This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.

Absolute calibration for a broad range single shot electron spectrometer

The design of CLIC is based on a two-beam scheme, where the short pulses of high power 30 GHz RF are extracted from a drive beam running parallel to the main beam. The 3 generation CLIC Test Facility (CTF3) will demonstrate the generation of the drive beam with the appropriate time structure, the extraction of 30 GHz RF power from this beam, as well as acceleration of a probe beam with 30 GHz RF cavities. The project makes maximum use of existing equipment and infrastructure of the LPI complex, which became available after the closure of LEP. In the first stage of the project, the "Preliminary Phase", the existing LIL linac and the EPA ring, both modified to suit the new requirements, are used to investigate the technique of frequency multiplication by means of interleaving bunches from subsequent trains. This report describes the design of this phase. Geneva, Switzerland 17 December 2001 1 CTF3 Design Report Preliminary Phase

CTF3 Design Report

Time-resolved spectroscopy at the picosecond laser-triggered electron accelerator ELYSE

Extension in far-infrared of the CLIO free-electron laser

DNA damage induced via dissociative attachment by low-energy electrons (0 to 20 eV) is well studied in both gas and condensed phases. However, the reactivity of ultrashort-lived prehydrated electrons ([Formula: see text]) with DNA components in a biologically relevant environment has not been fully explored to date. The electron transfer processes of [Formula: see text] to the DNA nucleobases G, A, C, and T and to nucleosides/nucleotides were investigated by using 7-ps electron pulse radiolysis coupled with pump-probe transient absorption spectroscopy in aqueous solutions. In contrast to previous results, obtained by using femtosecond laser pump-probe spectroscopy, we show that G and A cannot scavenge [Formula: see text] at concentrations of ≤50 mM. Observation of a substantial decrease of the initial yield of hydrated electrons ([Formula: see text]) and formation of nucleobase/nucleotide anion radicals at increasing nucleobase/nucleotide concentrations present direct evidence for the earliest step in reductive DNA damage by ionizing radiation. Our results show that [Formula: see text] is more reactive with pyrimidine than purine nucleobases/nucleotides with a reactivity order of T > C > A > G. In addition, analyses of transient signals show that the signal due to formation of the resulting anion radical directly correlates with the loss of the initial [Formula: see text] signal. Therefore, our results do not agree with the previously proposed dissociation of transient negative ions in nucleobase/nucleotide solutions within the timescale of these experiments. Moreover, in a molecularly crowded medium (for example, in the presence of 6 M phosphate), the scavenging efficiency of [Formula: see text] by G is significantly enhanced. This finding implies that reductive DNA damage by ionizing radiation depends on the microenvironment around [Formula: see text].

https://advances.sciencemag.org/content/advances/3/12/e1701669.full.pdf

Reactivity of prehydrated electrons toward nucleobases and nucleotides in aqueous solution

Recent years have seen an increasing interest in the use of intense, short pulse electron beams for pulsed radiolysis research. Laser driven photo-cathodes inserted in radio frequency (RF) guns are ideal candidates to provide electron beams for time-resolved spectroscopic observation of very fast chemical reactions. These guns have been developed through accelerator R&D programmes in the field of high brightness sources for other applications (linear colliders, free electron lasers). The Physical Chemistry Laboratory at the University of Paris-Sud has created a Fast Kinetics Centre for experimental pulse radiolysis with picosecond time resolution. At the heart of this new facility is a compact 4–9 MeV electron accelerator, ELYSE, using RF gun technology. It has been designed and built by the Linear Acclerator Laboratory at the University of Paris-Sud. We will describe the construction and commissioning of ELYSE, the first machine of this type in Europe.

/pdf/elyse-a-picosecond-electron-accelerator-for-pulse-radiolysis-4o3sff26m0.pdf

ELYSE¿A picosecond electron accelerator for pulse radiolysis research

The CLIO collaboration has started in 1986 in order to build an infrared laser at LURE at Orsay. It includes the design and construction of a new FEL dedicated rf linear accelerator. The goal is to make a broadly tunable laser (at least in the range 2–20 μm), of high peak power (MW range), and “medium” average power (a few tens of watts). It will be utilized as a “user facility” as well as for FEL fundamental studies.

The linac uses a gridded disperser cathode gun, a 500 MHz prebuncher, a fundamental buncher and one accelerating section powered by a 3 GHz klystron (with 12 μs long pulses). The final energy will be adjustable between 30 and 75 MeV. The desired characteristics are: peak current >50 A, total energy spread ≈1%, normalized emittance <150πmm mrad. The numerical simulations made with PARMELA indicate that these performances will be reached with an emittance better by a factor of 2–4. The accelerator is followed by an achromatic and nearly isochronous 60° bend. It will allow to select the particles within a given energy spread, before the undulator, and to analyse, with respect to time, their energy distribution after the undulator.

The optical cavity is 4.8 m long (32 ns roundtrip time), compatible with the laser risetime (typically 100 passes) and the klystron pulse length of 12 μs. The undulator is made of two independently adjustable identical parts, 0.96 m long (24 × 4 cm) each; the second one can be tapered. This will allow to optimize both the optical gain and energy extraction at different wavelengths. The laser is scheduled to operate by the end of 1990.

CLIO: Collaboration for an infrared laser at Orsay

CLIO (Collaboration for an Infrared Laser at Orsay) is a FEL users facility at LURE Laboratory, Orsay, France. The first laser oscillation has been obtained in January 1992 at 5 μm wavelength with an electron beam of 40 MeV from a S-band linac. The first user experiment was performed in April at a wavelength between 7 and 10 μm. Presently, the spectral range spans from 2.5 to 15 μm with beam energies from 50 to 30 MeV. The 2 m undulator, within a 4.8 m long optical cavity, is fed by the S-band linac (3 GHz) designed for 50 MeV ± 20 MeV with a beam current of 0.6 nC charge per bunch of 8 ps duration. We present several measurements of the accelerator performances such as rf stability, beam phase stability, bunch length, beam emittance and energy spectrum with and without laser.

Operation of the CLIO accelerator

The CLIO (Collaboration pour un laser infra-rouge a Orsay) project involves an FEL and a dedicated 50 MeV rf linac being built at Orsay. We have completed its 4 MeV injector. It consists of a pulsed thermionic gun, a 500 MHz subharmonic prebuncher and a standing-wave (3 GHz) buncher. The gun emits 1 ns wide pulses of 1 A at frequencies ranging from 31.25 to 500 MHz. These pulses are compressed by the injector to 100 A × 8 ps. The injector includes “wall current” type intensity and position monitors. For commissioning temporary diagnostic equipment has been added: a dipole magnet followed by a slit to analyse the energy distribution and a translating wire profile monitor to measure the emittance by varying the magnetic lenses focal length. Also an optical transition radiation foil can be inserted in the beam to measure the longitudinal distribution of the microbunches with a streak camera. The results of the first measurements characterizing the beam are presented.

J. Rodier

Papers

ELYSE¿A picosecond electron accelerator for pulse radiolysis research

CLIO: Collaboration for an infrared laser at Orsay

Operation of the CLIO accelerator

Commissioning the CLIO injection system

Accelerating Structure Developments for the LEP Injector Linacs (LIL)