3D Simulation of the Effects of Surface Defects on Field Emitted Electrons

The ev­er-grow­ing de­mand for high­er beam en­er­gies has dra­mat­i­cal­ly in­creased the risk of RF break­down, lim­it­ing the max­i­mum achiev­able ac­cel­er­at­ing gra­di­ent. Field emis­sion is the most fre­quent­ly en­coun­tered RF break­down where it oc­curs at re­gions of lo­cal­ly en­hanced elec­tric field. Elec­trons ac­cel­er­at­ed across the cav­i­ty as they tun­nel through the sur­face in the pres­ence of mi­cro­scop­ic de­fects. Upon Im­pact, most of the ki­net­ic en­er­gy is con­vert­ed into heat and stress. This can in­flict ir­re­versible dam­age to the sur­face, cre­at­ing ad­di­tion­al field emis­sion sites. This work aims to in­ves­ti­gate, through sim­u­la­tion, the physics in­volved dur­ing both emis­sion and im­pact of elec­trons. A newly de­vel­oped 3D field model of an 805 MHz cav­i­ty is gen­er­at­ed by COM­SOL Mul­ti­physics. Elec­tron track­ing is per­formed using a Mat­lab based code, cal­cu­lat­ing the rel­e­vant pa­ram­e­ters need­ed by em­ploy­ing fourth Order Runge Kutta in­te­gra­tion. By study­ing such be­haviours in 3D, it is pos­si­ble to iden­ti­fy how the cav­i­ty sur­face can alter the local RF field and lead to break­down and sub­se­quent dam­ages. The ul­ti­mate aim is to in­tro­duce new sur­face stan­dards to en­sure bet­ter cav­i­ty per­for­mance

Needle-guiding robot for laser ablation of liver tumors under MRI guidance

This paper presents the design, control and experimental evaluation of a needle-guiding robot intended for use in laser ablation (LA) of liver tumors under guidance by Magnetic Resonance Imaging (MRI). The robot provides alignment of a needle guide inside the MRI scanner bore and employs manual needle insertion. In order to minimize MR-image deterioration, the robot is actuated using plastic pneumatic cylinders and long pipes connecting to control valves located outside the MRI scanner room. A new Time Delay Control scheme (TDC) was employed to achieve high position accuracy without requiring pressure or force measurements in the MRI scanner. The control scheme was compared with experiments to a previously developed Sliding Mode Controller (SMC). A marker localization method based on the convolution theorem of Fourier transform was employed to register the robot in the MRI scanner coordinate system and to verify the position of the needle guide before the manual needle insertion. Experiments in a closed-bore MRI scanner showed a variation in SNR below 5%. A phantom study indicates that the targeting error in robot-assisted needle insertions is below 5 mm and suggest a potential time saving of 30 minutes compared to the manual MRI-guided LA procedure

Significance of pH-value for meat quality of broilers: Influence of breed lines

For determination of poultry quality shortly after slaughtering, physical criteria (pH-value, conductivity, colour, juice retention) are of importance. However, they are affected by breeding, transport, cooling and the storage period. PH-values of breast meat (genetically structured material) were recorded shortly after slaughtering (15 min p.m.) and differences between breeding line and gender were found (n=5109). The pH1-values ranged from 5.50 to 6.79. Male broilers showed significantly lower pH1-values than female ones (6.02:6.10). There were also significant differences concerning breeding line and gender. Meat quality (PSE, DFD) of broilers can be recorded quickly and accurately determining the pH1-value of breast meat. Threshold ranges to be considered are ≤ 5.8 (PSE), 5.9-6.2 (standard meat properties) and ≥ 6.3 (DFD). This classification is not to be compared to the deviation of pork

Design and control of 3-DOF needle positioner for MRI-guided laser ablation of liver tumours

This article presents the design and control of a pneumatic needle positioner for laser ablation of liver tumours under guidance by magnetic resonance imaging (MRI). The prototype was developed to provide accurate point-to-point remote positioning of a needle guide inside an MR scanner with the aim of evaluating the potential advantages over the manual procedure. In order to minimise alterations to the MR environment, the system employs plastic pneumatic actuators and 9 m long supply lines connecting with the control hardware located outside the magnet room. An improved sliding mode control (SMC) scheme was designed for the position control of the device. Wireless micro-coil fiducials are used for automatic registration in the reference frame of the MR scanner. The MRI-compatibility and the accuracy of the prototype are demonstrated with experiments in the MR scanner

In-situ Investigation of the Early Stage of TiO2 epitaxy on (001) SrTiO3

We report on a systematic study of the growth of epitaxial TiO2 films deposited by pulsed laser deposition on Ti-terminated (001) SrTiO3 single crystals. By using in-situ reflection high energy electron diffraction, low energy electron diffraction, x-ray photoemission spectroscopy and scanning probe microscopy, we show that the stabilization of the anatase (001) phase is preceded by the growth of a pseudomorphic Sr-Ti-O intermediate layer, with a thickness between 2 and 4 nm. The data demonstrate that the formation of this phase is related to the activation of long range Sr migration from the substrate to the film. The role of interface Gibbs energy minimization, as a driving force for Sr diffusion, is discussed. Our results enrich the phase diagram of the Sr-Ti-O system under epitaxial strain opening the roudeficient SrTiO phase.Comment: 8 pages, 7 figure

Electronic phase separation near the superconductor-insulator transition of Nd1+xBa2−xCu3O7−δ thin films studied by an electric-field-induced doping effect

We report a detailed study of the transport properties of Nd(1+x)Ba(2-x)Cu(3)O(7-delta) thin films with doping changed by field effect. The data cover the whole superconducting to insulating transition and show remarkable Similarities with the effect of chemical doping in high critical temperature superconductors. The results suggest that the add-on of carriers is accompanied by an electronic phase separation, independent on the details of the doping mechanism

THE EFFECTS OF FIELD EMITTED ELECTRONS ON RF SURFACE

The ever-growing demand for higher RF gradients has considerably increased the risk of breakdown in accelerating structures. Field emission is the most common form of RF breakdown that generates free electrons capable of inflicting irreversible damages on the RF surface. This paper presents a systematic experimental and simulation programme to understand possible sources and their influence on RF cavity operatio