fAccelerator Division Fermilabconferences.fnal.gov/cool05/Presentations/Monday/M07_Nagaitsev.pdf ·...

FermilabAccelerator Divisionf

Antiproton Cooling in the FermilabAntiproton Cooling in the FermilabRecycler RingRecycler Ring

Sergei NagaitsevFermilab Accelerator Division

Antiproton Cooling in the Fermilab Recycler Ring - Nagaitsev 2

FermilabAccelerator Divisionf Fermilab ComplexFermilab Complex

Tevatron

Main Injector\Recycler

Antiprotonsource

Proton source

D0

CDF

The Fermilab Collider is a Antiproton-Proton Collider operating at 980 GeV


FermilabAccelerator Divisionf Luminosity HistoryLuminosity History

Luminosity increase is mostly due to:Better performance of the injector chainIntroduction of the Recycler into operationsAlignment and lattice change in the TevatronImproved operations, focused studies


FermilabAccelerator Divisionf Antiprotons and LuminosityAntiprotons and Luminosity

The strategy for increasing luminosity in the Tevatron is to increase the number of antiprotons

Increase the antiproton production rate (Run 2 Upgrades)Provide a third stage of antiproton cooling with the RecyclerIncrease the transfer efficiency of antiprotons to low beta in the Tevatron


FermilabAccelerator Divisionf Antiproton ProductionAntiproton Production1x108 8-GeV pbars are collected every 2-4 seconds by striking 7x1012 120-GeV protons on a Nickel target8 GeV Pbars are focused with a lithium lens operating at a gradient of 760 Tesla/meter30,000 pulses of 8 GeV Pbars are collected, stored and cooled in the Debuncher, Accumulator and Recycler Rings

The stochastic stacking and cooling increases the 6-D phase space density by a factor of 600x106

8 GeV Pbars are accelerated to 150 GeV in the Main Injector and to 980 GeV in the TEVATRON


FermilabAccelerator Divisionf Combined ShotsCombined Shots

Extracting antiprotons from both the Accumulator and the Recycler for the same store eg.

Twelve bunches from the RecyclerTwenty four bunches from the Accumulator

ReasonsFlexibility in the Run II Upgrade schedule

• Natural merging of commissioning of electron coolingPush Recycler commissioning progress by plunging it into operationsLuminosity enhancement – larger amount of antiprotons for smaller emittances

• Accumulator stack size limited to <200 mA– Stacking Rate– Transverse emittance vs Stack Size

Combined Shot OperationConcept proposed in February ’04Dual energy ramps in the MI completed and tested by May ’04First Attempt 6/13/04Record Luminosity

• 103x1030cm-2sec-1 recorded 7/16/04 • 129x1030cm-2sec-1 recorded August 2005

Routine Operations - January 2005Obstacles

Stacking RateInjector Complex 8 GeV energy alignmentLongitudinal emittance in both the Accumulator and RecyclerTransfer time between Accumulator to Recycler


FermilabAccelerator Divisionf Combined ShotsCombined Shots

Luminosity enhancement – larger amount of antiprotons for smaller emittances

Accumulator stack size limited to <200 mA• Stacking Rate• Transverse emittance vs Stack Size


FermilabAccelerator Divisionf Recycler Recycler –– 8.9 8.9 GeV/cGeV/c storage ringstorage ring

At the end of August 2003The Recycler was “on the ropes”

• Lifetime was < 60hrs• Transverse emittance growth was 12π-mm-

mrad/hrTook drastic measures

• Lengthened the Fall 03 shutdown to bake the entire Recycler

• Instituted the Pbar Tax (Investment) to guarantee the Recycler adequate study time and access to the tunnel

Recycler bake-out was extremely successful

Transverse emittance growth reduced by a factor of 10-20Lifetime > 600 hours

Recycler commissioning has progressed rapidly

Using the Recycler in “Combined Shots” operations makes it a luminosity enhancement

• Operational January 2005 Transverse Damper commissioned August 2005

• Stacks larger than 150x10 pbarsnow possible

Stand alone Recycler shots to the Tevatron (Sept 2005)

• Stack of 190x1010 pbars in the Recycler

• 92x1030cm-2sec-1 LuminosityElectron Cooling commissioned July 2005

By the end of August 2005, electron cooling is used on every Tevatron shot


FermilabAccelerator Divisionf Beam Cooling in the RecyclerBeam Cooling in the Recycler

The missions for cooling systems in the Recycler are:The multiple Coulomb scattering (IBS and residual gas) needs to be neutralized.The emittances of stacked antiprotons need to be reduced between transfers from the Accumulator to the Recycler.The effects of heating because of the Main Injector ramping (stray magnetic fields) need to be neutralized.Transverse and longitudinal emittances of the recycled antiprotons need to be reduced by roughly 1/e in the 8-10 hour store length. (Presently not part of the mission; May be in the future)



Final goal for Recycler: Final goal for Recycler: Prepare 9 (6 Prepare 9 (6 eVeV--ss each) bunches for extractioneach) bunches for extraction


FermilabAccelerator Divisionf Final Recycler beam parametersFinal Recycler beam parameters

Short term goals:Recycler provides all Tevatron pbars250x1010 pbars delivers 5e1010 pbars per bunch in the Tevatron (75% efficiency to collisions, 36 bunches)Long. emittance (95%): 54 eV-sTransverse emittances (n, 95%): 5 µm-radSupports peak luminosities above 130x1030 1/(cm2s)

End of Run II:Up to 600x1010 pbarsSame emittances


FermilabAccelerator Divisionf Recycler heating ratesRecycler heating rates

Residual gas scattering: 0.5 µm-rad/hr (n, 95%)Transverse damper: < 0.2 µm-rad/hr (n, 95%)IBS rates (B-M model) for 250x1010 pbars,

54 eV-s as a function of transverse emittances:

0

2

4

6

8

10

12

14

16

3 3.2 3.4 3.6 3.8 4

Momentum spread (rms), MeV/c

Long

. diff

usio

n, (M

eV/c

)^2/

hr

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

3 3.2 3.4 3.6 3.8 4

Momentum spread (rms), MeV/c

Tr. e

mitt

. gro

wth

rate

, um

/hr3 µm-rad

5 µm-rad

7 µm-rad

3 µm-rad

5 µm-rad

7 µm-rad

Typical operating point


FermilabAccelerator Divisionf Recycler transfers with gated coolingRecycler transfers with gated cooling

New batch Cold Stack

Gated cooling: ON OFF


FermilabAccelerator Divisionf Gated Cooling ExperimentGated Cooling Experiment

Two segments of beam (25e10 pbars each): one cooled/gated and one not. The uncooled bunch shows natural emittance growth due to IBS and coulomb scattering.

0 10 20 30 40 50Time [min]

6

8

10

12

14

16

18

20

[eV

-s]

and

[π m

m-m

rad]

εL No Cooling

εV

Gated

εH

Gated

εV

No Cooling

Emittance Evolution

Run II Goal


FermilabAccelerator Divisionf Recycler stochastic cooling systemRecycler stochastic cooling system

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6 7 8

Time, hr

Bea

m c

urre

nt, e

10Lo

ng. e

mitt

., eV

-s

Long emittance

Number of pbars (90x1010)


FermilabAccelerator Divisionf Present stochastic cooling systemPresent stochastic cooling system

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6 7 8

Time, hr

Emitt

ance

(n, 9

5%),

umrm

s m

omen

tum

spr

ead,

MeV

/c

Emittance

RMS momentum spread


FermilabAccelerator Divisionf Cooling in barrier bucketsCooling in barrier buckets

Keep momentum spread constant, compress the bunch length by moving the rf barrier

Simulation (MOCAC) of electron cooling + IBS, 500 mA e-beam, 600x1010 pbars

100 eV-s

50 eV-s

30 minutes


FermilabAccelerator Divisionf Recycler Electron CoolingRecycler Electron Cooling

The maximum antiproton stack size in the Recycler is limited by

Stacking Rate in the Debuncher-Accumulator at large stacksLongitudinal cooling in the Recycler

Longitudinal stochastic cooling of 8 GeV antiprotons in the Recycler is being replaced by Electron Cooling

Electron beam: 4.34 MeV – 0.5 Amps DC – 200µrad angular spread


FermilabAccelerator Divisionf Electron beam parametersElectron beam parameters

Electron kinetic energy 4.34 MeV

Uncertainty in electron beam energy 0.3 %

Energy ripple ≤ 10-4

Beam current (max) 0.5 A DC

Duty factor (averaged over 8 h) 95 %

Electron angles in the cooling section(averaged over time, beam cross section, and cooling section length), rms ≤ 0.2 mrad


FermilabAccelerator Divisionf Recycler measured momentum Recycler measured momentum

distribution using distribution using SchottkySchottky1.5e11 pbars, εn = 2 µmMomentum acceptance (flat central part): about 0.5% (+/- 22 MeV/c)

0

0.01

0.02

0.03

0.04

0.05

0.06

-100 -50 0 50 100

Momentum offset, MeV/c

Dis

tr. fu

nctio

n, a

rb. u

nits

Initial distribution

Distribution after 30 min


FermilabAccelerator Divisionf Simulation of cooling demonstrationSimulation of cooling demonstration

Without cooling -- the momentum distribution remains flat over 0.3% span for 30 minutesCoasting beam, IBS+ECOOL simulation, εn = 2 µm-rad, Ie=0.1 A, rms angular spread = 0.5 mrad

0.00

0.01

0.02

0.03

0.04

0.05

0.06

-20 -15 -10 -5 0 5 10 15 20

Momentum offset, MeV/c

Dis

tr. fu

nctio

n, a

rb. u

nits

Initial distribution

Distribution after 30 min

Simulation of cooling after 30 min



First interaction observed!

Ener

gy d

istri

bfu

nctio

n (lo

g sc

ale)

First interaction First interaction –– July 09, 2005July 09, 2005

Initial

100 MeV/c


FermilabAccelerator Divisionf Electron energy adjusted down by 2 Electron energy adjusted down by 2 keVkeV


FermilabAccelerator Divisionf Energies aligned Energies aligned –– we were within 3 kV!we were within 3 kV!


FermilabAccelerator Divisionf First eFirst e--cooling demonstration cooling demonstration –– 07/15/0507/15/05

-0.002 -0.001 0 0.001 0.002

Fract. momentum spread

Dis

t. fu

nctio

n (a

rb. u

nits

)

Pbar beam: 63.5e10Barrier-bucket bunched.Bunch length 1.7-usTr. emittance (95%,n) kept at 4-pi mm-mradElectron beam current: 200 mATraces are 15 min apart


FermilabAccelerator Divisionf Electron cooling drag rateElectron cooling drag rate

For an antiproton with zero transverse velocity, electron beam: 200 mA, 3-mm radius, 300 eV rmsenergy spread and 200 µrad angular spread

0 1 2 3 4 5 6 7 80

2

4

6

8

10

12

14

Antiproton energy deviation, MeV

Long

itudi

nal d

rag

rate

, MeV

/hr

FFi

Ei.

Non-magnetized cooling force model


FermilabAccelerator Divisionf Equilibrium long. emittanceEquilibrium long. emittance

For a nearly constant drag force, F0 , the equilibrium momentum distribution is not gaussian but exponential: f(p) ~ exp(-|p|/p0), where p0 = D/(2F0) and D is the diffusion rate.The diffusion rate is mostly determined by the intra-beam scattering.

Log.

scal

eThe rms momentum spread is √2 p0 (keep at 3.5 MeV/c)For IBS: D ≈ 25 MeV2/hrNeed F0 ≈ 5 MeV/hr



Drag force measurements: Drag force measurements: electron energy jump by +2 electron energy jump by +2 keVkeV

Momentum distribution (log scale)

Beam emittance was measured by Schottky: 1.5 µm (n, 95%). In the cooling section this corresponds to a 0.9 mm radius (rms), electron current 200 mA

1.2 MeV per division


FermilabAccelerator Divisionf Drag force Drag force –– voltage jump +2 kVvoltage jump +2 kV

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Time, hr

Mom

entu

m, M

eV/c

22 MeV/hr


FermilabAccelerator Divisionf Cooling rate for small amplitudesCooling rate for small amplitudes

For small momentum deviations (< 1 MeV) the cooling force is linear: F ≈ - λp. The distribution function in momentum is close to being gaussian.

0.0001

0.001

0.01

0.1

1

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Momentum deviation, MeV/c

Dis

t. fu

nctio

n (lo

g. s

cale

)

rms spread2x10-5

λ

σ2

2 Drms =

4x1010 pbars


FermilabAccelerator Divisionf Cooling OFFCooling OFF--ONON

By turning the electron cooling OFF and ON again one can determine both the diffusion and cooling rates

0

0.1

0.2

0.3

0.4

0.5

0.6

0 100 200 300 400 500 600

Time, sec

Mom

entu

m s

prea

d, M

eV/c

rms

Electron beamcurrent, Amps

Cooling OFF:

Cooling ON:

D ≈ 2.8 MeV2/hrλ ≈ 25 hr -1(electron current 200 mA)

Fit ( ) Dtt += 2

0σσ

( ) ( )

λλ

λσσ

22exp

220

DtDt +−⎟⎠⎞

⎜⎝⎛ −=


FermilabAccelerator Divisionf Electron cooling in operationElectron cooling in operation

Electron coolingprior to extraction

Stochastic coolingafter injection


FermilabAccelerator Divisionf RecyclerRecycler--Only OperationsOnly Operations

Recycler has been participating in ColliderOperations in the Combined Shot mode because the Recycler Stack size has been limited to ~120x1010 pbars

Longitudinal CoolingTransverse Stability

With Electron Cooling operational and the transverse dampers commissioned, the Recycler stack size can now be increased to over 200x1010

pbars

The Collider complex is now transitioning from Combined Shot mode to Recycler-Only mode

Faster average stacking.Smaller pbar emittances in the TEV


FermilabAccelerator Divisionf Recycler Electron Cooling SummaryRecycler Electron Cooling Summary

Electron cooling commisioningElectron cooling was demonstrated in July 2005 two months ahead of schedule.By the end of August 2005, electron cooling was being used on every Tevatron shot

Electron cooling ratesDrag rate: 20 MeV/hr for particles at 4 MeVCooling rate: 25 hr-1 for small amplitude particleCan presently support final design goal of rapid transfers (30eV-sec every hour)Have achieved 500 mA of electron beam which is the final design goal. -0.002 -0.001 0 0.001 0.002

Fract. momentum spread

Dis

t. fu

nctio

n (a

rb. u

nits

)

Electron beam current: 200 mATraces are 15 min apart

Beam

Den

sity

(log

Sca

le)

Energy

Beam

Den

sity

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