IPAC2016 - List of Authors (Arnold, M.)

Paper	Title	Page
TUPOR025	Beam Break-up Measurements at the Recirculating Electron Accelerator S-DALINAC	1714
	T. Kürzeder, M. Arnold, L.E. Jürgensen, J. Pforr, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug IKP, Mainz, Germany
	Funding: Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05K13RDA Beam break-up (BBU) instability is an important limitation to the current which can be accelerated in a superconducting linac. In particular recirculating machines and Energy Recovery Linacs have to deal with that problem. Therefore, it is important to find strategies for increasing the threshold currents of these machines. The superconducting accelerator S-DALINAC at the Technische Universität Darmstadt provides electron beams in c.w. for nuclear physics experiments since 1991. It consists of a 10 MeV injector and a 40 MeV main linac where two and eight 20-cell elliptical 3-GHz cavities are operated in a liquid helium bath at 2 K. Using two recirculation beam lines the main accelerator can be used up to 3 times. Operational experiences have shown that the design-beam current of 20 μA could not be reached. One reason is the occurrence of BBU. We will report on measurements of the threshold current at various energy settings of the S-DALINAC. The results of a first test to increase the BBU limit by using skew quadrupole magnets in the first recirculation beam line will be presented.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR025
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TUPOR026	Final Design and Status of the Third Recirculation for the S-DALINAC*	1717
	M. Arnold, T. Kürzeder, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug IKP, Mainz, Germany
	Funding: *Work supported by DFG through CRC 634 and RTG 2128 Since 1991 the twice-recirculating superconducting accelerator S-DALINAC is providing electron beams for nuclear physics experiments. Due to a reduced quality factor of its cavities in comparison to their design values it was not possible to operate the accelerator with its maximum design energy of 130 MeV in cw mode. To provide electron beams of this energy in the future it was decided to add one recirculation beam line in order to use the main linac four times, operating the cavities on decreased accelerating gradients. The necessary modifications consist of several different aspects: A new beamline needs to be installed and other pre-existing beam line sections have to be modified for matching new boundary conditions. These new conditions are mainly a result of beam dynamics simulations and of the design of a new separation dipole magnet, which will bend the different beams energy-dependent in the various recirculation beam lines. We will present the implemented design and give a status report on the project.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR026
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THPMB004	Improving Energy Spread and Stability of a Recirculating Few-turn Linac	3222
	F. Hug IKP, Mainz, Germany M. Arnold, T. Kürzeder, N. Pietralla TU Darmstadt, Darmstadt, Germany R.G. Eichhorn Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Supported by the DFG through CRC 634, RTG 2128 and PRISMA cluster of excellence A non-isochronous recirculation scheme which helps cancelling out errors coming from the RF-jitters in a recirculating linac will be presented. Non-isochronous recirculation is the common operation mode for synchrotrons or microtrons. In such a scheme the recirculation arcs provide a non-zero longitudinal dispersion, while the particle bunches are accelerated at a certain phase off-crest with respect to the maximum of the accelerating field. In few-turn linacs and microtrons such beam dynamics can be used to reduce the energy spread. To do so the longitudinal phase advance needs to be set to a half-integer number of oscillations in phase space. Then errors from linac RF-systems cancel out and the energy spread remains closely to 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. We will present operational experience with the non-isochronous recirculation system of the twice recirculating superconducting accelerator S-DALINAC operated at TU Darmstadt including beam-dynamics calculations and measurements of the energy spread.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMB004
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Paper

Title

Page

Beam Break-up Measurements at the Recirculating Electron Accelerator S-DALINAC

1714

T. Kürzeder, M. Arnold, L.E. Jürgensen, J. Pforr, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
IKP, Mainz, Germany

Funding: Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05K13RDA
Beam break-up (BBU) instability is an important limitation to the current which can be accelerated in a superconducting linac. In particular recirculating machines and Energy Recovery Linacs have to deal with that problem. Therefore, it is important to find strategies for increasing the threshold currents of these machines. The superconducting accelerator S-DALINAC at the Technische Universität Darmstadt provides electron beams in c.w. for nuclear physics experiments since 1991. It consists of a 10 MeV injector and a 40 MeV main linac where two and eight 20-cell elliptical 3-GHz cavities are operated in a liquid helium bath at 2 K. Using two recirculation beam lines the main accelerator can be used up to 3 times. Operational experiences have shown that the design-beam current of 20 μA could not be reached. One reason is the occurrence of BBU. We will report on measurements of the threshold current at various energy settings of the S-DALINAC. The results of a first test to increase the BBU limit by using skew quadrupole magnets in the first recirculation beam line will be presented.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR025

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPOR026

Final Design and Status of the Third Recirculation for the S-DALINAC*

1717

M. Arnold, T. Kürzeder, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
IKP, Mainz, Germany

Funding: *Work supported by DFG through CRC 634 and RTG 2128
Since 1991 the twice-recirculating superconducting accelerator S-DALINAC is providing electron beams for nuclear physics experiments. Due to a reduced quality factor of its cavities in comparison to their design values it was not possible to operate the accelerator with its maximum design energy of 130 MeV in cw mode. To provide electron beams of this energy in the future it was decided to add one recirculation beam line in order to use the main linac four times, operating the cavities on decreased accelerating gradients. The necessary modifications consist of several different aspects: A new beamline needs to be installed and other pre-existing beam line sections have to be modified for matching new boundary conditions. These new conditions are mainly a result of beam dynamics simulations and of the design of a new separation dipole magnet, which will bend the different beams energy-dependent in the various recirculation beam lines. We will present the implemented design and give a status report on the project.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR026

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMB004

Improving Energy Spread and Stability of a Recirculating Few-turn Linac

3222

F. Hug
IKP, Mainz, Germany
M. Arnold, T. Kürzeder, N. Pietralla
TU Darmstadt, Darmstadt, Germany
R.G. Eichhorn
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Supported by the DFG through CRC 634, RTG 2128 and PRISMA cluster of excellence
A non-isochronous recirculation scheme which helps cancelling out errors coming from the RF-jitters in a recirculating linac will be presented. Non-isochronous recirculation is the common operation mode for synchrotrons or microtrons. In such a scheme the recirculation arcs provide a non-zero longitudinal dispersion, while the particle bunches are accelerated at a certain phase off-crest with respect to the maximum of the accelerating field. In few-turn linacs and microtrons such beam dynamics can be used to reduce the energy spread. To do so the longitudinal phase advance needs to be set to a half-integer number of oscillations in phase space. Then errors from linac RF-systems cancel out and the energy spread remains closely to 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. We will present operational experience with the non-isochronous recirculation system of the twice recirculating superconducting accelerator S-DALINAC operated at TU Darmstadt including beam-dynamics calculations and measurements of the energy spread.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMB004

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)