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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.

We report on exploiting information and communications technologies to build reliable and durable terahertz diagnostics for electron accelerator-based light and laser sources. Terahertz and electro-optical diagnostics is an ideal tool to investigate short-bunch electron beams and their emitted photons with the potential to devise methods for controlled and tailored radiation emission. We investigate electro-optical modulators to evaluate their potential for laser-based diagnostics at accelerators, which can serve as building blocks in frequency combs, terahertz generation and detection systems. We built a frequency comb spanning at least 250 GHz with a pulse length of less than 3.7 ps.

A key bottleneck for investigations of ultrafast processes is a detection scheme to record all individual spectra with high repetition rates to avoid averaging and to improve the signal-to-noise ratio. Here, we present spectral measurements of fs laser sources used for electro-optical detection with a KIT-developed linear sensor array and DAQ system adapted to light sources with MHz repetition rates. This system can be equipped with different sensor types covering a broad wavelength range. It can therefore be used for various applications and scientific questions. The presented exemplary applications range from accelerator-based diagnostics to table-top laser experiments.

At the KArlsruhe Research Accelerator (KARA), we use electro-optical sampling to measures profiles of compressed electron bunches during the microbunching instability. The observation of the complex dynamics of this instability is of special interest because it leads to intense THz radiation bursts. As the revolution frequency of the storage ring is 2.72 MHz, high detection rates are required to record the bunch profiles for every revolution with single-shot measurements. To achieve fast detection rates, we implemented a KIT-developed ultra-fast line array and recorded the electron bunch charge density for every revolution for 3.6 s with a data throughput of 1.4 GBytes/s.

An accurate and fast simulation tool for the analysis of quasi-optical output couplers in high power gyrotrons is under development. The electric field in the quasi-optical system is described by the electric field integral equation (EFIE) which is numerically solved by a Galerkin-type method of moments (MoM). To accelerate the simulations, a set of first order basis functions for curved triangles and the adaptive cross approximation algorithm (ACA) are used. The quasi-optical mode converters are parametrized by local B-Splines which can approximate launcher walls with perturbations very well. To speed up the calculations for highly oversized geometries, the software implementation supports parallelization on shared- and distributed-memory systems.

Photonic time-stretch enables to record electric field pulse shapes with picosecond resolution, at megahertz acquisition rates. Using this strategy, we could record the complex spatiotemporal evolution of relativistic electron bunches circulating in storage ring accelerators. We tested two complementary approaches. At SOLEIL, we monitored the THz pulses of coherent synchrotron that are emitted by the electrons. At ANKA, we monitored directly the electron bunch near-field.

In synchrotron radiation sources short pulses of coherent THz radiation is emitted when the length of electron bunches becomes sufficiently small. A detector system based on a superconducting NbN ultra-fast bolometer with an intrinsic response time of about 100 ps was jointly developed by the University of Karlsruhe (Institute of Micro- and Nanoelectronic Systems) and German Aerospace Center (Berlin) and implemented at the storage ring ANKA to time-resolve radiation emitted by single electron bunches.

The observation of betatron oscillations following a deflection by a kicker pulse offers the possibility to study various machine parameters. The damping of the centre-of-charge signal's amplitude for one bunch, for example, depends on chromaticity, energy loss, momentum compaction factor and impedance. A new multi-turn acquisition system based on LIBERA ELECTRON units (http://www.i-tech.si) has been installed in the ANKA storage ring. First analyses of the thus acquired data for different machine conditions reveal systematic limitations in the current ANKA multi-turn setup. Measurements preformed under varying conditions are presented and discussed with respect to the influence on future analysis.

Modern BPM electronics allow turn by turn acquisition of the position for both the injected and stored beam. This offers additional opportunities for diagnostics. In addition to the slow BPM acquisition system installed at ANKA, two LIBERA ELECTRON units (www.i-tech.si) have been installed. The system is used to investigate and optimize the Booster and the injection process into the Storage Ring. Tune and orbit in the Booster could be determined, as well as for the first turns in the Storage Ring. The stray field of the storage ring septum turned out to cause a bump of the stored beam. The settings of the kickers could be optimized for minimized orbit distortion. The phase space of the injected beam could be determined.

A new online network for radiation dose measurements offers the opportunity to register the dose rate at the ANKA storage ring every minute. The network consists of six mobile and two stationary monitors with a gamma and a neutron detector and a central computer. The analysis of the dose rate shows a strong correlation between beam energy, beam current, machine parameters and dose rate.

A synchrotron radiation source emits coherent infrared (IR) radiation when the electron bunch length is comparable to the wavelength of the emitted radiation (see for example [1, 2]). To generate coherent radiation in the far IR (THz) region, a ’low alpha mode’ has been devised at the ANKA storage ring operating at 1.3 GeV. The corresponding lattice has a significantly reduced momentum compaction factor. The spectral dependence of the emitted radiation is recorded at the ANKA-IR beam line, where the synchrotron light is produced in the fringe field of a bending magnet [3]. This edge radiation has the advantage of being more collimated than constant field radiation. This allows the observation of frequencies down to 1 cm-1through a modest vertical aperture, which would not be possible with classical constant field emission due to the increasing beam divergence with decreasing frequency. The onset of coherent emission is found at a synchrotron frequency of about 10 kHz. At 5 kHz, an intensity enhancement of up to 5 orders of magnitude, with respect to the incoherent emission, is observed in the spectral range between 1 and 65 cm-1.

Recently a novel approach to perform multi-turn extraction was proposed based on beam splitting in the transverse phase space by means of trapping inside stable islands. An experimental campaign was launched since the year 2002 to assess the feasibility of such an extraction scheme at the CERN Proton Synchrotron. During the year 2004 run, a high-intensity single-bunch beam was successfully split and the generated beamlets separated without any measurable losses. The latest experimental results are presented and discussed in details in this paper. These achievements represent a substantial step forward with respect to what achieved in previous years, as only a low-intensity bunch could be split without losses. Furthermore, this opens the possibility of using such a technique for routine operation with the high-intensity proton beams required for the planned CERN Neutrino to Gran Sasso Project.

The maximum electron current at ANKA is presently limited by multi-bunch instabilities during injection and ramping. In order to overcome this barrier an analog transverse multi-bunch feedback system was developed and commissioned. During the test phase of the feedback operation a beam stabilization by the feedback system was clearly demonstrated. In the first six months of operation the number of total or partial beam losses related to instabilities was distinctly reduced.

The electron storage ring at ANKA is designed as a variation of an eightfold DBA structure. Since its commissioning the facility has been operated with zero dispersion in the long straight sections resulting in an emittance of about 100 nmrad. Since mid 2004 ANKA is operated with dispersion distributed over the complete ring thus reducing the emittance to 50 nmrad. Optics calculations and measurements as well as operational experience will be discussed. In order to reduce the losses due to Touschek scattering, a lengthening of the bunches was done by modulation of the main frequency with twice the synchrotron frequency. An increase of the lifetime by 5 h could be achieved.

The CERN Proton Synchrotron machine is built using combined function magnets. The control of the linear tune as well as the chromaticity in both planes is achieved by means of special coils added to the main magnets, namely two pole-face-windings and one figure-of-eight loop. As a result, the overall magnetic field configuration is rather complex not to mention the saturation effects induced at top-energy. For these reasons a linear model of the PS main magnet does not provide sufficient precision to model particle dynamics. On the other hand, a sophisticated optical model is the key element for the foreseen intensity upgrade and, in particular, for the novel extraction mode based on adiabatic capture of beam particles inside stable islands in transverse phase space. A solution was found by performing accurate measurement of the nonlinear tune as a function of both amplitude and momentum offset so to extract both linear and nonlinear properties of the lattice. In this paper the measurement results are presented and the derived optical model is discussed in detail.

Recently a novel approach to the problem of multi-turn extraction was proposed. It consists of splitting the beam by adiabatic capture inside stable islands created in the transverse phase space by sextupoles and octupoles. Numerical simulations indicate that such a technique should be feasible and potentially superior to the method presently used at the CERN Proton Synchrotron. During 2002, intense efforts were devoted to the experimental verification of this newly proposed extraction mode. Finally, beam capture into the islands was observed. In this paper, the extraction principle is briefly reviewed and the experimental results are presented and discussed in detail.