PEP- II Linac Accelerator Systems Department The PEP-II Overview John Seeman SLAC Particle and Particle-Astrophysics Directorate PEP-II MAC Review January

PEP- II Linac Accelerator Systems Department

The PEP-II Overview

John SeemanSLAC Particle and Particle-Astrophysics Directorate

PEP-II MAC ReviewJanuary 18, 2006


Topics

• PEP-II brief status

• PEP-II future schedule

• PEP-II luminosity goals and projections

• PEP-II detailed upgrade plans


The PEP-II Team

•

August 2004


PEP-II e+e- Collider Overview•

BaBarDetector


The PEP-II e+e- asymmetric collider


PEP-II RF Cavities


PEP-II Interaction Region Components near BaBar

HER

LER

Collision point

BaBar


How the beams enter and exit the PEP-II Interaction Region


Two years ago before Trickle Injection

•

Fill and coastis not efficient


Present: Continuous Injection at PEP-II

•

HER current

LER current

Luminosity


PEP-II Highest Luminosity October 9, 2005

•

1034


•


1 x 1034 on October 9, 2005

•


PEP-II Monthly Peak Luminosity

• 1 x1034


•

Run 5A B


•


•

Prediction July 2003

Actual


•

Delayed start

Summer weather

Slope is good!

Power outage

Actual

Prediction April 2005

LER BPM event

Long down


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.


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.


Luminosity Equation for a Circular e+e- Collider

y is the beam-beam parameter (~0.065)

Ib is the bunch current (1 to 3 mA)

n is the number of bunches (~1700) y

* 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)

*341017.2

y

byEInxL


PEP-II Overall Parameters and Goals

Parameter Units DesignPresent in collision

2007 goal

I+ mA 2140 2950 4000

I- mA 750 1720 2200

Number bunches

1658 1732 1732

y* mm 15-20 11 8-8.5

Bunch length mm 15 11-12 8.5-9

y 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 designOver three times design


Expected PEP-II Delivered Integrated Luminosity

End of fiscal yearTotal 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


Integrated Luminosity Projection

NowNow

December 2006

Run 5b

Run 6

Run 7

Projection December 2006


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 y* 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.


Long Term Luminosity Projections

•


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


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”.


PEP-II Task Force Structure

•


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, …)


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 >4.0 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


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 y*– Reduce 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– Fast positron transverse growth rate

• Machine-detector interface– Reduce backgrounds in trickle charge– Reduce IP pressure with current


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.


Projects for Beam Current Increase (L=40%)

• 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– AIP: Q2 vacuum chamber 2006– AIP: IR2 Q2 high power bellows 2006– AIP: Klystron linearizer 2006– AIP: Longitudinal feedback processor 2006– OPS: Increased thermal monitoring 2005-2006– OPS: Feedback amplifier upgrades 2005-2006


Example: PEP-II RF Cavities (Fall 2006)

RF Cavities

Each cavity:850 kV500 kW476 MHzHOM loadsCeramicwindows


Klystrons and Power Supplies (Fall 2006)

•

R. Cassel et alC. Pearson et alKlystron group to produce 7 klystrons in 14 months


Example PEP-II kicker modules upgrades (Fall 2004+2005)

Longitudinal

TransverseBunch-by-bunch feedbacks with 4 nsec spacing


•

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

Dots show new vacuum chamber locations.

Done


Example: HER QF5L Chamber (Fall 2005)

Specifications

Design

ConstructionR. Pope


Example: LER/HER Q2 IR Vacuum Chamber (Fall 2006)

High power separation chamber

Thermal analysis of synchrotron radiation power (~100 W/cm) NEG

Vacuum Pump

S. Metcalfe


Example: HER Q4/5 Chambers (Fall 2006)

•

Q5R BPMQ4R BPM

27.5 inches14 inches

e-e-

Looking upbeam

BPM Timing BPMs

Electron BPMs

Electron BPMs

Electron BPMs


Example: Q4/Q5 Bellows Layout (Fall 2006)Example: Q4/Q5 Bellows Layout (Fall 2006)

• N. Kurita


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.


Analysis of BPM thermal properties and RF modes has been carried out

• Old design

Likely new design

KuritaNgNovokhatskiSmithJohnsonFeed through

BPM button

Connector


BPM Heating Model and Fix

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 0.5 1 1.5 2 2.5 3 3.5

ib

2.5

3

3.5

4.05

4.5

5

5.4

6

6.5

Relative Power vs. bunch current for 1740 bunches

Vrf

x

x

S. EcklundS. Ecklund

damagedBPMdamagedBPM

presentpresent

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 whena problem will occur.

Upgrade plan for Fall 2006:Repair LER Arc BPMs (~200), IR2 BPMs need to bemodified (~50), but the straight sectionBPMs are ok (~80). Add thermo-couples to many BPMs. Then we can go to short bunches and 4 A.

Planned fix:

arb. units

Bunch lengthening


Lower y* from 11 to 8.5 mm (L=30%)

• 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


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


Raising the Beam-Beam Parameters (L=10%)

• 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.


Beam-Beam Simulations•

Y. CaiU. WienandsK. Sonnad

Luminosity beam-beam simulations agree with present beam conditions.Simulations done for future beam conditions agree well with spread sheet estimates. Studies will continue.


PEP-II Beam-Beam Simulations

•

Full strong-strong simulationswith full bunch currents,parasitic collisions, and full EM fields aretracked to equilibrium.

L > 2 x 1034


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 >21034 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.

Documents

PEP- II Linac Accelerator Systems Department The PEP-II Overview John Seeman SLAC Particle and Particle-Astrophysics Directorate PEP-II MAC Review January