# Presentation: 421483

## Antiproton Source Operations Status

- Accelerator Advisory Committee
- Elvin Harms
- Fermilab Beams Division
- 4 February 2003

## Antiproton Source Operations Status

- Performance Achievements since last AAC
- Overcoming IBS/Core transverse emittance
- Core Cooling Upgrade
- ‘Shot’ lattice
- Stacking improvements
- Reliability
- Current Focii
- Transfers to Tevatron
- Transfers to Recycler
- Stacking
- Plans/Expectations
- Debuncher Cooling
- Accumulator cooling
- AP2/Debuncher
- Summary

- 4 February 03

## Overcoming IBS/Core Transverse Emittance

- Refer to Dave McGinnis’ excellent presentation on this subject from previous AAC summary follows
- New Core cooling installed early June 2002
- Shot Lattice integrated into operation July 2002
- Ramp remaining Pbars back to Stacking lattice routine beginning December 2002

- 4 February 03

## Overcoming IBS/Core Transverse Emittance

- Before July of 2002, the horizontal emittance of a typical 100 x 1010 antiproton stack was about a factor of two larger than the Run II handbook design value
- At a stack of 100 x 1010  pbars the normalized horizontal transverse emittance was about 17 -mm-mrad
- The Run II handbook specifies 8 -mm-mrad at 100 x 1010  pbars
- During the period of Nov. 2001 through July 2002, almost 100% of the manpower and machine study time of the Pbar Source department was devoted to trying to reduce the horizontal emittance
- We believe that the horizontal emittance growth was caused by
- Intra-beam scattering (60%)
- Trapped ions (40%)
- The intra-beam scattering (IBS) heating of the beam is worse now for Run II than it was in Run I because of the changes in beta functions that were the result of the Accumulator Lattice Upgrade

- 4 February 03

## Overcoming IBS/Core Transverse Emittance

- 4 February 03

## Overcoming IBS/Core Transverse Emittance

- A two-fold plan to reduce the transverse emittance was developed:
- Better transverse stochastic cooling of the Accumulator core
- The bandwidth was increased by a factor of 2
- The center frequency of the band was increased by a factor of 1.5
- Dual lattice operation mode of the Accumulator
- Keep the “fast stacking” lattice (=0.012) for pbar production
- During shot setup, ramp the lattice with the beam at the core orbit to the “IBS” lattice (=0.022)
- The “shot” lattice will reduce the intra-beam scattering heating by a factor of 2.5
- The “shot” lattice will increase the cooling rate by a factor of two increase in mixing due to the change in 

- Bandwidth

- Center freq.

- Better Mixing

- Ions

- IBS

- Reduced IBS

- 4 February 03

## Accumulator Core Cooling Upgrade

- Initial Run II system consisted of a 2-4 GHz band and a 4-6 GHz band
- The 2-4 GHz band is ineffective because of the small value of 
- The 4-6 GHz band suffers from poor signal to noise.
- Replaced both core bands with a 3 band Debuncher style system
- Better sensitivity
- More bandwidth (2x)
- Better mixing factor (1.5x)

- 4 February 03

## Accumulator Core Cooling Upgrade

- Project was started 30 October 2001 and completed 15 June 2002 (7.5 months)
- 6 new cooling systems
- 4 new ultra-high vacuum tanks
- The effective cooling rate of the new system is 1.4x faster than the combined rate of the old systems

- 4 February 03

## Accumulator Core Cooling Upgrade

- With full system equalizers the new system will be 2.5x faster than the combined rate of the old systems
- vertical ones installed during recent  shutdown
- With an 82 mA stack, we have a peak signal to noise ratio of 8 dB at 7.5 GHz for a 7  mm-mrad normalized emittance

- 4 February 03

## Accumulator Core Cooling Upgrade

- Hot off the Network Analyzer...
- Core vertical performance with new equalizers installed

- before

- now

- 4 February 03

## Accumulator “Shot” Lattice

- An Accumulator lattice with a much smaller IBS heating term was designed
- The lattice was designed with the following constraints
- No hardware changes to the present quadrupole configuration.
- Same betatron tunes as the present Run II lattice
- Zero dispersion in the odd straight sectors
- High dispersion in the even straight sectors
- Correct betatron cooling phase advances
- Correct kicker phase advances
-  t < 5.5 ( < 0.022)

- 4 February 03

## Accumulator “Shot” Lattice

- 4 February 03

## Accumulator “Shot” Lattice

- Ramp Development began 9 April 2002 and dual lattice mode became operational July 2002
- Ramps are 100% efficient
- Tunes are controlled to within 0.0005
- Orbits are controlled to within +/- 1mm
- Ramping from the Stacking Lattice to the Shot Lattice adds about 15 minutes to shot setup
- mainly due to cooling core to within grasp of 4-8 GHz Momentum system.

- 4 February 03

## Accumulator “Shot” Lattice

- Final step was to build ramps to move remaining Pbars back to Stacking lattice
- Initially sent remaining stack (typically <20 mA) to Recycler or dumped it
- Restored orbit correctors, cooling, cycled buses on stacking lattice
- Resume stacking
- Ramps built and tested to mimic effects of hysteresis between two lattices
- Process automated and put into routine operation in early December 2002
- 100% efficient
- Luminosity enhancement
- faster than cycling buses
- Stack preserved

- 4 February 03

## Overcoming IBS/Core Transverse Emittance

- Upgrades perform as expected
- Factor of 2-3 reduction in core transverse emittance
- Almost immediate +40% impact on Luminosity
-  process now a routine operation, minimal time impact

- 4 February 03

## Overcoming IBS/Core Transverse Emittance

- 4 February 03

## Stacking Improvements

- Peak stacking rate of 13 x 1010 pbars per hour achieved
- 9 November 2002
- compared to 11 x 1010 in April
- Peak stack size of 225 x 1010 achieved
- early December
- previous best of 221 in 1995
- Peak weekly average 8.5 x 1010 /hour

- 4 February 03

## Stacking Improvements

- 4 February 03

## Reliability

- Since instituting ramps back to the stacking lattice, a period of 33 days, 7 hours, 10 minutes passed where there was a continuous stack in the Accumulator – 2nd all-time best.
- Since last AAC, 9 stacks inadvertently lost due to failures in 38 weeks of operation – one loss/month
- Some systems are showing signs of age, particularly RF systems
- Preventative Maintenance is a _MUST_

- 4 February 03

## Transfers to Tevatron

- Since cooling and lattice upgrades installed, pretty much status quo
- Shot-to-shot tuning to minimize total longitudinal emittance – maximize coalescing efficiency
- h=4 cavity impedance changed during recent shutdown to allow higher (x4) unstacking RF voltage  x2 reduction in longitudinal emittance

- 4 February 03

## Transfers to Tevatron

- Recent emittance growth between Accumulator and MI
-  obstacle in AP1 removed during shutdown
- ‘original’ equipment
- likely shifted by AP1 vacuum anomaly in November
- expect minimal impact on performance

- AP1 obstacle

- 4 February 03

## Transfers to Tevatron

- Longitudinal emittance of all bunches now routinely measured and recorded in SDA

- AP1 Wall current monitor 4-bunch display

- 4 February 03

## Transfers to Recycler

- Support Recycler transfers under different conditions
- Shoot ‘off of top’
- ‘Leftovers’ after Tevatron is loaded
- Dedicated stacks & transfers
- Since December 16 using dedicated stacks (20 - 40 mA) for Recycler commissioning
- rapid turnaround: 1-hour stacking to stacking time, aiming for 30 minutes
- stay on Stacking lattice
- do not worry greatly about beam line tune up
- do not wait for core to completely cool, but asymptotic limit is reached anyway
- amount to unstack determined by longitudinal emittance instead of intensity
- typically empty the stack in one or two transfers
- procedures applicable to faster Shot Set-Up times

- 4 February 03

## Transfers to Recycler

- Single transfers as good as 80% Accumulator to Recycler
- Short-term ‘stashing’ efficiency ~67%
- Longer-term performance requires work

- 4 February 03

## Stacking

- With antiproton source emittances under control, the focus of the Antiproton Source Department has shifted to increasing the stacking rate
- We have achieved
- an initial stacking rate of 13 x 1010 /hr
- An average a production efficiency greater than 15x10-6 pbars/proton
- An initial production interval of 2.2 seconds, 2.0 has been tried
- A stack of 160 x 1010 in a 20 hr period
- Our immediate goal is to achieve the initial Run II design goal of 18.5x1010 pbars/hour with no stack
- Production efficiency = 16x10-6 pbars/proton on target
- Initial production interval of 1.5 seconds
- Be able to stack to a 200 x 1010 stack in a 20 hr period.
- Stack at 16 x 1010 /hr for a stack size of 50 mA
- Stack at 13 x 1010 /hr for a stack size of 100 mA
- Stack at 9 x 1010 /hr for a stack size of 150 mA
- Be able to shoot from a 200 x 1010 stack with emittances below 10 mm-mrad (normalized)

- 4 February 03

## Stacking

- Stacking goals are achievable if we can reduce the initial production cycle time from the present 2.2 seconds to the design 1.5 seconds

- 4 February 03

## Why is the Cycle Time so Slow?

- Beam must be cleared off the Stack tail deposition orbit before next beam pulse
- The more gain the Stack tail has, the faster the pulse will move
- The Stack tail gain is limited by system instabilities between the core beam and the injected beam
- For a given Stack tail gain, the larger the momentum spread of the injected pulse, the longer it takes to clear the pulse from the Stack tail Deposition orbit
- The momentum spread coming from the Debuncher is too large

- Debuncher Momentum Spread vs. Cycle Time

- 4 February 03

## Stacking Projects

- Debuncher Momentum Cooling Improvements
- Smaller momentum spread delivered to Accumulator, which would permit faster cycle time. Faster cycle time would increase stacking rate at low and high stacks
- Transverse Debuncher Notch Filters for Bands 1 & 2
- Removal of longitudinal lines would permit for larger transverse cooling gain which would permit faster stacking cycle times.
- Commission Core Momentum-Stacktail Compensation Legs
- Keep the stacktail stable at high stacks. Stacktail gain could be increased. Faster stacking at large stacks would result.
- Implement Core Momentum “Spreading” during stacking
- Keep the stacktail stable at high stacks. Stacktail gain could be increased. Faster stacking at large stacks would result.
- Stacktail Notch Filter Upgrade
- Increasing bandwidth of the stacktail will permit faster stacking rates
- Develop Improved Transverse Compensation of the Stacktail
- Reduce heating of the transverse heating of the core via the stacktail which would permit a faster rep rate at large stacks.
- AP1 Bunch by Bunch length monitor
- Measure effective longitudinal emittance provided by MI so we can identify sources of emittance growth in MI. Reduce bunch length on target will permit for a faster stacking cycle time.

- 4 February 03

## Debuncher Cooling

- Debuncher Momentum width reaches an asymptotic limit; it should not
- Better control (<1 ps) between center frequencies of individual bands will help
- upgraded control installed this shutdown
- Reduce notch filter dispersion of each band
- new equalizer design in progress

- 4 February 03

## Accumulator Cooling

- Stack Tail Compensation attempted
- Core feedback on the Stack Tail was reduced at Stack Tail frequencies as expected
- But, too much gain at the core made the core unstable
- _a bust_
- Next step
- commission higher flux core momentum system used during stacking
- run 2-4 GHz and 4-8 GHz systems simultaneously
- Don’t go to big stacks....

- 4 February 03

## AP2/Debuncher

- 13 shifts spent since August with reverse protons into Debuncher and up AP2.
- Procedures developed to rapidly establish reverse protons
- Stack can be maintained
- Parasitic measurements while stacking as well

- 4 February 03

## AP2/Debuncher

- Use DRF1 to bunch beam, adjust extraction frequency
- orbits
- explore momentum aperture

- 4 February 03

## AP2/Debuncher

- AP2 BPM’s
- Kicker noise at downstream end
- investigation continues

- 4 February 03

## AP2/Debuncher

- Scraper studies
- Debuncher admittance measurements
- Compare against measurements with circulating beam
- Calibrate incoming emittance
- Momentum spread measurements

- 4 February 03

## AP2/Debuncher

- AP2+Debuncher horizontal admittance: 20.8mm-mrad
- Nov 4 reverse proton measurement was 25.9
- The AP2+Debuncher vertical admittance: 11.8mm-mrad
- Nov 4 reverse proton measurement was 18.9

- 4 February 03

## AP2/Debuncher

- Shutdown work
- 2 vertical trims installed
- Documentation of apertures/positions begun in cooperation with Technical division
- Cables pulled for 10 Debuncher motorized quadrupole stands
- Stand installation planned for summer 2003
- Stand are ready to go

- 4 February 03

## Summary

- Emittance Control projects perform as hoped for and have lived up to their expectations
- Stacking and general Pbar performance continues to improve
- Stacking rate within 70% of Run II design
- Pbar transfers are mature and the process is flexible
- Stacking with fast repetition rate to achieve design rate is a priority
- limitations in Debuncher and Stack Tail cooling
- Longer-term work, specifically AP2/Debuncher aperture work is picking up

- 4 February 03