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In dieser Arbeit wurden zwei unterschiedliche Konzepte für einen Rebuncher mit mehreren Aperturen auf der Symmetrieachse des geplanten Bunchkompressors für das FRANZ-Projekt untersucht. Die besonderen Anforderungen sind die Zeitstruktur des Strahls und der geringe seitliche Abstand der unterschiedlichen Strahlwege...
For the transport of high-intensity hadron beams in low-energy beam lines of linear accelerators, the compensation of space charge forces by the accumulation of particles of opposite charge is an important effect, reducing the required focusing strength and potentially the emittance growth due to space charge forces. In this thesis, space charge compensation was studied by including the secondary particles in particle-in-cell simulations.
For this purpose, a new electrostatic particle-in-cell code named bender was developed. The software was tested using known self-consistent solutions for an electron plasma confined in an external potential as well as for a KV distributed beam in a periodic focusing lattice. For the simulation of compensation, models for residual gas ionisation by proton and electron impact were implemented.
The compensation process was studied for a 120 keV, 100 mA proton beam transported through a short drift section. Various features in the particle distributions were identified, which can not explained by a uniform reduction in the electric field of the beam. These were tied to the presence of thermal electrons confined within the beam potential. Using the Poisson-Boltzmann equation, their distribution could be reproduced and their influence on the beam for a wider range of parameters studied. However, the observed temperatures show a significant numerical influence. The hypothesis was formed, that stochastical heating present in particle-in-cell simulations is the mechanism leading to the formation of the observed (partial) thermal equilibrium.
For the low-energy beam transport line of the Frankfurt neutron source FRANZ, bender was used to predict the pulse shaping in the novel ExB chopper system. The code was also used for the design and the study of an electron lens for the Integrable Optics Test Accelerator at Fermi National Accelerator Laboratory. Aberrations due to guiding center drifts and the strong electric field of the electron beam as well as the current limits in such a system were investigated.
The ARMADILLO bunch compressor currently being designed at IAP is capable of reaching a longitudinal pulse compression ratio of 45 for proton beams of 150 mA at 2 MeV. It will provide one nanosecond proton pulses with a peak current of 7.7 A. The system guides nine linacμbunches deflected by a 5 MHz rf kicker and uses four dipole magnets - two homogeneous and two with field gradients - to merge them on the target. For longitudinal focusing and an energy variation of ±200 keV two multitrack rf cavities are included. ARMADILLO will be installed at the end of the Frankfurt Neutron Source FRANZ making use of the unique 250 kHz time structure. This contribution will provide an overview of the layout of the system as well as recent advances in component design and beam dynamics of the compressor.
Chopper systems are used to pulse charged particle beams. In most cases, electric deflection systems are used to generate beam pulses of defined lengths and appropriate repetition rates. At high beam intensities, the field distribution of the chopper system needs to be adapted precisely to the beam dynamics in order to avoid aberrations. An additional challenge is a robust design which guarantees reliable operation. For the Frankfurt Neutron Source FRANZ, an E×B chopper system is being developed which combines static magnetic deflection with a pulsed electric field in a Wien filter configuration. It will generate proton pulses with a flat top of 50 ns at a repetition rate of 250 kHz for 120 keV, 200 mA beams. For the electric deflection, pre-experiments with static and pulsed fields were performed using a helium ion beam. In pulsed mode operation, ion beams of different energies were deflected with voltages of up to ±6 kV and the resulting response was measured using a beam current transformer. A comparison between experiments and theoretical calculations as well as numerical simulations are presented.
This novel kind of neutron beam facility will provide 1 ns short neutron pulses with an approximately thermal energy distribution around 30 keV. The pulse repetition rate will be up to 250 kHz, the total proton number per pulse will be up to 6×1010 in the final stage, starting with a p – source current of 200 mA. A second target station will allow n – activation experiments by cw beam operation. An intense 2 MeV proton beam will drive a neutron source by the 7 Li (p,n) 7 Be reaction. The facility is under construction at the physics experimental hall of the J.W. Goethe – University. The 1m thick concrete tunnel was installed in 2009. In 2011 all rf amplifiers will be delivered and installed. Successful 200 mA proton source experiments in 2010 at a test stand will be followed by experiments on the 120 kV FRANZ terminal in 2011. The 250 kHz, 100 ns chopper in front of the rf linac is under construction, while the 2 MeV bunch compressor design was finished and the technical design of all components has started. The main accelerator cavity is under construction. First 2 MeV beam tests are expected for end of 2012.