Transcript Diapositive 1 - CERN Accelerator School

The RF System of the Probe Beam Linac in CTF3
Franck Peauger, Alban Mosnier, Daniel Bogard, Gilles Dispau, Wilfrid Farabolini, Patrick Girardot, Jean Luc Jannin, CEA/DSM/DAPNIA, 91191 Gif-sur-Yvette Cedex, France
Alexej Grudiev, Gerard Mcmonagle, Jean Mourier, CERN, Geneva, Switzerland
Probe Beam Linac Parameters
Schematic layout of CTF3
The probe beam linac aims at
simulating the main beam of
CLIC in order to measure
precisely the performances of
the 30 GHz accelerating
structures
Schematic layout of the probe beam linac (CALIFES)
Parameters
Energy
Norm. rms emittance
DAPNIA / IN2P3 / CERN Collaboration
Specifications
200 Mev
Observations
0.33 ns
< 20 π mm mrad
Fit in 30 GHz structure acceptance
Energy spread
<2%
Measurement resolution
Bunch charge
Bunch spacing
0.2 nC
0.33 ns
~ CLIC Parameters
Number of bunches
1 – 64
Measure 30 GHz structure transients
Rms bunchlength
3 GHz
Avoid beam disruption in high RF fields
< 0.75 ps
Bunch length < 0.75 ps
30 GHz
Acceleration with 30 GHz
33 ps
RF Gun
Power phase shifter
Layout of the RF System
Slow Phase
Shifter 360 °
RF Generator
2.99855 GHz
Fast Phase
Shifter 180 °
E Field
Solid State
Pre-amplifier
The Power Phase Shifter is a 3 GHz scaling of the
one studied at SLAC at 11.4 GHz and consists of a
circular waveguide operating on the TE01 mode and
two wrap-around mode converter
PFN (25 cells)
300 W – 3 GHz
320 kV – 360 A
7.6 µs – 5 Hz
 0.25% ripple during 5.5 µs
DC Power Supply
21.5kV
+
-
Thyratron
Pulse
Transformer
45 MW – 3 GHz Klystron
SF6
1:15
TE10□
H Field
TE01○
The circular waveguide has an area with an
expanded diameter, inducing a reduction of the
waveguide length.
The length of this widened guide can be varied to
produce a phase variation.
45 MW – 5.5 µs
BOC Cavity
Klystron Gallery
Parameters
Beam Tunnel
90 MW
Peak RF Power
The RF components operates
mainly under a vacuum of 10-9
mbar. Losses in rectangular
waveguides are 0.02 dB/m
(WR284 in Copper)
4.5 dB
Splitter
Circ
3 dB
Splitter
25 MW
Sensitivity
1° / mm
Maximum course
200 mm
Precision
0.5 °
Stability
0.1 °
Bandwidth |S11|
Electric field simulation (HFSS)
< 27 MHz @ -30 dB
Electric field
90 MW – 1.4 µs
4.5 dB
Splitter
W
Specifications
Ampl
SF6
F
W
Taking into account the losses
in RF components, a total power
of approximately 70 MW is
delivered to the linac,
Phase
adjustment
by length of
waveguides
Power Phase Shifter
7 MW
SW Gun
F = - 90°
F=0°
F=0°
15 MW
25 MW
22 MW
TW
Acceleration
TW bunching
z axis
Electric field superposition for two positions
TW
Acceleration
bellows
3D mechanical model
Surface = 1535 x 400 mm, Heigth = 508 mm
2D mechanical drawing
Weight = 270 kg
Transient calculation in traveling wave section
Pulse compressor cavity
E Field
The Pulse compressor system is based
on a high Q0 storage cavity working on a
“whispering gallery” mode TM10, 1, 1
Q0 = 197 800 (calculated with HFSS)
f0 = 2.9985 GHz
β = Qx / Q0 = 6
Vg
Kn-1
A specific code, based on the
coupled resonator model has
been developed to study the
transient effects in the traveling
wave sections
H Field
The LIL section is a quasi
constant gradient structure,
composed of 9 constant
impedance families linked by 4
linearly tapered transition cells
Vr
Kn
n-1
n
Vn-1
Vn Vn+1
Lkn-1
Good directivity
provided by λg/4
multi-hole coupler
Equivalent circuit
Φg(t)
1 
V 
2 n
Forward wave Vg
vc(t)
vg(t)
Lk n
Yn
Lkn+1
differential equation relative to cell n
ic(t)
1
n+1
G
n
L
C
1
Qn n
Vn  Vn  K n 1 Vn 1  K n 1  K n Vn  K n Vn 1
Backward wave Vr = Vc - Vg

1
1 d
Vgn 
Qnn
 n2 dt
V


J (r , t ) Ean (r ) dV
n
Differential equation
200
Vr    Vr    Vg    Vg
150

Reflection coefficient
2Q0
1   0

 1
 1
Electric Field Amplitude (MV/m)
Filling time
Phase
(deg)
For a phase step of 57°, and a phase
variation until 180° over the total pulse
length,
100
50
0
-7.00E-06
-5.00E-06
-3.00E-06
-1.00E-06
t (s)
2
- Sinusoidal voltage

v  e Ve j0t
- Vg varies slowly compared to 0
- High Q0 factor
 
1
0

Vg  0
1.5
Ampl (Vr)
Approximations :
A flat top pulse is obtained :
1
- Voltage amplification factor = 1.45
0.5
- Power
0
-7.00E-06
-5.00E-06
-3.00E-06
t (s)
[email protected]
-1.00E-06
amplification factor = 2.1
Time (s)
Cell number