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MOPAS078 | Digital RF Control for Spallation Neutron Source Accumulator Ring | controls, feedback, linac, simulation | 611 | |||||
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Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy. |
The proposed upgrade plan for RF control of the Spallation Neutron Source (SNS) accumulator ring requires that the new digital field control module (FCM) support both the conventional narrow-band feed forward control and a new beam-based feed forward control. Both are necessary for compensating the heavy beam loading in SNS ring. The ring FCM also has the integrated control and monitoring features for the cavity bias, cavity resonance, and tetrode grid boost. A user-friendly Epics GUI for all these FCM functionalities is also a part of the requirement. The ring FCM under development is being implemented on the hardware of the proven FCM of SNS Linac. Both the controller architecture and the design code of the digital hardware for the Linac system will be largely reused in the ring system. |
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WEZAB02 | Results on CLIC Proof of Principle from CTF3 | linac, collider, extraction, injection | 1979 | |||||
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The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme of Multi-TeV electron-positron collider by 2010. In its final configuration CTF3 will consist of a 150 MeV drive beam linac followed by a 42 m long delay loop and an 84 m combiner ring. The installation includes a two-beam test stand and a test decelerator. The linac and delay loop have been already commissioned, while the combiner ring will be completed by the first half of 2007. High gradient testing of accelerating structures is also under way. The status of the facility, the experimental results obtained and the future plans will be presented.
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WEPMN012 | Beam Loading Compensation Using Real Time Bunch Charge Information from a Toroid Monitor at FLASH | controls, klystron, gun, undulator | 2074 | |||||
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Funding: Deutsches Elektronen-Synchrotron - DESY |
At pulsed linear accelerators, fast proportional rf control compensates beam loading sufficiently for single or a few bunches. In the case of long bunch trains, additional measures have to be taken commonly by adding a compensation signal to the rf drive signals calculated from the predicted beam intensity. In contrast to predictive methods, techniques based on real time beam measurements are sensitive to fast changes of the beam intensity and bunch patterns. At FLASH we apply a beam loading compensation scheme based on toroid monitor signals. This paper presents the compensation scheme, the calibration procedure and the effect on the beam. |
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WEPMN024 | RF Feedback Control Systems of the J-PARC Linac | feedback, controls, linac, proton | 2101 | |||||
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The commissioning of the J-PARC 181MeV proton linac was started from October of 2006. The RF sources of the linac consist of 4 solid-state amplifiers and 20 klystrons. In each RF source, the RF fields are controlled by a digital RF feedback system installed in a compact PCI (cPCI) to realize the accelerating field stability of ±1% in amplitude and ±1 degree in phase. In this paper the performance of the RF feedback control systems will be reported in detail.
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WEPMN039 | Performance of J-PARC Linac RF System | controls, klystron, linac, feedback | 2128 | |||||
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High power operation of all the RF systems of J-PARC linac was started for the cavity conditioning in October 2006. Twenty 324-MHz klystrons have powered the accelerating cavities successfully, and the beam commissioning was started in November 2006. The performance of the RF drive and control system will be presented.
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WEPMN079 | Power Coupler for the ILC Crab Cavity | simulation, coupling, controls, dipole | 2212 | |||||
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Funding: This work was supported by the EC under the FP6 "Research Infrasctructure Action - Structuring the European Research Area" EUROTeV DS Project Contract no.011899 RIDS and PPARC. |
The ILC crab cavity will require the design of an appropriate power coupler. The beamloading in dipole cavities is considerably more variable than accelerating cavities, hence simulations have been performed to establish the required external Q. Simulations of a suitable coupler were then performed and were verified using a normal conducting prototype with variable coupler tips. |
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WEPMN080 | Development of Circuits and System Models for the Synchronization of the ILC Crab Cavities | controls, linac, target, kaon | 2215 | |||||
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Funding: The Commission of the European Communities under the 6th Framework Programme (Structuring the European Research Area) The UK particle physics and astromony research council. |
The ILC reference design report (RDR) recommends a 14 mrad crossing angle for the positron and electron beams at the IP. A matched pair of crab cavity systems are required in the beam delivery system to align both bunches at the IP. The use of a multi-cell, 3.9GHz dipole mode superconducting cavity, derived from the Fermilab CKM cavity. Dipole-mode cavities phased for crab rotation are shifted by 90 degrees with respect to similar cavities phased for deflection. Uncorrelated phase errors of 0.086 degrees (equivalent to 61fs) for the two cavity systems, gives an average of 180nm for the relative deflection of the bunch centers. For a horizontal bunch size of 655nm, a deflection of 180nm reduces the ILC luminosity by 2%. The crab cavity systems are to be placed ~28m apart and their synchronization to within 61fs is on the limit of what is presently achievable. This paper describes the design and testing of circuits and control algorithms under development at the Cockcroft Institute in the UK for proof of principle experiments planned on the ERLP at Daresbury and on the ILCTA test beamline at FNAL. Simulation results for measurement and control systems are also given. |
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WEPMN087 | Variable CW RF Power Coupler for 345 MHz Superconducting Cavities | coupling, vacuum, simulation, cryogenics | 2230 | |||||
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Funding: This work was supported by the U. S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC-02-06CH11357. |
This paper reports the development of a 5-10 kW cw variable coupler for 345 MHz spoke-loaded superconducting (SC)cavities. The coupler inserts an 80K copper loop into a 5 cm diameter coupling port on several types of spoke-loaded cavity operating at 2 - 4K. The coupling loop can be moved during operation to vary the coupling over a range of 40 dB. The coupler is designed to facilitate high-pressure water rinsing and low-particulate clean assembly. Design details and operating characteristics are discussed. |
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WEPMN101 | Coupling Interaction Between the Power Coupler and the Third Harmonic Superconducting Cavity | coupling, klystron, injection, cryogenics | 2268 | |||||
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Funding: U. S. Department of Energy |
Fermilab has developed a third harmonic superconducting cavity operating at the frequency of 3.9 GHz to improve the beam performance for the FLASH user facility at DESY. It is interesting to investigate the coupling interaction between the SRF cavity and the power coupler with or without beam loading. The coupling of the power coupler to the cavity needs to be determined to minimize the power consumption and guarantee the best performance for a given beam current. In this paper, we build and analyze an equivalent circuit model containing a series of lumped elements to represent the resonant system. An analytic solution of the required power from the generator as a function of the system parameters has also been given based on a vector diagram. |
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WEPMN116 | Plans for Precision RF Controls for FERMI@ELETTRA | controls, linac, klystron, feedback | 2310 | |||||
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FERMI@ELETTRA is a 4th generation light source under construction at Sincrotrone Trieste. It will be operated as a seeded FEL driven by a warm S-band linac presently serving as the injector for the ELETTRA storage ring. Operation as an FEL driver places much more stringent specifications on control of the amplititude and phase of the RF stations than in its present operation. This paper describes a conceptual design of an upgrade to the RF controls to achieve these specifications. The system consists of a stabilized distribution of the master oscillator signal providing a reference to local digital RF controllers . The RF reference distribution system takes advantage of recent breakthroughs in optical techniques where stabilized fiber lasers are used to provide a very accurate control of RF phases over long distances. The RF controller is based on recent improvements on modern digital systems, using a 14-bit high speed digitizer in combination with an FPGA and high speed DAC. This paper also presents experimental results of early tests performed as a feasibility study of the system.
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WEPMS025 | LANSCE-R Low Level RF Control System | controls, resonance, feedback, monitoring | 2388 | |||||
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The Los Alamos Neutron Science Center proton accelerator is scheduled for refurbishment. A new low level RF(LLRF) system is part of the refurbishment plan since the existing LLRF system is analog-based and requires significant setup and maintenance time. Both field and resonance control aspects of the current system do not have the flexibility to meet future performance requirements. The LANSCE accelerator provides both H+ and H- beams and due to the various user requirements there are a number of different beam pulse types varying in timing and current. In order to meet user needs, LANSCE must simultaneously transport both H+ and H- in the accelerator. These requirements have motivated the development of a new LLRF system based on software defined radio technology. The new system will include field control using feedback and adaptive feed forward techniques, an upgraded resonance controller with frequency agility to improve startup and fault recovery times and a high power amplifier pre-compensation controller for improved cavity fill times and amplifier efficiency. Among the challenges with implementing the new system are interfacing with existing subsystems of the accelerator.
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WEPMS080 | SRF Cavity Transient Beam Loading Detection - Simulation and Measurement | simulation, linac, accumulation, controls | 2517 | |||||
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Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy. |
Beam phase measurement based on detection of transient beam loading signal in a Superconducting (SC) cavity is utilized to setup the cavity synchronous phase. It has the potential to become a fast tune-up technique for a high intensity SC electron linac, as cavity phase could be determined precisely with only a few beam pulses. The paper introduces a transient detector study in the Spallation Neutron Source (SNS) proton linac, and discusses one of the major challenges - stochastic noise in the cavity RF system, which deteriorates the precision and increases the time needed for phase measurement with this technique. We analyze the influence of RF noise to the phase measurement in a simulation study with a beam-cavity model. Beam signal measurement with the cavity Low Level RF (LLRF) system and the initial experiment of prototype detectors are briefly introduced. |
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WEPMS081 | Simulation and Initial Test Result of the SNS Ring RF System | simulation, controls, beam-losses, feedback | 2520 | |||||
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Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy |
A simulation code has been developed for the study of the Spallation Neutron Source (SNS) ring RF control. The code uses the time-domain solvers to compute beam-cavity interactions, and FFT methods to simulate time responses of the linear RF system. The important ingredients of the system are considered in the simulation model, which include the beam loading, dynamic cavity detuning, circuit bandwidth, loop delay, proportional-integral (P-I) controller for feedback and adaptive feed forward, stochastic noise, with-in-turn RF parameter change, beam current fluctuation and beam bunch leakage, etc. The beam loss in the accumulation ring goes up as the beam power increases, and thus a precise control of bunching voltage phase and amplitude is required to limit beam loss. This simulation tool will help the development a correct RF control and to achieve the goal of minimizing the beam loss. |
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THPMN113 | Performance of Capillary Discharge Guided Laser Plasma Wakefield Accelerator | laser, electron, plasma, simulation | 2978 | |||||
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Funding: This work is supported by US DoE office of High Energy Physics under contract DE-AC02-05CH11231 and DARPA. |
A GeV-class laser-driven plasma-based wakefield accelerator has been realized at the Lawrence Berkeley National Laboratory (LBNL). The device consists of a 100 TW-class high repetition rate Ti:sapphire LOASIS laser system of LBNL and a gas-filled capillary discharge waveguide developed at Oxford University. Results will be presented on the generation of GeV-class electron beams with a 3.3 cm long preformed plasma channel. The use of a discharge-based waveguide permitted operation at an order of magnitude lower density and 15 times longer distance than in previous experiments that relied on laser-preformed plasma channels. Laser pulses with peak power ranging from 10-50 TW were guided over more than 20 Rayleigh ranges and high-quality electron beams with energy up to 1 GeV were obtained. The dependence of the electron beam characteristics on plasma channel properties and laser parameters are discussed. |
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THPMS028 | The Physical Picture of Beam Loading in the Blowout Regime | electron, plasma, laser, simulation | 3061 | |||||
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Funding: This work is supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345. |
The realization of high quality LWFA-produced electron beams requires laser pulses that remain focused for distances exceeding the Rayleigh length. It is often thought that a short pulse laser cannot be self-guided and some form of external optical guiding is needed. As short pulse lasers with higher power are rapidly coming online to test the LWFA concept it is vital to understand the nature of their propagation through centimeters of plasma. We argue that a degree of self-guiding is possible for short ultra-intense pulses that have been shown to lead to complete ponderomotive expulsion of plasma electrons. Furthermore, the generation of a high quality electron beam requires proper loading of the wake. We have developed a theoretical framework which predicts the maximum number of electrons which can be loaded in the wake, as well as the optimal charge density profile for beam loading. Using the PIC codes OSIRIS and QuickPIC we present designs of LWFA accelerators that verify our theoretical estimates as well as demonstrate the potential of LWFA to produce high energy electron beams with high beam quality. |
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THPMS072 | Superconducting Traveling Wave Ring with High Gradient Accelerating Section | feedback, resonance, coupling, controls | 3148 | |||||
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Considerable gain of a superconducting linac accelerating gradient provides using of a traveling wave structure instead of a standing wave accelerating section. Preservation of the superconducting structure advantages requires to put the TW accelerating section into a superconducting traveling wave ring (STWR). We discuss two variants of the STWR with one and two feeding couplers. The STWR application allows to increase the superconducting section accelerating gradient up to ~50 MV/m and essentially reduce the price of the section tuning system.
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THPAN038 | Generation and Acceleration of High Brightness Electron Bunch Train in ATF of KEK | electron, gun, injection, laser | 3312 | |||||
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Laser Undulator Compact X-ray source (LUCX) is a test bench for compact high brightness X-ray generator at KEK in order to demonstrate the possibility on K-edge digital subtraction angiography, based on the Compton Scattering. For this project, one of the challenging problems is to generate and accelerate high brightness multi-bunch electron beams, compensating the energy difference due to beam loading effect. In this paper, we calculate the transient beam loading voltage and energy gain from RF field in standing wave gun cavity and traveling wave accelerating tube for multi-bunch train, considering the process of propagation, buildup of RF field in them and the special RF pulse shape. We generated and accelerated 100 bunch electron beam train with 50nC, which beam loading effect was compensated effectively by adjusting the laser injection timing. By BPM and OTR system, we measured the electron beam energy bunch by bunch. The average energy of 100 bunch train is 40.5MeV and maximum energy difference bunch to bunch is 0.26MeV, the relative energy spread of single bunch is about 0.13%. The transverse emittance can be optimized roughly to 3.6 pimm.mrad.
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FROAC01 | The Spallation Neutron Source Accumulator Ring RF System | controls, proton, extraction, injection | 3795 | |||||
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Funding: SNS is managed by UT-Batelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy. |
The Spallation Neutron Source (SNS) accumulator ring is a fixed-frequency proton storage ring located at the output of the SNS Linear Accelerator (Linac). Its purpose is to convert 1 millisecond H- beam pulses from the SNS Linac into high-intensity 695 nanosecond pulses of protons for delivery to the neutron target. The RF bunching system controls longitudinal beam distribution during the accumulation process and maintains a 250+ nanosecond gap required for beam extraction. The RF system consists of three stations which operate at a beam revolution frequency of 1.05 MHz while a fourth station provides a second harmonic component at 2.1 MHz. The beam pulse at extraction consists of 1.6·1014 protons representing a peak beam current of 52 amperes. The system utilizes four 600kW tetrodes to provide the RF current necessary to produce the 40kV peak-bunching voltage and to control phase and amplitude at this high beam current. In this paper we review the design concepts incorporated into this heavily beam-loaded RF system and discuss its commissioning status. |
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