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Diamond crystals are characterised by wide band gap and high binding energy, making them suitable as solid-state particle detectors, beam-loss monitors and dosimeters in high-radiation environments, such as particle colliders. In order to use them as radiation and beam-loss monitors, our diamond detectors are calibrated in steady conditions with different radiation sources, comparing the measurement results with dedicated simulations. However large radiation bursts may lead to a non-linear signal response. For this purpose we studied their transient response to collimated, sub-picosecond, ∼1 GeV electron beam bunches, with a bunch charge of tens of pC, provided by the FERMI electron linac in Trieste. In these experimental conditions the ionisation generates large charge carrier density in the diamond bulk. This high charge causes a transient modification of diamond electrical properties, which affects the output signal shape. The observed signal evolution in the time domain shows fair agreement with a two-step numerical simulation of the diamond time response to these intense high-energy pulses.

We report on the observation of time-resolved quantum beats in the helium fluorescence from the transition 1s3p -> 1s2s, where the initial state is excited by XUV free-electron laser radiation. The quantum beats originate from the Zeeman splitting of the magnetic substates due to an external magnetic field. We perform a systematic study of this effect and discuss the possibilities of studying this phenomenon in the XUV and x-ray regime., 7 pages, 4 figures

During the last few years Europe has made enormous progress towards free electron laser (FEL)-based research infrastructures. The FLASH facility [1] at DESY in Hamburg, Germany, has been in user operation since the summer of 2005; FERMI@Elettra [2] in Trieste, Italy, is under construction; the European XFEL [3] in Hamburg will start construction in summer 2008; and several other FEL projects are being prepared in France, Germany, Italy, Poland, Sweden, Switzerland and the UK. In addition, a number of dedicated test facilities have become available, including the photo-injector test facility (PITZ) [4] and the cryomodule test bench (CMTB) [5] at DESY, the HoBiCaT facility for testing superconducting cavities [6] at BESSY, Berlin, Germany, the SPARC facility [7] at INFN-LNF in Frascati, Italy, and the ERL Prototype (ERLP) [8] at Daresbury Laboratory, UK. They have been strongly supported by the national stakeholders in order to prepare the design of new FEL sources.

FERMI@ELETTRA is a 4th generation light source under construction at Sincrotrone Trieste. It will be operated as a seeded FEL driven by a warm S-band Linac presently serving as the injector for the ELETTRA storage ring. Operation as an FEL driver places much more stringent specifications on control of the amplitude and phase of the RF stations than in its present operation. This paper describes a conceptual design of new RF controls to achieve these specifications. The system consists of a stabilized distribution of the master oscillator signal providing a reference to local digital RF controllers. The RF controller is based on recent improvements on modern digital systems, using a 16-bit high speed digitizer in combination with an FPGA and high speed DAC.

Results of the first experimental search for the effect of the prewave zone in near-infrared transition radiation are presented. A substantial difference in the spatial distribution of transition relation for two different wavelengths (450 nm and 1600 nm) was observed. Experimental data are in a good, though not complete, agreement with the theory.

Two recent theoretical studies [C. Liu et al., Phys. Rev. A 64, 010501 (2001); M. Zitnik et al., ibid. 65, 032520 (2002)] predict that the fluorescence lifetimes of helium doubly excited states converging to He+ N = 2 should be longer than that of the He+ 2p ion state. This effect is caused by the electric field of the outer electron which, through Stark mixing, gives the inner fluorescing electron some series specific, stabilizing 2s character. We have obtained the first experimental evidence that confirms this effect by measuring the lifetime of the 2p3d(1P0) doubly excited state. This was determined to be 190±30 ps compared to 100 ps for the He+ 2p ion state. The measurements were performed using short pulses of synchrotron radiation to form doubly excited states and recording the arrival time of photons from fluorescence.

Two recent theoretical studies [C. Liu, Phys. Rev. A 64, 010501 (2001)]; M. Zitnik, ibid. 65, 032520 (2002)]] predict that the fluorescence lifetimes of helium doubly excited states converging to He+ N=2 should be longer than that of the He+ 2p ion state. This effect is caused by the electric field of the outer electron which, through Stark mixing, gives the inner fluorescing electron some series specific, stabilizing 2s character. We have obtained the first experimental evidence that confirms this effect by measuring the lifetime of the 2p3d(1P0) doubly excited state. This was determined to be 190+/-30 ps compared to 100 ps for the He+ 2p ion state. The measurements were performed using short pulses of synchrotron radiation to form doubly excited states and recording the arrival time of photons from fluorescence.

During the commissioning of the Swiss Light Source (SLS) first operational experience has been gathered with the newly developed digital beam position monitor (DBPM) system. The DBPM performance could be characterized in all available operation modes, which are: single turn, turn-by-turn, closed orbit and tune. All modes can be selected independently for each sector of the booster and storage ring through the EPICS-based SLS control system by simple re-programming of the digital processing chain. Laboratory measurements as well as measurements on the SLS accelerators will be presented, offering insights in the operational experience and the performance of the DBPM system. In addition, a monitoring system (POMS) for the transverse mechanical positions of each BPM block in reference to the adjacent quadrupole magnets has been installed and commissioned. First results will be presented, showing a horizontal and vertical movement of the BPM blocks as a function of beam current (heat load on the vacuum chamber) in the SLS storage ring.

A new method for bunch length measurement has been developed at ELETTRA. It is based on a spectral observation of the synchrotron radiation light pulses. The single pulse spectrum is shaped by means of an optical process which gives the method an increased sensitivity compared to the usual spectral observations. Some simulations have been carried out to check the method in non-ideal conditions. The results of the first measurements are also presented.