# Presentation: 340698

## The FNAL Proton Complex and its Evolution                          for NuMI and mu2e 

- Dave McGinnis
- Fermilab Wine and Cheese
- September 15 2006

## Brief Post MECA History

- January 2006:  Peter Yamin & Jim Miller organized a meeting at BNL between Fermilab people & ex-MECO people interested in the possibility of a e conversion experiment at FNAL.
- We agreed to explore possible concepts for the required proton beam at Fermilab, &  if things look promising, to arrange a follow-up meeting at Fermilab (meeting taking place now).
- Over the last few months the Fermilab “group” has met once every 2-3 weeks with lots of discussion enlightened by some modest work.
- We think we have arrived at an attractive concept, but its at an early stage (no engineering and many details needing attention).
- Along the way we have been encouraged at FNAL (by Directorate & PAC) to explore the possibilities.

## Interested Fermilab Scientists

- * Ad hoc steering group members

- 15 Scientists
- 50% from Accelerator Division, 50% from Particle Physics Division

## Stages

- Stage 1: The Proton Plan.
- Booster aperture upgrades
- Slip stacking in the Main Injector
- Stage 2: SNUMI 1
- Slip Stacking in the Recycler
- Main Injector “Load and Go”
- Main Injector Cycle time reduces from 2.1 sec to 1.3 sec
- Stage 3: SNUMI 2
- Proton momentum stacking in the Accumulator
- Box Car stacking in the Recycler
- Main Injector “Load and Go”

## Booster Throughput Scenarios

- All the proton upgrades rely on increased Booster throughput

## Multi-stage Proton Accumulator Motivation

- Slip stacking multiple Booster batches in either the Main Injector or the Recycler is the central concept for proton fluxes up to 14x1016 protons/hour
- Longitudinal stacking at 8 GeV reduces the peak intensity requirement in the Booster
- Results in a smaller required aperture for the Booster
- Smaller space charge tune shift
- Reduced requirements on acceleration efficiency
- Above 14x1016 protons/hour, the number of batches stacked into the Recycler can not be increased further by slip stacking because of the rather severe amount of emittance dilution that is fundamental to the slip stacking process.
- Momentum Stacking has much smaller longitudinal emittance dilution than slip stacking and can be used in place of slip stacking to achieve proton fluxes greater than 14x1016

## Multi-stage Proton Accumulator Scheme

- Momentum stack in the Accumulator
- Inject in a newly accelerated Booster batch every 67 mS onto the high momentum orbit of the Accumulator
- Decelerate new batch towards core orbit and merge with existing beam
- Momentum stack 3-4 Booster batches
- Extract a single Accumulator batch
- Every 200 – 270 mS
- At an intensity of 3-4x a single Booster batch
- Box Car Stack in the Recycler
- Load in a new Accumulator batch every 200-270mS
- Place six Accumulator batches sequentially around the Recycler
- Load the Main Injector in a single turn

## Mechanics of Momentum Stacking

- The Accumulator was designed for momentum stacking
- Large momentum aperture ~ 84 x 2.8 eV-Sec
- Injection kickers are located in 9m of dispersion
- Injection kickers do not affect core beam
- 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

## Momentum Stacking

- Output longitudinal emittance = 84 * 0.38 eV-sec

- Input longitudinal emittance = 84 * 0.08 eV-sec

## New Transfer Lines to the Antiproton Source

- After acceleration in the Booster, the beam will be transferred _DIRECTLY_ to the Accumulator ring
- The Booster is connected to the Accumulator via a _new_ AP4 Line
- The line comes in A30 underneath the Debuncher The Accumulator is connected to MI-8 line for SNUMI injection via the new AP5 Line

## Mu2e and SNUMI

## -to-e Extraction Line

- The Accumulator is connected to the Debuncher for -to-e injection via the reversed D-A line (A-D line)
- The beam is slow spilled extracted from the Debuncher at either D30 or D50
- At D30, the extracted beam goes towards AP3
- At D350, the extracted beam heads west

## Location of Mu2E target and Detector

- Detector

**Target**

- Extracted
- Beam Line
- From
- Debuncher

**AP-10**

**AP-30**

**AP-50**

**MI-8**

**Giese Road**

## Resonant Slow Extraction

- Extraction scheme appears workable
- Studying details of resonance generation
-  Also comparing 2nd integer vs. 3rd integer
- Extraction loss a worry
- ~ 500W loss with typical (2-3%) resonant extraction inefficiencies
- Must be considered from the beginning in the design

- D4Q3

- D4Q2

- D50Q

- D5Q2

- options:

- MI/TeV style septum    - 80kV/1cm field region    - 3 m long

- Short version of MI style Lambertson    - ~ .8T field region    - +- 5” extraction aperture        - 1 m long

- Wide aperture C magnet     - ~.8 T     - 2 m

## Beam Requirements

- To reach MECO goal: Requires ~1020 primary 8 GeV protons per year with the right bunch structure.
- Bunch lengths short compared to the lifetime of muons orbiting a nucleus (1.1 ms for Al)
- with a bunch spacing longer than this time
- but not too much longer since we want to minimize peak rates.
- Experimental signature:
- mono-energetic electron & nothing else.
- To minimize backgrounds, when there is no incoming primary beam there must be no beam at the level of 1 part in 109.
- Ideal Bunch Structure for the slow muons (& for the primary protons)

## Proton Beam Specification

| Beam Energy | 8 GeV |
| --- | --- |
| Bunch Trains / sec:  fTRAIN | 0.682 |
| Bunch Spacing:   TB | 1.6 s |
| No. of bunches/train:   NB | 85×104 |
| No. protons/bunch:  nP | 2.16  107 |
| Bunch Length (2.5s) : tB | 150 ns  (s=60ns) |
| Protons/train  (4 batches) | 1.84  1013 |
| Protons/year (107 secs) | 1.25  1020 |

- Example:  4.6  1012 protons per Booster Batch & a 1.467s MI cycle

- Four years running  5  1020 protons  1.3  1018 stopped muons

## Beam Bunching for mu2e

- Bunch beam to a fraction of the Debuncher circumference
- < ~200ns of 1700ns
- Keep beam leakage outside that bunch length to a minimum
- Debuncher timings are similarto MECO/BNL
- Develop most effective/efficient bunching scheme
- barrier bucket
- Multi-harmonic
- Will need a fast kicker in the Debuncher ring to further clean gap.

- Multi-harmonic example
- rf multi-harmonic buncher
- Example: h=1, Vrf=30kV; h=2, Vrf = 15kV, h=3,  Vrf =10kV
- h=4: 7.5 50kV (to hold compressed beam)
- 0.055s for bunching

## Multi-stage Proton Accumulator Issues

- Once the SNUMI group provides a conceptual design report for slip-stacking in the Recycler, it will begin to further develop the concept of momentum stacking in the Accumulator.
- List of  Issues
- Momentum Stacking
- Booster throughput
- Transfer line design
- Space charge effects in the Accumulator and Recycler
- Radiation shielding
- Beam-loading
- Transition crossing in the Main Injector
- Instabilities (electron cloud, coupled bunch, etc.)
- Mu2e Accelerator Issues
- Slow Spill system in the Debuncher
- Beam loss in the Debuncher
- Extinction of unwanted particles in bunch gap
- Fast Kicker design for beam cleaning
- Dump design for beam cleaning
- Transfer line design to experiment

## Summary

- Momentum stacking has much smaller longitudinal emittance dilution than slip stacking and can be used in place of slip stacking to achieve proton fluxes much greater than 14x1016/hour
- Because the Accumulator was designed for momentum stacking, the present antiproton production complex can be converted into a multi-stage proton accumulator
- Accumulator -> Momentum Stacker
- Recycler -> Box Car Stacker
- Debuncher -> Slow Spill to mu2e
- The multi-stage proton accumulator can supply enough protons for a 1.1 MW 120 GeV beam and 1x1020 8 GeV protons / year for mu2e.