# Presentation: 809845

## Accumulator/Debuncher as Versatile Proton Facility

- Eric Prebys/FNAL-AD

## Motiviation

- If the proposed Proton Source upgrades are moderately successful, there will be excess 8 GeV proton capacity even in the NOvA era
- Up to 33 kW (~5e20 protons/year)
- Problem
- because the Booster lattice magnets are in a rapid cycling resonant circuit (i.e. no flat top), we are extremely limited as the beam structure we can provide
- 53 MHz with some ability to bunch rotate and control total batch length
- Specific need: Muon to Electron Conversion (mu2e, formerly MECO)
- Wants ~4E20 protons
- Short (<200 ns) bunches separated by 1-2 sec
- Not available from Booster

## MI 1.33sec=20 Booster Pulses

## Attractive Features of Debuncher

- Large Acceptance
- Low chromaticity
- Long, dispersion-free segments
- Lots of open straight sections after cooling hardware removed
- Problem:
- Getting protons there

## Present Operation of Debuncher/Accumulator

- Protons are accelerated to 120 GeV in Main Injector and extracted to pBar target
- pBars are collected and phase rotated in the “Debuncher”
- Transferred to the “Accumulator”, where they are cooled and stacked
- Antiproton capabilities not needed after collider program
- Not used in SNuMI I

## Original Proposal: Add-on to SNuMI (McGinnis) Scheme

- New AP4 line built to inject 8 GeV protons directly from Booster to accumulator, where they are momentum stacked.
- New AP5 line used to extract protons to Recycler, where they are boxcar stacked while the Main Injector is ramping.
- Recycler load transferred to Main Injector, where it is accelerated to 120 GeV for neutrino program.
- Could put some protons in Debuncher
- Problems:
- SNuMI not particularly likely at this point
- If SNuMI happens, there won’t be excess protons

##  Recycler “Boomerang Scheme” (Ankenbrandt and Popovic)

-  Recycler “Boomerang Scheme” (Ankenbrandt and Popovic)

- MI-8 to Recycler will be  built for NOvA

- New Extraction (doesn’t need to be fast)

- Existing “reverse proton” path

- Recycler(Main Injector Tunnel)

- Minor beamline modifications
- NO civil construction!!

## Momentum Stacking

- Inject in a newly accelerated Booster batch every 67 mS onto the low momentum orbit of the Accumulator
- The freshly injected batch is accelerated towards the core orbit where it is merged and debunched into the core orbit
- Momentum stack 3-4 Booster batches

- T<133ms

- T=134ms

## Longitudinal stacking in the Accumulator 

**Longitudinal stacking in the Accumulator **

- ΔEfull = 20 MeV

## Hybrid scheme 

**Accumulator **
- Momentum stack 1 to 6 booster batches
- Adiabatically bunch at h=1- **4kV**
- 500ns gap for kicker
- Some beam/halo cleaning in Acc and transfer
- Adiabatic easier at T=5.5
- Transfer to Debuncher
**Debuncher**
- h=1 90-degree phase rotation at fixed voltage
**40kV** - 0.007s
- Capture and store at h=4
- ~**200** to 250 kV ~0.02s;   = 42ns fairly long bunch
- Beam halo cleaning also  ....

## Bunch, Rotate, Store scenario

## Resonance driver placement

- Consideration
- Want to arrange drivers in groups, with the magnets in each group separated by ~multiples of  in 27
- Really only need two groups, but for the moment will work with three because of the natural symmetry of the Debuncher.
- Choose
- Six locations just inside of the ’07 quads at the ends of the straight sections

- Pairs indicated by color

## Basic Resonant Extraction Parameters

- Close to 29/3

- Large Acceptance

- A bit tight: will need to bump beam over prior to extraction

## Other Possibilities

- Single turn extraction for Muon Cooling experiments (mentioned by A. Jansson)
- Great flexibility in beam structure for other experiments
- Accelerator physics facility, particularly during experiment construction.
- In Project X era, can inject protons from Recycler for up to ~5 times more protons.

## Summary

- With small effort, we can adapt the Accumulator/Debuncher as a versatile proton facility.
- This would allow Fermilab to pursue the compelling physics of muon to electron conversion.
- Has potential for other uses
- Further reading
- Miller, Prebys, *et al*, “Expression of Interest: Muon to Electron Conversion Experiment at Fermilab”, FERMILAB-TM-2389-AD-E (and supporting references)
- Mu2e Collaboration Meeting talks
- https://indico.fnal.gov/conferenceDisplay.py?confId=1072