) Everything permanent C o : off axis masses torque C f : Friction torque (Ferrofluidic + bearings) fast mvt Motor acceleration is magnified By the gearbox slow mvt Everything is divided by the gearbox (with efficiency losses η) Friction & Permanent resistance Page 19

20 BRAGG AXIS : REQUIRED TORQUE FOR ENERGY SCANNING High motor power dissipation Torque In Nm Required torque for scanning [Nm] Direct drive technology High gearbox cascade r1 r2 run by steppers or brushless Shifts that way are due to acceleration change Few cases there! i=1 means direct drive operation attractive idea: Mechanically more simple Gearbox reduction ratio: i (no unit) Solving resolution with Fine motor steps Encoder overcomes motor Solving resolution with high Density motor steps Motor overcomes encoder A typical gear box Page 20

21 SPACE VELOCITY ACCELERATION AND TORQUE Angular triangular scans In degrees 10% 5% Space plot The acceleration of the scan is a fraction in % of the scan angle here 1 Acceleration of a full cycle at 5% ramping 2% Time in s Time in s Corresponding dynamic torque of this 5% ramping Angular Velocity in /s Nm Direct drive motor torque Motor 2 Motor torque with gearbox Motor 1 Time in s Time in s 2 Where the basic relation d θ ( t) = J 2 dt J is the total mass inertia of the Bragg axis C + C i Page 21

22 STABILITY ISSUES: OUTLINES Compton Scattering Isolated mechanisms Crystals Time constant Architectural analysis Mono deforms Crystal Cage design Flow Induced Vib. Page 22

23 GLOBAL VIBRATION CURING Crystal mount pbs Vibration cure: Typical stand weaknesses Pillar like jacks removed everywhere Base block bonded to floor Older BM29 mono 2008 Courtesy M. lesourd Page 23

24 LATERAL MOVE TRANSFER FUNCTION: UPGRADING A KOHZU STAND AT ID14 Lateral move transfer function High Values! DSP response Low Values! Lateral displacement transfer function TF With respect to floor y2 DSP response 2 = TF DSP DSP source source TF= y2 y1 Travels as high as possible Adjusting at higher level Bonding to floor y1 Page 24

25 TWO MONOS IN TEST AT THE ESRF ID6- (IN 2008) Elec noise Transfer Function records Wedge Jacks here Pillars here wedge Page 25 l Title New of DCM Presentation for spectroscopy l Date of an Presentation engineering l challenge Author - 13 May Y. Dabin

26 FLEXURE DESIGN: VERY HARD TO BE PERFECT MODAL ANALYSIS 8 Kg Virtual mass Mode at 21 Hz Mode at 31 Hz Mode at 36 Hz Simulation of a 2 nd crystal positioning Flexures: Difficult to make non-coupled movements Ideally: design single degree of freedom with piezo. Done for white beam optics (ESRF upgrade) Vibration wise: design target should be at 130 Hz Beamlines: Not enthusiastic to flexures Necking is deforming Page 26

27 SINGLE DOF FLEXURE BASED GONIOMETER 30 Kg rocking mass The problem to address is the availability of single DoF high resolution goniometer (low parasitic motion) 130Hz loaded at 30 Kg White beam mirror ESRF upgrade Not easy to implement for A crystal set Fine rocking : Rx:0 Ry:0 Rz: 15 nrd low parasitic motions Page 27

28 SCATTERED POWER FROM BM5 CRYSTAL BM Spectrum 150 W (per 1mrad horizontal divergence) Spatial distribution over the scoring plane Scoring plane 5 mm 50 mm 10 cm thick

29 RESULTS: SCATTERED POWER ON FIRST CRYSTAL Bragg angle [deg] scattering [%] r [%] Scattered power High energy position Bragg angle [deg] The scattered power has been calculated using Penelope code Here input power is 150 W The scattered power (fraction of energy irradiated) has been calculated using the incident white bending magnet spectrum shown. It is always less than 25% and less than 5-8% for usual Bragg angles (> 3 deg)

30 About 130mm 50 mm projection 45 about 45 about 150 W input beam Example of a 30 Bragg incidence On a 1 mrd beam width at 30m

31 TYPICAL SCATTERING SHIELDING Ceramic thermal break Global side Screen Shielding the Positioning Mechanisms 5 mm copper Local tungsten screens are 1 mm Page 31

32 Local screen For Xtals Global side Screen Shielding the Positioning mechanisms Global screen is 5mm Local screens are 1 mm tungsten

33 NEW DCM FOR SPECTROSCOPY AN ENGINEERING CHALLENGE REVIEW We a far from being blocked Still many issues Good dynamics analysis Heater Always a good Config. Labs have best operation analysis We are the users Shielding Labs have best experience for Stability issue Direct drive Good stage All fixed Gearbox motor Good plate Thank you for your attention High design validation Page 33