Enhanced susceptibility of CaF2(111) to adsorption due to ion irradiation

International audienceWe have investigated morphological changes of freshly cleaved CaF2(111) single crystal surfaces before and after ion irradiation. We show that with or without irradiation the surface undergoes serious changes within minutes after the cleavage if the samples are exposed to ambient conditions. This is most likely due to the adsorption of water and could be avoided only if working under clean ultra-high-vacuum conditions. Ion-induced modifications on this surface seem to act as centers for an increased rate of adsorption so that any quantitative numbers obtained by atomic force microscopy in such experiments have to be treated with caution

Swift heavy ion irradiation of SrTiO3 under grazing incidence

International audienceThe irradiation of SrTiO3 single crystals with swift heavy ions leads to modifications of the surface. The details of the morphology of these modifications depend strongly on the angle of incidence and can be characterized by atomic force microscopy. At glancing angles, discontinuous chains of nanosized hillocks appear on the surface. From the variation of the length of the chains with the angle of incidence the latent track radius can be determined. This radius is material specific and allows the calculation of the electron– phonon coupling constant for SrTiO3. We show that a theoretical description of the nanodot creation is possible within a two-temperature model if the spatial electron density is taken into account. The appearance of discontinuous features can be explained easily within this model, but it turns out that the electronic excitation dissipates on a femtosecond timescale, too rapidly to feed sufficient energy into the phonon system in order to induce a thermal melting process. We demonstrate that this can be solved if a temperature-dependent diffusion coefficient is introduced into the model

THE VARIAN 250 MeV SUPERCONDUCTING COMPACT PROTON CYCLOTRON: MEDICAL OPERATION OF THE 2nd MACHINE,PRODUCTION AND COMMISSIONING STATUS OF MACHINES

Varian Medical Systems Particle Therapy has successfully commissioned its 2nd superconducting compact proton cyclotron for use in proton therapy in 2008. The 250 MeV machine serves as proton source for treatments at the first clinical proton therapy center in Germany which opened in early 2009. Furthermore, Varian is currently commissioning and factory testing its 3rd machine. We report on the operation and performance of the 2nd machine as well as on the successful cool-down, quench testing, and magnetic shimming of the 3rd machine. In addition we present RF commissioning plans using a newly developed solid state amplifier, and plans for the upcoming factory beam commissioning in the new Varian cyclotron scanning nozzle test cell, scheduled for October 2010. Finally we provide a brief status and outlook on machines no. 4 to 7.IMP;Chinese Academy of Science

Research at Varian on applied superconductivity for proton therapy

Proton therapy is a rapidly increasing modality to treat cancerous tumors, but large-scale implementation, and therefore widespread availability for patients, is hindered by the size and upfront investment for treatment facilities. Superconducting technology can enable more compact, and therefore more affordable treatment systems, by increasing the magnetic field in the magnets for the proton accelerator (typically a cyclotron) and in the beam guidance up, over, and into the patient (the gantry). In this article, we discuss research at Varian Medical Systems Particle Therapy GmbH on various superconducting technologies for potential application in future, more compact cyclotrons and gantries. We discuss which technologies are feasible, and to what extent. We demonstrate why certain conductor choices are made, and show the development of novel new conductor and magnet technologies that will be required to enable the next generation of cryogen-free, conduction-cooled compact treatment systems. We conclude that superconductivity is certainly required for the next generation of proton treatment systems, but also that the amount of compactness that can eventually be achieved is not solely determined by the magnetic field strength that is generated in the magnets