1NSRRC XBPM and Beam Stability Mimi Workshop

Hideki AOYAGI

SPring-8 / JASRI

Sep11-12,2008

Overview of XBPMs at SPring-8Overview 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

2Requirements 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/mrad2. 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.

3Gap dependence of XBPM

Gap minimum Gap opened

Origin of gap dependence:

- Power of ID changes drastically, but radiations from BMs (backgrounds) do not change.

- Backgrounds are asymmetric and usually offset.

1st harmonic: 6 ~ 18 keV, Background: < several keV near beam axis of ID

Therefore, sensor with high efficiency at higher energy is essential.

4Two 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.

52. Photo-emission type

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

- Structures

- Performances

6Structure 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.

7Fixed-blade style

Fixed-blade style

for SPring-8 in-vacuum undulators,etc. (19 beamlines)

X-ray

8Three structures of photo-emission type

9Performances of photo-emission type

- Gap dependence

- Ring current dependence

- Filling pattern dependence

- Stability

10Gap dependence

Gap dependence: about 100m (Gap = 9.6 ~ 25 mm) about 300m (Gap = 9.6 ~ 50 mm)

Measured at BL47XUwith fixed-blade style

Reference point (Minimum gap )

11Reproducibility 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 BL47XUwith fixed-blade style

Reference point (Minimum gap )

12Ring current dependence

Reference point (Full filling, RC=100mA )

Order of measurements: 10mA 30mA 50mA 60mA 70mA 80mA 90mA 100mA (total 60min)

13Filling pattern dependence

A: Full filling like B: 203 bunchesC: 1/12-filling + 10 bunches D: 11 bunch train x 29E: 4 bunch train x 84 F: 10/84 + 73 bunches

* Reference point (Full filling, RC=100mA )

Order of measurements: A B C D E F (total 130min)

*

14Ring current / Filling pattern dependence

Beamline Hor. Ver. Hor. Ver.

BL10XU 0.8 0.5 2.1 0.9

BL11XU 2.1 1.5 9.7 2.9

BL13XU 0.5 0.8 5.3 2.5

BL20XU 0.8 2.2 2.7 1.4

BL24XU 0.6 0.8 2.4 2.5

BL29XU 2.3 0.5 6.1 0.5

BL35XU 0.6 1.2 1.6 0.4

BL37XU 0.9 0.9 0.8 3.4

BL39XU 0.7 1.2 5.7 0.4

BL40XU 0.6 0.8 0.4 0.8

BL41XU 1.5 0.5 1.2 2.8

BL46XU 1.4 0.2 1.0 1.3

BL47XU 1.2 0.3 8.1 2.3

Average 1.1 0.9 4.6 1.1

measured at Ring Currentsof 50, 60, 70, 80, 90, 100 mA

measured at 6 differentFilling Patterns

Standard deviation [m] of readouts

Real beam drifts are included in these values.Performances of XBPMs are better than these.

15Change in three hours

Reference: 2003/06/26 05:17Object 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.

16Change in a day

Reference: 2002/02/01Object 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).

17Change in long term during operation

RMS

H: 108 m V: 69 m

Reference: 2008/05/20Object day: 2008/08/01

(73 days later)

Real beam drifts are included in these number.

All Gaps are set at reference points (Minimum gaps).

18Trend at BL47XU

Gaps is set at reference points (Minimum gaps).

19Orbit correction by machine group

20Summary of performance (photo-emission type)

1. Gap dependencea few 100 m

2.* Ring current a few m

3.* Filling pattern dependencea 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.

21Stripline 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.

22Introduction

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 50The 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.

23Design

Key points for thermal properties

　　 - AlN for dielectric plateHigh therm. conductivity 150 W/m ・

KLow 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 structureImpedance matching

　　 - SMA feed through connectorCut-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 resolutionDimensions W = 1.5 mm t = 0.2 mm h = 1.65 mm

r = 8.6

SMA connector

SMA connector

Kobar (for

welding)

Cooling base (CuW)

Dielectric plate (AlN)

Metal line (OFHC copper)

photocathode

SR pulse

24Picture of detector head

Metal line (OFHC copper)

Dielectric plate (AlN)

Cooling base (CuW)

Kobar (for welding)

SMA feedthrough connector

60 mm

Vacuum side

Atmosphere

25Monitor chamber

For beam position monitor,

a pair of detector head is necessary.

But, only one of them was installed for

the beam test.

26Performance

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!

27Linearity

Good linearity supports the feasibility as pulse intensity monitor.

The intensity resolution : < １ % （ @ bunch current = 1 mA ）

( V

/ 50

)

28Timing 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.

29New 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 m

m

30Improvement in pulse shape

Ringing parts has been removed successfully.

31Summary

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: < 10m- 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.