| Paper | Title | Other Keywords | Page |
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| MOPPC015 | Proposal for an RF Roadmap Towards Ultimate Intensity in the LHC | cavity, klystron, feedback, injection | 154 |
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| The LHC is currently operated with 1380 bunches at 50 ns spacing and 1.4 E11 p per bunch (0.35A DC). In this paper the RF operation with ultimate bunch intensity (1.7 E11 p per bunch) and 25 ns spacing (2808 bunches per beam) summing up to 0.86A DC is presented. With the higher beam current, the demanded klystron power will be increased and the longitudinal stability margin reduced. In addition one must consider the impact of a klystron trip (voltage and power transients in the three turns latency before the beam is actually dumped). In this work a scheme is proposed that can deal with ultimate bunch intensity, without modification to the RF power system. Only a minor upgrade of the LLRF will be necessary: the field set point will be modulated according to the phase shift produced by the transient beam loading, thus minimizing the requested RF power while keeping the strong feedback for stability and reduction of RF noise. | |||
| TUPPR025 | Higher-Order Modes and Beam Loading Compensation in CLIC Main Linac | impedance, coupling, HOM, higher-order-mode | 1867 |
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| Compensation of transient beam loading is one of the major performance issues of the future compact linear collider (CLIC). Recent calculations, which consider only the most important fundamental mode, have shown that the 0.03% limit on the rms relative bunch-to-bunch energy spread in the main beam can be reached by optimizing the RF power pulse shape for the TD26, the CLIC baseline accelerating structure. Here, using HFSS and massively parallel ACE3P codes developed at SLAC, we perform an additional dedicated study of the influence of higher-order modes on the energy spread compensation scheme. It is shown that taking these modes into account in the accelerating structure does not increase the rms energy spread in the main beam above the CLIC specification level. Results of the HFSS and ACE3P simulations are also in a good agreement. | |||
| TUPPR026 | Conceptual Design of the CLIC Damping Ring RF System | cavity, damping, linac, coupling | 1870 |
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| In order to achieve high luminosity in CLIC, ultra-low emittance bunches have to be generated in both electron and positron damping rings. To achieve this goal, big energy loss per turn in the wigglers has to be compensated by the RF system. This results in very strong beam loading transients affecting the longitudinal bunch position and bunch length. In this paper, conceptual design of the RF system for the CLIC damping ring is presented. Baseline and several alternatives are discussed and the corresponding requirements for the cavities and the RF power sources are presented in order to meet stringent tolerances on the bunch-to-bunch phase and bunch length variations. | |||
| WEPPC080 | Minimizing Helium Pressure Sensitivity in Elliptical SRF Cavities | cavity, simulation, linac, factory | 2396 |
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| Superconducting cavities in CW operation with small beam loading can operate at high QL to significantly reduce power requirements. However, the resulting small bandwidth makes them vulnerable to microphonics from helium pressure fluctuations, which can detune the cavity and cause it to trip. In this paper, we present a mechanical optimization of elliptical cavities for minimization of df/dp, the sensitivity to helium pressure changes. Using the Cornell ERL main linac cavity as an example, an analytical model is developed to illustrate the factors that contribute to df/dp. Methods to reduce df/dp are presented. In addition, df/dp measurements made at the Cornell Horizontal Test Cryostat are presented and corrections to the model are made to account for the thickness of the welds in the helium vessel. | |||
| WEPPP073 | Dynamic Feedback Model for High Repetition Rate Linac-driven FELs | linac, feedback, FEL, cavity | 2879 |
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Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. One of the concepts for the next generation of linac-driven FELs is a cw superconducting linac driving an electron beam with MHz repetition rates. One of the challenges for next generation FELs is improve the shot-to-shot stability of the energy, charge, peak current, and timing jitter of the electron beam. The use of a cw RF system with MHz beam repetition rates presents an opportunity to use broadband feedback to stabilize the beam parameters. To understand the performance of such a feedback system, we are are developing a dynamic feedback model of the machine with a focus on the longitudinal beam properties. The model is being developed as an extension of the LITrack code and will include the dynamics of the beam-cavity interaction, RF feedback, beam-based feedback, and multibunch effects. In this paper, we will present the status of this model along with results. |
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| WEPPR003 | Longitudinal Dynamics of Intense Heavy-Ion Bunches in SIS-100 | impedance, space-charge, ion, heavy-ion | 2937 |
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| In the SIS-100 highest heavy-ion intensities have to be accelerated to deliver beam to the FAIR experiments. In the projected SIS-100 synchrotron the heavy ion bunches will be strongly affected by the longitudinal space charge force. Due to the limited RF bucket area all mechanisms which might cause longitudinal phase space dilution must be understood and controlled. Space charge effects, like the reduction in the RF voltage and the loss of Landau damping, have already been part of elaborate studies. It has been shown that cavity beam loading can deform the flattened bunch shape in the dual rf bucket. Among the different counter measures an inductive insert has been proposed in order to partially compensate the longitudinal space charge impedance. Optimized settings for the difference between the two rf phases in a dual rf bucket might be an option to reduce the effect of beam loading. In this contribution we will analyse the matched bunch distribution for SIS-100 parameters in single and dual rf buckets. Analytical and numerical studies of the interplay of longitudinal space charge, cavity beam loading and an inductive insert will be presented. | |||
| WEPPR007 | Simulation Calculation of Longitudinal Beam Distribution in J-PARC MR | injection, acceleration, simulation, extraction | 2949 |
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| The J-PARC accelerator complex consists of 3 accelerators, a linear accelerator, a rapid cycle synchrotron (RCS) and a Main Ring (MR) synchrotron. Simulation calculation of longitudinal beam distribution in J-PARC Main Ring has been performed. The effect that RF voltage pattern, space charge, and beam loading gave was examined. | |||
| THPPC002 | Design and Construction of Turnkey Linacs as Injectors for Light Sources | electron, simulation, linac, synchrotron | 3272 |
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Turnkey linacs were manufactured by Thales Communications & Security in order to inject electrons into boosters of SOLEIL*, ALBA and BESSY II synchrotrons. This paper will describe the beam dynamics tools and methods for the design and construction of those linacs. Cavities tuning and prebunching characterization methods will be given. Beam loading compensation and simulations will be explained. Specified and measured beam parameters will be compared.
* A. Setty et al, "Commissioning of the 100 MeV preinjector HELIOS for the SOLEIL synchrotron", EPAC 06, Scotland, Edinburgh, June 2006. |
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| THPPC005 | Design of Magnetic Alloy Resonant System (MARS) Cavity for J-PARC MR | cavity, impedance, acceleration, status | 3278 |
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| The Magnetic Alloy Resonant System (MARS) cavity is a new type of Magnetic Alloy (MA) cavity using an external energy storage system. It is proposed as a back-up system of the present J-PARC high-Q MA cavity using cut cores. MARS consists of un-cut core loaded wideband MA cavities combined with an energy storage system using high-impedance, FT3L, cut cores. The main cavities are water-cooled and already established at J-PARC RCS. The energy storage system will be relatively high-Q (>100) to be stable under heavy beam loading. It also has a higher impedance than the main cavity and is air-cooled. The design of this cavity system will be presented. | |||
| THPPC006 | Status of the J-PARC Ring RF Systems | cavity, impedance, synchrotron, proton | 3281 |
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| Due to the 11th march earthquakes, J-PARC was forced to stop operation. The restoration is following the schedule so that J-PARC is restarted in December. Before the earthquake, we had considerable success in the 400 kW equivalent proton beam in the RCS. Multi-harmonic RF feedforward was established, which contributes to the reduction of beam loss and stable acceleration in RCS. The MR synchrotron achieved stable 150 kW beam operation for the T2K experiment. This summer, we installed two new RF systems in MR. Eight RF systems in total allow a more stable beam acceleration and flexible bunch shape manipulation. Also, we prepare the RF feedforward to compensate beam loading in MR. To achieve a beam power in excess of 1 MW in MR, it is considered to double the MR repetition rate. We developed an annealing scheme for large magnetic alloy cores while inside a DC B-field that results in higher core impedance, and have succeeded in producing large FT3L cores in this summer. With such cores we can almost double the accelerating voltage without re-designing the existing RF sources. For the near future, we plan to replace the existing RF cavities with upgraded cavities using the FT3L cores. | |||
| THPPC008 | Coupling Factor Evaluation of the RF Input Coupler for the IFMIF/EVEDA RFQ Linac | rfq, coupling, linac, cavity | 3287 |
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| In the design of prototype RFQ linac for the IFMIF/EVEDA Project, a 175 MHz RFQ, which has a longitudinal length of 9.78m, was proposed to accelerate deuteron beam up to 5MeV. The operation frequency of 175MHz was selected to accelerate a large current of 125mA in CW mode. The overall driving RF power of 1.28 MW by 8 RF input couplers has to be injected to the RFQ cavity. As a part of the validation of the coupler design, the beta factor (coupling coefficient) was measured on Aluminum RFQ at INFN Legnaro with on-purpose, real-scale dummy aluminum couplers for the installed depths of L=27, 40, 45, 48 and 73 mm. In this article, measurement and calculation results performed with the 3D code HFSS for coupling factor evaluation will be presented in details. | |||
| THPPC011 | Design of an Accelerating Structure for a 500 GeV CLIC using Ace3P | damping, linac, wakefield, simulation | 3296 |
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Funding: Research Council of Norway An optimized design of the main linac accelerating structure for a 500 GeV first stage of CLIC is presented. A similar long-range wakefield suppression scheme as for 3 TeV CLIC based on heavy waveguide damping is adopted. The accelerating gradient for the lower energy machine is 80 MV/m. The 500 GeV design has larger aperture radius in order to increase the maximum bunch charge and length which is limited by the short-range wakefields. The cell geometries have been optimized using a new parametric optimizer for Ace3P and details of the RF cell design are described. Parameters of the full structure are calculated and optimized using a power flow equation. |
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| THPPC076 | Comparison of LLRF Control Approaches for High Intensity Hadron Synchrotrons: Design and Performance | controls, cavity, feedback, synchrotron | 3464 |
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Funding: Federal Ministry of Education and Research A usual and effective way to realize closed-loop controllers is to use cascaded SISO feedback and to rely on some kind of linear PID structure with parameters adjusted manually in simulations or experiments. Such a control may not reach optimal performance if the system is coupled or non-linear. Regarding intense beams, longitudinal beam loading can be compensated by detuning. But the coupling between phase and amplitude (or I and Q component) highly depends on the tuning, that is on the resonant frequency of the cavity. It is derived that cavity and beam dynamics thus show bi-linear nature, i.e. belong to a well investigated class of non-linear systems with appropriate control strategies available*. Different controller designs are compared in terms of performance but also design transparency, the need of previous knowledge like the expected magnitude of beam loading and adaptability to different conditions, e.g. during acceleration or if applied to the full range of ion species as at GSI. The performance evaluation is based on macro-particle tracking simulations. In particular avail and limits of an optimal (quadratic cost) MIMO controller for bi-linear systems are shown**. * H.K. Khalil: Nonlinear Systems, 3rd Edition, Prentice-Hall, 2002 ** Z. Aganović, Z. Gajić: Linear Optimal Control of Bilinear Systems, Springer-Verlag, 1995. |
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| THPPC077 | Resonance Control of Superconducting Cavities at Heavy Beam Loading Conditions | cavity, controls, resonance, LLRF | 3467 |
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Funding: The research leading to these results has received funding from the European Commission under the EuCARD FP7 Research Infrastructures grant agreement no. 227579 The SC cavities operated at high Q level need to be precisely tuned to the RF frequency*. Well tuned cavities assure the good field stability and require minimum level of RF power to reach the operating gradient level. The TESLA cavities at FLASH are tuned with the help of slow (step motors) and fast (piezo) tuners driven by the control system**. The goal of this control system is to keep the detuning of the cavity as close to zero as possible in the presence of disturbing effects (Lorentz force detuning and microphonics). The detuning of the cavity can be determined using a few measurement methods. The most common is to measure detuning from the phase derivative at the end of the RF pulse. In order to calculate the detuning during the whole RF pulse the cavity equation must be solved taking into account all the driving forces (RF power delivered to the cavity and beam contribution). This in not the trivial task, particularly in the heavy beam conditions, since all signals must be precisely calibrated. This work presents the methods and algorithms to evaluate and control the detuning of the superconducting cavities in the heavy beam loading conditions adequate for ILC operation. * Grecki M., Piezo operation experience at FLASH, LLRF-2011, DESY, 09.2011 ** Grecki M. et al. Piezo Control for Lorentz Force Detuned SC Cavities of DESY FLASH, IPAC'10, Kyoto, Japan, pp.1452-1454 |
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| THPPC084 | LHC One-turn Delay Feedback Commissioning | cavity, feedback, klystron, LLRF | 3482 |
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| The 1-turn delay feedback is an FPGA based feedback system part of the LHC cavity controller, which produces gain only around the revolution frequency harmonics. As such, it helps reduce the transient beam loading and effective cavity impedance. Consequently, it increases the stability margin for Longitudinal Coupled Bunch Instabilities driven by the cavity impedance at the fundamental and allows reliable operation at higher beam currents. The 1-turn delay feedback was commissioned on all sixteen cavities in mid-October 2011 and was used in operation for the rest of the run. The commissioning procedure and algorithms for setting-up are presented. The resulting improvements in transient beam loading, beam stability, and required klystron power are analyzed. The commissioning of the 1-turn delay feedback reduced the cavity voltage phase modulation from approximately six degrees peak-to-peak to below one degree at 400 MHz. | |||
| THPPP015 | A Clamped Be Window for the Dump of the HiRadMat Experiment at CERN | vacuum, synchrotron, simulation, cavity | 3758 |
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| At CERN, the High Radiation to Materials facility (HiRadMat) is designed to test accelerator components under the impact of high-intensity pulsed beams and will start operation in 2012. In this frame a LHC TED -type dump was installed at the end of the line, working in nitrogen over-pressure, and a 258μm-thick beryllium window was placed as barrier between the inside of the dump and the external atmosphere. Because of the special loading conditions, a clamped window design was especially developed, optimized and implemented, the more standard welded window not being suitable for such loads. Considering then the clamping force and the applied differential pressures, the stresses on the window components were carefully evaluated thanks to empirical as well as numerical models, to guarantee the structural integrity of the beryllium foil. This paper reports on choices and optimizations that led to the final design, presenting also comparative results from different solutions and the detailed results for the adopted one. | |||
| THPPP082 | RF Feedforward System for Beam Loading Compensation in the J-PARC MR | impedance, cavity, injection, proton | 3924 |
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| For acceleration of high intensity proton beams in the J-PARC MR, beam loading compensation is important. In the MA-loaded RF cavity in the MR, which has a Q-value in the order of 20, the wake voltage consists of the accelerating harmonic (h=9) and the neighbor harmonics (h=8, 10). We employ the RF feedforward method for the beam loading compensation, like in the J-PARC RCS, in which the impedance seen by the beam is greatly reduced by the feedforward. The full-digital feedforward system developed for the MR has a similar architecture to that of the RCS. The system compensates the beam loading of the important three harmonics (h=8, 9, 10). We present the structure of the RF feedforward system. Also, we report the preliminary results of the beam tests. | |||