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Beam phase retrieval based on higher order modes in cylindrical superconducting radio frequency cavities
摘要： The control of beam phase relative to the accelerating RF field within a superconducting cavity is important in many accelerator applications and is of particular importance for a free electron laser facility. As standard practice, the phase is usually inferred from the beam-induced transient field with respect to a timing reference. We report here on an alternative and novel means of beam phase determination based on beam-excited higher order electromagnetic modes and the accelerating electromagnetic mode, which are conveniently available from the same coupler. The monopole modes are immune to the electron beam offset and therefore are best suited for the task. A coupled circuit model is used to assist the development and to rapidly assess the facility of the method. Simulations based on the circuit model indicate that the resolution of this system depends critically on the signal to noise ratio. Beam-based measurements with a test setup were carried out at the European X-ray Free Electron Laser (XFEL), Germany. Based on this new method, we have routinely obtained a resolution of 0.1°. The best resolution observed with the current setup was 0.03°. These results agree very well with the predictions from those predicted by a circuit model. The system investigated here can be used to provide diagnostic information for the current low level RF system employed in the European XFEL. To this end, the associated electronics are under development. This monitor is the first of its kind that can deliver direct and online measurements of the beam phase with respect to the RF field.
关键词： higher order modes,accelerator applications,beam phase retrieval,free electron laser,superconducting radio frequency cavities
更新于2025-09-23 15:21:21
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Nickel doped TiO <sub/>2</sub> films by a modified laser plasma source for photocatalytic applications
摘要： We reports a study on pure and Ni-doped TiO2 thin ?lms produced via laser ablation technique. The novelty of the work consists that both synthesis and doping were carried out in a single process, using a modi?ed laser ion source to simultaneously make pulsed laser deposition (PLD) and low-energy ion implantation (by post-acceleration method). In particular, two titania ?lms were synthesized via PLD starting from a rutile target. One of the two ?lms was doped with Ni ions, accelerated with a voltage of 20 kV. The total implanted dose, evaluated by a Faraday cup, resulted to be 1 × 1014 ions/cm2. The crystalline phase of the obtained TiO2 ?lms was analysed by Raman spectroscopy. A higher photocatalytic activity, measured under UV irradiation using methylene blue, was estimated for the Ni-doped titania ?lm with respect the pure one.
关键词： Plasma generation (laser-produced, RF, x ray-produced),Accelerator Applications,Plasma diagnostics - probes
更新于2025-09-23 15:21:01
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Acceleration of carbon ion beams by an ultraviolet laser under conditions relevant for ion fast ignition of inertial fusion
摘要： The properties of carbon ion beams produced by a 100-kJ, 1-ps, KrF ultraviolet laser under conditions relevant for ion fast ignition (IFI) of DT fusion are numerically investigated using the 2D3V particle-in-cell code, and the possibility of achieving the ion beam parameters required for IFI is tested. The numerical simulations of carbon ion acceleration were carried out for ?at carbon targets of various thicknesses (LT) and for various laser beam apertures (dL) on the target, while the laser pulse duration and energy were ?xed. It was found that both the radiation pressure acceleration (RPA) mechanism and the sheath acceleration mechanism signi?cantly a?ects the characteristics of the ion beam, with the RPA dominating in the case of thicker targets (LT ～ 10–30 μm). The ion beam parameters depend to a signi?cant extent on the target thickness and the distance from the target. The mean and maximum ion energy decrease with the increase of LT from 3 μm to 30 μm, while the ion beam intensity, the beam energy ?uence and the total energy of the “useful part” of the ion beam (with an aperture ≤ 50 μm) reach maximum values at LT ～ 5–10 μm. For the optimal value of LT and a small distance x from the target (x ～ LT), the ion beam parameters are close to or higher than what is required for IFI. However, due to the angular divergence of the ion beam, the beam intensity and ?uence decrease with an increase in the distance from the target, and at x ≥ 0.5 mm the beam parameters are below the values required for fusion ignition. To reach these values, higher laser energies and/or more sophisticated schemes of ion acceleration are required.
关键词： Ion sources,Accelerator Applications,Accelerator modelling and simulations
更新于2025-09-19 17:13:59
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Proton beams of laser-hydrogenated metal targets
摘要： In this paper, we report a study on proton beams produced via laser interaction from hydrogenated solid targets useful for the development of new sources devoted to medical applications, such as hadron therapy and isotope production. The hydrogenation of the targets was made before the laser-matter interaction. In this study, we used as solid targets, pure samples of Ti, Ta and Al which in a ?rst phase were treated by laser cleaning (via KrF excimer laser at the irradiance I = 3×107 W/cm2) and then they were exposed to laser irradiation (1500 pulses, I = 3×107 W/cm2) under a constant ?ow of H2 (HiQ Hydrogen 6.0, highly pure). After that, the targets were maintained under H2 ?ow for 5 minutes, in order to promote a further hydrogen adsorption. We report laser ablation measurements performed at ?uences of 1.3, 2.5 and 5.0 J/cm2. The results on hydrogenated targets showed an increase of proton yield of 25% (Ti), 64% (Al) and 550% (Ta), with respect to the corresponding untreated ones.
关键词： Plasma generation (laser-produced, RF, x ray-produced),Ion sources (positive ions, negative ions, electron cyclotron resonance (ECR), electron beam (EBIS)),Accelerator Applications
更新于2025-09-19 17:13:59