Search

PSpice models for the SIS100 barrier bucket cavity and the ESR barrier bucket cavity have been created and compared with measurements.

Damping of longitudinal coherent bunched-beam oscillations are needed in SIS18 and SIS100 to stabilize the beam, prevent emittance growth and keep beamloss low during acceleration. In last year’s work several approaches of digital filters for beam-phase control have been examined. An FIR (finite impulse response) filter with 3 taps, cf. [1], has been successfully used at GSI in several machine experiments for a beam- phase control system and a longitudinal feedback system. In principle, much more taps can be used, but it is still an open topic, whether more complex filters will lead to better results. Therefore, a detailed control-theoretic study has been started and the progress is reported in the following.

At the GSI facility in Darmstadt, Germany, Barrier Bucket RF systems are currently designed for the SIS 100 synchrotron (part of the future FAIR facility) and the Experimental Storage Ring (ESR). The purpose of these systems is to provide single sine voltage pulses at the cavity gap. Due to the high requirements regarding the gap signal quality, the calculation of the pre-distorted input signal plays a major role in the system development. A procedure to generate the input signal based on the dynamic properties in the linear region of the system has been developed and tested at a prototype system. It was shown that this method is able to generate single sine gap signals of high quality in a wide voltage range. As linearity can only be assumed up to a certain magnitude, nonlinear effects limit the quality of the output signal at very high input levels. An approach to overcome this limit is to extend the input signal calculation to a nonlinear model of the system. In this contribution, the current method to calculate the required input signal is presented and experimental results at a prototype system are shown. Additionally, first results in the nonlinear region are presented., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The experimental storage ring (ESR), operated at the GSI facility in Darmstadt, Germany, allows experiments with a variety of ion species. In combination with the existing electron cooler, its RF cavities have been used to demonstrate longitudinal beam accumulation in order to increase the beam intensity. Limitations of the existing narrow-band cavities led to the development of a magnetic alloy (MA) based broad-band cavity for the generation of Barrier-Bucket signals. The application of a pre-distortion method demands high linearity of the driver amplifier and highlights the importance of its selection process. In this contribution, the cavity and amplifier system design is described and data measured at a prototype system are presented., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The main synchrotron SIS100 of the Facility for Antiproton and Ion Research (FAIR) will be equipped with a bunch-by-bunch feedback system to damp longitudinal beam oscillations. In the basic layout, one three-tap finite impulse response (FIR) filter will be used for each single bunch and oscillation mode. The detected oscillations are used to generate a correction voltage in dedicated broadband radio frequency (RF) cavities. The digital filter is completely described by two parameters, the feedback gain and the passband center frequency, which have to be defined depending on the longitudinal beam dynamics. In earlier works*, the performance of the closed loop control with such an FIR-filter was analyzed and compared to simulations and measurements with respect to the damping of coherent dipole and quadrupole modes, the first modes of oscillation. This contribution analyzes the influence of cavity beam loading on the closed loop performance and the choice of the feedback gain and passband center frequency to verify future high current operation at FAIR., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Several new rf cavity systems have to be realized for the FAIR synchrotrons and for the upgrade of the existing GSI synchrotron SIS18 [1]. For this purpose, a completely new low-level rf (LLRF) system architecture [2] has been developed, which is now used in SIS18 operation. Closedloop control systems stabilize the amplitude and the phase of the rf gap voltages. Due to component imperfections the transmission and the detection of the actual values lead to systematic errors without countermeasures. These errors prohibit the operation of the rf systems over the whole amplitude and frequency range within the required accuracy. To compensate the inevitable errors, the target values provided by the central control system are modified by socalled calibration electronics (CEL, [3]) modules. The calibration curves can be measured without the beam, but the desired beam behaviour has to be verified by experiments. For this purpose, a debunching scenario was selected as a SIS18 beam experiment that proved to be very sensitive to inaccuracies. In this contribution the results of this experiment are presented, showing for the first time at GSI by beam observation that the accuracy requirements are met based on predefined calibration curves.

The Mainz Energy-recovering Superconducting Accelerator (MESA), currently under construction at Johannes Gutenberg-Universität Mainz, requires a newly designed digital low-level radio frequency (LLRF) system. Challenging requirements have to be fulfilled to ensure high beam quality and beam parameter stability. First, the layout with two recirculations and the requirements will be shown from an LLRF point of view. Afterwards, different options for the control system are presented. This includes the generator-driven system, the self-excited loop and classical PID controller as well as more sophisticated solutions., Proceedings of the 59th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, ERL2017, Geneva, Switzerland

Due to technical reasons two of ten buckets have to stay empty in the planned SIS100 synchrotron at the GSI Helmholtzzentrum für Schwerionenforschung. The planned low level RF control systems consist of linear P and PI type controllers. These are responsible to maintain a desired phase and amplitude of the gap voltage. In addition the cavity is controlled to follow a prescribed resonance frequency ramp. In SIS100 the acceleration will be performed by ferrite cavities with comparatively small quality factors. Therefore, effects resulting from transient beam loading have to be expected. Influences due to empty buckets are analysed in the frequency domain and particle tracking simulations are carried out to estimate the effect on the overall system with particular consideration of emittance growth and particle loss., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

During acceleration in SIS18/SIS100 at GSI/FAIR longitudinal beam-oscillations are expected to occur. To reduce emittance blow-up, dedicated LLRF beam feedback systems are planned. To date longitudinal beam oscillations have been damped in machine experiments with a finite-impulse-response (FIR) filter controller with 3 filter taps. An alternative approach implementing the FIR filter as a derivative estimator controller is simulated and tested. This approach shares the same controller topology and can therefore be easily integrated in the system. It exploits the fact that the sampling rate of the feedback hardware is considerably higher than the frequency of the beam oscillations. It is therefore capable of damping oscillations without overshoot within one oscillation period.

Five different Ring RF Systems are required for the operation of FAIR (Facility for Antiproton and Ion Research). These systems have to operate at frequencies between 310 kHz and 3.2 MHz, with gap voltages up to 40 kVp and duty cycles from 5·10⁻⁴ up to cw. All systems will be realized using inductively loaded (ferrite or magnetic alloy) cavities driven by tetrode-based amplifiers fed by switch-mode power supplies. To stabilize the amplitude, resonance frequency and phase, versatile digital feedback and feedforward control will be used. This contribution will present the latest development on the power part and the LLRF of the four RF systems of the SIS100 (SIS100 Acceleration, SIS100 Bunch Compression, SIS100 Barrier Bucket and SIS100 Longitudinal Feedback) as well as the CR Debuncher system which is part of the Collector Ring. The progress of these systems varies by a large degree. This note will give an overview regarding the status of the design, procurement, realization, testing, optimization, commissioning and preparation for installation of these RF systems., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

It is well known that beamloading effects in acceler- ating cavities can have a serious impact on the beam quality. In order to prevent emittance growth and to keep beam loss low during acceleration, detailed simu- lations are necessary to evaluate the effects on the cavity and its low level RF feedback systems. This situation is aggravated by the fact that in a SIS100 scenario two out of ten buckets have to stay empty. Up to now the closed loop performance of the overall cavity system is still an open topic. Therefore a detailed study has been started.

At GSI, Darmstadt, Germany, a Barrier-Bucket (BB) RF System is currently under development for the Experimental Storage Ring (ESR). The system consists of two broadband RF cavities, each driven by a solid state amplifier, with the purpose to produce two voltage pulses per beam revolution. This will enable highly sophisticated longitudinal beam manipulations like longitudinal capture, compression and decompression or stacking of the beam. For the LLRF System, several requirements have to be fulfilled. Besides high standards concerning the pulsed gap signal quality (e.g. ringing, Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Damping of longitudinal coherent bunched-beam oscillations is needed in SIS18 and SIS100 to stabilize the beam, prevent emittance growth and keep beam loss low during acceleration. In last year’s work several approaches of digital filters for beam-phase control have been examined. An FIR (finite impulse response) filter with 3 taps, cf. [1], has been successfully used at GSI in several machine experiments for a beam-phase control system and a longitudinal feedback system. In this report an alternative FIR filter approach based on derivative estimation leads to better results as it damps dipole oscillations within one oscillation period whereas the former filter approach unveils its full potential only after one oscillation period.

The planned SIS100 heavy ion synchrotron at the GSI Helmholtzzentrum für Schwerionenforschung will possess twenty ferrite accelerating cavities in its final stage of extension. As at injection and at flat top during slow extraction of the planned acceleration cycles the RF voltage will be relatively low, not all cavities will be active in this part of operation. It is important to analyse the impact of the inactive cavities on the overall RF voltage and subsequently their implication on the longitudinal particle dynamics. Classical approaches for reducing the beam impedance consist of active detuning of the cavities to pre-described parking frequencies. The fact that two out of ten buckets have to stay empty in all SIS100 scenarios is of particular interest as additional frequency components appear in the excitatory beam current, which have to be considered when the cavity is detuned. Therefore multi-cavity particle tracking simulations, consisting of twenty cavities and their attached LLRF control systems, are carried out in order to analyse different possibilities to minimize the impact on the beam dynamics and emittance growth., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Energy Recovery Linacs promise superior beam quality: sharper and more intense. To reach these goals, resonance frequency control of the superconducting RF cavities is an important part. In this work, system identification procedures conducted at components of the S-DALINAC (Institute for Nuclear Physics, TU Darmstadt, Germany) are shown. This includes investigations of the piezo tuner’s effect on, e.g., the phase of the accelerating field when a periodic disturbance is applied. The results are compared to simulations of the modelled system and the impact of the applied controller is discussed., Proceedings of the 63th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, ERL2019, Berlin, Germany

Within the FAIR (Facility for Antiproton and Ion Research) accelerator complex, the SIS100 synchrotron will provide high intensity proton to heavy ion beams to the various beam lines and storage rings. This paper presents the recent progress of the SIS100 overall RF system in its preparation towards installation. The RF system is split into four separate sub-systems with a significant number of RF stations. Each RF station consists of a ferrite or MA loaded cavity, a tetrode-based power amplifier, a switching mode power supply unit and various analogue or digital LLRF components for feedback and feedforward control. Fourteen ferrite cavities will generate the accelerating field, while nine cavities loaded with magnetic alloy ring cores are used for bunch compression. The barrier bucket system, which is used to apply a pre-compression of the beam, as well as the longitudinal feedback system for stabilization of beam oscillations will be realized by in total four cavities of the same type., Proceedings of the 11th International Particle Accelerator Conference, IPAC2020, Caen, France

The planned SIS100 heavy ion synchrotron at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany will possess twenty ferrite accelerating cavities in its final stage of extension. During the intended acceleration cycles, the cavities will encounter significant beam loading effects, which have to be handled by the control systems. As both the generator- and beam-current act on the same system input, a feedforward disturbance compensation can be a promising approach to improve beam qualities and suppress instabilities induced by the beam current. Particle tracking simulations, incorporating twenty ferrite cavities and their attached LLRF control systems, are performed to analyse the sensitivity of the beam quality with respect to errors in the feedforward beam current compensation. The main focus lies on the time after injection from a pre-accelerator, where most cavities in the SIS100 do not provide any gap voltage and thus are particularly sensitive to induced voltages by beam currents if the cavities are not or only partly short-circuited., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

In this contribution, a new SIS18 rf accelerating system is presented whose cavities are based on magnetic alloy materials. The rf system works at harmonic number h=2 (f=0,43- to 2,8 MHz) and provides the necessary accelerating voltage (up to 50kVp) for SIS18 injector operation for FAIR with high intensity heavy ion beams in a fast operation mode with up to three cycles per second. The paper focusses on the cavity part and its cooling issues as well as the broadband characteristics. Due the lossy magnetic alloy ring core filling, which consists of high permeability Finemet FT3M ring cores (HITACHI), the cavities show a broadband behaviour and thus no cavity tuning during the acceleration ramp is necessary. To keep the bandwidth of the cavities as broad as possible they are cooled by a special mineral oil with low permittivity. Also the beam impedance and the power consumption of the rf system are discussed., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

For the Facility for Antiproton and Ion Research (FAIR) 14 ferrite loaded accelerating RF stations are planned for the first stage of realization of the SIS100 synchrotron. Each RF station has to provide a total peak gap voltage of up to 20 kVp in CW operation - tuneable in the range of 1.1 MHz up to 3.2 MHz to allow ion beam acceleration and beam gymnastics at different harmonic numbers and energy levels in the new facility. Each RF station consists of a tuneable ferrite cavity, a single ended tetrode amplifier and a dedicated power supply and control unit (PSU) ' including two bias current supplies for cavity- and control-grid(G1)-circuit-tuning. The ferrite cavity is based on the SIS18 cavity concept but has to provide a 1.25 times higher gap voltage of 20 kVp over a total length of 3 meters. The realization is done by a consortium consisting of RI Research Instruments GmbH as consortium leader and manufacturer of the cavity, Ampegon PPT GmbH (for the tetrode amplifier) and Ampegon AG (for the power supply unit). In this contribution, the system design is discussed, and commissioning results are presented. All main parameters are achieved with the RF station described., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The Collector Ring (CR), a storage ring intended to perform efficient cooling of secondary beams, is under construction at GSI in the scope of the FAIR project. The RF system of the CR has to provide a frequency range from 1.1 to 1.5 MHz and pulsed gap voltages of up to 200 kVp (0.2 to 1 Hz, max. 10⁻³ duty cycle) and up to 10 kVp in CW operation. Five identical RF stations will be built. Each RF station consists of an inductively loaded cavity, a tetrode based power amplifier, a semiconductor driver amplifier, a switch mode power supply and two digital feedback loops. The main components of the RF station are designed, built and commissioned in close collaboration between GSI and three companies: RI Research Instruments GmbH, Ampegon PPT GmbH and OCEM Energy Technology SRL. In 2016, the first of five RF stations has been integrated at GSI. In 2017 the system was successfully commissioned to demonstrate that all envisaged parameters have been achieved. This contribution will present the requirements imposed the system, the principal design of the overall system as well as of its key components, and the results of the commissioning of the first RF station., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

In the frame of the Facility for Antiproton and Ion Research (FAIR) 9 bunch compressor RF stations were ordered for the first stage of realization of the SIS100 synchrotron. For RF gymnastics referred to as bunch rotation, one RF station has to provide a sudden rise in gap voltage of up to 40 kVp within less than 30 μs. The system is designed for a maximum RF burst of 3 ms per second. The RF frequency will be pre-selectable between 310 kHz and 560 kHz at a harmonic number of h=2 with respect to the beam. Compressed bunches with a peak current > 150 A and a width < 50 ns are the goal. For this purpose, a 1.218 m long cavity was designed using iron-based magnetic alloy cores. Variable vacuum capacitors are attached for tuning. The cavity is driven by a cross-coupled push-pull tetrode amplifier. This scheme minimizes the influence of the tetrode's DC current at the working point to the cores. The energy for the pulsed system is stored in a relatively small capacitor bank which will be charged semi-continuously and a voltage-stabilizing device is added. Cavity and power amplifier were realized by AURION Anlagentechnik GmbH ' the power supply unit is designed and built by OCEM Power Electronics., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

A closed orbit feedback system is under development at the GSI SIS18 synchrotron for usage during the whole acceleration cycle including the acceleration ramp. Singular value decomposition (SVD) is the most widely used technique in global closed orbit correction for eigenmode decomposition, mode selection and pseudo-inversion of Orbit Response Matrix (ORM) for robust calculation of corrector magnet strengths. A new faster inversion technique based upon Discrete Fourier Transform (DFT) has been proposed for SIS18 ORM exploiting the Circulant symmetry, a class of matrices which can be diagonalized by the DFT using only one row or column of the matrix. The existence of a clear relationship between SVD modes and singular values to DFT modes and coefficients for such matrices has been described. The DFT based decomposition of Circulant ORM gives hints on physical interpretation of SVD and DFT modes of perturbed closed orbit in a synchrotron. As a first practical application, DFT modes were used to provide robustness against sensor failures such as one or two malfunctioning BPMs., Proceedings of the 16th Int. Conf. on Accelerator and Large Experimental Control Systems, ICALEPCS2017, Barcelona, Spain

After two-year's shutdown, the GSI accelerators plus the latest addition of storage ring CRYRING, will be back into operation in 2018 as the FAIR phase 0 with the goal to fulfill the needs of scientific community and the FAIR accelerators and detector development. Even though GSI has been well known for its operation of a variety of ion beams ranging from proton up to uranium for multi research areas such as nuclear physics, astrophysics, biophysics, material science, the upcoming beam time faces a number of challenges in re-commissioning its existing circular accelerators with brand new control system and upgrade of beam instrumentations, as well as in rising failures of dated components and systems. The cycling synchrotron SIS18 has been undergoing a set of upgrade measures for fulfilling future FAIR operation, among which many measures will also be commissioned during the upcoming beam time. This paper presents the highlights of the challenges such as re-establishing the high intensity heavy ion operation as well as parallel operation mode for serving multi users. The status of preparation including commissioning results will also be reported., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

In the scope of FAIR's scientific program higher beam intensities will be achieved and several new synchrotrons (including storage rings) are being built. The low-level RF (LLRF) systems of FAIR have to support multi-harmonic operations, barrier bucket generation and bunch compression in order to meet the desired beam quality requirements. All this imposes several requirements on the LLRF systems. For example the phase error of the gap voltage of a specific RF cavity must be less than 3 degrees. Thus, each individual component must have a better accuracy. The RF reference signals for the FAIR synchrotron RF cavity systems are generated by direct digital synthesis (DDS). Four so-called Group DDS modules are mounted in one crate. In the supply rooms, the reference signals of such a crate are then distributed to local cavity LLRF systems. Therefore, the precise phase calibration of Group DDS modules is of importance. A phase calibration method with respect to the absolute phases of DDS modules defined by means of the FAIR Bunch Phase Timing System (BuTiS) is developed, and its precision is under evaluation., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

During acceleration in SIS18/SIS100 at GSI/FAIR longitudinal beam-oscillations are expected to occur. To reduce emittance blow-up, dedicated LLRF beam feedback systems are planned. To date longitudinal beam oscillations have been damped in machine experiments with a finite-impulse-response (FIR) filter controller with 3 filter taps[1]. An alternative approach implementing the FIR filter as a derivative estimator controller is simulated and tested. This approach shares the same controller topology and can therefore be easily integrated in the system. It exploits the fact that the sampling rate of the feedback hardware is considerably higher than the frequency of the beam oscillations. It is therefore capable of damping oscillations without overshoot within one oscillation period., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

SIS100 is a unique heavy ion synchrotron designed for the generation of high intensity heavy ion and Proton beams. New features and solutions are implemented to enable operation with low charge state heavy ions and to minimize ionization beam loss driven by collisions with the residual gas. SIS100 aims for new frontier and world wide leading Uranium bam intensities. A huge effort is taken to stabilized the dynamics of the residual gas pressure and to suppress ion induced desorption. Fast ramped superconducting magnets have been developed and are in production with highest precision in engineering and field quality, matching the requirements from beams with high space charge. A powerful equipment with Rf stations for fast acceleration, pre- and final compression, for the generation of barrier buckets and provision of longitudinal feed-back shall allow a flexible handling of the ion bunches for the matching to various user requirements. Results obtained with FOS (first of series) devices, status of realisation and technical challenges resulting from the demanding goals, will be presented., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Four different types of RF cavities are realized for the heavy-ion synchrotron SIS100 which is built in the scope of the FAIR (Facility for Antiproton and Ion Research) project. The standard acceleration is performed by ferrite cavities. Barrier bucket cavities will allow a pre-compression of the beam by means of moving barriers. Bunch compressor cavities are used to realize a rotation in longitudinal phase space by 90 degrees, thereby reducing the bunch length. Finally, a longitudinal feedback system reduces undesired beam oscillations. In contrast to the ferrite-loaded accelerating cavities, the last-mentioned three cavity types are based on magnetic alloy (MA) material. Depending on the type of the cavity system, the realization is done by - or in close collaboration with - different industrial companies and institutions. In this contribution, the realization status of all these synchrotron RF systems is summarized., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The transfer of bunched ion beams between various synchrotrons is required for the multi-accelerator complex FAIR, presently under construction at GSI. To avoid a dedicated distribution infrastructure for radiofrequency (RF) signals between each source and destination synchrotron, a new approach has been developed to transmit bunch and bucket phase information using synchronous Ethernet. This allows to locally regenerate all reference signals needed for the RF synchronization prior to a bunch-to-bucket transfer, as well as the triggers to the kickers. The modular and configurable hardware implementation based on the White Rabbit network progresses towards a proof-of-principle demonstrator. Besides the synchronization of revolution and RF frequencies, the bunches in the source accelerator must be aligned in azimuth with respect to the buckets in the receiving synchrotron. To validate the feasibility of this azimuthal steering, measurements have been performed with protons in the CERN PS to evaluate the longitudinal emittance growth. They are complemented with tracking simulations using the BLonD code., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A fast closed orbit feedback system (bandwidth in the order of 1 kHz) is under development at the GSI SIS18 synchrotron for the orbit correction from injection to extraction including the acceleration ramp. The static process model, represented as the orbit response matrix (ORM), is subjected to the systematic optics changes during ramp e.g. beta function and phase advance variations at the locations of BPMs and steerers. In addition to these systematic variations, model mismatches may arise from dipole and quadrupole magnet errors, space charge dependent tune shift as well as BPM and steerer calibration errors. In this contribution, the effects of these model errors on the closed orbit correction are investigated which is necessary for the robust stability analysis of the feedback controller. For the robustness tests, the traditional SVD-based matrix pseudo-inversion is compared to a Fourier-based analysis. The results are achieved by detailed simulations in MADX., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

During acceleration in the heavy-ion synchrotrons SIS18/SIS100 at GSI/FAIR longitudinal beam oscillations are expected to occur. To reduce longitudinal emittance blow-up, dedi- cated LLRF beam feedback systems are planned. To date, damping of longitudinal beam oscillations has been demon- strated in SIS18 machine experiments with a 3-tap filter controller (e.g. *), which is robust in regard to control pa- rameters and also to noise. On acceleration ramps the control parameters have to be adjusted to the varying synchrotron frequency. Previous results from beam experiments at GSI indicate that a proportional tuning rule for one parameter and an inversely proportional tuning rule for a second parameter is feasible, but the obtained damping rate may not be opti- mal for all synchrotron frequencies during the ramp. In this work, macro-particle simulations are performed to evaluate, whether it is sufficient to adjust the control parameters pro- portionally (inversely proportionally) to the change in the linear synchrotron frequency, or if it is necessary to take more pa- rameters, such as bunch-length and synchronous phase, into account to achieve stability and a considerable high damping rate for excited longitudinal dipole beam oscillations. This is done for single- and dual-harmonic acceleration ramps., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

To reach high particle energies with synchrotrons, a chain of several accelerators is required, as the ratio of extraction and injection energy is in the range of 10 to 20 per synchrotron. Hence the beam must be transfered from one accelerator to the next one. This document deals with the bunch-to-bucket transfer method to inject particle bunches composing the beam from a source synchrotron to a target synchrotron. After we highlight the theoretical concept of the bunch-to-bucket transfer, we determine physical limitations due to the beam dynamics and the adiabatic aspect of the particle bunches. A summary of the currently performed bunch-to-bucket transfer scenarios between the accelerators at CERN is given and set in relation with the mentioned theoretical concepts.

The upgrade of the existing heavy ion synchrotron SIS18 as booster for the FAIR synchrotron SIS100 has been partly completed. With the achieved technical status, a major increase of the accelerated number of heavy ions could be reached. This progress especially demonstrates the feasibilty of acceleration of medium charge state heavy ions with high intensity and and the succesfull control of dynamic vaccuum effects and correlated charge exchange loss. Two further upgrade measures, the installation of additional MA acceleration cavities and the exchange of the main dipole power converter are in progress. For the FAIR synchrotron SIS100 all major components with long production times have been ordered. With several pre-series components, outstanding technical developments have been completed and the readiness for series production reached. The technical project status will be summarized., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Based on the Bunch Phase Timing System (BuTiS)* local analog radio frequency reference signals (RF references) like the particle revolution frequency and their multiple harmonics will be generated. These references are used to control the phase of the accelerator cavities to altering harmonics of the bunch revolution frequency. Delay or phase shifts from the FAIR-Center to references at the BuTiS endpoints are already compensated by the BuTiS receivers. Phase shifts from the RF reference generators to LLRF electronics can be compensated by controlling the output phases of the DDS modules of the RF references. However phase shift delays of multiple harmonics at the same interconnecting electrical path are not identical at the same time. Configurable electronics** manage phase calibration of the RF references to their endpoints. Calibration may depend on frequency and harmonic of the RF reference, aging as well as on thermal effects. The electrical length and impedance of interconnecting cables for phase control loops can be compensated. This is an important feature, in particular if control loops are switched between different harmonic frequencies., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

This paper deals with the analytical modeling of lossy coaxial transmission lines in the frequency range from 100 kHz to 50 MHz with focus on corrugated coaxial lines with polyethylene foam as dielectric. The considered transmission lines are used in low-level radio frequency (LLRF) systems (< 5 MHz) at GSI. These applications require a high precision in amplitude and phase for the transmitted signals where a detailed knowledge of the line properties is of significant interest. As the corresponding data sheets do not provide appropriate data, the necessary data have been computed. The obtained results from the purely analytical model were then compared with previous measurements for validation purposes., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

At the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany a high intensity antiproton beam will be produced. To provide the necessary 70 mA proton beam a dedicated proton linac (p-Linac) is under construction. The main acceleration will be provided by 9 novel CH-type cavities, of which 6 will be coupled in pairs to share the same klystron. To test the rf properties of these novel cavities, a test stand is under construction. An rf control system for the pulsed operation of these cavities has been developed at TU Darmstadt. It is based upon the digital cw rf control that is successfully in operation as part of the S-DALINAC at IKP Darmstadt. The latest developments will be presented., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Longitudinal oscillations of bunched beams in synchrotrons have been analyzed by accelerator physicists for decades, and a closed theory is well-known [1]. The first modes of oscillation are the coherent dipole mode, quadrupole mode, and sextupole mode. Of course, these modes of oscillation are included in the general theory, but for developing RF control systems, it is useful to work with simplified models. Therefore, several specific models are analyzed in the paper at hand. They are useful for the design of closed-loop control systems in order to reach an optimum performance with respect to damping the different modes of oscillation. This is shown by the comparison of measurement and simulation results for a specific closed-loop control system., 14 pages, 14 figures

This paper describes the development of a new rf accelerating cavity based on novel magnetic alloy materials (MA-materials) for operation at harmonic number h=2 (f=0,43- to 2,8 MHz) to provide the necessary accelerating voltage for SIS18 injector operation with high intensity heavy ion beams in a fast operation mode with three cycles per second. The acceleration system consist of three units which are able to operate independently from each other. That is important, since each ion for FAIR has to cross the h=2-rf-system and in the case of a damage a reduced operation has to be ensured. Since the cavities are filled with lossy MA-ring-cores, which are iron based Finemet FT3M ring cores from Hitachi, the cavities show a broadband behaviour and thus no cavity tuning during the acceleration ramp will be necessary. Due to the high saturation field strength of Finemet (1,2 T) the overall length of all three cavity units can be very short. This is an important feature since due to many insertions which were additionally inserted into the synchrotron ring SIS12/18 in the meantime, the available length in SIS12/18 for the cavity units is with 4 m very short., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Barrier bucket systems are planned for the SIS100 Synchrotron (part of the future accelerator facility FAIR) and the ESR storage ring to facilitate several longitudinal beam manipulations [9] [15]. In order to achieve a single-sine gap signal of the desired amplitude and quality, effects in the linear and nonlinear region of the RF systems have to be investigated and included in the design of the overall system. Therefore, the cavities and the amplifier stages are to be modeled in PSpice. In this contribution, a cavity model will be presented. In a first step, a model for the magnetic alloy (MA) ring cores, which highly account for the properties of the cavity, has been found based on measurement data. In a second step, the future setup of the cavity is systematically created using the MA ring core models. The model of the cavity allows simulations in frequency domain as well as time domain. The results show good agreement with former measurements., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The heavy ion synchrotron SIS18 at the GSI facility will be upgraded by a dual harmonic RF acceleration system in the process of using SIS18 as booster for the future FAIR SIS100 accelerator. The dual harmonic mode will extend the SIS18 operating towards higher beam currents. As a part of a large LLRF upgrade at the synchrotron RF systems at GSI, new FPGA and DSP based electronics have been designed, built and commissioned. To prove the functionality of the LLRF equipment as well as the general dual harmonic topology, machine development experiments using the existing cavities have been performed. During these experiments, the main parameters of the control loop were determined. Additionally, the impact of RF gap voltage amplitude and phase variations onto the ion beam have been investigated, like e.g. creation of a dual harmonic bucket or fast changes in harmonic number. The experiments showed a high sensitivity of the ion beam to small deviations in the phase between both harmonics and thereby confirmed the requirements on the high precision regarding phase accuracy of the electronic setup especially for the closed loop phase control systems., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

For sophisticated beam manipulation several ring accelerators at FAIR and GSI like the main synchrotron SIS100 and the ESR will be equipped with barrier bucket systems. Hence, the associated LLRF has to be applicable to different RF systems, with respect to the cavity layout and the power amplifier used, as well as to variable repetition rates and amplitudes. Since already the first barrier bucket pulse of a long sequence has to meet certain minimum demands, an open-loop control on the basis of calibration data is foreseen. Closed-loop control is required to improve the signal quality during a sequence of pulses and to adapt to changing conditions like temperature drifts. A test setup was realized that allows controlling the signal generator, reading out the oscilloscope as well as processing the collected data. Frequency and time domain methods can be implemented to approach the dynamics of the RF system successively and under operating conditions, i.e. generating single sine pulses. The setup and first results from measurements are presented as a step towards automated acquisition of calibration data and iterative improvement of the same., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

To damp undesired longitudinal oscillations of bunched beams, the main synchrotron SIS100 of FAIR (Facility for Antiproton and Ion Research) will be equipped with a bunch-by-bunch feedback system. This helps to stabilize the beam, to keep longitudinal emittance blow-up low and to minimize beam losses. The proposed LLRF (low level radio frequency) topology of the closed loop feedback system is described. In some aspects, it is similar to the beam phase control system* developed at GSI Helmholtzzentrum für Schwerionenforschung GmbH. The differences and challenges are pointed out, which are mainly the bunch-by-bunch signal processing followed by the generation of a correction voltage in dedicated feedback cavities. The adapted topology was verified at SIS18 during beam time in 2014 using LLRF prototype subsystems and the two existing ferrite-loaded acceleration cavities. The experimental setup to damp coherent longitudinal dipole oscillations is presented and evaluated with focus on the realized modifications, including ongoing and pending investigations. Finally, the current status of the longitudinal feedback system for FAIR is summarized., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

In combination with beam cooling, Barrier-Bucket operation allows an intensity increase of particle beams by concentrating particles in one bucket, while creating an empty bucket for the next injection (“longitudinal stacking”). This can be achieved by generation of two RF voltage single-sine waves as barrier pulses, of which one is shifted in time to compress the beam (Fig. 1).

To improve beam quality, the DELTA storage ring (TU Dortmund) conducted a number of orbit-feedback developments in the past, including a successful fast local orbit feedback project. To enable hadron accelerators to benefit from this knowledge, a collaboration was formed between DELTA, the storage ring COSY (Forschungszentrum Jülich) and the SIS18 accelerator (GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt). The goals were the development of a global fast orbit feedback system for the DELTA storage ring, the development of a local feedback for the COSY electron beam cooler section and a global feedback for the SIS18 accelerator. This thesis describes the development and application of a universal position measurement system, usable for electron and hadron accelerators and targeted to fast orbit feedback applications, in the framework of this collaboration. The developed distributed system has input capabilities for electron or hadron beam position monitors and output options for feedback tasks and different control system connections. It is connected by a versatile communication structure. The developed common hardware platform is re-programmable and therefore usable as an input device as well as for feedback- or other measurement tasks. It delivers data at a constant data rate of 10 kHz, resulting in a target feedback-rate of up to 1 kHz. It was used to evaluate beam position data globally at DELTA, locally at SIS18 and locally at the COSY beam cooler section. At DELTA, the system forms the basis for a future fast orbit feedback system, which is expected to significantly increase the beam quality for synchrotron radiation based research as well as ongoing electron-beam/laser interaction experiments. The system can also be used as a high precision data source for the slow orbit feedback system in operation. The COSY measurements show the possibility of a local fast orbit feedback system at the storage ring's electron cooler. The data analysis of the SIS18 accelerator suggests the utilization of a feedback system to improve beam quality during ramping. The system's structure is expected to be utilized in a future SIS100 accelerator feedback.