nsFFAG questions - conform

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15 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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NON
-
SCALING FFAGs:

questions needing answers

Andy Wolski

The Cockcroft Institute,

and the University of Liverpool Department of Physics.





BASROC
-
CONFORM Project Open Day

Daresbury Laboratory

11 May 2009


What makes an FFAG different?

Promises:


High average current, high energy beams


Relatively compact, low
-
cost accelerator


Challenges:


Difficult technical subsystems


Complicated beam dynamics


Non
-
equilibrium operation

Injection and Extraction


Fields must be turned on and off in

less than one revolution period.


Fields must be large enough to deflect

bunches through large angles.


Components must fit into a very

confined space.


Field quality, stability and overall

reliability are all issues.


Can we construct injection/extraction systems
that meet the operational
requirements within
the space constraints?

Magnets


Lattice needs a large number of identical unit cells.


Accelerator components, including the magnets, need
to achieve high quality in a very compact space.

Can we control the field quality in the magnets
well enough to avoid

detrimental nonlinear

effects in the beam

dynamics?

Can we predict these

effects with sufficient

accuracy?

RF System

Revolution period varies with energy.

Three options for acceleration:


Asynchronous


Fixed
rf

frequency and relative phase.


Simplifies
rf

system, but leads to complicated longitudinal dynamics.


Synchronous


RF frequency and phase synchronised with time of flight.


Simplifies longitudinal dynamics, but requires high bandwidth cavities, with

complicated controls.


Harmonic jump


Fixed frequency; voltage and

or phase maybe variable.


Can we accelerate? What are the real
advantages/disadvantages with each option?

Diagnostics

Diagnostics are essential for

commissioning, tuning and operation.

Basic measurements include:


Bunch charge.


Bunch position.


Charge distribution.

Transverse and longitudinal diagnostics

will be needed. Issues include:


Dynamic range.


Accuracy.


Bandwidth.


Stability.

What are the essential diagnostics? What
functionality and performance are needed?

100 MeV proton beam extracted
from KEK FFAG.

Y. Mori, M. Aiba, ICFA Beam
Dynamics Newsletter 43 (2007)
27
-
37.

Beam Dynamics

We need to:


avoid particle loss;


maintain stability of the
trajectory;


preserve beam quality.

Can we model the beam
dynamics with sufficient
accuracy?

How do we best control the
beam with the complicated
dynamics of a
nsFFAG
?

Variation of betatron tunes

with energy in a nsFFAG.

(Resonance crossing.)

Collective Effects

Charged particles in a bunch interact with each
other and with their environment in a variety of
different ways:


Space charge.


Wake fields, and beam loading.


Ion trapping.


Intrabeam scattering.


Incoherent and coherent synchrotron radiation.

What effects will be important in a non
-
scaling FFAG?

How do we design and operate a
nsFFAG

to
avoid detrimental collective effects?

Pushing the limits

What are the limits on performance of a non
-
scaling FFAG, and how can we overcome them?


Acceleration


What is the largest acceleration factor that could
be achieved in a non
-
scaling FFAG?


Beam current


Is
multibunch

operation feasible?


Beam quality and stability


What issues are associated with resonance
crossing?


Reliability

Summary

Non
-
scaling
FFAGs

will present challenges for
design, commissioning and operation.

To maximize the potential of
nsFFAGs
, we will
need a better understanding of:


performance possibilities of technical
subsystems, including injection/extraction,
magnets,
rf
, and diagnostics;


non
-
equilibrium, nonlinear beam dynamics;


design and construction for stable, reliable
operation of non
-
equilibrium accelerators.