Abstract
New projects being implemented or planned at CERN, such as the LHC Injectors Upgrade (LIU), the High-Luminosity LHC (HL-LHC) or the Future Circular Collider (FCC), motivate the change of several architectural paradigms in the Low Level RF systems (LLRF). In the upgraded Super Proton Synchrotron (SPS) LLRF, the distribution of RF, the revolution frequency, settings and synchronization timings will rely on a deterministic link, the White Rabbit (WR), exploiting a distributed topology. The digital electronics (FPGA) will now use a fixed frequency clock extracted locally in each node from this data stream. The paper presents a new solution for algorithms that treat beam-induced perturbations as they must solve the challenge to tune their processing to the instantaneous revolution frequency, Beam Synchronous Processing (BSP). We use dynamic resampling of uniform sampled data as tuning element between a sweeping spectrum and the static processing implemented with fixed frequency clocks. The paper applies the novel Beam Synchronous Processing method to transient beam loading compensation. It presents a One Turn delay FeedBack (OTFB) for the SPS based on a cascade of two variable ratio resamplers.
Highlights
1.1 Motivation and platformThe CERN LHC Injectors Upgrade (LIU) project plans to double the intensity extracted from the Super Proton Synchrotron (SPS) for injection into the Large Hadron Collider (LHC), requiring a major upgrade of the SPS 200 MHz RF system, including the power plant, layout and cavities [1]
The old system was using beam synchronous clocks for the electronics dealing with longitudinal instabilities (One Turn delay FeedBack, OTFB [3]), resulting in clock frequency sweeping during the acceleration ramp
The input resampler performs the conversion of the fixed sampling rate, at which the data arrives into this Beam Synchronous Processing (BSP) region, to a new sampling period proportional to the beam revolution period
Summary
The CERN LHC Injectors Upgrade (LIU) project plans to double the intensity extracted from the Super Proton Synchrotron (SPS) for injection into the Large Hadron Collider (LHC), requiring a major upgrade of the SPS 200 MHz RF system, including the power plant, layout and cavities [1]. This system is responsible for the acceleration of all beams by means of travelling wave structures that consist of a periodic arrangement of drift-tube cells with a p/2 phase advance between cells at the center frequency (200.222 MHz) [2]. It is entirely replaced with state-of-the-art technology during LS2, implemented on the uTCA platform [6]
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