Abstracts Brochure - CERN

TUPCH198
TUPCH199
TUPCH200
27-Jun-06 16:00 - 18:00 TUPCH — Poster Session
National Synchrotron Radiation Research Center (NSRRC) in Taiwan. An existing low-level RF system was modified
and expanded for function integration with the SRF modules.
LINAC RF Control System of Spallation Neutron Source
The new RF control system (LLRF) currently
L.R. Doolittle (LBNL) H. Ma (ORNL)
commissioned throughout SNS LINAC
evolved from three design iterations over
one year intensive R&D. Its digital hardware implementation is efficient, and has succeeded in achieving a minimum
latency of less than 150 ns which is the key for accomplishing an all digital feedback control for the full bandwidth.
The implementation also includes the provision of a time-shared input channel for superior phase differential measurement
between the cavity field and the reference. A companion co-simulation system for the digital hardware
was developed to ensure a reliable long-term supportability. A large effort has also been made in the software
development for supporting the operation of the commissioned systems to deal with the practical issues such as the
process automation, cavity filling, beam loading compensation, and the cavity mechanical resonance suppression.
Digital Low-level RF Control with Non-IQ Sampling for Higher Precision
The success of digital feedback with synchro-
L.R. Doolittle (LBNL) H. Ma (ORNL)
nous IQ sampling for cavity field control in
recent accelerator projects make this LLRF
control scheme a popular choice. This short-period synchronous sampling does not, however, average out wellknown
defects in modern ADC and DAC hardware. That limits the achievable control precision for digital IQ LLRF
controllers, while demands for precision are increasing for future accelerators such as ILC. For this reason, a collaborated
effort is developing a digital LLRF control evaluation platform to experiment using coherent sampling with
much longer synchronous periods, on the order of the cavity closed-loop bandwidth. This exercise will develop and
test the hardware and software needed to meet greater future RF control challenges.
Amplitude Linearizers for PEP-II 1.2 MW Klystrons and LLRF Systems
D. Van Winkle, J.D. Fox, T. Mastorides, C.H. Rivetta, D. Teytelman
(SLAC)
218
The PEP-II B-factory has aggressive current
increases planned for luminosity through
2008. At 2.2 A (HER) on 4 A (LER) currents,
longitudinal growth rates will exceed
the damping rates achievable in the existing low level RF and longitudinal low mode feedback systems. Klystron
gain non-linearity has been shown to be a key contributor to these increased growth rates through time domain
non-linear modeling and machine measurements. Four prototype klystron amplitude modulation linearizers have
been developed to explore improved linearity in the LLRF system. The linearizers operate at 475 MHz with 15 dB
dynamic range and 1 MHz linear control bandwidth. Results from lab measurements and high current beam tests
are presented. Future development progress and production designs are detailed.