# Presentation: 228351

## Antiproton Source Studies and Stacking              

**Keith Gollwitzer**
**Antiproton Source**
**Accelerator Division**
**Fermilab**
**May 6, 2006**

## Basic Outline

- Pbar Source operation
- Stacking
- Unstacking
- Reverse protons
- November - December Studies
- January Studies
- Other Studies
- Stacking record

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Pbar Source Operations

- Stacking
- Un-stacking
- Reverse Protons

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Stacking

- Protons
- Slip Stacking in Main Injector at 8GeV
- 120 GeV extracted out of MI into Beam line P1-P2-AP1
- Hit Nickel alloy target in AP0
- Secondaries Beam Line AP2
- Pulsed Magnet bends 8GeV negatives into AP2
- AP2 designed admittance >35 mm-mrad
- Accepted beam emittance: >330 mm-mrad
- “Left bend” momentum selects ~5%
- ~1% of the secondaries are antiprotons at the end of AP2
- Debuncher
- Designed admittance is 35 mm-mrad
- Bunch Rotation in 50 turns reduces the momentum spread
- Stochastic Cooling
- Factor of 10 in longitudinal phase space
- Factor of 7-10 in both transverse phase space dimensions
- D/A Beam Line
- Short transfer beam line; designed 10 mm-mrad acceptance
- Accumulator
- RF system decelerates from injection to deposition orbit
- Stochastic Cooling
- Preserve Longitudinal phase space while increasing particle density by factor of 5000
- Factor of 3-5 in both transverse phase space dimensions

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Other Modes of Operation

- Unstacking
- RF system accelerates from core to extraction orbit
- Extracted into beam line to send beam to MI (8GeV)
- AP3
- Goes around target station
- AP1
- P2
- P1

- Reverse Protons
- 8GeV protons from MI extracted into P1 to P2 to AP1 to AP3 to
- Accumulator
- Studies; or
- D/A transfer
- Studies; or
- Debuncher
- Studies; or
- Extract up AP2

- The pbar core is unaffected during reverse proton studies with the exception of Accumulator and some D/A studies

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Reverse Protons Pitfalls 

- Debuncher RF cavities decelerate beam
- Overhead in de-tuning/tuning RF cavities

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Proposal of 2 weeks of Studies 

- We had reached the point where the instrumentation and orbit control made it possible to attempt:
- Determining the orbit offset with respect to the center of the quadrupoles of the Debuncher ring and the AP2 beam line
- Correct the orbit to minimize the orbit-quad center offsets
- Set the AP2-Debuncher injection region
- Proposed two week period of studies
- Studies two shifts a day
- Third shift stack to support a lower luminosity collider program
- Ask for early December

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Best Laid Plans...

- Dave McGinnis at the All Experimenters’ Meeting prior to Thanksgiving was describing the two week block of pbar studies
- Tevatron component failure during meeting
- Tuesday/Wednesday
- Scramble to find people for holiday weekend for start of studies
- Finished preliminary studies to set procedures to be used during studies period
- Institute third shift to investigate D/A beam line
- 15 days of reverse protons
- Debuncher: beam-quad center offsets, orbit correction and centered devices about new orbit
- D/A beam line studies done on owl shifts
- AP2 & Debuncher Injection region: scanning and setting strengths of kicker and septum
- AP2: beam-quad center offsets & orbit correction
- 4 days of stacking studies/start-up
- Steer secondaries beam onto AP2 reverse proton BPM positions
- Center Debuncher devices about beam
- General tune-up of kickers, RF, cooling systems, etc.

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Debuncher Work - 1

- Determination of orbit-quad center offset
- Change quad excitation and look for orbit change
- 68 quads have shunts
- 10 quads have ability to control excitation alone
- The rest are paired symmetrically about mid-point of straight section
- Concern about excitation of two quads at one time and determining offsets for each quad
- Did quad excitation orbits for nominal orbits as well as for two 1-bumps per plane
- Checked for consistency of change in offset determination with the change of orbit due to the 1-bumps
- Vertical Orbit Correction
- Attempted global fit to minimize orbit-quad center offsets
- Re-checked orbit-quad center offsets: no improvement
- Use of motorized quad stands as correction devices
- Local orbit corrections to minimize orbit-quad center offsets
- Re-check while working around the ring: all <1mm offset

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Debuncher Vertical Orbit Change

- Several places the orbit changed by ~1cm
- Angle change at injection area
- All vertical trims and a majority of the motorized quad stands were used to perform the correction

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Debuncher Work - 2

- Horizontal Orbit Correction
- Injection Region was only done
- Horizontal orbit-quad center offsets determined
- Centered motorized devices about orbit
- Total of 72 motors
- Lattice measurements were performed

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Setting Injection Region

- Extracted beam up AP2 from Debuncher and determine orbit-quad center for the three down-stream most quads
- Determined horizontal closed orbit and AP2 orbit are centered in quads.
- Set vertical closed orbit to nestle under the septum
- Determine kicker strength to center beam in septum
- Determine septum strength to put beam in the center of the three AP2 quads

- Gollwitzer -- UEC Meeting

- 5/6/2006

## AP2 Work

- Able to have reverse protons every 20 seconds
- Determine downstream AP2 orbit-quad center offsets
- Not able to do upstream due to bussed quads and few BPMs to make offset determination
- Corrected orbit to minimize offset
- Summary of orbit changes for reverse protons
- Several places big changes, largest 2cm
- Large vertical angle at the end of AP2
- Lattice measurements
- Installed new lattice which believed to better match Debuncher

- Gollwitzer -- UEC Meeting

- 5/6/2006

## AP2 Orbit Change

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Debuncher Limiting Aperture

- Running Wave  Debuncher transverse Schottkys

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Stacking Studies

- Steered secondaries to the vertical BPM positions found during the reverse proton studies
- Steered to horizontal downstream BPM positions
- Upstream, the momentum distribution affects the horizontal position
- Problems with AP2 orbit “wandering”
- Traced to 120GeV protons starting with Main Injector
- Associated with amount of time between cycles
- Consistent cycle time is best
- Developed auto orbit correction program
- Does 120GeV proton correction
- Then does AP2 secondaries correction
- Identified need for additional AP2 trims
- Centered Debuncher pickups

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Wandering Orbits and Autotune

- 5mm

- AP1

- H

- V

- H

- V

- Horiz.          AP2         Vert

- 10mm

- Before

- After

- 5mm

- 10mm

- Gollwitzer -- UEC Meeting

- 5/6/2006

## January

- Wrote up results from the December studies period
- Prepared to install new AP2 trims
- Prepared to remove Debuncher transverse Schottkys
- Determined if had more Debuncher quad shunt freedom, then be able to change lattice
- Increase Debuncher admittance
- Removes Vertical Band 4 Arrays as limiting aperture
- Control was split for 6 pairs of quads
- Second Tevatron Component failure

- Gollwitzer -- UEC Meeting

- 5/6/2006

## January Accesses

- Removed Debuncher transverse Schottkys
- Tune measurements
- replaced by stochastic cooling pickups
- Installed two of four AP2 trims
- Commissioned new trims
- Obstruction search of AP2 beam pipe
- Nothing Found

- Gollwitzer -- UEC Meeting

- 5/6/2006

## January Studies

- Reverse protons to correct horizontal Debuncher orbit to quad centers in straight sections
- Correction in arcs would lead to energy change that we were not prepared to do at the time
- Installed new Debuncher Lattice
- Small change to AP2 lattice for matching
- Centered Debuncher Devices about reverse proton orbit

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Debuncher Extraction

- Different horizontal orbit also affected extraction
- Optimized _D_ebuncher _EX_traction bump for D/A transfers
- Ramp correctors near end of Debuncher stacking cycle so that cooled smaller beam is closer to septum when kicker fires
- Also tuned extraction kicker and septum strengths to steer beam in D/A beam line

- Extraction Channel of Septum

- Time in cycle

***Large Injected Beam***
***Beam Cooled during cycle.***
***Rapidly ramp DEX bump at end of cycle. Puts beam    next to septum.***

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Next Limiting Aperture

- Running Wave identified the Extraction Kicker as the limiting aperture in both planes.
- Vertically bumped beam 2mm and essentially achieved goal
- Horizontally could bump beam 8mm and make admittance larger; but bump in dispersion changes beam energy

- Shutdown work includes a new motorize extraction kicker stand

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Stacking Cycle Time Study

- Last = 10th

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Accumulator Aperture

-  Spent 41⁄2 shifts of beam study time to improve the   Accumulator aperture (February).
- Identified an                                                                     aperture                                                                restriction
- Quad pickup                                                                has been                                                                  removed
- Scanned all                                                                 moveable                                                                 devices

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Accumulator Admittance

| Date |  | Injection | Central  | Core |
| --- | --- | --- | --- | --- |
| 8/25/1999 | H
V | 8.3 
9.6  | 10.0 
9.4  | 8.2 
7.7  |
| 2/15/2006
Start of studies | H
V |  | 6.3 
7.4  |  |
| 2/17/2006
End of studies | H
V | 6.3 
9.2  | 7.0 
7.9  | 6.6 
6.6  |

**Improvement**: Horizontal – 11%, Vertical – 7%
- Apertures remain substantially smaller than they were in 1999.

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Intensity Study – 4s Cycle Period

- Injected intensity into Accumulator

- Intensity at end of Debuncher cycle

- Intensity at end of AP2

- Stacking rate

- Proton beam on target

- Normalized to Beam on Target and 6 Booster turns

- Cooling was optimized after each change of proton intensity

- Many other diagnostics and settings were recorded
- - Flux to Accumulator is fine
- -- Look to Accumulator Cooling

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Stacktail & Core 4-8 GHz Systems

- Had been using 4-8 GHz system as a helper for the 2-4 GHz core system. Decided it was time to move to 4-8 GHz.
- Because the 4-8 GHz core system runs at twice the frequency, the electrodes are 1⁄2 the size so the system has a factor of two smaller momentum reach.
- Moving the core closer to Stacktail to accommodate the smaller reach resulted in system instabilities at moderate stacks.
- Several attempts were made and we learned from each
- We now
- Use the 2-4 GHz core momentum system to augment the hand-off between the Stacktail and the 4-8 GHz core momentum system
- Run the 4-8 GHz core momentum system at MUCH larger gain.
- Plans to increase the gain of the system
- Run the Stacktail during deposition debunching to pre-form the distribution to match the Stacktail profile
- Result --- 20.1 mA/hr

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Core 4-8 GHz Bandwidth

- 1 GHz of bandwidth at 7 GHz is ~3x more powerful than 1 GHz of bandwidth at 2.5 GHz
- By replacing the trunk coaxial cable with optical fiber, the 4-8 GHz system will be 5.7x more powerful than the  2-4 GHz system

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Stacking Performance

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Stacking Performance

- Best stacking for 1 hour for each day
- Average Stacking rate for a week

- Gollwitzer -- UEC Meeting

- 5/6/2006

## Summary

- We were able to take advantage of the Tevatron failures
- Two long periods of studies
- Due to instrumentation and orbit control upgrades of the past few years, significant progress was done on the Debuncher admittance and progress made on the AP2 orbit
- Work that keeps the proton beam on target consistent has been very helpful in stacking studies and progress
**Seen an almost 25% increase in stacking rate.**

- Gollwitzer -- UEC Meeting

- 5/6/2006