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| MOZCM01 | Commissioning and Operation of the 1.5 GeV Harmonic Double Sided Microtron at Mainz University | linac, dipole, injection, microtron | 51 | |||||
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In December 2006 the 4th stage of the Mainz Microtron MAMI has been succesfully set into operation expanding the 855MeV output energy of the existing three racetrack microtron cascade (MAMI B) to 1508MeV. This new recirculating cw electron accelerator is realised as a worldwide unique Harmonic Double Sided Microtron (HDSM, [*]). Since February 2006, after only 14 day of commissioning, the HDSM serves as part of the MAMI C accelerator cascade in routine 24h a day operation for nuclear physics experiments. We will give a brief overview of the design and construction of the HDSM and describe in detail the experiences gained during commissioning and the first year of operation.
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[*] A. Jankowiak et al., "Status Report on the Harmonic Double Sided Microtron of MAMI C", Proceedings EPAC2006, Edinburgh, p. 834 |
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| MOPC059 | BBU Limitations for ERLs | dipole, linac, beam-transport, lattice | 199 | |||||
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The BBU threshold in ERLs is a limitation on the maximum beam current due to the interaction of the electron bunches and the Higher Order Modes (HOMs) contained within the RF cavities. Several factors are involved in determining the threshold current; from the cavity the Q, R/Q and degeneracy of the modes all play an important part. From the beam transport the values of the lattice functions α, β and μ have an effect. We will discuss the limits on these variables to provide a BBU current threshold greater than 100 mA for a multiple cavity machine and what will be required to provide higher currents. Also three different cavity profiles were investigated with the aim of reducing the BBU threshold. The TESLA 9-cell cavity was used as a baseline for comparison against possible 7-cell cavity designs, using the TESLA cell shape for their inner cells. The ends of the 7-cell cavities join to different sized beampipes, with radii of 39 mm and 54 mm, to allow the most of the HOMs to propagate to a broadband HOM absorber. Two different beampipe to cavity to transitions were investigated. The optimised 7-cell cavity will be shown to provide an increase in the BBU threshold.
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| WEOBG01 | CLIC RF High Power Production Testing Program | damping, target, beam-losses, linac | 1909 | |||||
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The CLIC Power Extraction and Transfer Structure (PETS) is a passive microwave device in which bunches of the drive beam interact with the impedance of the periodically loaded waveguide and generate RF power for the main linac accelerating structure. The demands on the high power production (~ 150 MW) and the needs to transport the 100 A drive beam for about 1 km without losses make the PETS design rather unique and the operation very challenging. In coming years the intensive PETS testing program will be implemented. The target is to demonstrate full performance of the PETS operation. The testing program overview and test results available to date will be presented.
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| WEPP087 | Observation and Mitigation of Multipass BBU in CEBAF | linac, dipole, damping, optics | 2722 | |||||
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The CEBAF recirculating accelerator at Jefferson Lab consists of two linacs carrying beam for up to five passes of acceleration. The Beam Break-Up (BBU) phenomenon was anticipated during design of the accelerator. The threshold beam current to induce BBU was calculated to be approximately 20 milliamperes, far above operational current. No sign of BBU was ever seen in more than a decade of operation. A specially designed acceleration cavity in a recently installed cryomodule was found to cause a BBU instability under special conditions with as low as 40 uA of injected beam current. This presented an opportunity to study BBU in a five-pass accelerator. In this paper we will discuss multipass BBU, show observational data, and discuss the ways we have developed to maintain the instability threshold current to values above those required for operation.
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| WEPP161 | Preliminary Experiments on a Fluidised Powder Target | target, factory, collider, vacuum | 2862 | |||||
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In order to achieve higher resolutions the next generation of accelerator facilities is designed to operate with beam powers orders of magnitude higher than that handled by the current technology. So it is believed that the existing target and beam dump designs will be unsuitable to survive beam interactions depositing powers in the order of several megawatts. Good target design is important for the physics yield from experiments and crucial to the reliable operation of the facility. Furthermore the choice of target is strongly associated with the safety and cost of design (i.e., economic viability) of the entire facility. This article proposes a new target technology based on fluidised powder believed to be suitable for application at higher beam powers whilst avoiding some of the problems associated with other technologies. A conceptual system design for the application of the fluidised powder target to the requirements of a future neutrino facility, is presented. The preliminary experimental results presented, show the effect of some of the parameters which are expected to determine the performance, physics yields and reliability of operation of the new powder system.
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