Higher Order Modes (HOMs) can severely limit the operation of superconducting cavities in a linear accelerator with high beam current, high duty factor and complex pulse structure. Therefore, the full HOM spectrum has to be analysed in detail to identify potentially dangerous modes already during the design phase and to define their damping requirements. For this purpose a dedicated beam dynamics simulation code, Simulation of higher order Mode Dynamics (SMD), focusing on beam-HOM interaction, has been developed in the frame of this project. SMD allows to analyse the beam behaviour under the presence of HOMs, taking into account many important effects, such as for example the HOM frequency spread, beam input jitter, different chopping patterns, as well as klystron and alignment errors. SMD is used to investigate in detail into the effects of HOMs in the Superconducting Proton Linac (SPL) at CERN and in particular their potential to drive beam instabilities in the longitudinal and transverse direction. Based on these results, HOM damping requirements for the HOM coupler design are then defined. In addition, the linear accelerators of the European Spallation Source (ESS) and the Spallation Neutron Source (SNS) are analysed with respect to HOM impact and the results are compared with the SPL simulations.

/pdf/study-of-higher-order-modes-in-superconducting-accelerating-oh4z2wi4ci.pdf

Study of Higher Order Modes in Superconducting Accelerating Structures for Linac Applications

The Superconducting Proton Linac (SPL) at CERN is part of the planned injector upgrade of the LHC. Initially used at low duty cycle as LHC injector it has the potential to be upgraded as a high power proton driver for neutrino physics and/or radioactive ion beams. In this paper the influence of the beam parameters on the build-up of Higher Order Mode (HOM) voltages is studied together with their interaction on the beam. For this purpose we use bunch tracking simulations in the longitudinal and transverse plane in order to define Beam Break-Up (BBU) limits. These simulations take into account changing values for the HOM frequency spread and are carried out using various distances between the HOM frequencies and the main machine lines.

/pdf/higher-order-mode-beam-breakup-limits-in-the-superconducting-3nli7qrf6l.pdf

Higher order mode beam breakup limits in the superconducting cavities of the spl

It is desired to measure the linac current of a charged particle beam with a consistent accuracy over a dynamic range of over 120 dB. Conventional current transformers suffer from droop, can be susceptible to electromagnetic interference (EMI), and can be bandwidth limited. A novel detector and electronics were designed to maximize dynamic range of about 120 dB and measure rise-times on the order of 10 nanoseconds.

High dynamic-range high speed linac current measurements *

At the SNS a beam current measurement technique, called CHuMPS (Chopper Machine Protection System) has been developed that is fast, has a large dynamic range, and is droop free. Combined with the LEBT (Low Energy Beam Transport) chopper controller, a beam in gap measurement is possible that can accurately measure the beam in the chopper gaps. The beam in gap measurement can then provide machine protection in the case of chopper failure. The same application can also measure waste beam from the ring injection stripper foil and provide fast protection from stripper foil failure.

High dynamic range current measurements with machine protection

The spallation neutron source (SNS) accelerator systems are ramping up to deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. Enhancements or additions have been made to several instrument systems to support the ramp up in intensity, improve reliability, and/or add functionality. The beam current monitors now support increased rep rates, the Harp system now includes charge density calculations for the target, and a new system has been created to collect data for the beam accounting and present the data over the web and to the operator consoles. The majority of the SNS beam instruments are PC-based and their configuration files are now managed through the Oracle relational database. A new version for the wire scanner software was developed to add features to correlate the scan with beam loss, parking in the beam, and measuring the longitudinal beam current. This software is currently being tested. This paper also includes data from the selected instruments.

https://epaper.kek.jp/p07/PAPERS/THOBC01.PDF

Status of various sns diagnostic systems

It is desired to measure the effectiveness of the LEBT (low energy beta transport) chopper system. Since this chopper is required to chop the H- beam to a 1% level, it is, therefore, required to accurately measure the beam during the chop. A system is developed with a high dynamic range that can both accurately measure the beam to tune the chopper system as well as provide an input to the MPS (machine protection system) to stop the beam in the event of a chopper system failure. A system description, beam based calibration, and beam measurements are included.

High-Dynamic-Range Current Measurements in the Medium-Energy Beta Transport Line at the Spallation Neutron Source

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High-Dynamic-Range Current Measurements in the Medium-Energy Beta Transport Line at the Spallation Neutron Source