2. Wideband, solid-state driven RF systems for PSB and PS longitudinal damper.
M.Paoluzzi BE/RF 9 September 2014

3. Summary Configuration and limits Amplifier topology
RF Currents and amplifier in the PSB
RF Currents and amplifier in the PS Damper

4. Configuration and limits
At low and mid frequency, stacking more cores across
a gap linearly adds up the core impedances.
At high frequency the response is mainly limited by the structure capacitance that becomes effective earlier.
Full exploitation of wideband characteristics when using a single core on each side of the gap.
Core dimensions dictated by PSB limitation 330/200/25 mm, indirect cooling.
750 W
Water Tin=18 ˚C
Water Tout=33 ˚C
Flow = 3 litres/min
Assuming a maximum temperature of 100°C and a reasonable duty cycle each ring can dissipate 1 kW.
Power compatible with compact solid state amplifier.
2 rings 800Vpk above 400 kHz

5. Amplifier topology
Space available for the amplifier limited in the PSB.
In the available volume W power stages, combiner, driver and ancillaries could be stacked.
Power stages connectable as:
Single ended amp (16 to 1 combiner 3kW) two amps per gap.
Push Pull amp (2x 8 to 1 combiner 2x1.5kW) one amp per gap.
Input circuit with paralleled gates and driven by a high impedance stage (differential capacitive input for FB).
Important parameter :
N number of 200 W modules
n voltage transformation ratio drain to out.
Differential output : N=8, n=12
Single ended output : N=16, n=16

6. RF Currents
With narrowband ferrite loaded cavities the beam-cavity interaction is mainly limited to the harmonic component at cavity resonance.
The wideband response of the Finemet® loaded cells requires acting on more harmonics.
Assuming the gap impedance to be purely resistive (Rgap), frequency independent and driven by the generator and beam currents , to obtain the gap current:
IGap=VGap/Rgap
the generator must supply:
This simple relation can be applied to compute the generator current required for acceleration by setting VGap at the fundamental frequency at the required value.
It can also be used for computing what’s needed for cancelling the higher harmonic components zeroing the corresponding VGap.

7. MOSFETs’ saturation currents:
Currents in the PSB
Assume the acceleration cycles shown below and system composed of 12 accelerating cells (700Vpk each).
Maximum current is required around 1.74 MHz
Stable phase 45 and 50 degrees for 1.4 1013 and 2.5 1013 protons respectively.
The right hand side plots show the computed shapes of the beam and generator currents.
The maximum required generator currents are 16 A and 26 A.
With ID/IB = 1.5 the Push-Pull amplifier version can be used.
MOSFETs’ saturation currents:
Green VRF151
Violet SD2942
Blue MRF151
Red MRFE6VP6300

8. System with push pull amplifier
Amplifier for PSB
Feedback loop gain =10dB
System with push pull amplifier

9. Currents in the PS damper
2012
LIU Parameters
Beam type
LHC25ns
LHC50ns
TOF
Fixed target
Damper
Active
Inactive
Possibly active
Beam intensity
ppp
ppp
ppp
ppp
up to ppp
DC current
1.0 A
1.5 A
1.16 A
0.8 A
3.2 A
Current per spectral component, short bunch approximation
2 A
3 A
2.32 A
1.6 A
6.4 A
Peak current at transition
10.2 A
15.5 A
11.9 A
50 A
25 A
Bunch length
18 ns
40 ns
20 ns
Intensity per bunch at extraction
ppb
ppb
coasting beam
Peak current at extraction
17.3 A
26.8 A
100 A
4 ns
Duration of peak
~0.3 ms
~ 1ms
To produce the required 5 kV maximum voltage a six-cell system is used for the PS Damper.
A consistent part of the required RF current and power will be used for wake field cancellation.
Radiation issues impose the amplifier installation at some distance for the cavities (No FB possible).
The single ended amplifier solution gives more reserve.
MOSFETs’ saturation currents:
Green VRF151
Violet SD2942
Blue MRF151
Red MRFE6VP6300

10. Amplifier for the PS Damper
System with single ended amplifier