15-01-2014, 03:43 PM
Prototype Control System for Compensation of Superconducting Cavities Detuning Using
Piezoelectric Actuators
[attachment=59901]
Abstract
Pulsed operation of high gradient superconducting
radio frequency (SCRF) cavities results in dynamic Lorentz
force detuning (LFD) approaching or exceeding the bandwidth
of the cavity of order of a few hundreds of Hz. The resulting
modulation of the resonance frequency of the cavity is leading
to a perturbation of the amplitude and phase of the accelerating
field, which can be controlled only at the expense of RF power.
Presently, at various labs, a piezoelectric fast tuner based on an
active compensation scheme for the resonance frequency control
of the cavity is under study. The tests already performed in the
Free Electron Laser in Hamburg (FLASH), proved the possibility
of Lorentz force detuning compensation by the means of the piezo
element excited with the single period of sine wave prior to the RF
pulse. The X-Ray Free Electron Laser (X-FEL) accelerator, which
is now under development in Deutsche Elektronen—Synchrotron
(DESY), will consists of around 800 cavities with a fast tuner
fixture including the actuator/sensor configuration. Therefore, it
is necessary to design a distributed control system which would
be able to supervise around 25 RF stations, each one comprised
of 32 cavities.
INTRODUCTION AND BACKGROUND
INEAR accelerators such as FELs (Free Electron Lasers)
use superconducting resonant cavities to accelerate elec-
tron beam to high energies. The cavities are powered by pulsing
RF waves that interact with the walls made of niobium due to
the Lorentz forces.
EXPERIMENTAL RESULTS
The prototype 32-channel piezo control system was tem-
porarily installed in the FLASH facility. The system was
connected to three 8-channel piezo driver units to be able to
compensate 24 cavities equipped with piezo elements in the
accelerating modules ACC 3, 5 and 6. A proper MatLab script
was written to measure the detunings of all tested cavities using
data from monitoring ADCs and DOOCS server. The FLASH
accelerator modules ACC 2, 3 and ACC 4, 5, 6 were operated
with gradients of 15.34 MV/m and 11.66 MV/m, respectively.
The cavity detuning was first measured without compensation
and then the compensation system was turned on. The piezo
feedforward tables were tuned with proper amplitude and time
advance to the RF field pulse to obtain the successful result on
Lorentz force detuning compensation.
CONCLUSIONS AND DISCUSSION
Compensation of Lorentz force detuning at high operating
gradients was successfully demonstrated by using a prototype
piezo control system and fast piezo tuners mounted in ACC 3, 5
and 6 modules in FLASH accelerator. The control system was
tested using basic feedforward control scheme.
Piezoelectric Actuators
[attachment=59901]
Abstract
Pulsed operation of high gradient superconducting
radio frequency (SCRF) cavities results in dynamic Lorentz
force detuning (LFD) approaching or exceeding the bandwidth
of the cavity of order of a few hundreds of Hz. The resulting
modulation of the resonance frequency of the cavity is leading
to a perturbation of the amplitude and phase of the accelerating
field, which can be controlled only at the expense of RF power.
Presently, at various labs, a piezoelectric fast tuner based on an
active compensation scheme for the resonance frequency control
of the cavity is under study. The tests already performed in the
Free Electron Laser in Hamburg (FLASH), proved the possibility
of Lorentz force detuning compensation by the means of the piezo
element excited with the single period of sine wave prior to the RF
pulse. The X-Ray Free Electron Laser (X-FEL) accelerator, which
is now under development in Deutsche Elektronen—Synchrotron
(DESY), will consists of around 800 cavities with a fast tuner
fixture including the actuator/sensor configuration. Therefore, it
is necessary to design a distributed control system which would
be able to supervise around 25 RF stations, each one comprised
of 32 cavities.
INTRODUCTION AND BACKGROUND
INEAR accelerators such as FELs (Free Electron Lasers)
use superconducting resonant cavities to accelerate elec-
tron beam to high energies. The cavities are powered by pulsing
RF waves that interact with the walls made of niobium due to
the Lorentz forces.
EXPERIMENTAL RESULTS
The prototype 32-channel piezo control system was tem-
porarily installed in the FLASH facility. The system was
connected to three 8-channel piezo driver units to be able to
compensate 24 cavities equipped with piezo elements in the
accelerating modules ACC 3, 5 and 6. A proper MatLab script
was written to measure the detunings of all tested cavities using
data from monitoring ADCs and DOOCS server. The FLASH
accelerator modules ACC 2, 3 and ACC 4, 5, 6 were operated
with gradients of 15.34 MV/m and 11.66 MV/m, respectively.
The cavity detuning was first measured without compensation
and then the compensation system was turned on. The piezo
feedforward tables were tuned with proper amplitude and time
advance to the RF field pulse to obtain the successful result on
Lorentz force detuning compensation.
CONCLUSIONS AND DISCUSSION
Compensation of Lorentz force detuning at high operating
gradients was successfully demonstrated by using a prototype
piezo control system and fast piezo tuners mounted in ACC 3, 5
and 6 modules in FLASH accelerator. The control system was
tested using basic feedforward control scheme.