The PEP-II Overview

1
The PEP-II Overview

• John Seeman
• SLAC Particle and Particle-Astrophysics
  Directorate
• PEP-II MAC Review
• January 18, 2006

2
Topics

• PEP-II brief status
• PEP-II future schedule
• PEP-II luminosity goals and projections
• PEP-II detailed upgrade plans

3
The PEP-II Team

August 2004
4
PEP-II ee- Collider Overview

BaBar Detector
5
The PEP-II ee- asymmetric collider
6
PEP-II RF Cavities
7
PEP-II Interaction Region Components near BaBar
LER
HER
BaBar
Collision point
8
How the beams enter and exit the PEP-II
Interaction Region
9
Two years ago before Trickle Injection

Fill and coast is not efficient
10
Present Continuous Injection at PEP-II

Luminosity
LER current
HER current
11
PEP-II Highest Luminosity October 9, 2005

1034
12

13
1 x 1034 on October 9, 2005

14
PEP-II Monthly Peak Luminosity

1 x1034
15

Run 5
A
B
16

17

Actual
Prediction July 2003
18

Slope is good!
Prediction April 2005
Summer weather
Power outage
Actual
Long down
Delayed start
LER BPM event
19
Recent Operation for Run 5b

• PEP-II turn-on (Run 5b) in mid-November.
• PEP-II operated through the holiday break.
• Luminosity ramped rapidly to 8.6 x 1033.
• For the past month we have had three problems
• IR 6 HER vacuum leak
• IR4 LER vacuum spikes and instability
• IR2 LER/HER vacuum spikes and instability
• Several talks are dedicated to these issues.

20
PEP-II Long Term Run Schedule

• Run 5a April-September 2005 (done).
• Down October 2005 (safety small upgrades)
• Run 5b November 2005-July 2006
• Down August-November 2006 (major upgrades for
  PEP-II BaBar LCLS installation)
• Run 6 December 2006-August 2007
• Down September-November 2007
  (safety LCLS installation)
• Run 7 December 2007-September 2008.

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Luminosity Equation for a Circular ee- Collider

• xy is the beam-beam parameter (0.065)
• Ib is the bunch current (1 to 3 mA)
• n is the number of bunches (1700)
• by is the IP lattice optics function (vertical
  beta) (10 mm)
• E is the beam energy (3.1 and 9 GeV) (fixed)
• Luminosity (1033 cm-2 s-1)

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PEP-II Overall Parameters and Goals
Parameter Units Design Present in collision 2007 goal
I mA 2140 2950 4000
I- mA 750 1720 2200
Number bunches 1658 1732 1732
by mm 15-20 11 8-8.5
Bunch length mm 15 11-12 8.5-9
xy 0.03 0.044-0.065 0.054-0.07
Luminosity x1033 3.0 10 20
Int lumi / day pb-1 130 662 1300
Five times design
Over three times design
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Expected PEP-II Delivered Integrated Luminosity
End of fiscal year Total PEP-II Projection Delivered Yearly change Running months each year Peak Luminosity x 1033
FY2004 256/fb 117/fb 10 9.2
FY2005 311 55 5.5 10
FY2006 456 145 9 12
FY2007 635 179 8 17.5
FY2008 1001 366 11 21

Projection December 2005
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Integrated Luminosity Projection
Projection December 2006
December 2006
Run 7
Now
Now
Run 6
Run 5b
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PEP-II Upgrades

• PEP-II luminosity has increased steadily over the
  past years due to carefully planned hardware
  upgrades and operational improvements. We are
  embarking on the next phase.
• The next factor of two in PEP-II luminosity
  (1 to 2 x1034/cm2/s) will come from
• Increasing each beam current by 40.
• Lowering by from 11 to 8.5 mm giving 30.
• Increasing the beam-beam parameters by 10.
• Keeping detector backgrounds at the predicted
  levels.
• Maintaining (and improving) accelerator
  reliability.

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Long Term Luminosity Projections

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PEP-II Limitations and How to Fix Them

• Categories of limitations and upgrades
• Hardware upgrades (AIP and OPS)
• Operational issues
• RF and longitudinal feedback
• Transverse feedback
• Lattice and optics
• Beam-beam interaction
• Reliability
• Beam position monitors (BPMs)
• Instrumentation
• Machine-detector interface and backgrounds

28
Task Force Approach

• Task forces have been addressing PEP-II issues
  for several years to deal with accelerator issues
  with the goal to provide more luminosity and
  higher integrated luminosity.
• We have started several new task forces this run
  to deal near-term and longer-term issues.
• All the task forces leaders meet on Wednesdays to
  provide a common focus and clear overall
  leadership.
• Each task force has identified key issues to
  address and has proposed machine studies,
  hardware improvements, and personnel changes.
• Machine studies are performed about twice each
  week. (Tuesday and Thursday day shifts)
• Accelerator improvement projects AIP are
  identified and started.
• Smaller hardware projects are addressed when
  identified and are funded by operations OPS.

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PEP-II Task Force Structure

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We appreciate contributions of outside groups!

• BaBar collaborators
• USA members
• Foreign members
• LBL accelerator and engineering staff
• Machine Advisory Committee (Chair D. Rice)
• SLAC Accelerator Research staff
• ILC accelerator physicists
• SLAC support groups (engineering, software, )

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Task Force Action Item List

• 1) RF Fill all klystron sockets with working
  tubes and plan for future.
• 2) RF Get LLRF working on all stations with no
  trips.
• 3) Dynamics Get longitudinal beam motion stable
  at higher currents and no trips.
• 4) Dynamics Get transverse beam motion stable at
  higher current with no trips.
• 5) Optics Fix beta beats, dispersion, and
  coupling in LER.
• 6) Optics Analyze chromatic solenoid
  compensation in the IR for LER.
• 7) Optics Look for magnets (quadrupoles) with
  incorrect fields.
• 8) Steering Find sources of orbit jitter and
  drift. Turn on Global Orbit Feedbacks.
• 9) Beam-Beam Turn on the LER wiggler to half
  strength then full strength.
• 10) Beam-Beam Improve specific luminosity to
  gt4.0 at high currents.
• 11) Beam-Beam Lower horizontal tunes to closer
  to half integer.
• 12) Reliability Account for downtime and beam
  tuning in a way that is better for
• PEP-II improvement. What are the major items to
  fix in advance.
• 13) BPM Determine the BPM operating strategy for
  LER. New LER Arc BPM frequency or better
  analysis.
• 14) Instrumentation New IP dither and better SLM
  analysis
• 15) MDI/ Backgrounds Improve the interface and
  backgrounds of PEP-II and BaBar

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Accelerator Physics Studies Needed for 2x1034

• Better understanding of beam-beam effects
• Parasitic crossings
• Small crossing angles
• Higher tune shifts
• Reduce beam aborts
• RF trips
• Longitudinal instabilities
• Transverse instabilities
• Better backgrounds
• Better magnetic lattice optics
• Lower by
• Reduce b beats
• Improve luminosity tuning knobs
• Increase LER emittance with wigglers
• Continue to improve HOM damping at higher
  currents
• Determine instability growth rates in LER/HER at
  high currents
• Transverse
• Longitudinal
• Electron cloud

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Accelerator Improvement Projects (AIP)

• X-Y BPM upgrades 2005-2006
• New HER Q5 vacuum chambers 2005-2006
• New HER/LER Q2 chambers 2006
• HER-10 RF station 2006
• HER-11 RF station 2006
• New transverse digital delay 2005
• HER power supply upgrade for higher tunes 2006
• LLRF comb-2 project 2005-2006
• New HER Q4 vacuum chambers 2006
• NEW IR2 Q2 bellows 2006
• LER IR HOM absorber 2006
• HER IR HOM absorber 2006
• Klystron linearizer 2006
• LER BPM monitor upgrade 2006
• LER new high power bellows 2006
• LER NEG vacuum chamber upgrade 2006
• New Longitudinal feedback processor 2006

Cost of remaining AIP projects is about 8 M
spread over two years. PEP-II AIP expenditures
from 1999-2005 averaged about 5 M each year.
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Projects for Beam Current Increase (DL40)

• HER (1.7 A ? 2.2 A)
• AIP HER-10 RF station 2006
• AIP HER-11 RF station 2006
• AIP HER Q5 vacuum chamber 2005 and 2006
• AIP HER Q4 vacuum chamber 2006
• AIP IR HOM absorber 2006
• OPS Cooling water exchanger modifications 2005
• OPS IR DS7 transition
• LER (2.9 A ? 4 A)
• AIP IR HOM absorber 2006
• AIP High power bellows 2006
• AIP LER Q4 chambers
• AIP LER Q5 chambers
• OPS Abort window spoiler upgrade
• Both rings
• AIP New transverse feedback digital delay 2005
• AIP Low Level RF Comb-2 project 2005-2006

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Example PEP-II RF Cavities (Fall 2006)
Each cavity 850 kV 500 kW 476 MHz HOM
loads Ceramic windows
RF Cavities
36
Klystrons and Power Supplies (Fall 2006)

R. Cassel et al
C. Pearson et al
Klystron group to produce 7 klystrons in 14 months
37
Example PEP-II kicker modules upgrades (Fall
20042005)
Longitudinal
Bunch-by-bunch feedbacks with 4 nsec spacing
Transverse
38

Many of the new vacuum chambers for higher
current are near the IP

Dots show new vacuum chamber locations.
Done
39
Example HER QF5L Chamber (Fall 2005)
Specifications
Construction
R. Pope
Design
40
Example LER/HER Q2 IR Vacuum Chamber (Fall 2006)
Thermal analysis of synchrotron radiation power
(100 W/cm)
NEG Vacuum Pump
S. Metcalfe
High power separation chamber
41
Example HER Q4/5 Chambers (Fall 2006)
BPM

Electron BPMs
Timing BPMs
Electron BPMs
Q5R BPM
Looking upbeam
Q4R BPM
Electron BPMs
14 inches
27.5 inches
42
Example Q4/Q5 Bellows Layout (Fall 2006)

N. Kurita
43
Problem with LER Beam Position Monitor Units

A situation with transverse offset bunches, high
bunch currents and short length positron bunches
caused a vacuum failure in a BPM in June 2005.
The problem is systemic. We have carefully
analyzed the situation.
44
Analysis of BPM thermal properties and RF modes
has been carried out
Old design

Kurita Ng Novokhatski Smith Johnson
Connector
Feed through
BPM button
Likely new design
45
BPM Heating Model and Fix
We have a numerical model (Ecklund) of BPM
heating including bunch charges, bunch lengths
(RF voltage), and transverse position offsets. We
can now reasonably predict when a problem will
occur.
Bunch lengthening
arb. units
damagedBPM
present
Planned fix
Upgrade plan for Fall 2006 Repair LER Arc BPMs
(200), IR2 BPMs need to be modified (50), but
the straight section BPMs are ok (80). Add
thermo- couples to many BPMs. Then we can go to
short bunches and 4 A.
S. Ecklund
46
Lower by from 11 to 8.5 mm (DL30)

• HER
• OPS Raise RF voltage from 14 MV to 18 MV.
• AIP HER-10 RF station
• AIP HER-11 RF station
• OPS Install several SLAC klystrons to replace
  aging klystrons for more power.
• AIP HER power supply upgrade for higher tunes
  2006 (? lower momentum compaction)
• OPS Lattice optics correction in the IR
• LER
• Raise RF voltage from 4 MV to 6.4 MV.
• AIP LER BPM monitor upgrade (2006).
• OPS Install several SLAC klystrons to replace
  aging klystrons for more power.
• OPS Lattice optics corrections in the IR

47
Lattice-Optics Work

• Improve Orbit Response Matrix (ORM) tool
• Improve Model Independent Analysis (MIA) model
• Continue beam-based alignment (BBA)
• Improve on-line optic models
• Develop improved interaction region adjustment
  knobs
• Begin daily comparisons of model and real tunes
• Improve model versus measurement agreement

Tenenbaum, Wienands, Wittmer, Cai
48
Raising the Beam-Beam Parameters (DL10)

• HER
• OPS Arc and IP orbit, coupling, dispersion
  corrections ongoing
• LER
• OPS Arc BPM conversion 952 to 476 MHz processors
  2006 (tbd)
• AIP Arc and IP orbit, coupling, dispersion
  corrections ongoing
• Both rings
• AIP X-Y BPM conversion 2005-2006
• OPS Improve higher specific luminosity with IP
  lattice adjustments
• OPS Lower horizontal tune closer to half integer
  ongoing
• OPS Global Orbit Feedbacks (GOF) re-commissioned
  2005
• OPS Run additional beam-beam simulations finding
  better beam parameters.

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Beam-Beam Simulations

Luminosity beam-beam simulations agree with
present beam conditions. Simulations done for
future beam conditions agree well with spread
sheet estimates. Studies will continue.
Y. Cai U. Wienands K. Sonnad
50
PEP-II Beam-Beam Simulations

L gt 2 x 1034
Full strong-strong simulations with full bunch
currents, parasitic collisions, and full EM
fields are tracked to equilibrium.
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PEP-II Conclusions

• PEP-II turn-on in Run 5 is going well (in spite
  of the power outage and summer heat). In October
  achieved a new luminosity record (1x1034)
• PEP-II has delivered 333 fb-1 since May 1999.
• Recent instabilities are being addressed.
• Trickle injection in both rings all of the time.
  Run time is up.
• Planned upgrades towards gt2?1034 are on track.
• Accelerator issues with PEP-II are being studied.
• Task Forces are under way to address these
  accelerator issues
• A run plan is in place with a target of 1 ab-1 in
  2008.