Transcript thwdfel01 roper

Modelling the photon transport system
of the ALICE FEL using wavefront
propagation
Mark D Roper
Accelerator Science & Technology Centre
STFC Daresbury Laboratory
Talk Outline
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The Alice FEL & beamline
The modelling code
The propagation results
Conclusion
Questions
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
The ALICE FEL
• ALICE energy recovery linac with cavity FEL
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26 MeV beam energy
60 to 80 pC bunch charge
27 mm undulator period, 40 periods, variable gap
5.5 to 9 µm wavelength
100 µs macro-pulse at 10 Hz
1625 pulses within macro-pulse (16.25 MHz)
Pulse duration ~1 ps
Pulse energy ~3 µJ
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
The FEL Beamline
A complicated path dictated by the building
M1, M2, M4, M5, M6 are plane mirrors, 45° AoI
M3 is a toroidal collimating mirror, 75 mm diameter, 72.5° AoI.
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
The FOCUS Code
• Developed by Steven Higgins and Marion Bowler
• The Sommerfeld Propagation Integral is used for
propagation from every position R on a surface to
each point r on the next surface (mirror or image
plane)
where da is a surface
element on an aperture
(surface),  is the
wavelength, n is the
normal to the surface,
and the dot product gives
the obliquity factor.
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
The FOCUS Code
• The field at a set of points on a plane can be read in, or
Gaussian sources can be generated internally.
– Input field files are either ascii files compatible with the PHASE code
of Bahrdt, or binary files compatible with the FEL code Genesis1.3.
• Realistic surfaces can be generated by adding deviations to a
perfect surface (toroid, ellipse, plane), or by reading in the
surface positions at a set of points.
• The code is part of suite which can take input radiation field
pulses, Fourier transform to obtain the field as a function of
frequency, propagate individual frequencies and inversely
transform the fields to generate the output field pulse as a
function of time.
• The code is written in C++ and runs under Windows.
• Simple text I/O is used. The visualisation is carried out using
small stand-alone IDL codes.
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
The Propagations - Source
• A field file at the position of the out-coupling hole
was generated with Genesis and was used as the
source of the propagations
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
At the position of the diamond window
3.5 mm out-coupling hole
Mark D Roper
1.5 mm out-coupling hole
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Halfway between M2 and M3
3.5 mm out-coupling hole
Mark D Roper
1.5 mm out-coupling hole
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
At the position of M3
3.5 mm out-coupling hole
Mark D Roper
1.5 mm out-coupling hole
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
At the position of M5
3.5 mm out-coupling hole
Mark D Roper
1.5 mm out-coupling hole
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
12 m after the position of M3
3.5 mm out-coupling hole
Mark D Roper
1.5 mm out-coupling hole
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Conclusions
• Wavefront propagation has been used to
demonstrate the diffractive effects when mirrors
are overfilled
• The cavity out-coupling hole needs to be
considered as part of the optical design.
• The FEL output shows a near-perfect Gaussian
TEM00 mode.
• The value of wavefront propagation in FEL
beamline modelling is clearly demonstrated.
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory
Thank you for your attention
Mark D Roper
8 March 2012
FLS2012, Thomas Jefferson National Laboratory