Transcript Introduction

FFAG Concepts and Studies
David Neuffer
Fermilab
Outline
 Introduction
 Feasibility studies use Linacs and recirculating linacs
 Need to develop “cheaper” acceleration
 FFAG Acceleration ??
 Fixed-field permits fast-acceleration
 ~10 turns possible ….
 FFAG Lattice styles (DIMAD simulations):
 “scaling” FFAG – Machida & Mori
 “non-scaling” FFAG – Johnstone
 FMC-like –Dejan Trbojevic
 Longitudinal Motion Constraints
 simulations
2
Study 2 Costs ….
 Study I, II -Factory – feasible but too expensive

Biggest cost item: acceleration (~600M$)
3
FFAG Acceleration?
 Linacs/RLA’s require a lot of rf
 RLA multiple-pass transports + spreader/recombiners
complicated and expensive
 Muons decay too quickly for fast-cycling magnets
 Need: Fixed-field lattice that can accept beam over large
energy spread (620 GeV ?) for multipass return
transports:
FFAG lattice ?
 With same transport for all turns can accelerate over more
turns: less rf.
 FFAG lattice can have large momentum acceptance;
large transverse acceptance; need less cooling
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POP-first Proton FFAG
 First Proton FFAG built and
operated
 All systems verified
(magnet, rf, injection)
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FFAG magnet- 150 MeV FFAG
 Figure shows yoke-free FFAG
triplet used for 150 MeV proton
FFAG
 150 MeV FFAG is under
construction (magnets done)
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PRISM – low-energy muon ring
 Low-energy muon source
e experiments …
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Japan Neutrino Factory Scenario
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JNF Scenario
 Use 50 GeV p-bunch to
produce pions
 Capture beam in 20-T  5-T
transport channel
 Short decay line; inject beam
directly into low-energy FFAG
 Capture beam in low-frequency
rf bucket
 Accelerate up chain of FFAGs
to 20GeV
 Inject into 20GeV storage ring
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“Scaling” FFAGS
 Lattice
Advantages:
•Naturally Zero chromaticity
Disadvantages:
•Large negative bends (large circumference …)
•Nonlinear fields (from rk expansion)
•Not isochronous
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JNF- FFAGs lattice design
 Lattices are “scaling” radialsector FFAGs
 Triplet focusing with reversebend D-quads
 Low to high energy orbit width
is ~0.5m




0.3  1.0 GeV,
1  3.0 GeV
3.010 GeV
10 20 GeV FFAGs
 Lattices have been generated
using SAD, DIMAD
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Parameters for JNF FFAG lattices
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Acceleration and Decay
 Acceleration must avoid
muon decay
dN 
ds
dE
ds
1
N
L
 eVrf
m c 2
 LeVrf
E
 0
N 0  E 
N

m c 2
 LeVrf

E0



E

e
V
s
0
rf


 Need ~1MV/m to avoid
decay (2 MV/m gradient
in cavities)
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Acceleration Parameters
 For acceleration, use superconducting (smaller-radius) FFAGs
 At 1MV/m, ~ 10 turns acceleration / FFAG
 Assume harmonic h = 1 on lowest-energy FFAG; keep frequency
constant
 h = 1  4.75 MHz rf (???)
 Initial beam from decay
 300150MeV/c; 10ns

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Scenario requires ~2MV/m rf
 Harmonic=1 (for lowest energy
FFAG) implies 4.75 MHz;
 Harmonic=2 implies 9.5 MHz;
works OK in 1-D simulation
 Experience indicates 26MHz
cavity is more realistic
(Iwashita)
 Use 26 MHz + 3rd harmonic ?
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Longitudinal Motion in FFAG
 Equations of motion:
E n  E n1  eVrf sin(n )
 P  k 1 

s
n  n1  2h  
 1
 Ps  



1
 Motion is not very isochronous
 h = 1 and h = 2 accelerations
are OK;
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Injection and Extraction
 Requires fast, large-aperture
kickers; particularly for lowenergy FFAGs
 Risetime for 1GeV FFAG must
be less than 200ns; 20 GeV
FFAG can be > 1s
 Example: 150MeV FFAG
will need 500g, 0.6m, 150ns
 1GeV FFAG needs ~0.53 T-m
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“Non-scaling” FFAG (Johnstone)
 620 GeV lattice; C=2100m
F
D
 Basic lattice unit is FODO cell
~7m long;
 Primary bending magnet is
“D”;
 Lattice is more isochronous
 (transition at ~13 GeV)
 B = constant (tune varies
with energy)
 Good linear behavior …
(but large chromaticity …)
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Dejan Trbojevic Lattice
 1020 GeV
 270m circumference
 Strong focusing to very
small dispersion:
 6cm
 No negative bends at
central energy
 Chromaticity corrected:
Tune (E) more nearly
constant (but does cross
integers)
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Summary
 FFAG accelerators have been built and operated at KEK




POP FFAG
150 MeV FFAG (under construction)
PRISM (proposed)
RIKEN radioactive ion FFAG
 FFAG accelerators could be used in neutrino factory
 Need magnet, rf , injection/extraction R&D
 Muon production and cooling options to be explored
 Comparisons with other design approaches are not completed
 FFAG or RLA or linac or ???
 Cost estimates ???
 Integration into complete neutrino factory scenario is also required
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