BEPCII Background Issues Collimators and Masks Jun Xing
BEPCII Background Issues: Collimators and Masks Jun Xing (IHEP) Mini-workshop on BEPCII Background Study Mar. 10 -12, 2008, Beijing • Experimental Study of Decrease the dose in IR • Collimators and masks plan
Experimental Study of Decrease the dose in IR • BEPCII OVERVIEW • The colliding mode • The SR mode
BEPCII OVERVIEW 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 Ge. V 2 to 2. 1 Ge. V 2 and also the dedicated synchrotron radiation beam with 2. 5 Ge. V. For the colliding beams the luminosity is optimized at 1. 89 Ge. V with 1 1033 cm-2 s-1, which is two orders larger than the luminosity of the BEPC. • Layout • Interaction region • Commissioning
The Layout of BEPCII storage ring RF region Straight Section for SR wiggler Straight Section in R 2 out arc 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 Interaction Region (IR)
Crotch pipe is the aperture bottleneck of the colliding mode The Layout of the IR
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: 26 530 m. A Lum. >1032 cm-2 s-1
The colliding mode • The detectors and collimators installed in the ring • The dose in the IR • Progress to decrease the dose
The detectors and collimators installed in the ring The dose measurements with Pin Diodes, Rad. FETs, beamloss monitors(BLM), TLDs, OSLs and CR 39 s. 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. Radiation Detectors Arrangement Pin diode 1# 2# 3# 4# 5# 6# BLM 56# 57# 58# 61# 62# 63#
Collimators installed in the storage ring (*temporary moveable collimators) x (m) S (m) y (m) 0. 015 Dx (m) △ x (2 ) △ y (2 ) half aperture IP 0 1 0 e+R 3 OCH 02 e-R 4 OCH 02 -8. 2 23. 6 -0. 04 -0. 189 12. 5 x(min) 26 mm(min) Moveable e+R 3 OCH 08 e-R 4 OCH 08 27 17. 3 2 -0. 78 12 x+5‰ E 31 mm e+R 4 ICH 8* e-R 3 ICH 8* 27. 5 17 1. 6 0. 82 12 x+5‰ E 30 mm e+R 3 OCV 2* e-R 4 OCV 2* -7. 9 60 -0. 27 12 y 28 mm e+R 4 ICV 9* e-R 3 ICV 9* 28. 5 17 0. 7 12 y 15 mm
Collimators installed in the storage ring (*temporary moveable collimators) e- R 3 ICH 8*&CV 9* e+ R 3 OCH 08 e+ R 4 ICH 8*&CV 9* e- R 4 OCH 02&CV 02* e- R 4 OCH 08
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.
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).
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.
The dose is brought by the fast beam loss caused by the beam_beam interaction sometimes.
Current of e- Dose rate beam abort brings dose sometimes.
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.
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.
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.
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
e+ injection and abort e- injection and abort The dose in the IR is decreased effectively.
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.
Collimators installed in the storage ring (*temporary moveable collimators) main beam loss areas during the injection period of the SR mode e- R 3 ICH 8*&CV 9* e+ R 3 OCH 08 e+ R 4 ICH 8*&CV 9* e- R 4 OCH 02&CV 02* e- R 4 OCH 08
the dose rate in IR during the injection tuning of the SR mode
the dose rate in IR during the steady run of the SR mode
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”
Collimators plan in the storage ring x (m) S (m) y (m) 0. 015 Dx (m) △ x (2 ) △ y (2 ) half aperture IP 0 1 0 e+R 3 OCH 02 -8. 2 23. 6 -0. 04 -0. 189 12. 5 x(min) 26 mm moveable e+R 3 OCH 14 e-R 4 OCH 14 -46. 8 16 1. 03 -1. 4 12 x+5‰ E 26 mm e+R 1 ICH 2 e-R 2 ICH 2 109. 7 21. 7 1. 66 3. 162 12 x+5‰ E 32 mm e+R 4 ICH 8 e-R 3 ICH 8 27. 5 17 1. 6 0. 82 12 x+5‰ E 30 mm e+R 3 OCV 2 e-R 4 OCV 2 -7. 9 60 -0. 27 12 y 28 mm e+R 3 OCV 15 e-R 4 OCV 15 -50. 1 17 -1. 74 12 y 15 mm e+R 2 OCV 16 e-R 1 OCV 16 -69. 8 15 -1. 516 12 y 14 mm e+R 4 ICV 9 e-R 3 ICV 9 28. 5 17 0. 7 12 y 15 mm
Collimators plan in the storage ring(*installed) e- R 2 ICH 2 e+ R 1 ICH 2 e- R 1 OCV 16 e+ R 2 OCV 16 e- R 4 OCV 15 e+ R 3 OCH 14 e+ R 3 OCH 08* e- R 3 ICH 8&CV 9 e+ R 3 OCH 02&CV 02 e+ R 4 ICH 8&CV 9 e- R 4 OCH 02*&CV 02 e- R 4 OCH 14 e- R 4 OCH 08*
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
Thank you!
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