Accelerators 2007
Wakefields and the nsFFAG
Roger Barlow
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide2
Wakefields
• Leading particles affect trailing particles through induced charges and currents
• Simulation in Merlin and other programs
• Investigate through EM codes
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide3
From bunches to point particles
Bunch wake (modes 1-4) Delta wake (modes 1-4)
Fourier Deconvolution
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide4
Fourier Fact
The Fourier Transform of a ‘Causal Function’ – f(x) which is zero for all x<0 – can be written explicitly
Write series as (r goes from –N to N )dr=b0+ak sin(kr/N) + bk cos(kr/N)
Or d=b0+S a + C bTo have dr=0 for all (-N+1)<r<0 requires
a =(2/N) ( S b0 + S C b)To have d-N=0 requires
b0=b1-b2+b3-b4…For any b, the causality requirement uniquely specifies
b0 and a
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide5
FFAG Progress
Like a synchrotron
Strong Focussing (‘Alternating Gradient’)
Dipole field increases with particle energy
But through path variation not time variationdB/dt not B/t
Orbit changes with energy
RF changes slightly
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide6
EMMA
Proof of principle machine
10 to 20 MeV electrons
42 cells
~16m circumference
RF every other cell
1.3GHz, TESLA frequency
magnets ~ 5cm x 2.5cm
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide7
EMMA
FuturePresent
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide8
EMMA Progress
Production Magnets ordered
RF prototypes ordered
Main components on site Summer 2008
Assembly 2008-9
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide9
Other FFAG stuff
PAMELA – design for hadron therapy machine
Applications –
• Medical/Biological (Surrey)
• Neutron source (Leeds)
• ADSR (Manchester/Leeds)
Manchester Christmas Meeting
Roger Barlow - Accelerators Slide10
Plan
Work on ILC - insofar as we are allowed
Work on CLIC (much in common)
Build and run EMMA
Look at other nsFFAG uses