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| MOPVA013 | Application of Non-Isochronous Beam Dynamics in ERLs for Improving Energy Spread and Beam Stability | 873 |
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Funding: Work supported by DFG through the PRISMA cluster of excellence EXC 1098/2014 and Research Training Group GRK 2128 Non-isochronous recirculation is the common operation mode for synchrotrons or microtrons. In such a non-isochronous recirculation scheme the recirculation paths provide a non-zero longitudinal dispersion while the accelerating field is operated at a certain phase off-crest with respect to the maximum. In few turn linacs like ERLs and in microtrons non-isochronous beam dynamics can be used to reduce the energy spread by cancelling out any rf-jitters coming from the linac cavities. To do so the longitudinal phase advance needs to be tuned to a half-integer number of oscillations in longitudinal phase space. Then the total energy spread after main linac acceleration conserves the value at injection. In addition to the improved energy spread the beam stability of few-turn recirculators can be increased as well using such a system. Such concept provides an inherent beam stability and has been introduced many years ago [*] and proven to work successfully in a few-turn recirculator already [**]. We will present beam dynamics calculations for the application of nonisochronous beam dynamics in single- and multi-turn energy recovery linacs at different longitudinal working points. [*] H. Herminghaus, NIM. A 314 (1992) 209. [**] F. Hug et al., Proc. of LINAC '12 (2012) 531. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA013 | |
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| MOPVA014 | Injector Linac Stability Requirements for High Precision Experiments at MESA | 876 |
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Funding: Work supported by DFG through the PRISMA cluster of excellence EXC 1098/2014 and Research Training Group GRK 2128 MESA is a recirculating superconducting accelerator under construction at Johannes Gutenberg-Universität Mainz. It will be used for high precision particle physics experiments in two different operation modes: external beam (EB) mode and energy recovery (ERL) mode. The operating beam current and energy in EB mode is 0.15 mA with polarized electrons at 155 MeV. In ERL mode an unpolarized beam of 1 mA at 105 MeV will be available. In a later construction stage of MESA the beam current in ERL-mode shall be upgraded to 10 mA. In order to achieve high beam stability and low energy spread in recirculating operation the acceleration in the main linac sections will be done on edge of the accelerating field while the return arcs provide longitudinal dispersion. On certain longitudinal working points this can result in a setting where rf jitters from main linac do not contribute to the resulting energy spread of the final beam at all [*,**]. Then the resulting energy spread is only determined by the energy spread provided by the inector linac. Within this contribution we will investigate the requirements on the stability of the MESA injector linac MAMBO for achieving the experimental goals. [*] H. Herminghaus, NIM. A 314 (1992) 209. [**] F. Hug et al., Proc. of LINAC '12 (2012) 531. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA014 | |
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| MOPVA057 | Structural Investigations of Nitrogen-Doped Niobium for Superconducting RF Cavities | 996 |
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Funding: Work supported by BMBF through 05H15RDRBA. Niobium is the standard material for superconducting RF (SRF) cavities. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. Enhancing the surface properties of the superconducting material in the range of the penetration depth is also beneficial. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram the cubic delta-phase of NbN has the highest critical temperature (16 K). Already slight nitrogen doping of the alpha-Nb phase results in higher quality factors.* Nb samples will be N-doped at the refurbished UHV furnace at IKP Darmstadt. The first results on the structural investigations of the processed Nb samples at the Materials Research Department of TU Darmstadt are presented. * Grassellino et al., Proc. SRF2015, MOBA06, 48. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA057 | |
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| TUPAB030 | Construction and Status of the Thrice Recirculating S-DALINAC | 1384 |
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Funding: Work supported by DFG through RTG 2128 and CRC 634. From 1991 until 2015 the S-DALINAC (Superconducting-DArmstadt-LINear-ACcelerator) was operated as a twice recirculating electron accelerator. Its design energy of 130 MeV in cw-operation was not reached so far due to a lower quality factor of the SRF cavities and thus a higher dissipated power to the helium bath. In 2015/2016 a third recirculation has been built. Enabling a fourth passage through the main linac, the accelerating gradients can be reduced to fit the resulting dissipated power to the available cooling power for running at design energy. The upgrade to a thrice recirculating accelerator required the reconstruction of main parts of the existing lattice as well as an installation of a new beam line. All magnets had to be aligned carefully in position and orientation using high-precision metrology sensors. This contribution will present an overview of the construction and the alignment process. A latest status of the commissioning will be given. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPAB030 | |
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