status of the recycler

f

Status of the RecyclerStatus of the Recycler

Paul DerwentDOE Tevatron Operations Review

March 27, 2007

2007 DOE Tevatron Operations Review – Paul Derwent 2

f The RecyclerThe Recycler

Fixed energy (8 GeV) Permanent magnet storage ring Same tunnel as Main Injector Antiproton ‘stash’ for Collider operation

Goals:• 600e10• 54 eV s• 10 mm mr (95% normalized)• Extract 95% ~1/day

Accept transfers from Accumulator• ~25e10 every hour• <15 eV s• <12 mm mr (95% normalized)


f Beam CoolingBeam Cooling

Mixture of stochastic and electron cooling Stochastic:

• 0.5-1 GHz and 1-2 GHz momentum• 2-4 GHz transverse • Cooling rate proportional to beam intensity

• Cool injected beam before merging into cold stash

Electron Cooling:• 0.5 A 4.34 MeV electron beam• Need transverse overlap of antiproton and electron

beam• Cooling rate independent of beam intensity


f Electron CoolingElectron Cooling Electron beam: 4.34 MeV – 0.5

Amps DC – 200rad angular spread

Max beam current 730 mA Circulated in cooling section

In U-Bend mode currents of 1500 mA has been obtained.


f Recycler OperationRecycler Operation

Fully integrated into Collider operations All collider stores in last year are “Recycler Only”

Routinely provide >250e10 for Collider stores Max: ~440e10 Longitudinal Emittance: 50-80 eV s Transverse Emittance: 3-7 mm mr (95%

normalized)

~40e10 every 2.5 hours


f Typical WeekTypical Week

Recycler Stash & Accumulator Stack for a week 43 transfers from Accumulator to Recycler 5 transfers from Recycler to Tevatron

• ~310e10 available, transfer out 95%• 5-7 mm mr (95% normalized)


f HighlightsHighlights

Change in Working point: Space charge tune shifts

• pbar beam as function of intensity / density [0.425,0.415] -> [0.455,0.463] Improvement in Lifetime at large stashes

Implementation of Adaptive Feed Forward RF Correction Uniform bunch intensity for collider operation

Optimization of procedures for large stashes Cooling performance Extraction performance


f Tune footprintTune footprint

0.3

0.5

0.3

0.5

0.4

0.4

Current working point and its shift with intensity

Approximate tune spread before mining

Approximate tune spread in the mined state

Tune diagram with resonance lines up to 5th order. At mining, axial particles may reach 3rd resonance lines.

Original Working point

A. Shemyakin


f Adaptive RF CorrectionAdaptive RF Correction

Implementation of adaptive feed forward RF correction Integral of barrier buckets gives a flat potential well Flat potential well -> uniform time distribution For extraction, grow additional barrier buckets to make 9 slices which are

transferred to Tevatron Uniform time distribution -> uniform bunch density in Tevatron

Martin Hu, Dan Broemmelsiek, Nathan Eddy


f ImplementationImplementation

Correction Off Correction On

Martin Hu, Dan Broemmelsiek, Nathan Eddy


f Change in Tevatron Bunch StructureChange in Tevatron Bunch Structure

Store 5008Without Correction:

100% variation25% RMS

Store 5245With Correction:

25% variation7% RMS


f LowlightsLowlights

DCCT (main intensity monitor) failed in December Impact on measurement of:

• Transfer efficiencies• Lifetimes• Schottky emittance measurements

Alternative monitors: • Sensitive to AC components : changes in RF structure• Toroid• Resistive wall monitor

Have replacement in hand, will occur during shutdown


f SummarySummary

Recycler is fully integrated into Tevatron operations

Operational improvements contribute to Collider Performance Tune working point Adaptive RF correction

Pushing beam intensities and luminosities


f BackupsBackups


f Extraction WaveformsExtraction Waveforms

RF Mining Waveform

Each Parcel is extractedand bunched at 2.5MHz


f Tune shift estimationTune shift estimation

Two effects The beam interacts with image charges and currents

(coherent tune shift) Motion of an individual particle is affected by the beam’s

space charge and image charges and currents (incoherent tune shift)

y0y a

h

h

Effect of the image charges and currents in the vacuum chamber, magnets, and magnetic shielding is modeled by two plates.The current density is assumed to be constant across the beam.

For estimations, h = 20 mm (RR vacuum chamber is 100 X 48 mm)

A. Shemyakin, Recycler Dept


f Tune shift estimation Tune shift estimation

Space charge tune shift (round beam)

Incoherent tune shift

Coherent tune shift

Formulas are from Handbook of Accelerator Physics and Engineering, by A.Chao and M.Tigner

BFmradmm

N

BFa

NPr

n

ppRRpsc ][

]10[012.0

)2( 95

12

2332

95

222

15.01

138

1

nsc

scLaslettsc

x

yinc

BF

BFh

a

1295 100018.015.0 pnsc

xy

cohNBF

Symbols:

rp – classical proton radius

Np – number of pbars

PRR- RR perimeter

- RR tune (25)

, - relativistic factors

a- beam radius

BF- bunching factor, jav/jmax

n95- transverse normalized 95% emittanceA. Shemyakin, Recycler Dept


f NumbersNumbers

In this case, the main factor that determines crossing resonances by individual particles is the direct space-charge field.

However, in tune measurements we see only the coherent tune shift.

15.01024.0 xy

inc

Estimation for Np = 200, BF~ 0.5, n95~ 2 :

0036.0xy

coh



f SummarySummary

Measured tune shift due to pbar space charge is in agreement with a simple estimation.

The estimated incoherent tune shift is significantly larger and goes as high as 0.1 in the time of mining.

The tunes change ~ 0.001 after turning on electron cooling. The change takes ~0.5 hr, correlates with changes in the peak pbar density, and has no explanation.

The power in 21 MHz signal correlates rather with coldness of pbars then with the presence of the electron beam.

A response to the increase of the e-beam current from 0.1 to 0.2 A is ~ -310-5 and doesn’t contradict to an estimation.

Response to turning off the clearing voltage in the cooling section is small and corresponds to , i.e. ~ 1% relative density of secondary electrons. The 10% density required to explain the radial dependence of the drag force and the discrepancy of the electron beam size measurement does contradict to the measurement.

1~sec_2

e

e

nn


status of the recycler

Documents