Diagnostics and Optimization Procedures for Beamline Control at BESSY

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

2. PC EPICS-IOC PLC EPICS-IOC PC EPICS-IOC PLC PC BESSYBeamlines BESSY Beamline UE112 Insertion Device (ID) Switching Mirror Unit (SMU) 1 Plane Grating Monochromator (PGM) 1 Experimental Chamber PGM 1 Plane Grating Monochromator (PGM) 2 Switching Mirror Unit (SMU) 2 Experimental Chamber PGM 2a Experimental Chamber PGM 2b • 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 Result in demanding quality requirements for: • 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. • Beam Position: • Correction of drift caused by thermal changes using SMU. • Storage ring stability. • Examples of experimental requirements: • Focus size down to 20 mm2 to achieve PEEM resolution of 1 nm. • High energy resolution of E/DE > 100000. • Fast energy scan with combined movement of insertion device and monochromator. • High degree of polarization.

4. To IDCP-IOC CAN2 (CALMVP) EPICS IOC Monochromator To SMU Renishaw Length Encoder CAN (ESD) Plane Gratings M3 RON 905 Grating Rotation E2 E1 4 × IK320 (Heidenain) M1 E2 E1 Grating Translation To IK320 PMAC2-VME (Delta Tau) Renishaw Length Encoder M4 IOC(VxWorks) Mirrors RON 905 E2 E1 Mirror Rotation M2 Mirror Translation E2 E1 To IK320 To MCCP-IOC Terminal Server Measuring- PC (OS/2) CA-Gateway IDCP-IOC IP (LAN) Channel Access (EPICS) User PC X-Terminal Monochromator Hardware Details

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

7. 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). Feedback System • Heidenhain System • 4 Channel RON905-UHV Angular Encoder. • IK320 Counter Cards. • 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.

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

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

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

11. Compensation of Non-Linearities of Nanomotion Piezo Motors Velocity vs. Controller Output • Model with Non-linearities • Static non-linear at the input of the system. • System dynamics approximately linear. Lookup-Table for Linearization • 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.

12. A Non-Linear Filter for PMAC2-VME • Monochromator Characteristics • Static Non-Linear • Dynamic Non-Linear • Time Variant • Disturbances • 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. 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.