Design of Interaction Region

Gang Xu

Accelerator Physics Group

IHEP, Beijing, Oct. 14, 2001

Content

• Introduction to BEPCII• Requirements to IR design from accelerator

physics• Detector boundary condition• IR beam line layout• IR Magnets• Background and consideration of new design• Summary

Introduction to BEPCII

• 2-ring collider— factory type machine

• Synchrotron radiation facility

• Basic parameters

(next page)

e-

RFRF SR

e+

IP

Introduction to BEPCII(continued)

Energy E(GeV) 1.55 Energy spread(10-4) 4.23

Circumference C(m) 237.53 Emittance εx/εy(μm) 0.21/0.003

Energy loss/turn U0(keV) 55.8 Momentum compact α 0.036

RF frequency frf(MHz) 499.8 β*x /β*

y(m) 1/0.015

RF Voltage Vrf(MV) 1.5 Chromaticity ξx/ξy 13.3/28.5

Total current/beam I(A) 1.116 Tunes νx/νy/νz 6.64/7.58/0.047

Particle number Nt 5.51×1012 Crossing angle θx(mrad) ±11

SR Power P(kW) 62.3 Bunch spacing Sb(m) 2.4

Bunch number Nb 93 Damping time τx/τy/τz(ms)

44/44/22

Bunch current Ib(mA) 12 Beam-beam parameter 0.04/0.04

Bunch length σz(cm) 1.5 Luminosity(1033cm-2s-1) 1.0

Natural bunch length σz0(cm) 1.1 Effective impedance() 0.7

Tab. 1 Main parameters

Requirements to IR design from accelerator physics

• Rapidly separate the beams into two rings• Squeeze the vertical beta function to 1.5cm• Compensate the coupling from detector solenoid• Connect the two outer rings to provide the

synchrotron radiation• Keep the background in the acceptable level• All accelerator components in IR must stay in the

space limited by the detector• HOM heating due to the mask and the

discontinuity of vacuum chamber should be considered

Boundary condition• Detector geometric condition

Boundary condition(continued)

Summary of the main geometric conditions

1. The first accelerator component must be after 0.5m away from IP

2. Before 1.15m, the outer aperture of components must be less than Φ384mm

3. Before 1.9m, the outer aperture of components must be less than Φ756mm

• Detector solenoid(Bs=1T, new design value 1.2T)

Boundary condition(continued)

500 1000 1500 2000 2500 3000

2000

4000

6000

8000

10000

SCB&ASOL SCQ ISPB

Gauss

mm

• Aperture of IR vacuum chamber(Half )

For collision beam

1. 14σx+xoffset+10mm c.o.d.(εx=0.25μm)

2. 14 σy+5mm c.o.d. (full coupling εy=0.125μm)

For injection beam

3. 16σx+xoffset+3mm c.o.d.

For SR photons(collision beam)

4. Out of the trajectories of SR photons

from 10 σ particles

Boundary condition(continued)

IR beam line layout

• Crossing angle θx(mrad)=±11 relative to the detector solenoid axis• Beam comes to IP from outer ring then goes into inner ring• 1st S.C. magnet has combined anti-solenoid(ASOL) and bending coil(SCB), the latter is used in synchrotron radiation mode• Both electron and positron are off the axis of SCQ• All S.C. coils are in one cryostat• ISPB is a septum type magnet, it will bend the beam in inner ring• OQ1, IQ1, OQ2, IQ2 are special magnets with dual aperture, beam goes through their axes.

IR beam line layout(continued)

60

40

25.3

70

106

120

19001550

1150

360

7.2

606

βy max<120m(βy *=1.5cm)180m(βy

*=1cm), βx max<6m in s=0~1.9m

IR Magnets(Superconducting)

• Anti-solenoid ASOL with integral strength 1.42 T·m, 0.6m away from IP, it will be extended onto SCQ to cancel the effect of the solenoid fringe field

• SCB placed at the same location as ASOL with integral strength 0.26 T·m

• SCQ with strength 17.6T/m and effective length 0.4m, 1.15m away from IP

IR special magnets(Normal)

D to IP

(m)

L

(m)

D between e± BSC(H×V)strengthentry exit entry exit

(mm) (mm) (mm) (mm)

ISPB 2.25 0.4 78 108 72×72 90×64 0.6T

OQ1 2.90 0.4 131 167 101×59 106×58 12T/m

IQ1 3.55 0.5 190 235 129×47 136×42 12T/m

OQ2 4.55 0.5 281 326 82×72 78×73 12T/m

IQ2 5.55 0.5 372 417 106×38 101×35 12T/m

Background issue and consideration of new design

Since the beam coming from outer ring is off axis in the SCQ, this will lead to synchrotron radiation. From the previous plot, the minimum distance between beryllium pipe and the trajectory of the photon is only 7.2mm. This situation must be improved.

7.2

6040

25.3

70

106

19001550

1150

10

140

Three improvement methods

• Increase the radius of the beryllium pipe• Add a bending coil on SCQ to cancel(or

partially) the bending field due to the off axis for the beam in outer ring, this will lead to BSC increasing from Φ120 to Φ140

• Place SCQ to the center of outer ring beam orbit, this will lead to the equivalent BSC increasing from Φ120 to Φ170

Before doing the improvement, we need to know

• What is the acceptable level of the synchrotron radiation?

• The more detail boundary conditions in IR

• The acceptable heating power of each IR component

Summary

• IR design is very preliminary

• Due to the background issues we must do more detail IR design

• Many items are not taken into account such as background from the loss particle, vacuum, beam diagnostics, …