1. BEPCII Background Issues: Collimators and Masks
Jun Xing (IHEP)
Mini-workshop on BEPCII Background Study
Mar , 2008, Beijing
Experimental Study of Decrease the dose in IR
Collimators and masks plan

2. Experimental Study of Decrease the dose in IR
BEPCII OVERVIEW
The colliding mode
The SR mode

3. BEPCII OVERVIEW Layout Interaction region Commissioning
BEPCII is an upgrade project of the Beijing Electron-Positron Collider (BEPC). It will provide the colliding beams with the center-of-mass from 1.0 GeV2 to 2.1 GeV2 and also the dedicated synchrotron radiation beam with 2.5 GeV. For the colliding beams the luminosity is optimized at 1.89 GeV with 11033 cm-2s-1, which is two orders larger than the luminosity of the BEPC.
Layout
Interaction region
Commissioning

4. The Layout of BEPCII storage ring
RF region
Straight Section for SR wiggler
Straight Section in R2 out arc
Straight Section for e- injection kicker
Straight Section for e+ injection kicker
Straight Section for e+ injection
Straight Section for e- injection
Straight Section for e+ injection kicker
Straight Section for e- injection kicker
Straight Section for SR wiggler
Straight Section for SR wiggler
Interaction Region (IR)

5. Crotch pipe is the aperture bottleneck of the colliding mode
The Layout of the IR

6. 2007 Oct.24,
commissioning start
2007 Oct.25,23:09
electron beam stored
2007 Oct.31,20:45
positron beam stored
2007 Nov.18,12:03
first collision
2008 Feb.1,8:26
530mA  530mA
Lum.>1032cm-2s-1

7. The colliding mode The detectors and collimators installed in the ring
The dose in the IR
Progress to decrease the dose

8. The detectors and collimators installed in the ring
The dose measurements with Pin Diodes, RadFETs, beam-loss monitors(BLM), TLDs, OSLs and CR39s.The Pin diodes and the BLM were used in the experimental study for real_time response.The measurement result of the Pin diodes will be used here for convenience.
Pin diode 1# 2# 3# 4# 5# 6#
BLM
56#
57#
58#
61#
62#
63#
Radiation Detectors Arrangement

9. Collimators installed in the storage ring
(*temporary moveable collimators) S
(m) x y Dx
△x
(2)
△y
half aperture IP 1
0.015
e+R3OCH02
e-R4OCH02
-8.2
23.6
-0.04
-0.189
12.5x(min)
26mm(min)
Moveable
e+R3OCH08
e-R4OCH08 27
17.3 2
-0.78
12x+5‰ E
31mm
e+R4ICH8*
e-R3ICH8*
27.5 17
1.6
0.82
30mm
e+R3OCV2*
e-R4OCV2*
-7.9 60
-0.27
12y
28mm
e+R4ICV9*
e-R3ICV9*
28.5
0.7
15mm

10. (*temporary moveable collimators)
Collimators installed in the storage ring
(*temporary moveable collimators)
e- R3ICH8*&CV9*
e+ R4ICH8*&CV9*
e+ R3OCH08
e- R4OCH08
e- R4OCH02&CV02*

11. the dose in the IR
The IR(designed 14x) is the aperture bottleneck of the storage ring for colliding mode. Large dose occurred here while injection or the stored beam losted. The maximum integral dose in one day in the IR is about several times higher than the design value.

12. The dose measurement in the IR shows:
The stored beam brings little dose.
The total integral dose from the electron beam is much higher than that from the positron beam.
The injetions of electron brought most dose.
The dose was brought by the beam loss caused by the beam_beam interaction sometimes.
Beam abort brings dose sometimes.
Much intergral dose occurres while the beam from the linac can direct into the storage ring and lost near the IR(upstream).

13. e+ injection
e- injection
e- injection
Dose rate in IR
Injections bring most doses. The dose from the electron beam is much higher than that from the positron beam.

14. The dose is brought by the fast beam loss caused by the beam_beam interaction sometimes.

15. beam abort brings dose sometimes.
Current of e-
Dose rate
beam abort brings dose sometimes.

16. The dose occurres even there is no beam in the storage ring.
The beam from the linac can direct into the storage ring and lost near the IR.

17. Progress to decrease the dose
Increase the injection efficiency by optimization of the injection parameters: optics correction, tuning the time delay and the strength of the injection kickers to minimize the oscillation of the injected beam, optimize the orbit in the IR.
During optimization of the injection efficiency, the aperture in the IR of the electron ring was found only about 12x, much smaller than the designed value(14x).There is not enough time to study on it since the commissioning will be ended soon.

18. Progress to decrease the dose(continue)
14x
13x
12x
3x for injected beam
The collimators in the electron transport line were used to limit the energy spread(±3‰) and the emittance(aperture 3x) of the injected beam.

19. Progress to decrease the dose(continue)
Temporary beam abort system were used to let the beam lose in injection region by using injection kickers and a local bump in that region.
The trigger interlock of the electron gun with the kicker means there is no beam coming from the linac in the time that is out of the injection period.
Let the injection beam directly into the beam dump in the transport line during the linac commissioning period

20. The dose in the IR is decreased effectively.
e+ injection and abort
e- injection and abort
The dose in the IR is decreased effectively.

21. The SR mode
The IR isn’t the bottleneck of the aperture in the SR mode and the steady run of the SR mode brings little dose in the IR. The injection status is changed sometimes and the lowering of the injection efficiency brings a large dose in IR as in the beginning commissioning of the SR mode.

22. Collimators installed in the storage ring
(*temporary moveable collimators)
main beam loss areas during the injection period of the SR mode
e- R3ICH8*&CV9*
e+ R4ICH8*&CV9*
e+ R3OCH08
e- R4OCH08
e- R4OCH02&CV02*

23. the dose rate in IR during the injection tuning of the SR mode

24. the dose rate in IR during the steady run of the SR mode

25. Collimators and masks plan
The 5 temporary moveable collimators in the ring will be installed in the transport line to restrict the injection beam(energy spread,emittance,instability of the energy and the orbit).
More collimators and masks* will be installed in the ring,expected to decrease the background in the IR. (It’s hardly to find the suitable places for installation because of the tight space)
Interlock system and beam abort system are also in progress for the protection of the BESIII.
*masks plan refer to the report of “BEPCⅡ Background Issues: Integrated Radiation Measurement  and Radiation Protection”

26. Collimators plan in the storage ringx y Dx
△x
(2)
△y
half aperture IP 1
0.015
e+R3OCH02
-8.2
23.6
-0.04
-0.189
12.5x(min)
26mm
moveable
e+R3OCH14
e-R4OCH14
-46.8 16
1.03
-1.4
12x+5‰ E
e+R1ICH2
e-R2ICH2
109.7
21.7
1.66
3.162
32mm
e+R4ICH8
e-R3ICH8
27.5 17
1.6
0.82
30mm
e+R3OCV2
e-R4OCV2
-7.9 60
-0.27
12y
28mm
e+R3OCV15
e-R4OCV15
-50.1
-1.74
15mm
e+R2OCV16
e-R1OCV16
-69.8 15
-1.516
14mm
e+R4ICV9
e-R3ICV9
28.5
0.7

27. Collimators plan in the storage ring(*installed)
e- R2ICH2
e+ R1ICH2
e- R1OCV16
e+ R2OCV16
e- R4OCV15
e+ R3OCV15
e- R4OCH14
e+ R3OCH14
e- R3ICH8&CV9
e+ R4ICH8&CV9
e+ R3OCH08*
e- R4OCH08*
e+ R3OCH02&CV02
e- R4OCH02*&CV02

28. Summary
The BESIII will be safe since the dose in the IR has been decreased effectively and the protection system will be installed together.
The eletron injection needs more machine study and should be optimized furtherly.
The background during the data taking of the BESIII needs experimental study

29. Thank you!