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Status of the Recycler

Status of the Recycler. Paul Derwent DOE Tevatron Operations Review March 27, 2007. The 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)

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Status of the Recycler

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  1. Status of the Recycler Paul Derwent DOE Tevatron Operations Review March 27, 2007

  2. The 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) 2007 DOE Tevatron Operations Review – Paul Derwent

  3. Beam 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 2007 DOE Tevatron Operations Review – Paul Derwent

  4. Electron Cooling • Electron beam: 4.34 MeV – 0.5 Amps DC – 200mrad angular spread • Max beam current 730 mA Circulated in cooling section • In U-Bend mode currents of 1500 mA has been obtained. 2007 DOE Tevatron Operations Review – Paul Derwent

  5. Recycler 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 2007 DOE Tevatron Operations Review – Paul Derwent

  6. Typical 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) 2007 DOE Tevatron Operations Review – Paul Derwent

  7. Highlights • 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 2007 DOE Tevatron Operations Review – Paul Derwent

  8. 0.5 0.4 0.3 0.3 0.4 0.5 Tune footprint Current working point and its shift with intensity Approximate tune spread before mining Original Working point 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. A. Shemyakin 2007 DOE Tevatron Operations Review – Paul Derwent

  9. Adaptive 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 2007 DOE Tevatron Operations Review – Paul Derwent

  10. Implementation Correction Off Correction On Martin Hu, Dan Broemmelsiek, Nathan Eddy 2007 DOE Tevatron Operations Review – Paul Derwent

  11. Change in Tevatron Bunch Structure Store 5008 Without Correction: 100% variation 25% RMS Store 5245 With Correction: 25% variation 7% RMS 2007 DOE Tevatron Operations Review – Paul Derwent

  12. Lowlights • 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 2007 DOE Tevatron Operations Review – Paul Derwent

  13. Summary • Recycler is fully integrated into Tevatron operations • Operational improvements contribute to Collider Performance • Tune working point • Adaptive RF correction • Pushing beam intensities and luminosities 2007 DOE Tevatron Operations Review – Paul Derwent

  14. Backups 2007 DOE Tevatron Operations Review – Paul Derwent

  15. Extraction Waveforms RF Mining Waveform Each Parcel is extracted and bunched at 2.5MHz 2007 DOE Tevatron Operations Review – Paul Derwent

  16. Tune 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) 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. h y a y0 h For estimations, h = 20 mm (RR vacuum chamber is 100 X 48 mm) A. Shemyakin, Recycler Dept 2007 DOE Tevatron Operations Review – Paul Derwent

  17. 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 • 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% emittance A. Shemyakin, Recycler Dept 2007 DOE Tevatron Operations Review – Paul Derwent

  18. Numbers 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. Estimation for Np = 200, BF~ 0.5, n95~ 2 : A. Shemyakin, Recycler Dept 2007 DOE Tevatron Operations Review – Paul Derwent

  19. Summary • 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 ~ -310-5and 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. A. Shemyakin, Recycler Dept 2007 DOE Tevatron Operations Review – Paul Derwent

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