Maria Elena Angoletta

The new digital-receiver-based system for antiproton beam diagnostics

An innovative system to measure antiproton beam intensity, momentum spread and mean momentum in CERNs Antiproton Decelerator (AD) is described. This system is based on a state-of-the-art digital receiver (DRX) board, consisting of 8 digital down-converter (DDC) chips and one digital signal processor (DSP). An ultra-low-noise, wide-band AC beam transformer (0.2 MHz -30 MHz) is used to measure AC beam current modulation. For bunched beams, the intensity is obtained by measuring the amplitude of the fundamental and second RF Fourier components. On the magnetic plateaus the beam is debunched for stochastic or electron cooling and longitudinal beam properties (intensity, momentum spread and mean momentum) are measured by FFT-based spectral analysis of Schottky signals. The system thus provides real time information characterising the machine performance; it has been used for troubleshooting and to fine-tune the AD, thus achieving further improved performances. This system has been operating since May 2000 and typical results are presented.

Upgrades to the digital receiver-based low-intensity beam diagnostics for CERN AD

The CERN AD low-intensity beam multidiagnostics (LIMD) has been upgraded as planned since 2001 by adding tune measurements during ramps and plateaus, based on the beam transfer function (BTF) method. This relies on transversally exciting the beam by a deflector and deriving the BTF and coherence function from FFTs of excitation and beam response recorded by digital receivers (DRX). These, continuously tuned to a betatron sideband, pass data to a digital signal processor (DSP) on the DRX board for data processing. The upgrades discussed also include increased longitudinal frequency range, noise reduction measures and digital flags for setup of data acquisition (DAQ) and processing parameters.

JACoW : Machine Development Studies in the CERN PS Booster, in 2016

The paper presents the outstanding studies performed in 2016 in preparation of the PS Booster upgrade, within the LHC Injector Upgrade project (LIU), to provide twice higher brightness and intensity to the High-Luminosity LHC.Major changes include the increase of injection and extraction energy, the implementation of a H− charge-exchange injection system, the replacement of the present Main Power Supply and the deployment of a new RF system (and related Low-Level), based on the Finemet technology. Although the major improvements will be visible only after the upgrade, the present machine can already benefit of the work done, in terms of better brightness, transmission and improved reproducibility of the present operational beams. Studies address the space-charge limitations at low energy, for which a detailed optics model is needed and for which mitigation measurements are under study, and the blow-up reduction at injection in the downstream machine, for which the beams need careful preparation and transmission. Moreover they address the requirements and the reliability of new beam instrumentation and hardware that is being installed in view of LIU.

A New Orbit System for the CERN Antiproton Decelerator

This contribution will describe the new orbit system foreseen for the Antiproton Decelerator (AD) located at CERN. The AD decelerates antiprotons from 3.57 GeV/c down to 100 MeV/c, with an intensity ranging from 1×10 7 to 5×10 particles. The orbit system developed is based on 7 34 horizontal and 29 vertical electrostatic beam position monitors (BPMs) fitted with existing low noise front-end amplifiers. After amplification, the BPM signals will be digitized and down-mixed to baseband, decimated and filtered before computation to extract the position. The digital acquisition part of the orbit measurement system is based on the VME Switched Serial (VXS) enhancement of the VME64x standard and includes VITA57 standard FPGA Mezzanine Cards (FMC). The system is foreseen to measure complete orbits every 2.5 ms with a resolution of 0.1 mm. INTRODUCTION The AD ring [1] is a synchrotron where ~3x10 7 antiprotons produced from a production target are injected at 3.57 GeV/c. After RF manipulation and stochastic cooling, the beam is decelerated in several stages involving additional stochastic cooling, electron cooling and RF manipulation, before the antiprotons are extracted at 100 MeV/c. The AD revolution frequency varies from 1.59 MHz down to 174.5 kHz during the deceleration cycle. Fig. 1 shows a schematic view of the AD deceleration cycle and the essentials of its operation. Figure 1: Basic AD deceleration cycle. The present AD orbit system [2] has a limited performance in terms of time resolution since it is a multiplexed system acquiring signals from one BPM at a time. This allows for a complete orbit measurement only every 1.2 seconds. The new requirement of orbit measurements on the deceleration ramps involves moving to a parallel system where each BPM signal has its own analogue to digital converter (ADC) channel. The new beam position system will use the same 63 BPMs as well as the head amplifiers of the present system, but with the reception amplifiers, the digital acquisition system as well as the front-end software totally updated. The aim for the new system is to measure complete orbits every 2.5 ms with a resolution of 0.1 mm. FRONT-END ELECTRONICS Beam Position Monitors The new orbit system acquires the signals from 34 horizonal and 29 vertical electrostatic BPMs. The sigma (Σ) signal is provided by a specific annular electrode while the delta (Δ) signals are derived from two semi-sinusoidal electrodes. The Δ signal level in the electrodes for 1x10 particles is 4.2 μVp with a BPM differential sensitivity of 0.1 μVp/mm.

Beam Loss in the Low Energy Ion Ring (LEIR) in the Light of the LHC Injector Upgrade for Ions (LIU-Ions)

For the LHC injector upgrade for Ions (LIU Ions), the Low Energy Ion Ring (LEIR) is requested to deliver twice the intensity per extraction compared to the last Pb54+ ion run in 2013 [1]. As the number of injected ions has been increased into LEIR, a fast loss is observed during the RFcapture of the electron cooled ion beam, and this loss today leads to an effective saturation of the available ion intensity at extraction. Based on chromaticity measurements with Pb54+ beam in LEIR with bunched beam and during acceleration in February 2013 [2], we suspected the chromaticity of the LEIR machine to be wrong in the vertical plane. To investigate the stationary behavior of the LEIR machine, we have developed a new method to measure the machine chromaticity on the low energy flat bottom of LEIR during a single cycle, where the ion beam is un-bunched and coasting. The new method controls the ion beam momentum by the LEIR electron cooler beam rather than the LEIR RF-system. The new method uses the LEIR Schottky system to measure the applied momentum change rather than the radial beam position offset in dispersive regions. The existing tune measurement system is used to measure the tune in the same way as in the classic way involving the RF-system and bunched ion beam. The new method allows a single-cycle-chromaticity measurement of coasting and un-bunched beam with high accuracy and no dependency of cycle-to-cycle machine variation.

Ions for LHC: Beam Physics and Engineering Challenges

The first phase of the heavy ion physics program at the LHC aims to provide lead-lead collisions at energies of 5.5 TeV per colliding nucleon pair and ion-ion luminosity of 1027cm-2s-1. The transformation of CERN’s ion injector complex (Linac3-LEIR-PS-SPS) presents a number of beam physics and engineering challenges, which are described in this paper. In the LHC itself, there are fundamental performance limitations due to various beam loss mechanisms. To study these without risk of damage there will be an initial period of operation with a reduced number of nominal intensity bunches. While reducing the work required to commission the LHC with ions in 2008, this will still enable early physics discoveries.