1. Diagnostics and Optimization Procedures for Beamline Control at BESSY A. Balzer, P. Bischoff, R. Follath, D. Herrendörfer, G. Reichardt, P. Stange

2. Insertion Device (ID) Switching Mirror Unit (SMU) 1 BESSY Beamline UE112 Plane Grating Monochromator (PGM) 1 Plane Grating Monochromator (PGM) 2 Switching Mirror Unit (SMU) 2 Experimental Chamber PGM 2a Experimental Chamber PGM 2b Experimental Chamber PGM 1 PLCEPICS-IOC PLC PC BESSY Beamlines Two Beamlines at UE112 ●PGM 1: Photon energy range from 15..600 eV. ●PGM 2: Optimized flux and resolution at a photon energy range 5..250 eV. ●The Beamline at UE112-PGM 2 splits into branches for temporary and permanent experimental setups.

3. Requirements on Beamline Control Examples of experimental requirements: ●Focus size down to 20  m 2 to achieve PEEM resolution of 1 nm. ●High energy resolution of E/  E > 100000. ●Fast energy scan with combined movement of insertion device and monochromator. ●High degree of polarization. Beam Position: ●Correction of drift caused by thermal changes using SMU. ●Storage ring stability. Beamline mechanics and beamline control: ●Fast and accurate positioning of the monochromator drive at nm scale. ●Large rotation angles of monochromator mirror (30°) and grating (50°) with an angular resolution of marcsec. Result in demanding quality requirements for:

4. Monochromator Hardware Details 4 × IK320 (Heidenain) PMAC2-VME (Delta Tau) IOC (VxWorks) CAN (ESD) CAN2 (CALMVP) To IDCP-IOC To SMU EPICS IOC Grating Rotation Mirror Translation RON 905 M3M3 Plane Gratings M1M1 E1E1 E2E2 E1E1 E2E2 Grating Translation To IK320 Renishaw Length Encoder RON 905 E1E1 E2E2 M4M4 M2M2 Mirror Rotation E1E1 E2E2 To IK320 Renishaw Length Encoder Mirrors Monochromator IP (LAN) CA-Gateway Measuring- PC (OS/2) X-Terminal Terminal Server User PC IDCP-IOC To MCCP-IOC Channel Access (EPICS)

5. Monochromator Control Program (MCCP) EPICS IOC (MVME162 running VxWorks) ●Operator Interface (EPICS PVs). ●Communication with Insertion Device IOC and SMU-PLC via CAN bus. ●Communication with motor controller. ●A set of EPICS variables that describe the current state of the beamline. ●Waveforms of feedback and servo data. ●Histograms of position data. ●Calculation of error propagation.

6. Control Problems – Hammerstein and Wiener Model Profile Generator ●Realtime Monochromator Drive ●Static non-linear input. ●Linear part. ●Dynamic non-linear and time variant (at nm scale). Disturbances ●Vibrations ●Others Feedback ●Non-linearities (quadrature error) ●Noise Linear Dynamic Non-linear Time Variant Static Non-linear

7. Feedback System Problems ●Quadrature errors have to be corrected since accuracy at marcsec scale is desired. ●Compensation run of IK320 counter cards fails due to vibrations. ●Accuracy of the encoder restricted by the generated sinusoidal signals. Data Acquisition (DAQ) for Determination of Quadrature Error ●Data rates up to 4kHz from IK320 counter card. ●Calibration run as fast as 2 seconds. ●On the fly. ●Phase shift, unequal gain and zero offsets are corrected. (Heydemann, 1984). Heidenhain System ●4 Channel RON905-UHV Angular Encoder. ●IK320 Counter Cards.

8. EPICS Soft-IOC for Determination and Correction of Quadrature Errors Linux (VMware) ●Simple interface to EPICS records. ●Open source library for numerical algorithms. ●Cost effective. ●High computation power compared to hardware IOCs (MVME162). Beamline

9. Experimental Verification Data Acquisition at Beamline EPICS ●Slow Control ●CA Client for Computation Correction of Encoder Signals at Beamline Verification: Literature values of absorption spectra.

10. Control Problems – Nanomotion Drive Linear Dynamic Non-linear Time Variant Static Non-linear

11. Compensation of Non-Linearities of Nanomotion Piezo Motors Model with Non-linearities ●Static non-linear at the input of the system. ●System dynamics approximately linear. System Identification Experiment ●Specifically designed identification experiment. ●Fast realtime capturing of control output and position. ●Least squares estimation to fit and validate a parameterized model. Velocity vs. Controller Output Lookup-Table for Linearization

12. A Non-Linear Filter for PMAC2-VME User Written Servo Filter for PMAC2-VME ●DSP code written in assembly language. ●Compensation of static non-linearities. ●Non-linear integral gain to overcome time variant and dynamic non-linearities. ●Disturbance rejection. ●Performance of Nanomotion drive improved by a factor of 4. Monochromator Characteristics ●Static Non-Linear ●Dynamic Non-Linear ●Time Variant ●Disturbances Following error in nm and servo output.

13. Conclusions ●EPICS records and Linux based software are used for computation of the Heydemann algorithm using open source libraries. This computation has been experimentally verified. ●System identification experiments and a non-linear servo filter have been used to improve monochromator performance and accuracy. ●Simple and straightforward tuning process of the control loop. ●Disturbance rejection and smooth positioning minimizes vibrations and positioning errors.