Prsentation PowerPoint

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Design of the RF photo-injector for the CTF3
experiment G. Bienvenu, B. Jacquemart, J.
Prevost, M. Desmond S. Mercier, C. Prevost, R.
Roux Laboratoire LAL, Université dOrsay, France
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-RF design 2D3D -Beam dynamics -Magnetism
Technical drawings
Vacuum
Test the calculations with a prototype
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RF 2D design Poisson
Fr 3.003 GHz Rs 6 MW Q 14530
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Beam loading and coupling
It requires a coupling 2.9 for the gun to be
matched in presence of beam
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RF 3D design HFSS
25 mm
10 mm
Coils

• Hole coupling
• Over-coupled
• symmetric

Coaxial coupling Strong coupling gt Antenna
goes deeply in the gun Big gradient with the
iris Breakdown hazards

• 3 conditions
• Fr
• Coupling
• Field flatness

Dimensions of the cells and the coupling hole
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Field Symmetry in the 3rd cell
Blow-up of the emittance
Asymmetry of transverse fields (couplers)
Solution racetrack shape of the cell instead of
cylindrical (J. Haimson)
y
Straight part 0.6 mm
x
Integral 5.10-4
7.10-4
3.5.10-5
Integral 10-4
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Dynamics of the electron beam
Accelerating sections
RF gun
coil
5.45 19.6 3.2 1.07 0.36
E (MeV) ex(pmmmrad) sx (mm) sz (mm) sg /g ()
Electric field from 2D design
PARMELA
I 3.51 A
Compensation of the space charge forces
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Vacuum
Monte-Carlo based simulations of the residual
pressure
P1
P2
P3

• Useless above 40 l/s
• Weak help of a supplementary pumping

20 l/s
20 l/s
minimize the out-gassing rate High temperature
bake
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Supplementary pumping
42 holes drilled in the gun walls
F 4 mm
cathode
envelop
Envelop around the gun coated with NEG
widening
Pumping holes
by 2
Pressure
1.10-9 mbar
Only hope reduce the out-gassing rate
(10-3) with a high t bake-out
Copper in oven 3 days, t 550C Fast cooling
with Ar jet 150C gtNo grain
Residual pressure lt 10-10mbar
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Impact on the RF design
Impact on Q and Rs negligible (-5) But presence
of a 4 MV/m peak electric field at the entrance
of the tubes gtbreakdown hazards?
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Impact on the magnetic coils
Aim Bz max ? 0.27 T on the gun, 0 on the
cathode Difficulties few available space, big
inner diameter (180 mm)
Several magnetic arrangements studied with
POISSON 2 coils possible but too close to
the current density limits gt3 coils with
moderate currents -375 A, 170 A and 250 A
coils
Beam dynamics simulations done with the POISSON
field e 18.3 pmmmrad
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ConclusionPerspectives
1) RF gun simulations completed, technical
drawing for prototype ready, OFHC copper rod
ordered technical drawings of preparation
chamber almost finished (delays in the drawings
due to improvements in RF design, vacuum and
magnetism) 2) Laser technical cahier des
charges written, waiting for a decision from the
administration 3) NEPAL room RF source
new RF pilot with the synchronization with the
laser almost finished klystron available but
waiting for a regional funding for the
modulator room itself cleaned and
renovation ordered radiation safety 2
levels of security - to stay in the existing
Basic Nuclear Installation (heavy to manage) -
work elsewhere with a lower requirement on the
radiation safety (ICPE in french) but it means
a bigger job and amount of money to build this
new room.