FFAG

Hardware development for EMMA

Electron Model with Many Applications

Electron Model with Muon Applications

C. Johnstone, Fermilab

NuFact05

INFN, Frascotti, Italy

June 21-26, 2005

FFAG

Design Information• Background

– Scaling vs. nonscaling

• Ring components– Rf– magnets

• Diagnostics– BPMs– OTRs– Single Wire Scanners

FFAG Scaling

vs.Linear Non-Scaling

As a function of momentum Parallel orbits Constant optical properties Orbit change, r, linear

As a function of momentum Nonparallel orbits Varying optics

resonance crossing Orbit change ~quadratic Smaller aperture requirements Simple magnets

min

FFAG

Optical layouts of FFAGs

• Scaling and nonscaling lattices can have identical optical structures

– FODO

– Doublet

– Triplet

Rf drifts

• The important difference is in the TOF vs. p, which is of particular importance for the linear non-scaling lattice: the FODO is 1.5 x (T1 + T2) as compared with the triplet (lower T implies less phase slip, more turns for fixed, high frequency rf)

FFAG

Momentum Compaction of Orbits

• Momentum Compaction,

– Measure of orbit similarity as a function of momentum (also isochronicity for relativistic beams)

– Measure of the compactness of orbits - 0, aperture 0

p

p

C

Cring

FFAG

Momentum compaction in scaling FFAGs

• Scaling FFAGs:

• Pathlength or TOF always increases with p

constant) a is(p

prC

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Momentum compaction in linear nonscaling FFAGs

• Linear non-scaling FFAGs:

)(

choices technicalare ''3.0

energyhigh at bend added0;

energy lowat bend reverse0;

quad. Fin point field-0 dipole, pure a ismagnet CF

-point gradient -0 theas definedorbit reference a is where

0

0

0

pppr

lBrlBp

pp

pp

p

p

p

cellF

F

Fo

Fo

cellcellF

FFAG

Cont….

• But, the transverse excursion cannot be ignored at low energy

• Eventually this transverse correction

overtakes the net decrease with low

momentum and C turns around

giving an approximate quadratic

dependence of C and TOF.

22

222

)1( FFt

Ft

lllr

lllr

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F

FFAG

What does this mean?

• Scaling FFAG can have only 1 fixed point, or orbit with is synchronous with the rf (fixed points are “turning” points in the phase slip relative to the rf waveform)– 1 turning point implies the beam slips back and forth across the rf crest

twice

• Linear nonscaling FFAG can have 2 fixed points (or 1)– Beam can optimally cross the rf crest 3 times

• By using two fixed points for maximal acceleration,

the ratio of extraction energy can be ~3:2

for nonscaling vs. scaling FFAGs Fixed points

FFAG Electron Model - Non-scaling Demonstration of New Accelerator Physics

Gutter Acceleration

asynchronous acceleration within a rotation manifold outside the rf bucket.

Momentum Compaction

Unprecedented compaction of momentum into a small aperture.

“Uncorrectable” Resonance Crossing

Rapid crossing of many resonances including integer and ½ integer; multi-resonance crossings in a single turn

Evolution of phase space

Under resonance conditions and gutter acceleration

Validate concept for muon acceleration

Characterize and optimize the complex parameter space for rapid muon accelerators

FFAGElectron Model - Construction

6m

– similar to the KEK ATF without straight sections (scaled down from 1.5 GeV to 20 MeV). Host: Daresbury Laboratory U.K. downstream of their 8-35 MeV Energy Recovery Linac Prototype (ERLP) of the 4th Generation Light Source (4GLS).

6m

FFAG Radiofrequency system

Adopt TESLA-style linear RF distribution scheme to reduce number of waveguides

R=1M, Q=1.4104

Where possible adopt designs already existing at the host laboratory.

1.3 GHz preferred over 3 GHz: reducing RF while magnet length is fixed, implies magnets become a smaller number of RF wavelengths. This implies smaller phase slip and more turns.

Adopt 1.3 GHz ELBE buncher cavity to be used at Daresbury 4GLS

Frequency variation of few 10-4 to investigate 1 or 2 fixed points operation.

20 cm straight for installation

FFAG Quadrupole Magnet

Fermilab Linac quadFermilab Linac quad

The 5cm-long upgrade Fermilab linac quadrupole has peak pole-tip field near 3.5 kG, and the bore is 5cm. This is ideal for the 3 cm orbit swing envisioned for the ring. The gradient is stronger than required and will likely require a different coil.

General requirements:•Gradient: 7 T/m•Slot length: 10 cm•Aperture: 40 mm wide, 25 mm high•Rep rate <1Hz

FFAGCombined function magnet

SpecificationsDipole component of 0.15 – 0.2 T

Slot length: 10 cmMagnetic length: 7cm

Quad component of ~4T/mMagnet spacing: 5 cmAperture (good field): 50 mm wide, 25 mm highField uniformity 1% at pole tipSpace for internal BPM1Hz operation or less

No coolingNo eddy current problems

FFAG

Dipole plus quad field lines

Dipole only field lines

Power the dipole component with permanent magnets

CompactNo power issuesThermally stable PM material

Power the quadrupole component with a (modified) Panofsky coil

Compatible with rectangular apertureRelatively short endsPermanent quad + trim coil ±20%

Magnet Concept (Vladimir Kashikhin, FNAL)

FFAG

Advantage of variable quad and dipole fields?

• Variable quad was felt to be most important for phase advance and resonance crossing controol

• Variable dipole allows exploration of acceleration with 1 fixed point (1/2 synchrotron oscillation around “bucket”) or 2 (gutter acceleration– Measure phase space and emittance dilution

• Both: different C /TOF parabolas– Asymmetric vs. symmetric

– Correct for errors/end field PotentialFixed points

FFAG

FFAG Combined Function MagnetV.S.Kashikhin, June 21, 2005

The proposed combined function magnet has C-type iron yoke and separate dipole and quadrupole windings. Each winding powered from individual power supply. They can be connected in series in accelerator ring. Dipole component

of magnetic field formed by parallel surfaces of iron poles. Quadrupole field component formed by sectional quadrupole winding placed into the pole slots. Such configuration provides independent regulation both field components.

Magnet parametersMagnet configuration C- type

Dipole field 0.15 TAdjustable quadrupole gradient 0 – 6.8 T/m

Dipole winding ampere-turns 7600 AQuadrupole pole winding ampere-turns 11638 A

Magnet body length 50 mm

CF magnet with independently variable dipole and quad fields

FFAG

2D modeling of new CF magnet

Flux lines at maximum dipole and quadrupole currents. Dipole coil (blue),Quadrupole (red).

FFAG Diagnostics • Diagnostic designs described here

– BPMs • bunch train/single bunch operation• Turn by turn data

– OTRs (Optical Transition Radiation)• Foils + detection• 108/bunch or lower for a bunch train• 109/bunch for single bunch operation – will require closer

examination for 108/bunch, single bunch operation

• Other diagnostics– Single Wire Scanners

• orbits are non-overlapping,• step increment microns

– Pepperpot • phase space measurements in extraction line

FFAG

1.3GHz button-type BPMs (FNAL Main Injector)1 set per magnet3 to 5 cm aperture20 micron resolution Internal mountingTurn by turn for ~10 turns109 electrons/bunch~66 nsec rotation period

BPM Specification - General

Digital receiver210 MHz adc sample rate12 bit resolution Single-bunch excitation of a filter as shown

105 MHz center frequency10 MHz bandwidthFilters must be stable and matched

adc must be synched to beam

BPM (Jim Crisp, FNAL)

-1

-0.5

0

0.5

1

0 20 40 60 80 100

FNAL MI BPM

Hardware and Single Bunch Operation

FFAG

FFAG

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FFAGEXAMPLE: Profiles from an OTR foil in the 120 GeV AP-1 proton line at Fermilab

FFAG

FFAG Beam Profile Diagnostics for the Fermilab Medium Energy Electron Cooler

Abstract—The Fermilab Recycler ring will employ an electron cooler to store and cool 8.9-GeV antiprotons. The cooler will be based on a Pelletron electrostatic accelerator working in an energy-recovery regime. Several techniques for determining the characteristics of the beam dynamics are being investigated. Beam profiles have been measured as a function of the beam line optics at the energy of 3.5-MeV in the current range of 10-4-1A, with a pulse duration of 2µs. The profiles were measured using optical transition radiation produced at the interface of a 250µm aluminum foil and also from YAG crystal luminescence.

15 20 25 30 35 40 450

20

40

60

80Horizont. profiles

10.12 mm

Marks on the OTR

SPA05=14 A

SPA05=9 A

SPA05=11 A

SPA05=0 A

I=0.975 A, F=-4 kV.

I(x),

rel. u

nits

X, mm

. 3-D image of the electron beam obtained with OTR monitor

Variation of the beam X-profile versus SPA05 lens current

FFAG Electron Model - Demonstrates:

Asynchronous 2-fixed pt. gutter Acceleration

Unprecedented compaction of momentum

Resonance Crossing

Evolution of phase space and

comparison with simulation

Validate concept for muon acceleration

FFAG Electron Model - Hardware and Measurements:

Full Complement of Diagnostics designed or available including

- Large aperture BPMs, OTR foils and detectors

- Single Wire Scanners, Pepperpots

Magnetic components designed or under design; short: 5-6 cm and strengths appear technically reasonable

Measure:

-orbits, orbit stability, injection stability

- probe injection phase space with a pencil beam

- tolerances : field, injection, contributions of end fields

-Evolution of phase space and comparison with simulation under different conditions of acceleration and resonance crossing

- optimization and operational stability of accelerator conditions