Muon Front Ends

Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory and Muon Collider

Contents

Future Accelerator Projects Requiring Muon Front Ends

Neutrino Factory

Muon Collider

Choice of Particle – why Muons?

Design Components and Options

Research Currently Underway

By both Grahame Rees and myself

The Neutrino Factory

Goal: To fire a focussed beam of neutrinos through the interior of the Earth

What’s the point?

Constrains post-Standard Model physics

But why does this involve muons?

Neutrinos appear only as decay products

Decaying an intense, high-speed beam of muons produces collimated neutrinos

The Neutrino Factory

p⁺ à p⁺ à m⁺ à e⁺n_en_m

Uses 4-5MW proton driver

Could be based on ISIS

The Muon Collider

Goal: to push the energy frontier in the lepton sector after the linear collider

p⁺ à p⁺,p⁻ à m⁺,m⁻à

Why Collide Muons?

Design Challenges

Must accelerate muons quickly, before they decay

Synchrotron acceleration is too slow

But once g is high, you have more time

High emittance of pions from the target

Use an accelerator with a really big aperture?

Or try beam cooling (emittance reduction)

In reality, do some of both

Muon Front End Components

Targetry, produces pions (p^±)

Pion to muon decay channel

Uses a series of wide-bore solenoids

“Phase rotation” systems

Aim for either low DE or short bunch length

Muon ionisation cooling (as in “MICE”)

Expensive components, re-use in cooling ring

Muon acceleration (RLAs vs. FFAGs)

The Decay Channel

Has to deal with the “beam” coming from the pion source

Pion half-life is 18ns or 12m at 200MeV

So make the decay channel about 30m long

Grahame designed an initial version

Used S/C solenoids to get a large aperture and high field (3T mostly, 20T around target)

Needed a better tracking code…

The Decay Channel (ctd.)

Developed a more accurate code

Used it to validate Grahame’s design…

3.1% of the pions/muons were captured

…and parameter search for the optimum

Within constraints: <4T field, >0.5m drifts, etc.

Increased transmission to 9.6%

Increased in the older code (PARMILA) too

Fixed a problem in the original design!

Two Phase Rotation Options

Chicane (2001)

FFAG-style magnets

Shortens the bunch

Have optimised matching

2.4% net transmission

No cooling?

31.4MHz RF (2003)

Reduces the energy spread

180±75MeV to ±23MeV

Feeds into cooling ring

RAL Design for Cooling Ring

10-20 turns

Uses H₂(l) or graphite absorbers

Cooling in all 3 planes

16% emittance loss per turn (probably)

Tracking and optimisation later this year…

BACKUP!

In case the time is longer than my slides.

Muon Acceleration Options

Accelerators must have a large aperture

Few turns (or linear) in low energy part, so muons don’t decay

Recirculating Linacs (RLAs, studied first)

FFAGs (cyclotron-like devices)

Grahame is playing with isochronous ones

NuFact Intensity Goals

“Success” is 10²¹ m⁺/yr in the storage ring

Tracking & Optimisation System

Distributed Computing

~450GHz of processing power

Can test millions of designs

Genetic Algorithms

Optimisation good up to 137 parameters…

Accelerator design-range specification language

Includes “C” interpreter

The Decay Channel

Has to deal with the “beam” coming from the pion source

Decay Channel Lattice

12 parameters

Solenoids alternated in field strength and narrowed according to a pattern

137 parameters

Varied everything individually

Improved Transmission

Decay channel:

Original design: 3.1% m⁺ out per p⁺ from rod

12-parameter optimisation à 6.5% m⁺/p⁺

1.88% through chicane

137 parameters à 9.6% m⁺/p⁺

2.24% through chicane

Re-optimised for chicane transmission:

Original design got 1.13%

12 parameters à 1.93%

137 parameters à 2.41%

Optimised Design for the Decay Channel (137 parameters)

Why did it make all the solenoid fields have the same sign?

Original design had alternating (FODO) solenoids

Optimiser independently chose a FOFO lattice

Has to do with the stability of off-energy particles

Design Optimised for Transmission Through Chicane

Nontrivial optimum found

Preferred length?

Narrowing can only be due to nonlinear end-fields


	Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory and Muon Collider


	Future Accelerator Projects Requiring Muon Front Ends
		Neutrino Factory
		Muon Collider
	Choice of Particle – why Muons?
	Design Components and Options
	Research Currently Underway
		By both Grahame Rees and myself


	Goal: To fire a focussed beam of neutrinos through the interior of the Earth
		What’s the point?
	Constrains post-Standard Model physics
		But why does this involve muons?
	Neutrinos appear only as decay products
	Decaying an intense, high-speed beam of muons produces collimated neutrinos


	p⁺ à p⁺ à m⁺ à e⁺n_en_m
	Uses 4-5MW proton driver
		Could be based on ISIS


	Goal: to push the energy frontier in the lepton sector after the linear collider
	p⁺ à p⁺,p⁻ à m⁺,m⁻à


	Must accelerate muons quickly, before they decay
		Synchrotron acceleration is too slow
		But once g is high, you have more time
	High emittance of pions from the target
		Use an accelerator with a really big aperture?
		Or try beam cooling (emittance reduction)
		In reality, do some of both


	Targetry, produces pions (p^±)
	Pion to muon decay channel
		Uses a series of wide-bore solenoids
	“Phase rotation” systems
		Aim for either low DE or short bunch length
	Muon ionisation cooling (as in “MICE”)
		Expensive components, re-use in cooling ring
	Muon acceleration (RLAs vs. FFAGs)


	Has to deal with the “beam” coming from the pion source
	Pion half-life is 18ns or 12m at 200MeV
		So make the decay channel about 30m long
	Grahame designed an initial version
		Used S/C solenoids to get a large aperture and high field (3T mostly, 20T around target)
	Needed a better tracking code…


Developed a more accurate code
Used it to validate Grahame’s design…
	3.1% of the pions/muons were captured
…and parameter search for the optimum
	Within constraints: <4T field, >0.5m drifts, etc.
	Increased transmission to 9.6%
		Increased in the older code (PARMILA) too
	Fixed a problem in the original design!


Chicane (2001)
	FFAG-style magnets
	Shortens the bunch
	Have optimised matching
		2.4% net transmission
	No cooling?
31.4MHz RF (2003)
	Reduces the energy spread
		180±75MeV to ±23MeV
	Feeds into cooling ring


	10-20 turns
	Uses H₂(l) or graphite absorbers
	Cooling in all 3 planes
	16% emittance loss per turn (probably)
	Tracking and optimisation later this year…


	Accelerators must have a large aperture
	Few turns (or linear) in low energy part, so muons don’t decay
	Recirculating Linacs (RLAs, studied first)
	FFAGs (cyclotron-like devices)
		Grahame is playing with isochronous ones


	Distributed Computing
		~450GHz of processing power
		Can test millions of designs
	Genetic Algorithms
		Optimisation good up to 137 parameters…
	Accelerator design-range specification language
		Includes “C” interpreter


	12 parameters
		Solenoids alternated in field strength and narrowed according to a pattern
	137 parameters
		Varied everything individually


Decay channel:
	Original design: 3.1% m⁺ out per p⁺ from rod
	12-parameter optimisation à 6.5% m⁺/p⁺
		1.88% through chicane
	137 parameters à 9.6% m⁺/p⁺
		2.24% through chicane
Re-optimised for chicane transmission:
	Original design got 1.13%
	12 parameters à 1.93%
	137 parameters à 2.41%


	Original design had alternating (FODO) solenoids
	Optimiser independently chose a FOFO lattice
	Has to do with the stability of off-energy particles


	Nontrivial optimum found
	Preferred length?
	Narrowing can only be due to nonlinear end-fields