Modified Lattice of the Compact Storage Ring in the cSTART Project at Karlsruhe Institute of Technology

A very large ac­cep­tance com­pact stor­age ring (VLA-cSR) is under de­sign at the In­sti­tute for Beam Physics and Tech­nol­ogy (IBPT) of the Karl­sruhe In­sti­tute of Tech­nol­ogy (KIT, Ger­many). The com­bi­na­tion of a com­pact stor­age ring and a laser wake­field ac­cel­er­a­tor (LWFA) might be the basis for fu­ture com­pact light sources and ad­vanc­ing user fa­cil­i­ties. Mean­while, the post-LWFA beam should be adapted for stor­age and ac­cu­mu­la­tion in a ded­i­cated stor­age ring. Mod­i­fied geom­e­try and lat­tice of a VLA-cSR op­er­at­ing at 50 MeV en­ergy range have been stud­ied in de­tailed sim­u­la­tions. The main fea­tures of a new model are de­scribed here. The new de­sign, based on 45° bend­ing mag­nets, is suit­able to store the post-LWFA beam with a wide mo­men­tum spread (1% to 2%) as well as ul­tra-short elec­tron bunches in the fs range from the Fer­n­in­frarot Linac- Und Test- Ex­per­i­ment (FLUTE). The DBA-FDF lat­tice with re­laxed set­tings, split el­e­ments, and higher-or­der op­tics of tol­er­a­ble strength al­lows im­prov­ing the dy­namic aper­ture to an ac­cept­able level. This con­tri­bu­tion dis­cusses the lat­tice fea­tures in de­tail and dif­fer­ent pos­si­ble op­er­a­tion schemes of a VLA-cSR

Status of Operation With Negative Momentum Compaction at KARA

For fu­ture syn­chro­tron light source de­vel­op­ment novel op­er­a­tion modes are under in­ves­ti­ga­tion. At the Karl­sruhe Re­search Ac­cel­er­a­tor (KARA) an op­tics with neg­a­tive mo­men­tum com­paction has been pro­posed, which is cur­rently under com­mis­sion­ing. In this con­text, the col­lec­tive ef­fects ex­pected in this regime are stud­ied with an ini­tial focus on the head-tail in­sta­bil­ity and the mi­cro-bunch­ing in­sta­bil­ity re­sult­ing from CSR self-in­ter­ac­tion. In this con­tri­bu­tion, we will pre­sent the pro­posed op­tics and the sta­tus of im­ple­men­ta­tion for op­er­a­tion in the neg­a­tive mo­men­tum com­paction regime as well as a pre­lim­i­nary dis­cus­sion of ex­pected col­lec­tive ef­fects

On Possibility of Alpha-buckets Detecting at the KIT Storage Ring KARA (Karlsruhe Research Accelerator)

Computer studies of longitudinal motion have been performed with the objective to estimate the possibility of detection of alpha-buckets at the KIT storage ring KARA (Karlsruhe Research Accelerator). The longitudinal equations of motion and the Hamiltonian were expanded to high order terms of the energy deviation of particles in a beam. Roots of third order equation for three leading terms of momentum compaction factor and free energy independent term were derived in a form suitable for analytical estimations. Averaged quadratic terms of closed orbit distortions caused by misalignment of magnetic elements in a ring lead to orbit lengthening independent of particle energy deviation. Particle transverse excursions were estimated and are taken into account. Simulations have been bench-marked on existing experiments at Metrology Light Source (MLS) in Berlin (Germany) and SOLEIL (France). Parameters of three simultaneous beams and alpha buckets at MLS and SOLEIL have been reproduced with high accuracy. A computer model of KARA was used to predict behavior and the dynamics of possible simultaneous beams in the ring

Effect of Negative Momentum Compaction Operation on the Current- Dependent Bunch Length

New operation modes are often considered during the development of new synchrotron light sources. An understanding of the effects involved is inevitable for a successful operation of these schemes. At the KIT storage ring KARA (Karlsruhe Research Accelerator), new modes can be implemented and tested at various energies, employing a variety of performant beam diagnostics devices. Negative momentum compaction optics at various energies have been established. Also, the influence of a negative momentum compaction factor on different effects has been investigated. This contribution comprises a short report on the status of the implementation of a negative momentum compaction optics at KARA. Additionally, first measurements of the changes to the current-dependent bunch length will be presented

Different Operation Regimes at the KIT Storage Ring KARA (Karlsruhe Research Accelerator)

The KIT storage ring KARA operates in a wide energy range from 0.5 to 2.5 GeV. Different operation modes have been implemented at KARA, so far, the double-bend achromat (DBA) lattice with non-dispersive straight sections, the theoretical minimum emittance (TME) lattice with distributed dispersion, different versions of low-compaction factor optics with highly stretched dispersion function. Short bunches of a few ps pulse width are available at KARA. Low-alpha optics has been simulated, tested and implemented in a wide operational range of the storage ring and is now routinely used at 1.3 GeV for studies of beam bursting effects caused by coherent synchrotron radiation in the THz frequency range. Different non-linear effects, in particular residual high-order components of the magnetic field, generated in high-field superconducting wigglers have been studied and cured. Based on good agreement between computer simulations and experiments, a new operation mode at high vertical tune was implemented. The beam performance during user operation as well as at low-alpha regimes has been improved. A specific optic with negative compaction factor was simulated, tested and is in operation

The new Felsenkeller 5 MV underground accelerator

The field of nuclear astrophysics is devoted to the study of the creation of the chemical elements. By nature, it is deeply intertwined with the physics of the Sun. The nuclear reactions of the proton-proton cycle of hydrogen burning, including the 3He({\alpha},{\gamma})7Be reaction, provide the necessary nuclear energy to prevent the gravitational collapse of the Sun and give rise to the by now well-studied pp, 7Be, and 8B solar neutrinos. The not yet measured flux of 13N, 15O, and 17F neutrinos from the carbon-nitrogen-oxygen cycle is affected in rate by the 14N(p,{\gamma})15O reaction and in emission profile by the 12C(p,{\gamma})13N reaction. The nucleosynthetic output of the subsequent phase in stellar evolution, helium burning, is controlled by the 12C({\alpha},{\gamma})16O reaction. In order to properly interpret the existing and upcoming solar neutrino data, precise nuclear physics information is needed. For nuclear reactions between light, stable nuclei, the best available technique are experiments with small ion accelerators in underground, low-background settings. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso/Italy, using a 0.4 MV accelerator. The present contribution reports on a higher-energy, 5.0 MV, underground accelerator in the Felsenkeller underground site in Dresden/Germany. Results from {\gamma}-ray, neutron, and muon background measurements in the Felsenkeller underground site in Dresden, Germany, show that the background conditions are satisfactory for nuclear astrophysics purposes. The accelerator is in the commissioning phase and will provide intense, up to 50{\mu}A, beams of 1H+, 4He+ , and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity.Comment: Submitted to the Proceedings of the 5th International Solar Neutrino Conference, Dresden/Germany, 11-14 June 2018, to appear on World Scientific -- updated version (Figure 2 and relevant discussion updated, co-author A. Domula added

Air-stable Solid-state Photoluminescence Standards for Quantitative Measurements Based on 4'-phenyl-2,2':6',2''-Terpyridine Complexes with Trivalent Lanthanides

Correct photoluminescence quantum yield (PLQY) determination in the solid state is vital for numerous application fields, such as photovoltaics, solid lighting or the development of phosphors. In order to increase the limited number of suitable standards for such determinations, two new Ln 3+ -based complexes with 4′-phenyl-2,2′ : 6′,2"-terpyridine γ-[Ln 4 (OAc) 12 (ptpy) 2 ] ( 1-Eu with europium and 1-Tb with terbium) are presented. The corresponding complexes show solid-state QYs of 58(4) % and 46(3) %, respectively, exhibiting broadband absorption in the UV range from 380-200 nm. As Ln 3+ ions in general exhibit narrow f - f transitions, spectral regions with a broadness of 20-35 nm can be checked. Both complexes have suitable thermal stability, up to 270 °C, and are stable with respect to air and humidity, for 1-Eu up to 75 % and for 1-Tb up to 53 % relative humidity. These complexes are altogether suitable as standards to increase the reliability of PLQY determination and proposed to be used for a relative PLQY determination in the solid stat

Longitudinal Beam Dynamics and Coherent Synchrotron Radiation at cSTART

The compact STorage ring for Accelerator Research and Technology (cSTART) project aims to store electron bunches of LWFA-like beams in a very large momentum acceptance storage ring. The project will be realized at the Karlsruhe Institute of Technology (KIT, Germany). Initially, the Ferninfrarot Linac- Und Test-Experiment (FLUTE), a source of ultra-short bunches, will serve as an injector for cSTART to benchmark and emulate laser-wakefield accelerator-like beams. In a second stage a laser-plasma accelerator will be used as an injector, which is being developed as part of the ATHENA project in collaboration with DESY and Helmholtz Institute Jena (HIJ). With an energy of 50 MeV and damping times of several seconds, the electron beam does not reach equilibrium emittance. Furthermore, the critical frequency of synchrotron radiation is 50 THz and in the same order as the bunch spectrum, which implies that the entire bunch radiates coherently. We perform longitudinal particle tracking simulations to investigate the evolution of the bunch length and spectrum as well as the emitted coherent synchrotron radiation. Finally, different options for the RF system are discussed

Systematic Studies of the Micro-Bunching Instability at Very Low Bunch Charges

At KARA, the KArlsruhe Research Accelerator of the KIT synchrotron, the so called short bunch operation mode allows the reduction of the bunch length down to a few picoseconds. The micro- bunching instability resulting from the high degree of longitudinal compression leads to fluctuations in the emitted THz radiation, referred to as bursting. For extremely compressed bunches at KARA, bursting occurs not only in one but in two different bunch-current ranges that are separated by a stable region. This work presents measurements of the bursting behavior in both regimes. Good agreement is found between data and numerical solutions of the Vlasov-Fokker-Planck equation.Comment: 6 pages, 5 figures, to be submitte