| Paper | Title | Page |
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| MOPAB19 | Space-Charge Compensation of Intense Ion Beams by Nonneutral Plasma Columns | 67 |
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Gabor lenses were conceived to focus a passing ion beam using the electrical field of a confined nonneutral plasma column. Beside its application as focusing device, in Gabor lenses space-charge effects can be studied in detail. The influence of the electron distribution on emittance and space-charge dominated ion beams was investigated in beam transport experiments*. In this contribution we want to emphasize one result of these experiments. The measurements indicated a strong contribution of secondary electrons on beam dynamics. Secondary electrons are produced within the transport channel, particularly by interaction of the beam with the surface of the slit-grid emittance scanner. This might lead to an increase of the filling degree and to an improved focusing performance of the lens. Assuming that the loss and production rates within the lens volume and the transport channel determine the equilibrium state of the nonneutral plasma column, the electron cloud was characterized as a function of the external fields and the residual gas pressure in small-scale table top experiments. In this contribution experimental results will be presented in comparison with numerical simulations.
* K. Schulte, “Studies on the focusing performance of a Gabor lens depending on nonneutral plasma properties”, PhD thesis, 2013. |
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| WEO1AB01 | Upgrade of the UNILAC for FAIR | 245 |
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| The UNIversal Linear Accelerator (UNILAC) at GSI has served as injector for all ion species from protons for uranium for the past four decades. Especially its 108 MHz Alvarez type DTL providing acceleration from 1.4 MeV/u to 11.4 MeV/u has suffered from material fatigue. The DTL will be replaced by a completely new section with almost the same design parameters, i.e. pulsed current of up to 15 mA of 238U28+ at 11.4 MeV/u. However, operation will be restricted to low beam duty cycles as 200 μs at 10 Hz. Since preservation of beam quality is mandatory, a regular focusing lattice, as along an Alvarez section for instance, is aimed for. A new source terminal & LEBT dedicated to operation with 238U4+ is under design. The uranium sources need to be upgraded in order to provide increased beam brilliances and for operation at 3 Hz. Revision of the subsequent 36 MHz RFQ electrode design has started as well as the layout activities of the section providing transition from the 36 MHz section to the 108 MHz DTL. | ||
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Slides WEO1AB01 [1.325 MB] | |
| WEO4LR02 | The Particle-in-Cell Code Bender and Its Application to Non-Relativistic Beam Transport | 304 |
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A new non-relativistic, electrostatic Particle-in-Cell code named bender has been implemented to facilitate the investigation of low-energy beam transport scenarios. In the case of high-intensity beams, space-charge compensation resulting from the accumulation of secondary particles - electrons for positively charged ion beams - is an important effect. It has been shown, that the distribution of compensation electrons can have a significant influence on the beam and lead to an emittance growth. To improve the understanding of the dynamics of the compensation and the resultant self-consistent steady state, ionization of residual gas as well as secondary electron production on surfaces have been implemented and used to study a number of test systems. We will present first results of these compensation studies as well as further applications of the code, among them the chopper section of the future FRANZ facility [1].
* C. Wiesner et al., Experimental Performance of an E×B Chopper System, Proc. of IPAC 2014, THPME015 |
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Slides WEO4LR02 [5.373 MB] | |