SIMULATIONS OF THE ACCELERATION IN TWO-BEAM
TEST STAND IN CTF3 AND COMPARISON
WITH THE MEASUREMENTS
Oleksiy Kononenko
BE/RF/SR, CERN
1. Analyzed Energy Measurements
Analyzed energy measurements (events) in TBTS including the corresponding
timestamps are gathered here:
http://elogbook.cern.ch/eLogbook/eLogbook.jsp?shiftId=1032364
http://elogbook.cern.ch/eLogbook/eLogbook.jsp?shiftId=1032385
http://elogbook.cern.ch/eLogbook/eLogbook.jsp?shiftId=1032677
Temperature, C
37
50
55
60
Number of Events
17
6
5
11
Table 1. Total number of the analyzed events at different temperatures
2. HFSS Simulations
Figure 1. One quarter of the TD24_tank (12WDSDVG1.8T) accelerating structure
installed in TBTS
0
-5
-10
-15
dB
S11
S
-20
12
-25
-30
-35
-40
11.85
11.9
11.95
12
12.05
Frequency, GHz
Figure 2. Results of the S-parameters HFSS simulation
-2-
7000
+
abs(V )
6000
Voltage, V
5000
4000
3000
2000
1000
0
11.96
11.97
11.98
11.99
12
12.01
12.02
12.03
12.04
Frequency,GHz
Figure 3. Accelerating voltage for the input power of 4W in frequency domain
3. Acquisition System
-3-
Figure 4. PETS and accelerating structure in TBTS layout
In the acquisition data array dt_CK_COND_TBTS_EventAcquisition
structure was used. Input signal PSI0631 appeared to be non reliable so the
PPI0431 signal was used:
pxPPetsOutFwd_values – power amplitude, 2ns time step
pxUSignal28_values – power phase, 4ns time step
petsAttAttP – is a fraction of the power which goes from PETS to AS
accAttTranP – is an attenuation by the coupler before the AS (!)
where x=1,2,3 and px are the consecutive pulses. Finally to calculate the power at
the input of the AS the following formula was used:
Pin = pxPPetsOutFwd_values * petsAttAttP * accAttTranP
For the transmitted through the AS power PTI0631 signal was used:
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pxPAcs1OutFwd_values – power, 2ns step
pxUSignal12_values – phase, 4ns step
The data (power amplitude and phase) were averaged over the 3 consecutive
pulses for each energy measurement:
30
|P |
1

20
1
|P |
2
2
10
|P |
3

|P
Power, MW / Phase, Degrees
0
3
|
mean

mean
-10
-20
-30
-40
-50
-60
-70
0
50
100
150
200
250
Time, ns
Figure 5. Averaging of the power amplitude and phase over the 3 consecutive
pulses
4. Simulation of the Energy Gain
-5-
To calculate accelerating voltage in TBTS we use this formula:
Vacc(t) = conv(Pin(t), VR(t))
where VR(t) is the time response of the structure, Pin(t) is an input power.
35
30
Energy Gain, MeV
25
20
CTF3, t=37C
Simulation, f=0MHz
Steady-state, f=0MHz
CTF3, t=50C
Simulation, f=0MHz
CTF3, t=55C
Simulation, f=0MHz
CTF3, t=60C
Simulation, f=0MHz
Steady-state, f=0MHz
15
10
5
0
0
10
20
30
40
50
60
Peak Power, MWt
70
80
90
100
Figure 6. No detuning simulations and measurements of the acceleration in TD24
at different temperatures.
To simulate detuning of the structure the frequency response of the structure
shown in Fig. 3. was shifted in frequency by Δf. Assuming that initially the
structure was +10 MHz off at 30C and taking into account that there is 1 MHz per
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5C detuning dependence we introduce detuning in the simulation and compare it
with the measurements.
35
30
Energy Gain, MeV
25
20
15
CTF3, t=37C
Simulation, f=9MHz
Steady-state, f=9MHz
CTF3, t=50C
Simulation, f=6MHz
Steady-state, f=6MHz
CTF3, t=55C
Simulation, f=5MHz
Steady-state, f=5MHz
CTF3, t=60C
Simulation, f=4MHz
Steady-state, f=4MHz
Steady-state, f=0MHz
10
5
0
0
10
20
30
40
50
60
70
80
90
Peak Power, MWt
Figure 7. Simulations and measurements of the acceleration in TD24
at different temperatures.
5. Calculation of the transmitted power
To calculate a transmitted power for a given input pulse Pin(t) we use the
following formula:
Ptrans(t) = conv(Pin(t), S12(t))
where S12(t) is an inverse Fourier transform of S12(f) shown in the Fig. 2.
-7-
100
35
Simulation
30
Measurement
Power, MW
25
20
15
10
5
0
0
50
100
150
200
250
Time, ns
Figure 8. Measured transmitted pulse (measurement with the timestamp of
1292350133766000000) and the corresponding simulated one.
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