Digital Low Level RF Control Techniques and Procedures Towards the International Linear Collider

In this work digital Low Level Radio Frequency (LLRF) control techniques and procedures developed and successfully tested in the scope of the International Linear Collider (ILC) are described.One central requirement for the operation of ILC is the high gradient near (5% below) quench limit operation during the whole flattop of multiple cavities driven by a single klystron. In order to achieve such an operation, for every cavity the driving power (Pk) and the loaded quality factor (QL) have to be controlled individually. Thus this operation mode is called PkQL operation. At the superconducting RF test facility (STF) at KEK in the scope of the Quantum Beam (QB) project two superconducting 9-cell cavities were driven by a single klystron. At this setup an automated procedure was developed and tested, resulting in the world's first actual and fully successful PkQL operation. A stable one hour long-time run with a beam of in average 6.4 mA current was achieved. The cavity gradients were 16 and 24 MV/m and with this 5% below the virtual quench limits of 16.8 and 25.2 MV/m. The achieved vector sum gradient and phase stabilities were Delta A/A = 0.009% and Delta phi = 0.009 deg., respectively. Furthermore in a simulation a successful automated PkQL setting procedure and PkQL operation for 39 cavities fulfilling all ILC requirements were demonstrated.Due to the PkQL operation a further requirement in scope of ILC is to operate the cavities at high loaded quality factors. In order to demonstrate the feasibility of such an operation, the loaded quality factors of both superconducting 9-cell cavities at KEK STF in the scope of the QB project were set to QL,cav1 = QL,cav2 = 2*10^7. Under this condition a stable one hour long-time operation with a beam of in average 6.1 mA current was conducted. Both cavity gradients were 20 MV/m. The achieved vector sum gradient and phase stabilities were Delta A/A = 0.011% and Delta phi = 0.015 deg., respectively.At ILC it is planned to operate the klystrons 7% in power below their full saturation. Due to the saturation behavior in amplitude the control gain converts to 0 at this region, which inhibits effective control. In order to keep the control gain constant up to the point of saturation and with this allowing effective control up to this point, predistortion-type FPGA-based klystron linearization algorithms were decided to be used. Four different kinds of algorithms have been developed, successfully tested, and compared. The best algorithm is based on lookup tables combined with a linear interpolation. In a simulation it was demonstrated that an extension of this algorithm with an adaptive grid spacing further improves the linearization performance.For offline tests of the klystron linearization algorithms an FPGA-based klystron and cavity simulator was developed, implemented, and tested

Development and test of a universal FPGA-based Arc Detector for accelerating cavities at the facility for Antiproton and Ion Research FAIR [10.08.2011]

OnTEAM metadata: GDSID: DOC-2011-Nov-83; Attribute ID: LIBRARY-thesis_ma-2011-001; Title: [GSI Ma 2011-01] Development and test of a universal FPGA-based Arc Detector for accelerating cavities at the facility for Antiproton and Ion Research FAIR [10.08.2011]; Author(s): Omet, Mathieu; Corporate author(s): ; Publication date: 20111116; Creator: manton; Creation date: 16.11.2011 16:02:19; Change date: 16.11.2011 16:44:09; Access: Welt; Attribute type: Text.Thesis.MA; Directory path: ['GSI Publications', 'GSI as Publisher']; Attribute path: ['Infrastructure', 'Library and Documentation', 'thesis_ma', 'Added in 2011']; File name(s): ['DOC-2011-Nov-83-1.pdf']; File title(s): ['']; File access: ['GSI-intern'

Automatic Testing of Cryomodules in Scope of the European XFEL

At the European X-Ray free electron laser (XFEL) [1] a total of 102 cryomodules will be installed, each comprising eight 1.3 GHz superconducting 9-cell RF cavities. Every module is tested and characterized prior to tunnel installation. This is done at the accelerator module test facility (AMTF) [2] at Deutsches Elektronen-Synchrotron (DESY).One of these tests is to measure the vector sum (VS) amplitude and phase stability under feedback (FB) [3] operation. Since the preparation and execution of these FB tests consist of many steps, a set of scripts automatizing the procedure was written.Thereby the time consumption for the FB test could be reduced by more than half. Furthermore, the possibility of committing mistakes was minimized. The features of the scripts as well as the experience gained are described. The data processing scheme from data storage to report generation is outlined. Statistics about all other low level radio frequency (LLRF) tests and the general module performance are also presented

Piezo Controls For The European XFEL

The European X-Ray Free Electron Laser (E-XFEL) accelerator is a pulse machine. The typical time duration of a radio frequency (RF) pulse is about 1.3 ms. The RF power transmitted to the superconducting RF (SCRF) cavity as a set of successive pulses (10 Hz repetition rate), causes strong mechanical stresses inside the cavity. The mechanical deformations of the RF cavity are typically caused by the Lorentz force detuning (LFD). The cavity can be tuned to a 1.3 GHz resonance frequency during the RF pulse using fast piezo tuners. Since the E-XFEL will use around 800 cavities (each cavity with double piezos), a distributed architecture with multi-channel digital and analog control circuits seems to be essential. The most sought-after issue is high-voltage, high-current piezo driving circuit dedicated to multi-channel configuration. The driving electronics should allow a maximum piezo protection against any kind of failure. The careful automation of the piezo tuners control and its demonstration for the high gradient conditions a real challenge. The first demonstration of piezo controls applied for chosen RF stations of the E-XFEL linear accelerator (linac) are presented and obtained results are briefly discussed within this paper

Application of disturbance observer-based control in low-level radio-frequency system in a compact energy recovery linac at KEK

A disturbance observer (DOB)-based control for a digital low-level radio-frequency (LLRF) system in a compact energy recovery linac (cERL) at KEK has been developed. The motivation for this control approach is to compensate for or suppress the disturbance signal in the rf system such as beam loading, power supply ripples, and microphonics. Disturbance signals in specified frequency ranges were observed and reconstructed accurately in the field-programmable gate array and were then removed in the feedforward model in real time. The key component in this DOB controller is a disturbance observer, which includes the inverse mathematical model of the rf plant. In this paper, we have designed a DOB control-based approach in order to improve the LLRF system performance in disturbance rejection. We have confirmed this approach in the cERL beam commissioning