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1ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Interaction Region of PEP-II
M. Sullivan
for the
ILC MDI workshopJanuary 6-8, 2005
2ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Outline
•Initial IR design parameters
•Initial beam parameters
•Detector constraints
•IR design
•Present performance and issues
•New beam parameters
•Luminosity background
•Summary
3ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
SLAC beam lines
4ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Layout of the PEP-II Ring
5ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Initial IR Design Parameters
• Energy asymmetry of 9 on 3.1 GeV• Head-on collision• Bunch separation of 1.26 m• 25 mm separation between BSC envelopes at
2.8 m (room for a septum magnet)• SR masking
– No direct hits on the detector beam pipe– No surfaces that can one bounce to the detector
beam pipe– This leaves mask tip scattering as the dominate SR
source
6ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Initial Beam Parameters
• Collision Frequency 238 MHz• Number of bunches 1650• Bunch spacing 1.26 m• Charge/bunch (L/H) 5.9x1010 2.1x1010 • IP Beta X,Y 0.50, 0.015 m• Emittance X, Y 48, 1.5 nm-rad• Bunch size (x, y, z) 155, 4.7, 10000 µm• Currents (L/H) 2.1 A 0.75 A• Luminosity 3x1033 cm-2 sec-1
7ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Detector Constraints
• Detector acceptance minimum angle of 300 mrad• Detector magnetic field of 1.5T• Minimum thickness beam pipe
– 4 µm Au– 800 µm Be– 1 mm water– 400 µm Be
• Detector center shifted in Z +0.37 m
8ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
9ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Present status
• We have achieved y*s of 10 mm
• With x*s of 30 cm
• Bunch lengths are estimated to be 11-13 mm• Total beam currents of 2.450 A on 1.550 A
(1.590 on 2.540 on last shift)• No sign of SR backgrounds• Fairly large luminosity background• Total current in the support tube up to 4.1 A!
• Heating in the IR support tube (from Q2 to Q2) OK so far
• NEG pump heating by HOM power
10ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Past and Present HOM heating
• IR Be bellows• NEG pumps in the LER• Q1/Q2 bellows
• Bellows in region 4• Bellows in region 10
11ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
IR Vacuum Chambers
12ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Bellows Detail
Transverse H11 mode can couple through the RF shield
RF shieldBe is coated with about 4 m of Au
Al heat sink
Be to SS braze
SS sleeves
Cu pipe
13ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Forward VTX BLWS Cooling
14ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
VTX Bellows Cooling Installation
15ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Lab test data of NEG outgassing as a function of temperature
LER NEG Pump Temperatures
Upstream LER side
NEG Pressure vs NEG Temperature
0
1
10
100
1000
10000
0 100 200 300 400 500 600 700
NEG temperature deg F
NE
G p
res
su
re (
nT
orr
)
350 °F
16ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
LEB Fans
17ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
HEB Fans
18ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
New Beam Parameters
• Collision Frequency 238 MHz• Number of bunches 1710• Bunch spacing 1.26 m• Charge/bunch (L/H) 12.6x1010 3.5x1010 • IP Beta X,Y 0.30, 0.008 m• Emittance X, Y 60, 1.0 nm-rad• Spot size (x, y, z) 134, 2.8, 9000 µm• Currents (L/H) 4.5 A 2.2 A• Luminosity 2x1034 cm-2 sec-1
19ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Issues for the near future
• Run 5 goals that affect the IR• LER current of 3.3 A• HER current of 1.8 A• Higher bunch currents more HOM power• Shorter LER bunch length more HOM power
• Lower y*s to 9 mm
• Lower LER x* to 30 cm
• Increase LER emittance to 50 nmrad
Total of 5.1 A !
BSCs
20ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Issues for the farther future
• Ultimate goals that affect the IR• LER current of 4.5 A• HER current of 2.2 A• Still higher bunch currents more HOM power
• Still shorter bunch lengths more HOM power
• Lower y*s to 8 mm
• Lower LER x* to 30 cm
• Increase LER emittance to 60 nmrad
Total of 6.7 A !!
BSCs
21ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Present machine parameters
LER x*= 30
cm and LER x = 22 nmrad
LER x* may
be a little low, but it is the value for run 5
BSC just clears the present Q2 chamber on the forward side
Plenty of room on the backward side
BSCs
22ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
BSCs
Expected LER beam size for run 5
LER parameters: x
* = 30 cm x = 50 nmrad
BSC is defined as 15 + 2mm (uncoupled)
BSC violated at the septum
Just enough room for the beam
New chamber being built and RFI by April or May
23ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
LEB+HEB HOM Power ~ ib2 z
-2
24ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Be Vertex Pipe and Bellows
25ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Luminosity versus Crossing Angle
• Normalized Lsp vs. e- angle
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-1000 -500 0 500 1000
XP[e-] (murad)
Lsp
/ L
sp(X
P=
0)
by-4, msrd
by-4, fit
sp. by-2, msrd
sp. by-2, fit
Without parasitic crossing
Withparasitic crossing
26ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. SullivanComparisons between stronger B1s,
crossing angles and energy changes• The parasitic crossing separations are:
Present design 3.22 mm30% Stronger B1 (Nd) 3.6-3.8 mm (12-17%)Stronger B1 (volume) 3.5-3.9 mm (9-21%)With +/- 0.5 mrad x angle 3.9-4.0 mm (21-24%)
• The energy differences for the crossing angle option are:
HER 8.9732 to 8.7450 (-2.5%)LER 3.1186 to 3.2000 (+2.6%)
• Increase the energy asymmetry AND remove last B1 sliceVery preliminary look with head-on collisions:HER energy 8.9732 9.427 GeV +5.1% and LER energy 3.1186 2.969 GeV - 4.8% PC separation of 3.55 mm (10%)
27ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
Synchrotron radiation masking has been checked OK with a 7mm beta y*
Local beam-gas and coulomb should be essentially unchanged since the geometry is almost the same and the masking is the same. These backgrounds should slowly improve as the total number of A-hrs increases
Radiative Bhabhas as a background that increases as the luminosity increases
Detector Backgrounds in the Future
28ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
87.57
6.56
5.5
4
3.532.5
21.51
0.5
4.55
HER Radiative Bhabhas
-7.5 -5 -2.5 0 2.5 5 7.5
0
10
20
30
-10
-20
-30
m
cm
M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M
3.1 G
eV
3.1 G
eV
9 GeV
9 GeV
29ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
32.5
2 1.51
0.5
LER Radiative Bhabhas
-7.5 -5 -2.5 0 2.5 5 7.5
0
10
20
30
-10
-20
-30
m
cm
M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M
3.1 G
eV
3.1 G
eV
9 GeV
9 GeV
30ILC MDI workshopJanuary 6-8, 2004
PEP-II IRM. Sullivan
The PEP-II interaction region has performed very well
The PEP-II accelerator is starting to move into a new area of performance where HOM power will play a much larger role. The higher beam currents and higher bunch currents contribute to the higher HOM power as well as to higher SR power.
So far we have addressed two major issues in the IR concerning HOM heating – Be bellows heating and NEG pump heating. Other regions will bear watching as well as other vacuum components.
The IR upgrade is looking at modifying the B1 bending magnets to improve the beam separation at the 1st parasitic crossing while maintaining head-on collisions. Stronger magnetic material is needed to do this. However, we have not found a material that is comfortably rad-hard.
The option of adding a small crossing angle (+/- 0.5 mrad) using the present hardware can be done by changing the beam energies by about +/- 2.5%.
Detector backgrounds that are a function of the luminosity will become more important as the luminosity increases
Summary