| Paper | Title | Other Keywords | Page |
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| TUPFI053 | Transient Beam Loading Effects in Gas-filled RF Cavities for a Muon Collider | cavity, plasma, ion, electron | 1463 |
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Funding: Research supported by the U.S. Department of Energy. A gas-filled RF cavity can be an effective solution for the development of a compact muon ionization cooling channel. One possible problem expected in this type of cavity is the dissipation of significant RF power through the beam-induced plasmas accumulated inside the cavity (plasma loading). In addition, for the higher muon beam intensity, the effects of the beam itself on the cavity fields in the accelerating mode are non-negligible (beam loading). These beam-cavity interactions induce a transient phase which may be very harmful to the beam quality. In this study, we estimate the transient voltage in a gas-filled RF cavity with both the plasma and conventional beam loading and discuss their compensation methods. |
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| TUPME052 | Sub-harmonic Buncher Design for the CLIC Drive Beam Injector | coupling, electron, linear-collider, collider | 1685 |
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| The CLIC (Compact LInear Collider) is based on two beam concept where a high current drive beam provides the energy needed for acceleration of the main beam. The CLIC drive beam accelerator starts with a high current injector using a sophisticated sub-harmonic bunching system. This paper will focus on the design of the Sub Harmonic Bunchers (SHBs) the first RF components of the injector. A backward traveling wave structure has been optimized for this task. It will be shown also how to avoid asymmetrical fields inside the coupler cells and how to compensate beam loading by changing the phase velocity in comparison to the beam velocity. | |||
| TUPME053 | General Beam Loading Compensation in a Traveling Wave Structure | bunching, linac, electron, storage-ring | 1688 |
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| The well-known beam loading in a traveling wave structure is in fact a resistive beam loading which bunches travel on the crest. This type of beam loading could be compensated by increasing RF feed power. But generally, bunches could travel on each phase. General beam loading compensation is well-known for a single cell cavity and it is done by changing the RF feed power and detuning the structure together. In this paper, the concept of detuning for a TW structure will be shown and the evolution of fundamental mode beam-induced field will be derived and finally, it will be shown how to compensate beam loading by changing the phase velocity in comparison to the beam velocity. | |||
| TUPME054 | Experimental Study of the Effect of Beam Loading on RF Breakdown Rate in CLIC High-gradient Accelerating Structures | linac, optics, beam-losses, luminosity | 1691 |
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| RF breakdown is a key issue for the multi-TeV high-luminosity e+e− Compact Linear Collider (CLIC). Breakdowns in the high-gradient accelerator structures can deflect the beam and decrease the desired luminosity. The limitations of the accelerating structures due to breakdowns have been studied so far without a beam present in the structure. The presence of the beam modifies the distribution of the electrical and magnetic field distributions, which determine the breakdown rate. Therefore an experiment has been designed for high power testing a CLIC prototype accelerating structure with a beam present in the CLIC Test Facility (CTF3). A special beam line allows extracting a beam with nominal CLIC beam current and duration from the CTF3 linac. The paper describes the beam optics design for this experimental beam line and the commissioning of the experiment with beam. | |||
| WEPWO048 | Investigation of a Ridge-loaded Waveguide Structure for CLIC X-band Crab Cavity | cavity, damping, HOM, impedance | 2411 |
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| In conventional crab cavities the TM11 mode is used to deflect the beam. In a linear collider such as CLIC, it is necessary to damp all the other modes, namely the accelerating i.e. lower order mode (LOM), same order mode (SOM) and higher order modes (HOMs). In addition to this, as the TM11 mode is not the fundamental mode, it is generally not excited with the highest shunt impedance. This necessitates damping of the high shunt impedance modes to acceptable level. Here we report on the investigation of an alternative design of the X-band crab cavity for CLIC based on ridge-loaded waveguide. In this type of cavity, the deflecting mode is the fundamental mode and has the maximum shunt impedance. However, the geometry of the cavity is chosen to optimise the ratio of group velocity to shunt impedance to minimise the effect of beam loading. The other modes are excited above the crabbing mode and are damped using wave-guides. Another advantage of this type of cavity is, unlike the conventional TM11 mode cavities, the e.m. surface fields do not peak at the iris. This provides ample margin to optimise the cavity geometry and reach the desired field distribution. | |||
| WEPEA020 | Commissioning of Beam Loading Compensation System in the J-PARC MR | impedance, cavity, injection, extraction | 2540 |
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| Beam loading compensation is indispensable to accelerate high intensity proton beams in the J-PARC MR. The MA-loaded rf cavities in the MR are driven by the single harmonic (h=9) rf signals, while the cavity frequency response covers also the neighbor harmonics (h=8, 10). The wake voltage induced by the beam consists of the three harmonics (h=8, 9, 10). We employ the rf feedforward method to compensate the beam loading of these harmonics. The full-digital feedforward system was developed for the MR. We have successfully commissioned the feedforward patterns for all of eight cavities by using high intensity beams with 1.0·1014 ppp. We present the commissioning results. The impedance seen by the beam is reduced and the longitudinal oscillations due to the beam loading are reduced. By the beam loading compensation, high power beam operation at the beam power of 200 kW has been achieved. | |||
| WEPFI013 | The Damped C-band RF Structures for the European ELI-NP Proposal | damping, linac, dipole, photon | 2726 |
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| The gamma beam system of the European ELI-NP proposal foresees the use of a multi-bunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 14 travelling wave C-Band structures, 1.8 m long with a field phase advance per cell of 2π/3 and a repetition rate of 100 Hz. Because of the multi-bunch operation, the structures have been designed with a damping of the HOM dipoles modes in order to avoid beam break-up (BBU). In the paper we discuss the design criteria of the structures also illustrating the effectiveness of the damping in the control of the BBU. Prototype activity is finally illustrated. | |||
| WEPFI062 | Precise Cavity Tuning System of a Low Output-impedance Second-harmonic Cavity at ISIS | cavity, impedance, resonance, cathode | 2836 |
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| A very low output-impedance (~35ohms) second-harmonic cavity system is being developed for high intensity proton accelerators. The final amplifier is comprised of a grounded cathode scheme with a feedback loop from anode to grid. Due to the Miller effect, the grid voltage waveform is seriously distorted even if only a few percent of sub-harmonic or higher harmonic are mixed in the generator current. Such distortion is much enhanced by the beam loading. In order to eliminate the effect of this distortion upon the phase detector used to achieve precise cavity tuning, a swept bandpass filter was applied to the grid voltage at the phase detector input. Filter design details and the result of high power tests are reported. | |||
| WEPME009 | Recent Developments of the European XFEL LLRF System | LLRF, controls, cavity, laser | 2941 |
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| The European XFEL is comprised of more than 800 TESLA-type super-conducting accelerator cavities which are driven by 25 high-power multi-beam klystrons. For reliable, reproducible and maintainable operation of linac, the LLRF system will process more than 3000 RF channels. Beside the large number of RF channels to be processed, stable FEL operation demands field stability better than 0.010deg in phase and 0.01% in amplitude. To cope with these challenges the LLRF system is developed on MTCA.4 platform. In this paper, we will give an update of the latest electronics developments, advances in the feedback controller algorithm and measurement results at FLASH. | |||
| WEPME022 | Overview of the CSNS/RCS LLRF Control System | cavity, controls, LLRF, feedback | 2977 |
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| The CSNS/RCS RF system consists of 8 ferrite-loaded RF cavities (h=2), each with individual digital LLRF control electronics. The injection and extraction energy of the beam are 80MeV and 1.6GeV respectively with a repetition rate of 25Hz. The RF system is designed to provide the maximum RF voltage of 165kV. The RF frequency range is from 1.02MHz at injection to 2.44MHz at extraction. The CSNS/RCS LLRF control system is based on FPGA, and composed of 7 control loops to achieve required acceleration voltage amplitude and phase regulation. A number of prototype and the first formal system have been completed and tested. In this paper we present an overview of the LLRF control system, and some operational results. | |||