Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 1 PEP-II Interaction Region Upgrade M. Sullivan for the Super-B Factory Workshop Hawaii

1Super-B Factory WorkshopJanuary 19-22, 2004

IR UpgradeM. Sullivan

PEP-II Interaction Region Upgrade

M. Sullivan

for the

Super-B Factory WorkshopHawaii

January 19-22, 2004



Outline

•Present design

•Upgrade parameters

•Why upgrade the IR

•1st IR Upgrade Attempt

•Beta functions

•Crossing angle

•Present IR Upgrade Study

•SR fans and power

•SR backgrounds

•Summary



Machine Parameters that are Important for the IR

PEP-II KEKBLER energy 3.1 3.5 GeVHER energy 9.0 8.0 GeVLER current 1.96 1.51 AHER current 1.32 1.13 A y

* 12.5 6.5 mm

x* 25 60 cm

X emittance 50 20 nm-radEstimated y

* 5 2.2 m

Bunch spacing 1.26 2.4 mNumber of bunches 1317 1284Collision anglehead-on 11 mradsBeam pipe radius 2.5 1.5 cm

Luminosity 7.21033 11.31033 cm sec





PEP-II Proposed Upgrade Plans

Now Projected UpgradeLER energy 3.1 3.1 3.1 GeVHER energy 9.0 9.0 9.0 GeVLER current 1.8 3.6 4.5 AHER current 1.0 1.8 2.0 A

y* 12.5 8.5 6 mm

x* 28 28 28 cm

X emittance 50 40 40 nm-radEstimated y

* 4.9 3.6 2.7 m

Bunch spacing 1.89 1.26 1.26 mNumber of bunches 1034 1500 1700Collision angle head-on head-on head-on mradsBeam pipe radius 2.5 2.5 2.5 cm

Luminosity 6.61033 1.81034 3.31034 cm sec



Lower the vertical beta function to 6-7 mm

Keep maximum betas low

Lower the beam-beam effect from the parasitic crossings

Possibly get enough separation to allow filling every RF bucket

Why Upgrade (Initial motivations)



Replace the last 20 cm of each B1 magnet with quadrupole field (50% stronger than QD1 field)

Introduce a crossing angle to recover beam trajectories so we don’t have to redesign or move any magnets. We need a certain amount of separation at QF2.

Relatively easy change to make

Moves the focusing closer to the IP

Initial upgrade attempt



0 2.5 5 7.5-2.5-5-7.5

0

10

20

30

-10

-20

-30

Meters

Ce

ntim

ete

rs2x1034 Interaction Region with a ±3.25 mrad Xangle

M. Sullivan Jun. 14, 2000

QD1

QD4QF5

QF2

QD4 QF5

QD1 QD1

QD1

QF2

Extra focusing

Extra focusing

9 GeV

9 GeV



Beta functionsLow-energy beam

Present designbeta x* (cm) beta y*(mm) beta x max beta y max50 15 94 11235 12.5 135 13550 6 75 277

With Initial Attempt50 6 106 213

High-energy beamPresent design

50 15 520 45035 12.5 735 54050 6 528 1085

With Initial Attempt50 6 546 1057



Crossing angle

Early last year, Ohmi-san from KEK announced that his beam-beam simulation code indicated a rapid luminosity degradation as a function of increasing crossing angle. Last summer, Yunhai Cai at SLAC confirmed Ohmi’s beam-beam result. The effect is most pronounced for very high tune shifts (~0.1).

Parasitic crossings

The introduction of a crossing angle increases the beam separation at the parasitic crossings which would lower the effect we presently see from parasitic crossings in by2 bunch patterns. Lowering y

* also increases parasitic crossing effects since the y at the PC is larger.

Crossing angle and parasitic crossings



Plot of luminosity degradation as a function of increasing crossing angle (courtesy of Yunhai Cai)



0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

LER First PC y,

l = 9 mm

by*=0.9 cmby*=0.8 cmby*=0.7 cmby*=0.6 cmby*=0.5 cm

2PC/I P

/2 (mrad)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

LER First PC y,

l = 7 mm


2PC/I P

/2 (mrad)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

HER First PC y,

l = 9 mm


2PC/I P

/2 (mrad)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

HER First PC y,

l = 7 mm


2PC/I P

/2 (mrad)

LER PC tune shifts vs /2 for different y* normalized to

the IP tune shift for l (bunch length) = 9 and 7 mm

HER PC tune shifts vs /2 for different y* normalized to

the IP tune shift for l = 9 and 7 mm

The tune shift from the first parasitic crossing normalized to the main collision tune shift as a function of crossing angle and plotted for various y

* values for PEP-II (courtesy of Marica Biagini)



Keep head-on collisions

Increase the beam separation at the 1st parasitic collision as much as possible

Allow for 6-7 mm y*

Do not change QF2 septum magnet

Present Working Design Constraints



Stronger B1 magnet to increase separation at 1st parasitic crossing

20% stronger first 5 slices (first 12.5 cm with the weakest field and the largest lever arm)

Slightly increase the beam energy asymmetry 9.1 x 3.08 GeV

Stronger, closer QD1 magnets30% stronger slices for 1st 5 slices

Move radial ion pump behind B1 to behind QD1

Put higher strength focusing in present pump place

Minimal hardware change

Higher strength material has higher temperature coefficient

Present Working Design



Modified Head-on design



Orbit comparison with upgrade and present design

Work in progress

1st horizontal corrector

1st vertical corrector

+z side

LER beam



+z side

HER beam

1st horizontal corrector

1st vertical corrector

Work in progress



Need to correct the position and angle in the x and y orbit on the +Z and –Z sides for each beam (8 orbits in total – two constraints for each orbit)

Too many variables for 8 total correctors

Allow adjusting the vertical collision point

Allow adjusting the horizontal collision angle

Allow the new sections of QD1 to have a variable offset (variable bending – but it affects both beams)

Allow (small) beam energy adjustments as long as we are still on the 4S resonance

Steps toward a new design



Beta functions (revisited)Low-energy beam

Present designx* (cm) y* (mm) x max (m) y max (m)50 15 94 11235 12.5 135 13550 6 75 277

With upgrade #150 6 106 213

With upgrade #250 6 99 21335 6 134 213

High-energy beamPresent design

50 15 520 45035 12.5 735 54050 6 528 1085

With upgrade #150 6 546 1057

With upgrade #250 5 570 97035 5 795 970



The proposed high beam currents (4.5A LER and 2A HER) will generate a large amount of SR in the IR

The HER vacuum elements were designed for 2A so the HER parts should be OK. There is some question about the High-Power Downstream Dump that absorbs the HER B1 SR power

There are 2 vacuum chambers that see the LER SR power that need to be looked at more closely

The LER downstream crotch chamber that sees B1 radiation

The upstream LER SR mask for the Be beam pipe. It sees upstream QD1 radiation

SR fans and power







The present power levels on the multi-tipped LER SR mask are about 30 W/mm at 2.1A beam current. This goes to 50 W/mm at 3.6A and 65 W/mm for 4.5 A of LER beam. This mask is under study. Presently it looks like this chamber may just work at 3.6 A but that it will need to be rebuilt for a 4.5 A beam

The crotch chamber design allowed for overlapping B1 radiation fans. This can only happen when the detector solenoid is off. We never intend to run high current beams with the solenoid off so we have some margin here.

SR fans and power (cont.)



The present LER SR mask (multi-tipped mask) does? (not completely checked yet) an adequate job of shielding the detector if we upgrade the B1 and QD1 magnets. We are trying to maintain the beam orbits such that the present design will work with minor modifications.

In any case, the extra power from the higher current LER beam means that SR backgrounds have to be studied in more detail

The very high beam current of the LER means that we need to check to make sure that back-scattered photons from the downstream crotch chamber do not strike the detector beam pipe

SR backgrounds



The initial upgrade proposal replaced the last 4 slices of the B1 magnets with quadrupole field. This allows for lower beta y* values with a smaller increase in the maximum beta y.

The replacement of the B1 slices with quad field introduces a ± 3.3 mrad crossing angle at the IP which reduces the beam-beam effect at the 1st parasitic crossing. However, recent beam-beam simulations indicate a luminosity reduction for beams with a crossing angle.

An alternative proposal currently under study is to strengthen the IP end of QD1 effectively moving the center of the magnet closer to the IP. At the same time, increase the beam separation at the 1st parasitic crossing by increasing the strength of the initial B1 slices. This maintains the PEP-II head-on collision.

The high beam currents of the upgrade plans generate significant SR power in the IR that must be handled

SR backgrounds look like they can be controlled but have not yet been thoroughly studied

Summary

Documents

Super-B Factory Workshop January 19-22, 2004 IR Upgrade M. Sullivan 1 PEP-II Interaction Region Upgrade M. Sullivan for the Super-B Factory Workshop Hawaii