Transcript Diapositiva 1

CAS course "Introduction to Accelerator Physics" – Zakopane, Poland, 1 – 13 October 2006
C. Pagani, A. Bosotti, P. Michelato, N. Panzeri, R. Paparella, P. Pierini
INFN Milano - LASA, Italy
Abstract
A coaxial (blade) tuner solution has been developed for the compensation of the Lorentz force detuning of the superconducting cavities under the high gradient
pulsed operation foreseen for ILC operation. The device is based on prototypes successfully tested at DESY in 2002 both on CHECHIA and on the
superstructures inserted in the TTF string. An improvement of the tuner characteristics has now been designed by the integration of fast tuning capabilities by
means of piezo-ceramic element. Two prototypes of the new INFN coaxial piezo blade tuner have been manufactured and will be tested in the near future at
DESY and BESSY after integration with the cavities. Meanwhile also the control electronics is under developing based on a FPGA electronic platform, a
SIMCON 3.1 board from DESY LLRF group led by S. Simrock. Once completed it will allow to implement a first prototype of a complete blade tuner control
system. Here the blade tuner design and its main characteristics are presented, together with the latest results from the activity on electronics.
Two complete prototypes, including He tanks and piezo actuators, have
been manufactured. Tests were initially foreseen on summer 2006 at
DESY and BESSY after the final tuner integration with two existing TTF
cavities, but higher priorities for the Module 6 assembly operation at
DESY lead to a delay in the testing program.
Piezo system:
The threaded bars:
Recently, a fast, piezo-based,
tuning action has been added
to the blade tuner concept. In
the picture it’s possible to see
the piezoelectric elements
acting between the ring-blade
assembly and the outer ring.
The four threaded bars, parallel to the piezo elements
accomplish two different tasks: first of all they are needed
during transportation, handling and assembly phases to
avoid inelastic deformations of the bellow. In this case
they are tightly bolted at both ends to provide stiffness to
the system. Furthermore, in the operating condition, the
inner bolts are loosened by few hundredths of mm and the
bars act as safety devices in case of piezo mechanical
failure or overpressure conditions inside the Helium tank
The piezo actuators provide
fast tuning capabilities needed
for Lorentz Force Detuning
(LFD) compensation and
microphonics stabilization.
The movement
leverage:
The bending rings:
The ring-blade assembly, consists
of three different rings: one of the
external rings is rigidly connected
to the helium tank, while the
central one is symmetrically
divided in two halves.
Modified Helium
tank:
The central arm is connected to
the bending system to produce
the right rotation and the correct
axial movement for the tuning.
The rings are connected by thin
titanium plates (blades) that can
change the cavity length
(compression and tension) as a
results of an azimuthally rotation
in opposite direction of the two
halves of the central ring.
Because the tuner is fixed
to the helium tank, a
bellow is needed between
the two fixed rings. The
position of pad supports
has been reviewed in order
to minimize the bending
forces on the helium tank
bellow and, of course, on
piezo elements.
Two existing blade
tuner assemblies have
been equipped with a
revised leverage
system. With respect to
the original system
used for the TTF
superstructures, the
leverage system has
been rotated to one
side, in order to avoid
the mechanical
interferences with the
Invar rod providing the
cavity longitudinal
alignment in the TTF
CRY3 design.
Tuner control system schematic view:
Step
Motor
Controller
Courtesy of DESY LLRF group
Motor
Driver
Open
Loop
Controller
Analog equipment:
• Phase detector
Plant
• Filter amplifier
• Piezoelectric actuator
driver
Phase
Detector
+
RF
reference
-
Closed
Loop
Controller
+
+
• RF line (probe, delay
etc.)
Piezo
Driver
FPGA
Digital
Controller
A preliminary approach to the needs of open loop control of the
Lorentz Force Detuning is to generate a custom piezo control signal
with proper and tunable shape and timing
(referred to a master sync input signal).
A simple and low chip-area consuming FPGA algorithm that
handle such issue has been implemented.
Digital equipment:
SIMCON 3.1 board main features:
• Fast ADC & DAC
RF Probe
• Signal processing stage
(DSP or FPGA)
•
•
•
•
•
single low latency PCB board, VME standard based
10 analog input channels, AD6645 ADC’s up to 105 MSPS, 14 bit
4 analog output channels, AD9772A DAC’s up to 160 MSPS, 14 bit
XILINX Virtex II-Pro FPGA chip - main processing unit
ALTERA ACEX FPGA chip - VME and Internal Interface interpreter
• tunable delay from master sync
• custom shape and length of the pulse
• 10 ms time resolution to build up the pulse pattern
• only 1% of chip logic resources needed
• up to 10 ms pulse length
• discrete state-space implementation
The Closed Loop stage could instead be forced to implement, for the
sake of stability and performance of the loop, a digital filter with
detailed transfer function, both in amplitude and phase.
Then an algorithm has been developed for state-space
computations FPGA implementation, in this particular case the
design has been chosen in order to keep as low as possible
the logic resources requested.
• 32 bit fixed-point computations
• 7% of chip logic resources needed
State Space
Order
Maximum achievable
sampling frequency
[kHz]
64
20
32
100
16
300
Simulink schematic of State-Space algorithm