| 1. |
- Abrahamsson, Johan, 1977-, et al.
(författare)
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A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings
- 2014
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:9
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Tidskriftsartikel (refereegranskat)abstract
- Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.
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| 2. |
- Ali, Hasan, 1985-, et al.
(författare)
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An electron energy loss spectrometer based streak camera for time resolved TEM measurements
- 2017
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 176, s. 5-10
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Tidskriftsartikel (refereegranskat)abstract
- We propose an experimental setup based on a streak camera approach inside an energy filter to measure time resolved properties of materials in the transmission electron microscope (TEM). In order to put in place the streak camera, a beam sweeper was built inside an energy filter. After exciting the TEM sample, the beam is swept across the CCD camera of the filter. We describe different parts of the setup at the example of a magnetic measurement. This setup is capable to acquire time resolved diffraction patterns, electron energy loss spectra (EELS) and images with total streaking times in the range between 100 ns and 10 μs.
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| 3. |
- Bhattacharyya, Anirban, et al.
(författare)
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Wave propagation in a fractal wave guide
- 2017
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Ingår i: in Proceedings of the 8th International Particle Accelerator Conference (IPAC 2017), Copenhagen, Denmark, May, 2017.. - 9783954501823
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
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| 5. |
- Ekström, Joakim, 1982-, et al.
(författare)
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Exact Probability Distribution for the ROC Area under Curve
- 2023
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Ingår i: Cancers. - : MDPI. - 2072-6694. ; 15:6
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Tidskriftsartikel (refereegranskat)abstract
- Simple Summary This contribution allows for the computation of exact p-values and for conducting accurate statistical hypothesis tests of ROC AUC-values. As a result, the development of diagnostic tests is facilitated. This work is illustrated via simulated data and through the development of proteomic blood biomarkers for the early detection of cancer. The Receiver Operating Characteristic (ROC) is a de facto standard for determining the accuracy of in vitro diagnostic (IVD) medical devices, and thus the exactness in its probability distribution is crucial toward accurate statistical inference. We show the exact probability distribution of the ROC AUC-value, hence exact critical values and p-values are readily obtained. Because the exact calculations are computationally intense, we demonstrate a method of geometric interpolation, which is exact in a special case but generally an approximation, vastly increasing computational speeds. The method is illustrated through open access data, demonstrating superiority of 26 composite biomarkers relative to a predicate device. Especially under correction for testing of multiple hypotheses, traditional asymptotic approximations are encumbered by considerable imprecision, adversely affecting IVD device development. The ability to obtain exact p-values will allow more efficient IVD device development.
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| 6. |
- Farabolini, W., et al.
(författare)
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Recent Results from CTF3 Two Beam Test Stand
- 2014
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Ingår i: Proceedings, 5th International Particle Accelerator Conference (IPAC 2014).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Johansson, Simon, et al.
(författare)
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Ljuset : svindlande snabbt, obegripligt att förstå
- 2005
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Ingår i: Tsunami. - 1651-5803. ; :2
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- "Ljuset –svindlande snabbt, obegripligt att förstå”, är en populärvetenskaplig uppsats grundad på vårt projektarbete om ljuset. Det vi begränsat oss till och följaktligen avhandlar i denna uppsats är frågor som rör ljusets hastighet samt hur man mäter och har mätt denna och frågor som rör ljusets natur där vi tar upp bland annat vågpartikeldualism, fotoelektrisk effekt och kvantfysik. Dessutom har varje del ett avsnitt som handlar om hur vi själva genomförde ett antal experiment angående några av dessa saker på Högskolan i Gävle. Uppsatsen är tänkt att vara lättfattlig men utan att reducera djupet i ämnet.
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| 11. |
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| 12. |
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| 13. |
- Ögren, Jim, et al.
(författare)
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Aligning linac accelerating structures using a copropagating octupolar mode
- 2017
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Ingår i: Physical Review Accelerators and Beams. - College Park, MD : American Physical Society. - 2469-9888. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- We propose a novel method to align accelerating structures such as those used in the Compact Linear Collider (CLIC) by exploiting a mode that copropagates with the normal accelerating mode. This mode has an octupolar dependence in the transverse direction and is caused by radial waveguides intended to damp higher-order modes. The nonlinear dependence of the octupolar mode makes it possible to determine the center of the structure from the nonlinear dependence of the transverse kick, observed on a downstream beam position monitor, while changing the transverse position of the beam with respect to the accelerating structures. We discuss the method, its tolerances and disentangling the individual misalignments of two adjacent accelerating structures that are powered from a single source.
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| 14. |
- Ögren, Jim, et al.
(författare)
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Beam-based Alignment of CLIC Accelerating Structures Utilizing Their Octupole Component
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Alignment of the accelerating structures is essential foremittance preservation in long linear accelerators such as the Compact Linear Collider (CLIC). The prototype structures for CLIC have four radial waveguides connected to each cellfor damping wakefields and this four-fold symmetry is re-sponsible for an octupole component of the radio-frequency fields, phase-shifted 90 degrees with respect to the accelerating mode. The octupole field causes a nonlinear dependence of the transverse beam deflection with respect to the position within the accelerating structure. By transversely moving the beam with two upstream steering magnets, and observing the deflection with beam position monitors or screens, the electromagnetic center of the structure can be found. Wediscuss the applicability of this method for aligning the beamin the accelerating structures.
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| 15. |
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| 16. |
- Ögren, Jim, 1986-
(författare)
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Beam Diagnostics and Dynamics in Nonlinear Fields
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Particle accelerators are indispensable tools for probing matter at the smallest scales and the improvements of such tools depend on the progress and understanding of accelerator physics. The Compact Linear Collider (CLIC) is a proposed, linear electron–positron collider on the TeV-scale, based at CERN. In such a large accelerator complex, diagnostics and alignment of the beam are crucial in order to maintain beam quality and luminosity. In this thesis we have utilized the nonlinear fields from the octupole component of the radio-frequency fields in the CLIC accelerating structures for beam-based diagnostics. We have investigated methods where the nonlinear position shifts of the beam are used to measure the strength of the octupole component and can also be used for alignment. Furthermore, from the changes in transverse beam profile, due to the nonlinear octupole field, we determine the full transverse beam matrix, which characterizes the transverse distribution of the beam.In circular accelerators, nonlinear fields result in nonlinear beam dynamics, which often becomes the limiting factor for long-term stability. In theoretical studies and simulations we investigate optimum configurations for octupole magnets that compensate amplitude-dependent tune-shifts but avoid driving fourth-order resonances and setups of sextupole magnets to control individual resonance driving terms in an optimal way.
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| 17. |
- Ögren, Jim, et al.
(författare)
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Compensating amplitude-dependent tune-shift without driving fourth-order resonances
- 2017
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 869, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- If octupoles are used in a ring to correct the amplitude-dependent tune-shift one normally tries to avoid that the octupoles drive additional resonances. Here we consider the optimum placement of octupoles that only affects the amplitude-dependent tune-shift, but does not drive fourth-order resonances. The simplest way turns out to place three equally powered octupoles with 60° phase advance between adjacent magnets. Using two such octupole triplets separated by a suitable phase advance cancels all fourth-order resonance driving terms and forms a double triplet we call a six-pack. Using three six-packs at places with different ratios of the beta functions allows to independently control all amplitude-dependent tune-shift terms without exciting additional fourth-order resonances in first order of the octupole excitation.
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| 18. |
- Ögren, Jim
(författare)
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ELEPHANT : A MATLAB-code for Hamiltonians, Lie algebra, normal form and particle tracking
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report we explain the structure and functionality of ELEPHANT: a MATLAB-code developed for particle tracking and treating Hamiltonians in the Lie formalism with applications for accelerator physics. The code can operate on Hamiltonians and using the similarity transform and the Campbell-Baker-Hausdorff formula to express a map as an effective Hamiltonian and a linear map.The code can also express a map in a normal form and from this calculate the amplitude-dependenttune-shifts. Finally, the code can analyze the standard linear transverse dynamics and do particletracking. The purpose of the code is to treat nonlinear fields analytically and cross-check with tracking results.
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| 19. |
- Ögren, Jim, et al.
(författare)
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Measuring the full transverse beam matrix using a single octupole
- 2015
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Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 18:7
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Tidskriftsartikel (refereegranskat)abstract
- We propose a method to fully determine the transverse beam matrix using a simple setup consisting of two steering magnets, an octupole field and a screen. This works in principle for any multipole field, i.e., sextupole, octupole magnet or a radio frequency structure with a multipole field. We have experimentally verified the method at the Compact Linear Collider Test Facility 3 at CERN using a Compact Linear Collider accelerating structure, which has an octupole component of the radio frequency fields. By observing the position shifts of the beam centroid together with changes in transverse beam size on a screen, we determined the full transverse beam matrix, with all correlations.
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| 20. |
- Ögren, Jim, et al.
(författare)
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Optimum resonance control knobs for sextupoles
- 2018
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 894, s. 111-118
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the placement of extra sextupoles in a magnet lattice that allows to correct third-order geometric resonances, driven by the chromaticity-compensating sextupoles, in a way that requires the least excitation of the correction sextupoles. We consider a simplified case, without momentum-dependent effects or other imperfections, where suitably chosen phase advances between the correction sextupoles leads to orthogonal knobs with equal treatment of the different resonance driving terms.
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| 21. |
- Ögren, Jim, et al.
(författare)
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Surface Characterization and Field Emission Measurements of Copper Samples inside a Scanning Electron Microscope
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Vacuum breakdown in normal-conducting accelerating structures is a limiting factor for high gradient acceleration.Many aspects of the physics governing the breakdown process and its onset are yet to be fully understood. At Uppsala University we address these questions with an in-situ experi-mental setup mounted in an environmental scanning electron microscope. It consists of a piezo motor driven tungsten needle and a sample surface mounted on a piezo stage, allowing for nano-meter 3D-position control. One of the piezomotors controls the needle-sample gap while the two otherscan across the surface. A DC-voltage up to 1 kV is applied across the gap and field emission currents from a coppersurface are measured with an electrometer. Here we presentthe setup and some initial results.
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