1 NSRRC XBPM and Beam Stability Mimi Workshop Hideki AOYAGI SPring-8 / JASRI Sep11-12,2008 Overview of XBPMs at SPring-8 1. Introduction - Requirements for XBPMs - Gap dependence for ID beamlines 2. Photo-emission type (in use) - Structures - Performances 3. Stripline XBPM (under developing) - Structures - Performances 4. Summary

2 Requirements on XBPMs for high power undulator radiation High Resolution and good stability - Resolution of micron order should be achieved. Beam divergences are ~ 20 / 5 μrad ( hor. / ver. ), which correspond to beam sizes of ~ 400 / 100 μm ( hor. / ver. ) at XBPM position (20 m from ID). - Long term stability is also important. Durability against Severe Heat Load - Diamond is best material. Blade type is working well. Max. power density is ~ 500 kW/mrad 2. Metal will melt immediately. Fast Response - Response time of < 1 msec needs for high frequency diagnostic. - Simultaneous diagnostic over beamlines is also important. No dependence of ID gap, ring current, filling pattern and so on - As for ID gap dependence, Photo-conduction type is recommendable. Contamination of background radiation from the fringing field of BMs causes intrinsic problem on ID gap dependence.

3 Gap dependence of XBPM Gap minimumGap opened Origin of gap dependence: - Power of ID changes drastically, but radiations from BMs (backgrounds) do not change. - Backgrounds are asymmetric and usually offset. 1 st harmonic: 6 ~ 18 keV, Background: < several keV near beam axis of ID Therefore, sensor with high efficiency at higher energy is essential.

4 Two types of XBPM Photo-emission type : (in use) -Simple structure, high resolution, good stability. - Working well especially for BM beamline. -But the problem of gap dependence for undulator beamlines can not be solved. Because detective efficiency is high in the soft X-ray region, and low in the hard X-ray region. Photo-conduction type : -Diamond can be used for detector head. Superior thermal property, and electric property, semi-transparent against hard X-ray -Detective efficiency can be suppressed in soft X-ray region, and enhanced in hard X-ray region.  Suitable for undulator radiation - However, quality of diamond is still the most serious problem.

5 2. Photo-emission type Photo-emission type XBPMs are used for all insertion device beamlines at SPring-8. - Structures - Performances

6 Structure of detector head - Four blades are placed in parallel to the beam axis in order to reduce heat load. - CVD diamond is used because of excellent heat property Collector Surface of diamond is metallized.

7 Fixed-blade style for SPring-8 in-vacuum undulators, etc. (19 beamlines) X-ray

8 Three structures of photo-emission type

9 Performances of photo-emission type - Gap dependence - Ring current dependence - Filling pattern dependence - Stability

10 Gap dependence Gap dependence: about 100  m (Gap = 9.6 ~ 25 mm) about 300  m (Gap = 9.6 ~ 50 mm) Measured at BL47XU with fixed-blade style Reference point (Minimum gap )

11 Reproducibility of gap dependence After weeks, behaviors of gap dependence are changed, especially in vertical. Because the correlation of ID and background radiation may be changed by slow F.B. in long term. Measured at BL47XU with fixed-blade style Reference point (Minimum gap )

12 Ring current dependence Reference point (Full filling, RC=100mA ) Order of measurements: 10mA  30mA  50mA  60mA  70mA  80mA  90mA  100mA (total 60min)

13 Filling pattern dependence A: Full filling like B: 203 bunches C: 1/12-filling + 10 bunchesD: 11 bunch train x 29 E: 4 bunch train x 84F: 10/ bunches * Reference point (Full filling, RC=100mA ) Order of measurements: A  B  C  D  E  F (total 130min) *

14 Ring current / Filling pattern dependence Real beam drifts are included in these values. Performances of XBPMs are better than these.

15 Change in three hours Reference: 2003/06/26 05:17 Object day: 2003/06/26 08:30 (3 hours later) RMS H: 3.5  m V: 1.7  m Real beam drifts are included in these number. All Gaps are set at reference points (Minimum gaps). Filling pattern dependence was measured during this period.

16 Change in a day Reference: 2002/02/01 Object day: 2002/02/02 (23hours later) RMS H: 3.2  m V: 4.7  m Real beam drifts are included in these number. All Gaps are set at reference points (Minimum gaps).

17 Change in long term during operation RMS H: 108  m V: 69  m Reference: 2008/05/20 Object day: 2008/08/01 (73 days later) Real beam drifts are included in these number. All Gaps are set at reference points (Minimum gaps).

18 Trend at BL47XU Gaps is set at reference points (Minimum gaps).

19 Orbit correction by machine group

20 Summary of performance (photo-emission type) 1. Gap dependence a few 100  m 2.* Ring current a few  m 3.* Filling pattern dependence a few  m 4.* Change in a day 3~5  m during operation 5.* Change in long term (10 weeks) nearly 100  m 6. Resolution < 1  m in horizontal,< 0.5  m in vertical * The re-producibility of the closed orbit may affect these performances.

21 Stripline XBPM Pulse-by-pulse SR beam monitor with microstripline structure is under developing in order to diagnose pulse-by-pulse beam intensity, beam position, and timing.

22 Introduction The present XBPMs at the SPring-8 front ends have slow response time, which is about 100 nsec. So, time constant (  =RC) must be shortened. (The R is 50  The C must be small.) In generally, a high heat proof detector head having small C is very difficult to design, because an area that contacts to a cooling base must be large for good heat contact. (The diamond blade has a clamping area of 60mm x 10mm.) To improve radio frequency (RF) property, we have applied the microstripline structure to the detector head that is operated in photoemission mode.

23 Design Key points for thermal properties - AlN for dielectric plate High therm. conductivity 150 W/m ・ K Low therm.expansion coef. 4.6×10 -6 / ℃ - CuW for cooling base High therm. conductivity 180 W/m ・ K Low therm.expansion coef. 6.5×10 -6 / ℃ ( cf : OFHC copper 17 ×10 -6 / ℃ ) - Tapered photocathode Reduction of heat density Key points for RF properties - Microstripline structure Impedance matching - SMA feed through connector Cut-off frequency: 9 GHz  18GHz - 50  termination of one side of strip- lines Elimination of reflection - design flexibility of line width and length Sufficient signal for high resolution Dimensions W = 1.5 mm t = 0.2 mm h = 1.65 mm  r = 8.6 SMA connector Kobar (for welding) Cooling base (CuW) Dielectric plate (AlN) Metal line (OFHC copper) photocathode SR pulse

24 Picture of detector head Metal line (OFHC copper) Dielectric plate (AlN) Cooling base (CuW) Kobar (for welding) SMA feedthrough connector 60 mm Vacuum side Atmosphere

25 Monitor chamber For beam position monitor, a pair of detector head is necessary. But, only one of them was installed for the beam test.

26 Performance 2 nsec Each pulse (2 nsec separation) can be observed independently. FWHM is 0.2 nsec. FWHM 0.2 nsec Observation of pulse train Real time oscilloscope (4 GHz B.W.) Sampling oscilloscope (50GHz B.W.) 4.8  sec 2/21 filling + 18 bunches (step) mode Observation of all pulses Unipolar signal!

27 Linearity Good linearity supports the feasibility as pulse intensity monitor. The intensity resolution : < １ % bunch current = 1 mA ） ( V / 50  )

28 Timing resolution Observation of the isolated pulse with various Gap positions of IDs The shifts of the synchronous phase can be observed. Timing jitter: < 10 psec （ nearly equal to the effect of synchrotron oscillation) (averaged by 11 times) Min.gap of the standard ID corresponds to the power of about 10kW.

29 New type of stripline XBPM １ ２ Radiation from BM ３ - RF property has been improved. 1. Cutoff frequency was improved. 9GHz  18GHz 2. Connection was modified for impedance matching. 3. Stripline is perpendicular to the beam.  Only for a timing monitor or an intensity monitor (less sensitivity against beam position) ２ 32 mm

30 Improvement in pulse shape Ringing parts has been removed successfully.

31 Summary 1. Photo-emission type (in use) - Three structures to match various ID beamlines - Fixed-blade style, horizontal-blade-drive style, and four-blade-drive style - Performances - Gap dependence:a few 100  m - Ring current / Filling pattern dependence: a few  m - Stability: 3 ~ 5  m in a day, ~100  m in long term 2. Stripline XBPM (under developing) - Structures - Microstripline structure for RF property - AlN and CuW for thermal property - Performances - pulse-by-pulse position monitor: < 10  m - pulse intensity monitor: < 1 % - pulse-timing monitor: <10psec - Timing monitor (new type) - RF property has been improved. - Beam test is going on here at NSRRC.