Developments of Photon Beam Monitors in NSRRC (TLS) J.R. Chen, C.K. Kuan, T.C. Tseng, and G.Y. Hsiung National Synchrotron Radiation Research Center XBPM Workshop, NSRRC, Hsinchu, September 11-12, 2008

Outline I. Introduction II. Photon Beam Position Monitor (PBPM) III. Beam Size Monitor (BSM) IV. Photon Beam Intensity (Io) Monitor V. Conclusion

I. Introduction 1. To operate a stable synchrotron light source, precise photon beam monitors are highly demanding. 2. Photon beam position monitors (PBPM), beam size monitors (BSM) and photon beam intensity monitors have been developed for the 1.5 GeV Taiwan Light Source (TLS) at NSRRC. Most of the technologies developed at TLS are to be used to the 3GeV Taiwan Photon Source (TPS). 3. Challenges are foreseen to meet the requirements from the TPS, which has an emittance of 1.6 nm-rad.

Main Parameters Stored beam energy: 1.5 GeV Current: 300 mA (top-up) Beam lifetime: hr Radiofrequency: 500 MHz Emittance: ~ 25 nm-rad Beam size:~150 μm (H) (dipole)~ 38 μm (V) Reliability Machine up time: > 97% Trip rate: < 1 / week Orbit stability: < 1μm (rms) Orbit drift: < 5μm / 10hr Photon beam stability (ΔI/I): < 0.1% Taiwan Light Source (TLS)

Main Features of the TPS Low emittance and high brightness -- Brightness >10 21 p/s/0.1%bw/mm 2 /mrad 2 10 keV) -- Emittance ε< 2 nm-rad High stability -- Photon intensity fluctuation <0.1%  Beam orbit fluctuation <~0.2 µm (dσ/σ ≈ 5%)  Beam size fluctuation <~0.1 µm High reliability -- High injection efficiency (>90%) -- Machine Up-time >98% -- Trip rate < 1/week Superconducting Technologies Top-up injection/ Same-tunnel Booster

II. Photon Beam Position Monitor 1. PBPM for TLS ID fronts 2. PBPM Structure 3. Test Data blade PBPM for EPU

PBPM-1 PBPM-2 Two PBPM’s, with distance ~ 1.5 m in between, for the ID front ends of TLS. ID Front End (ID PBPM, TLS)

PBPM for ID front ends 2-blade PBPM  Vertical position 4-blade PBPM  Hor. and ver. positions 12-blade PBPM  blades uniformly distributed in radial directions  separately (longitudinal) mounted to diminish the cross-talk

PBPM Structure BEAM UP-BLADE DOWN-BLADE COOLING HOLDER BIAS non-destructive photoemission material: 1050 aluminum alloys (low atomic number  low absorption), high thermal conductivity and high photoelectric yield in VUV Bias: +130 V applied to the bias-plate(s) surrounded the blades to attract the scattered photoelectrons.

Compact PBPM-B (BM) BEAM BIAS PLATE UP BLADE DOWN BLADE COOLING HOLDER Linear Motion Feedthrough 35CF Flange

Test data of TLS BM PBPM (18Y) 0.5 µm Resolution: < ±0.5 µm (rms)

Test data of TLS ID PBPM (FE05) E-beam ID PBPM (FE05) Resolution: < ±0.5 µm (rms)

Gap-change of EPU5.6 Changes of the photon beam positions monitored by the PBPMs at different sections during the gap-change of the EPU5.6 EPU5.6: λ u = 56 mm; N = 66; L = 3.9 m; G min = 18 mm Max. Field: B x = 0.444T; B y = 0.696T

Test data of PBPM (12 blades) (EPU phase changed) -- The feature of the 12-blade PBPM is to measure the intensity profile of the undulator light in non-destructive way. -- The center of the beam axis can be identified by carefully analyzing the distribution pattern on the blades. -- The deviation in intensity distribution is helpful to resolve the EPU problem. I-10, I-11: different trend? I-2, I-3: same trend.

III. Beam Size Monitor (BSM) 1. Pinhole type 2. Interferometer type

Beam Size Monitor ( pinhole type) (R4BM1, old) Cu mirror Water cooled windows Reflect mirror Lens CCD (Deformed by heat) Reflect mirror

Beam Size Monitor (Interferometer type, BL10B) Beam Be Mirror Quartz window Flat mirror BSM-Y Focus lens Polarizer Band pass filter Magnifying glass Double slit CCD BSM-X -- Due to the diffraction limitation and the optical aberrations, the resolution of the (visible) SR image beam size monitor is far beyond micron and sometimes is not sensitive to the variation of the electron beam in the study of the storage ring instability. -- A more precise monitor system was thus necessary for the TLS. Water cooled

Beam Size Monitor Beamline (BL10B) (Interferometer type) The Be mirror is a mirror with high reflectivity to the visible light and deep radiation penetration to minimize the surface thermal distortion. The optical components should be of high quality to minimize the distortion effect. In order to minimize the thermal effect, the Be mirror is located far away from the source point and closed to the detecting optical system. The system is a non contact method and easier to construct.

Measurement of BSM

(1) If I 1 = I 2 |  = V (2) Beam Size Monitor (Interferometer type, BL10B)

Table: Photon beam size comparison of theoretical, SRI monitor and pinhole Image monitor Beam SizeTheoreticalSRIPinhole (before improvement) yy 48  m47  m120  m xx 135  m162  m260  m

Diagnostics BL (BL10, TLS ) IV. Photon Beam Intensity (Io) Monitor

Io Monitor (BL10A) BM Source: Gaussian Distribution (1 σ v ≈39 μm) Beam profile by pinhole scan Pinhole (d= 50 μm) Scanning stage resolution = 0.1 μm Spherical Mirror, ρ≈70m coated material: Au, incidence angle 87.5 Detector

Io monitor (Design Considerations) Mechanical stability  Vibration isolation  Rigid support  Temperature stability Pinhole size Resolution of scanning stage Material of detector

Material Reflectivity and photoelectric cross-section –Mirror: coating material  Au –Detector : coating material  Au

Io Monitoring System Improvement PZT Source After improvement Temperature fluctuation : Air ≈ < ± 0.1 ℃ Cooling water ≈ ± 0.01 ℃ Mirror support : Mechanical stability Thermal stability Scanning stage: Piezo-stage Resolution ≈ 0.1μm After improvement

Thermo-mechanical Effects on Photon Intensity (pin hole) Monitor (TLS) △ T ≈ 0.1˚C △ I/I ≈ 0.4% For photon beam monitors, △ I/I < 0.1% :  △ T ~ 0.01˚C ( Water temperature fluctuation)( Air temperature fluctuation) △ T ≈ 0.5˚C △ y ≈ 5 μm

TLS Improvement ( ) (d/2 ~ 2σ) (1μm rms) 0.05% 0.06% 0.08% 0.12% (3%  0.1%)

Conclusion 1. The data from TLS photon beam monitors showed the good performance of TLS after improvements. 2. (PBPM, BSM and Io monitors) Temperature and vibration stabilities are crucial to the performance of photon beam monitors. A temperature stability of < ± 0.1 ℃ is generally required, and < ± 0.01 ℃ for sensitive devices. 3. (PBPM) 12-blade PBPM seemed promising to resolve the performance of EPU. 4. (BSM) The results of the interferometer BSM at TLS shows good sensitivity to the photon beam size variation; and < ~1  m variation is detectable. A better approach should be developed for the TPS to get a better resolution.