Terahertz diagnostic systems based on frequency combs without moving parts

We exploit information and communications tech-nologies to build a radio frequency-driven frequency comb spanning several hundred gigahertz. We investigated electro-optic modulators, which can serve as building blocks in frequency combs, terahertz generation and terahertz detection systems. These devices have high potential for applications in robust laser-based diagnostics at electron accelerators. During the last year, we have reduced the pulse length generated by a frequency-comb without moving parts by more than one order of magnitude to less than 150 fs, fitting a Lorentzian-type autocorrelation function

Continuous bunch-by-bunch spectroscopic investigation of the micro-bunching instability

Electron accelerators and synchrotrons can be operated to provide short emission pulses due to longitudinally compressed or sub-structured electron bunches. Above a threshold current, the high charge density leads to the micro-bunching instability and the formation of sub-structures on the bunch shape. These time-varying sub-structures on bunches of picoseconds-long duration lead to bursts of coherent synchrotron radiation in the terahertz frequency range. Therefore, the spectral information in this range contains valuable information about the bunch length, shape and sub-structures. Based on the KAPTURE readout system, a 4-channel single-shot THz spectrometer capable of recording 500 million spectra per second and streaming readout is presented. First measurements of time-resolved spectra are compared to simulation results of the Inovesa Vlasov-Fokker-Planck solver. The presented results lead to a better understanding of the bursting dynamics especially above the micro-bunching instability threshold.Comment: 12 pages, 11 figure

High throughput data streaming of individual longitudinal electron bunch profiles in a storage ring with single-shot electro-optical sampling

The development of fast detection methods for comprehensive monitoring of electron bunches is a prerequisite to gain comprehensive control over the synchrontron emission in storage rings with their MHz repetition rate. Here, we present a proof-of-principle experiment with at detailed description of our implementation to detect the longitudinal electron bunch profiles via single-shot, near-field electro-optical sampling at the Karlsruhe Research Accelerator (KARA). Our experiment is equipped with an ultra-fast line array camera providing a high-throughput MHz data stream. We characterize statistical properties of the obtained data set and give a detailed description for the data processing as well as for the calculation of the charge density profiles, which where measured in the short-bunch operation mode of KARA. Finally, we discuss properties of the bunch profile dynamics on a coarse-grained level on the example of the well-known synchrotron oscillation.Comment: 8 pages, 5 figure

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

First Steps Toward an Autonomous Accelerator, a Common Project Between DESY and KIT

Reinforcement Learning algorithms have risen in popularity in recent years in the accelerator physics community, showing potential in beam control and in the optimization and automation of tasks in accelerator operation. The Helmholtz AI project "Machine Learning toward Autonomous Accelerators" is a collaboration between DESY and KIT that works on investigating and developing RL applications for the automatic start-up of electron linear accelerators. The work is carried out in parallel at two similar research accelerators: ARES at DESY and FLUTE at KIT, giving the unique opportunity of transfer learning between facilities. One of the first steps of this project is the establishment of a common interface between the simulations and the machine, in order to test and apply various optimization approaches interchangeably between the two accelerators. In this paper we present the first results on the common interface and its application to beam focusing in ARES, and the idea of laser shaping with spatial light modulators at FLUTE

Machine Learning Based Spatial Light Modulator Control for the Photoinjector Laser at FLUTE

FLUTE (Ferninfrarot Linac- und Test-Experiment) at KIT is a compact linac-based test facility for novel accelerator technology and a source of intense THz radiation. FLUTE is designed to provide a wide range of electron bunch charges from the pC- to nC-range, high electric fields up to 1.2 GV/m, and ultra-short THz pulses down to the fs-timescale. The electrons are generated at the RF photoinjector, where the electron gun is driven by a commercial titanium sapphire laser. In this kind of setup the electron beam properties are determined by the photoinjector, but more importantly by the characteristics of the laser pulses. Spatial light modulators can be used to transversely and longitudinally shape the laser pulse, offering a flexible way to shape the laser beam and subsequently the electron beam, influencing the produced THz pulses. However, nonlinear effects inherent to the laser manipulation (transportation, compression, third harmonic generation) can distort the original pulse. In this paper we propose to use machine learning methods to manipulate the laser and electron bunch, aiming to generate tailor-made THz pulses. The method is demonstrated experimentally in a test setup