| 1. |
- Beckmann, M., et al.
(författare)
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How well do we know the circumference of a storage ring?
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 771, s. 115-120
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Tidskriftsartikel (refereegranskat)abstract
- High precision nuclear physics experiments in storage rings require precise knowledge of the beam energy. In the absence of electron cooling, which provides this information, one can use the frequency of the radio frequency system in conjunction with knowledge of the circumference of the ring. We investigate to which precision the latter can be determined in the presence of magnet misalignment and orbit correction.
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| 2. |
- Bhattacharyya, Anirban Krishna, et al.
(författare)
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Minimization of power consumption during charging of superconducting accelerating cavities
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 801, s. 78-85
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Tidskriftsartikel (refereegranskat)abstract
- The radio frequency cavities, used to accelerate charged particle beams, need to be charged to their nominal voltage after which the beam can be injected into them. The standard procedure for such cavity filling is to use a step charging profile. However, during initial stages of such a filling process a substantial amount of the total energy is wasted in reflection for superconducting cavities because of their extremely narrow bandwidth. The paper presents a novel strategy to charge cavities, which reduces total energy reflection. We use variational calculus to obtain analytical expression for the optimal charging profile. Enemies, reflected and required, and generator peak power are also compared between the charging schemes and practical aspects (saturation, efficiency and gain characteristics) of power sources (tetrodes, IOTs and solid state power amplifiers) are also considered and analysed. The paper presents a methodology to successfully identify the optimal charging scheme for different power sources to minimize total energy requirement.
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| 3. |
- Holz, Michael, et al.
(författare)
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Envelope dynamics and stability with non-linear space-charge forces
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 951
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Tidskriftsartikel (refereegranskat)abstract
- We developed a model to calculate the stability of Gaussian beam distributionswith non-linear space-charge forces in the presence of random and skewquadrupoleerrors. The eect of the space-charge force on the beam matrix iscalculated analytically including full cross-plane coupling in 4D phase space,which allows us to perform fast parameter studies. For stability analysis, wend the xed points of the beam including the space-charge forces and constructa Jacobi-matrix by slightly perturbing the periodic solution. The stability ofenvelope oscillations is inferred by eigenvalue analysis. Furthermore, we employenvelope tracking as a complementary method and compare the results ofthe eigenvalue analysis with FFT data from the tracked envelope. The nonlinearityof the space-charge force in combination with lattice errors and beamcoupling opens up for envelope-lattice resonances and envelope coupling resonances.Hitting these resonances leads to envelope blow-up, causing an eectivebeam mismatch. Therefore, we nally examine the eect of beam mismatch onthe envelope tune-shift and its stability.
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| 4. |
- Jacewicz, Marek, et al.
(författare)
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Spectrometers for RF breakdown studies for CLIC
- 2016
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 828, s. 63-71
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A e+e- collider of several TeV energy will be needed for the precision studies of any new physics discovered atthe LHC collider at CERN. One promising candidate is CLIC, a linear collider which is based on a two-beam acceleration scheme that efficiently solves the problem of power distribution to the acceleration structures. The phenomenon that currently prevents achieving highaccelerating gradients in high energy accelerators such asthe CLIC is the electrical breakdown at very high electrical field.The ongoing experimental work within the CLIC collaboration is trying to benchmark the theoretical models focusing on the physics of vacuum breakdown which is responsible for the discharges. In order to validate the feasibility of accelerating structures and observe the characteristics of the vacuum discharges and their eroding effects on the structure two dedicated spectrometers are now commissioned at the high-power test-stands at CERN. First, the so called Flashbox has opened up a possibility for non-invasive studies of the emitted breakdown currents during two-beam acceleration experiments. It gives an unique possibility to measure the energy of electrons and ions in combination withthe arrival time spectra and to put that in context with accelerated beam, which is not possible at any of the other existing test-stands.The second instrument, a spectrometer for detection of the dark and breakdown currents, is operated at one of the 12 GHz stand-alone test-stands at CERN. Built for high repetition rate operation it can measure the spatial and energy distributions of the electrons emitted from the acceleration structure during a single RF pulse. Two new analysis tools: discharge impedance tracking and tomographic image reconstruction, applied to the data from the spectrometer make possible for the first time to obtain the location of the breakdown inside the structure both in the transversal and longitudinal direction thus giving a more complete picture of the vacuum breakdown phenomenon.
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| 5. |
- Johnson, M., et al.
(författare)
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Arrival time measurements of ions accompanying RF breakdown
- 2008
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 595:3, s. 568-571
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Tidskriftsartikel (refereegranskat)abstract
- Radio-frequency structures for future normal-conducting linear accelerators are limited in accelerating gradient levels by RF breakdown in the structures due to extreme electric field levels. We report of experiments conducted at the CLIC Test Facility CTF3 where the breakdown is sometimes accompanied by a burst of ions that shows a spectrum consistent with hot coulomb explosions.
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| 6. |
- Muranaka, Tomoko, et al.
(författare)
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Instrumental developments for in situ breakdown experiments inside a scanning electron microscope
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 657:1, s. 122-125
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Tidskriftsartikel (refereegranskat)abstract
- Electrical discharges in accelerating structures are one of the key issues limiting the performance of future high energy accelerators such as the Compact Linear Collider (CLIC). Fundamental understanding of breakdown phenomena is an important part of the CLIC feasibility study. The present work concerns the experimental study of breakdown using Scanning Electron Microscopes (SEMs). An SEM gives us the opportunity to achieve high electrical gradients of 1 kV/mu m which corresponds to 1 GV/m by exciting a probe needle with a high voltage power supply and controlling the positioning of the needle with a linear piezo motor. The gap between the needle tip and the surface is controlled with sub-micron precision. A second electron microscope equipped with a Focused Ion Beam (FIB) is used to create surface corrugations and to sharpen the probe needle to a tip radius of about 50 nm. Moreover it is used to prepare cross-sections of a voltage breakdown area in order to study the geometrical surface damages as well as the elemental composition of the breakdown.
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| 7. |
- Nordhage, Örjan, et al.
(författare)
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Can Hydrogen Pellets be Vaporized by the Stored Beam?
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 569:3, s. 701-705
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Tidskriftsartikel (refereegranskat)abstract
- We outline a potential problem in terms of extra gas load when a high-intensity particle beam with small beam size traverses hydrogen pellets. We also investigate whether secondary electrons can escape the pellets and thereby alleviate the thermal process and thus the rate of evaporation. Finally we model the pellet heating induced by antiproton beam fluxes to be expected at PANDA.
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| 8. |
- Olvegard, Maja, et al.
(författare)
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Time-resolved momentum and beam size diagnostics for bunch trains with very large momentum spread
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 797, s. 234-246
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Tidskriftsartikel (refereegranskat)abstract
- We propose a novel method to measure he Lime -resolved momentum dislribulion and size of beams with very large momentum spread. To demonstrate the principle we apply the method to the beam at the end of a Compact Linear Collider decelerator, where conventional diagnostic methods are hampered by the large energy spread of the drive beam after up to 90% of its kinetic energy is converted into microwave power. Our method is based on sweeping the beam in a circular pattern to determine the momentum distribution and recording the beam size on a screen using optical transition radiation. We present an algorithm to extract the time-resolved momentum distribution. Furthermore, the beam size along the bunch train can be extracted from the image left On a screen by sweeping the beam linearly. We introduce he analysis technique and show simulation results that allow us to estimate the applicability, in addition, we present a conceptual design of the technical realization.
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| 9. |
- Olvegård, Maja, et al.
(författare)
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Effect of large momentum spread on emittance measurements
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 707, s. 114-119
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the systematic errors in emittance measurements with quadrupole scans and four screens due to large momentum spread in the beam. This is particularly relevant in the drive beam complex of CLIC and the test beam line TBL in the CTF3 facility at CERN. We also discuss methods to adapt the model to correct for the systematic errors.
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| 10. |
- Ruber, Roger, et al.
(författare)
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The CTF3 Two-beam Test Stand
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 729, s. 546-553
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Tidskriftsartikel (refereegranskat)abstract
- The Two-beam Test Stand (TBTS) has been constructed and operated at the CLIC test facility CTF3 at CERN. The TBTS comprises two parallel and independent electron beam lines and has been designed to demonstrate the feasibility of a two-beam high gradient acceleration concept as proposed for the Compact Linear Collider (CLIC). In the CLIC scheme, the RF power is extracted from a high current drive beam using RF power extraction structures while the main beam is accelerated using this RF power which is fed into high gradient high frequency normal conducting accelerating structures. The Two-beam Test Stand is a unique facility to demonstrate the feasibility of the CLIC two-beam high gradient acceleration concept and to test the individual CLIC components and complete two-beam CLIC modules. The TBTS is particularly well suited to investigate the effects on the beam of RF breakdown in the high gradient accelerating structures. We report on the design, construction and commissioning of the Two-beam Test Stand.
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