1. RF Pulse Compression system for CTF3.
MDK Workshop, CERN, Geneva, April 2001
RF Pulse Compression system for CTF3.
I.Syratchev, CERN
MDK-2001
CERN
Switzerland

2.  RF Pulse Compression is the only way to
increase RF power level from the number
of klystrons available for CTF#3.
 RF phase/amplitude modulation is the tool
to control the RF pulse shape in a system -
klystron plus “SLED”-like RF pulse compressor.

3. RF Pulse Compression system for CTF3.
The flat pulse after the cavity based pulse compressor (LIPS), with
modulation of the input RF phase (PM).
The linear part of the phase slop will be
compensated with the frequency shift:
Tout = 
LIPS cavity Q0 =1.8x105, =8
2.3
Input
phase
Output 
2.1
6.5 sec
RF phase, degree
Power gain
5.5 sec
Time, ns
Time, ns

4. RF Pulse Compression system for CTF3.
The effect of residual RF phase sage and energy spread. R. Corsini
Energy spread
The residual phase
envelops after two
RF stations
1=60
2=80
1=80
2=60
1
minimized
2
Single bunches profiles after re-combination.
No energy spread

5. RF Pulse Compression system for CTF3.
The flat pulse after the cavity based pulse compressor (LIPS), with
modulation of the input RF phase-to-amplitude (PTA).
Time
LIPS
LIPS+PTA 1 2
Amplitude 1 2
Comparison between PTA and PM
Pros:
 Output pulse flat both in
RF amplitude and phase.
 Easy RF power level control.
 Better stability of operation.
Cons:
 Less efficient (~10%).
 Two klystrons needed.

6. RF Pulse Compression system for CTF3.
Power gain. PM
PTA
Klystron pulse, sec
Power gain
LIPS
Modified
# LIPS modification is mainly the adjusting of the cavity coupling.

7. RF Pulse Compression system for CTF3.
System operation stability.
The examples of the compressed RF pulse
distortion due to the klystron RF phase ripples.
Because of the energy spread, the
demand on the compressed pulse
flatness :
P/P < 2%
Time
Power
a) RF Phase modulation. Klystron
RF phase ripples 30 peak-to-peak.
The main sources of instability:
Klystron RF phase and amplitude
jitter as result of HV supply
instability. 1
Time
Power
b) RF Phase-to-amplitude modulation.
Klystron RF phase ripples 100 peak-to-peak. PM
P/P, %
PTA
Klystron’s RF phase amplitude
of ripples, degree.

8. RF Pulse Compression system for CTF3.
System operation stability. 2
The frequency deviation of the
storage cavity, mainly because
of the temperature variation.
The identity of the LIPS
cavities resonant frequencies. 3
F=-10 kHz
-3 kHz
-1 kHz
Time, ns
Power 2
P/P, % 3
F, kHz
To keep the flatness of the compressed pulse within specified P/P, the
temperature stabilization of the cavity must be < ± C.

9. RF Pulse Compression system for CTF3.
System operation stability.
Algorithm of the fast correction of the cavity frequency shift.
Standard “SLED”
Pulse
RF phase
modulation
Flat pulse
Distorted pulse
-10 kHz
Re-adjustment of the
RF phase modulation in
a fast local feedback
system of the klystron.
Old
New
Temperature control
system.
Flat pulse
RF phase
modulation

10. RF Pulse Compression system for CTF3.
Experiments with high RF power level. R. Bossart, December 2000.
Klystron output
RF phase
100
1.92
~100
Time
RF power
RF phase
1sec
Klystron
LIPS
RF phase
Time, ns
Klystron drive phase
Initial
RF phase ripples
correction
Parameters:
Q unloaded x105
Coupling
Tin sec
Tout sec
P out/in /18 MW
P gain/teor /2.04
P/P < 1%

11. RF Pulse Compression system for CTF3.
Barrel Open Cavity pulse compressor.
3 GHz version.
WHY?
1. We need at least four more RF pulse compressors.
2. The BOC has one cavity, operating in a travelling wave
regime - solves the problem of the cavity’s pair identity.
3. Easy to manufacture than LIPS. We can do it in CERN.
4. The test prototype is preparing for the high RF power test.

12. RF Pulse Compression system for CTF3.
The Barrel-cavity theory.
The eigen-frequency of the Barrel cavity with
Emnq oscillation is the solution of the next equation:
mn is a root of the Bessel function that for the
big m can be approximated as:
The optimal radius r0, when the external caustic
has the smallest height comes from:
where  and  are derived from:
Finally the height of the external caustic and Q-factor
of the cavity are: z
 = 
 =  r0 -d d 2h r 2a
Cavity profile

13. RF Pulse Compression system for CTF3.
The shape of the 3.0 GHz Barrel-cavity.
R150
R100(L)
any
R50(R2)
Q=1.9780*105
F= GHz
R *
R228(R1) *
197.75*
11.627(a)
60.150() R

14. RF Pulse Compression system for CTF3.
The modes of the 3.0 GHz Barrel-cavity.
H11,1,2
E10,1,1
H9,1,4
E8,1,3
H7,1,6
2.907 GHz
3.000 GHz
2.918 GHz
GHz
2.922 GHz
E7,2,1
E6,1,5
E5,2,3
3.081 GHz
GHz
3.097 GHz

15. RF Pulse Compression system for CTF3.
General view and technical sketch of the 3.0 GHz BOC
RF pulse compressor.

16. RF Pulse Compression system for CTF3.
Discussion...
Questions ?...