LBNL, Berkeley, California
Traditional rf processing systems have involved heterodyned rf processing based on mixing a Local Oscillator to up and down convert rf signals through a baseband I/Q or Mag/Phase processing channel. These systems were traditionally custom engineered for each accelerator application. Recent technical developments in rf processing and the development of sufficiently fast reprogrammable digital processing functions lead to development of general-purpose rf processing functions which can incorporate a mix of heterodyned and direct digital down/up-converted processing ("software radio"). This general-purpose approach allows one design of hardware to be applicable to many rf processing tasks, where the firmware and software in the programmable functions define the application. An example design, with applications to linac LLRF control loops and electro-optic timing reference stabilization is presented.
BARC, Trombay, Mumbai
Indian Institute of Technology Bombay, Mumbai
CERN, Geneva
An RF system model has been created for the CERN Linac2 Tanks. RF systems in this linac have both single and double feed architectures. The main elements of these systems are: RF power amplifier, main resonator, feed-line and the amplitude and phase feedback loops. The model of the composite system is derived by suitably concatenating the models of these individual sub-systems. For computational efficiency the modeling has been carried out in the base band. The signals are expressed in in-phase - quadrature domain, where the response of the resonator is expressed using two linear differential equations, making it valid for large signal conditions. MATLAB/SIMULINK has been used for creating the model. The model has been found useful in predicting the system behaviour, especially during the transients. In the paper we present the details of the model, highlighting the methodology, which could be easily extended to multiple feed RF systems.
NETS, Fuchu-shi
KEK, Ibaraki
Intermediate-frequency conversion technique has been widely used for rf signal detection. However, this technique has disadvantages such as temperature dependence higher order modes of downconverters. One of our recent attractive developments is the high-speed data acquisition system that combines commercial FPGA board ML555 and fast ADC (ADS5474 14bit, maximum 400MS/s and bandwidth of 1.4 GHz). Direct measurements of 1.3 GHz rf signals are carried out with 270 MHz sampling. The direct sampling method can eliminate a down-converter and avoid calibration of non-linearity of the down-converter. These results are analyzed and compared with conventional measurement system.
SLAC, Menlo Park, California
Funding: Work supported by U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) begins operation this year with 83 new stripline beam position monitor (BPM) processors. System requirements include several-micron position resolution for single-bunch beam charge of 200 pC. We describe the processing scheme, system specifications, commissioning experience, and performance measurements.