Determination of low level RF control requirements for superconducting cavities from microphonics measurements (original) (raw)
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RF Control Requirements for the CEBAF Energy Upgrade Cavities
Linac 2000, 2000
The 6 GeV CEBAF accelerator at Jefferson Lab is arranged in a five-pass racetrack configuration, with two superconducting radio frequency (SRF) linacs joined by independent magnet transport arcs. It is planned to increase the accelerator energy to eventually support 12 GeV operations. To achieve this, a new 7-cell superconducting cavity is being built to operate at an average accelerating gradient of 12.5 MV/m with an external Q of 2.2 x 10 7. The present RF system, composed of an analog control loop driving a 5 kW klystron, will not easily support the narrower bandwidth cavities at the higher gradients. A new RF control system that may incorporate digital feedback, driving an 8 kW klystron is being proposed. In designing a system it is important to understand the control limitations imposed by the cavity, such as microphonics, Lorentz force detuning and turn-on transients. This paper discusses these limitations and the resulting design constraints for new RF controls.
RF Control Modelling Issues for Future Superconducting Accelerators
The development of superconducting accelerators has reached a high level of maturity following the successes of ATLAS at Argonne, CEBAF at Jefferson Lab, the TESLA Test Facility at DESY and many other operational accelerators. As a result many new accelerators under development (e.g. SNS) or proposed (e.g. RIA) will utilize this technology. Covering all aspects from cw to pulsed rf and/or beam, non-relativistic to relativistic particles, medium and high gradients, light to heavy beam loading, linacs, rings, and ERLs, the demands on the rf control system can be quite different for the various accelerators. For the rf control designer it is therefore essential to understand these issues and be able to predict rf system performance based on realistic rf control models. This paper will describe the features that should be included in such models and present an approach which will drive the development of a generic rf system model.
Analysis of performance limitations for superconducting cavities
The performance of superconducting cavities in accelerators can be limited by several factors, such as: field emission, quenches, arcing, rf power; and the maximum gradient at which a cavity can operate will be determined by the lowest of these limitations for that particular cavity. The CEBAF accelerator operates with over 300 cavities and, for each of them, the authors have determined the maximum operating gradient and its limiting factor. They have developed a model that allows them to determine the distribution of gradients that could be achieved for each of these limitations independently of the others. The result of this analysis can guide an R&D program to achieve the best overall performance improvement. The same model can be used to relate the performance of single-cell and multi-cell cavities.
New RF control system for the 12 GeV energy upgrade of the CEBAF accelerator at Jefferson Lab
Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2008, 2008
The CEBAF Accelerator at Jefferson Lab presently consists of 50 MeV injector, two anti-parallel superconducting linacs and two arcs for transporting beam between the linacs. By the mid-1990s, the accelerator was providing electrons up to 5.75 GeV. The 12 GeV Upgrade is a major accelerator project aimed at doubling the energy by adding 10 (five per linac) new high gradient cryomodules, each providing 100 MV of field. The new cryomodule will consist of eight 7-cell superconducting cavities operating at an average accelerating gradient of and with an external . The high gradient, very high quality factor and large Lorentz detuning coefficient (K L up to 4) pose significant challenges beyond what the present analog low level RF (LLRF) control systems can handle reliably; therefore, a new digital LLRF control system has been developed. The main highlights of the new RF Control system include: a RF frontend with low temperature drift and good linearity, a large FPGA platform for digital signal processing, an EPICS Input Output Computer (IOC) using a PC-104 and a digital Self Exciting Loop (SEL) based algorithm. This paper provides an overview of the 6 GeV and 12 GeV Upgrade CEBAF machines, a summary of sources of cavity field variation that drive LLRF system performance, and discusses recent developments and progress in Jefferson Lab's new LLRF system design.
Operational optimization of large-scale SRF accelerators
Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366), 1999
Unlike other types of accelerator subsystems, because of the flexibility in setting the gradient in each cavity, an SRF linac has many operational degrees of freedom. The overall linac has an operational envelope (beam voltage and current) that depends on acceptable reliability, cryogenic capacity, and RF power budget. For economic and end-user physics reasons, one typically wants to run as close to the edge of the operational envelope as possible. With about 160 cavities in each of the CEBAF linacs, we have been forced to treat this problem in a very general way, and satisfy other non-fundamental needs as energy lock and rapid recovery from failures. We present a description of the relevant diverse constraints and the solution developed for CE-BAF.
Optimization of the RF cavity heat load and trip rates for CEBAF at 12 GeV
2017
The Continuous Electron Beam Accelerator Facility at Jefferson Lab has 200 RF cavities in the north linac and the south linac respectively after the 12 GeV upgrade. The purpose of this work is to simultaneously optimize the heat load and the trip rates for the cavities and to reconstruct the Pareto-optimal front in a timely manner when some of the cavities are turned off. By choosing an efficient optimizer and strategically creating the initial gradients, the Paretooptimal front for up to 15 cavities turned off can be established in about 20 seconds.
RF System Development for The CEBAF Energy Upgrade
2002
A planned upgrade of the present 6 GeV CEBAF accelerator at Jefferson Lab will increase its energy to 12 GeV. To achieve this, new 7-cell superconducting cavities are being built to operate at an average accelerating gradient of 19.5 MV/m with and external Q of 2.2 x 10 7 . The present RF system composed of an analog control loop driving 5 kW klystrons will not support the new cavities and their intended gradients. In light of this, we have been developing both a new RF control system based on a Self Excited Loop using digital feedback and a new high efficiency 13 kW Klystron. It is also intended to use the new RF system for both the Jefferson Lab IR FEL upgrade and the Rare Isotope Accelerator (RIA). This paper discusses these developments and reports on their progress.
Precision vector control of a superconducting RF cavity driven by an injection locked magnetron
Journal of Instrumentation, 2015
The technique presented in this paper enables the regulation of both radio frequency amplitude and phase in narrow band devices such as a Superconducting RF (SRF) cavity driven by constant power output devices i.e. magnetrons. The ability to use low cost high efficiency magnetrons for accelerator RF power systems, with tight vector regulation, presents a substantial cost savings in both construction and operating costs compared to current RF power system technology. An operating CW system at 2.45 GHz has been experimentally developed. Vector control of an injection locked magnetron has been extensively tested and characterized with a SRF cavity as the load. Amplitude dynamic range of 30 dB, amplitude stability of 0.3% r.m.s, and phase stability of 0.26 degrees r.m.s. has been demonstrated.
An automated 476 MHz RF cavity processing facility at SLAC
The 476 MHz accelerating cavities currently used at SLAC are those installed on the PEP-II B-Factory collider accelerator. They are designed to operate at a maximum accelerating voltage of 1 MV and are routinely utilised on PEP-II at voltages up to 750 kV. During the summer of 2003, SPEAR will undergo a substantial upgrade, part of which will be to replace the existing 358.54 MHz RF system with essentially a PEP-II high energy ring (HER) RF station operating at 476.3 MHz and 3.2 MV (or 800 kV/cavity). Prior to installation, cavity RF processing is required to prepare them for use. A dedicated high power test facility is employed at SLAC to provide the capability of conditioning each cavity up to the required accelerating voltage. An automated LabVIEW based interface controls and monitors various cavity and test stand parameters, increasing the RF fields accordingly such that stable operation is finally achieved. This paper describes the high power RF cavity processing facility, highlighting the features of the automated control system and illustrating its operation with some recent high power processing results.
2016
The higher efficiency and higher availability (faulttolerant oriented) of RF & Cavity system (with beam loading) to operate at, the more dynamic details needs to be identified, so as to have the abilities (a) to work at nonlinearities, (b) to work close to limitation, and (c) to change operation point quickly and correctly. Dynamic detail identifications rely heavily on high precision measuring and characterizing basic cavity parameters (QL, R/Q, dynamic detuning, phase and amplitude) and system behaviours under beam-RF-cavity interactions. It is especially challenging to characterize these dynamics under varying operating points or environment. Advanced technologies in LLRF and ICS providing real time/online characterizing will be the key enablers for addressing such challenges. However, to be successful, the deployment of these technologies must be embedded within local conditions taking into account available resources, existing hardware/software structures and operation modes. S...