E. Merle

AIRIX prototype technological results at CESTA

AIRIX Flash X-ray Radiographic facility is based on a 4 MeV-3,5 kA pulsed electron injector and a 16 MeV induction accelerator. The accelerator will consist of 64 induction cells powered by 32 H.V. generators operated at 250 kV. The final 20 MeV electron beam will be focused on a target designed for X-ray conversion. At CESTA, PIVAIR is a testbed designed as a validation step of AIRIX up to 8 MeV. The injector has been connected with 16 accelerating cells, increasing electron beam energy to 7.2 MeV. Two kinds of induction cells have been developed and tested. A focusing experiment is planned for electron beam spot diameter measurements. After this step, beam focusing on a target will be experimented for X-ray source characterization.

Status of the AIRIX accelerator

AIRIX is a linear induction accelerator that will be used for flash X-ray radiography. It will deliver a 20 MeV, 3.5 kA, 60 ns electron beam. This accelerator is now under installation at PEM. The injector, that produces a 3.5 kA, 4 MeV, 60 ns electron beam and 16 induction cells powered by 8 high voltage generators (250 kV per cell) are already operational. At this point, the AIRIX LIA has the same dimension than the PIVAIR prototype installed at CESTA. This paper relates the electron beam characterization that we have made to compare the two accelerators. Those experiments consist first, on beam imaging to validate beam transport code at three points on the beam line. In a second time we measure the energy of the beam with the time-resolved spectrometer to control the acceleration of the beam and to precisely tune the chronometry of the machine. Finally, we measure the emittance of the beam with the Pepper-pot method to compare the value before and after acceleration. We will present also the accelerator update and the experiments we plan to do when the 64 induction cells and the 32 HV generators will be installed.

Status of the AIRIX induction accelerator

AIRIX Induction Accelerator (16-20 Mev, 3.5 kA, 60 ns) has been designed at CESTA for flash X-ray application. After two years of experimental studies on prototype cells and High Voltage Generators we started in 1994 the PIVAIR milestone which is a validation step at 8 MeV for AIRIX. The PIVAIR injector has been assembled and tested; it produces a 3.5 kA electron beam at 4 MeV with good voltage flatness (/spl plusmn/0.35%) and low emittance. An accelerating module of eight induction cells has been constructed and four cells have been first connected with the injector. The other ones will be added this year and will use ferrite cores with high magnetic flux variation specially developed by CEA for this application. First results on beam characteristics are given in this paper as well as progress achieved in diagnostic technologies, cell alignment and beam transport studies.

AIRIX and PIVAIR accelerator status

AIRIX flash X-ray Radiographic facility is based on a 4 MeV- 3,5 kA pulsed electron injector and a 16 MeV induction accelerator. The accelerator will consist of 64 induction cells powered by 32 H.V. Pulsed generators operated at 250 kV. The final 20 MeV electron beam will be focused on a target designed for X-ray conversion. At CESTA, PIVAIR is a testbed designed as a validation step of AIRIX up to 8 MeV. The injector has been connected with 16 accelerating cells, increasing electron energy to 7.2 MeV. Two kinds of induction cells have been developed and tested. A focusing experiment has been performed for electron beam spot diameter measurements. PIVAIR is now currently used for beam focusing on a target, allowing X-ray source characterization and X-ray detector developments. The last technical improvements have been decided before beginning the induction cells and pulsed generators industrialization. AIRIX accelerator is now under construction: the 4 MeV injector has been commissioned and the first accelerating cells and pulse generators have been qualified at the rated voltage. A first beam test and characterization after 16 induction cells acceleration is planned by the end of 98 in order to validate industrial production.

Beam transport and characterization on AIRIX prototype at CESTA

Designed to produce an X-ray dose of 500 rads @ 1m, AIRIX flash X-ray Radiographic facility will consist of 4 MeV/3.5 kA pulsed electron injector and 16 MeV induction accelerator powered by 32 H.V. generators. Construction of PIVAIR accelerator (8 MeV AIRIX prototype) is now ended at CESTA. The injector has been connected with 16 accelerating cells in order to study beam transport and centering procedures. Accurate, time resolved diagnostics have been used to measure beam characteristics and a tickler experiment has been planned to estimate BBU instabilities. In this paper all experimental data recently obtained is discussed and first conclusions for AIRIX are given.

Design and progress of the AIRIX induction accelerator

A new electron accelerator is now being studied and designed for flash radiography application. It consists of a pulsed injector (4 MeV-3,5 kA-60 ns) and an induction accelerator increasing the energy of the electrons up to 20 MeV. We briefly describe the Injector built by PSI and similar to the DARHT injector at LANL. We present studies and experimental tests carried out in order to design and build new induction cells and high voltage generators suitable for this application. Information is given on the PIVAIR milestone planned for a beforehand validation of the whole AIRIX machine. Cavity is separated from the last output line by a segmented radial insulator interface with a water resister allowing the resistance matching of the diode.<<ETX>>

AIRIX induction accelerator development at CESTA

AIRIX induction accelerator (16-20 MeV, 3.5 kA, 60 ns) has been designed at CESTA for flash X-ray radiography application. It is based on a 4 MeV, 3.5 kA pulsed electron injector and a 16 MeV induction accelerator. It is scheduled to be operational in 1999. The prototype PIVAIR is a validation step for AIRIX at 8 MeV. It comprises an injector (4 MeV, 3.5 kA, 60 ns) and 16 induction cells supplied by 8 high voltage generators (250 kV, 70 ns). Two different cell technologies have been tested (rexolite insulator or ferrite under vacuum) and will be compared in this paper. Results on beam characteristics, beam transport and beam centering procedure will be given as well as a validation of a BBU instabilities code.

Diagnostics development for high current electron accelerators at CESTA

Some applications of induction accelerators require high quality electron beams and among them we are mainly interested in free electron laser (FEL) experiments and the achievement of the AIRIX high performance Radiographic Hydrotest Facility. In both cases small emittance and energy spread are needed to fulfil the experimental requirements. Beam diagnostics have been developed in order to allow a better knowledge of the main parameters and hence to optimize it. Since pulsed accelerators, and namely induction linacs, have essentially time dependant characteristics, it is necessary for most of the diagnostics to be time resolved. We describe the emittance measurement which uses the Cerenkov radiation from a thin window on a gated camera to record and process the image of a pepper-pot. A new electron magnetic spectrometer is presented which includes high energy resolution optical fibers and streak camera recording. Other diagnostics are discussed such as beam position measurements.<<ETX>>

First operation of the LELIA induction accelerator at CESTA

An induction linac has been studied and built in order to acquire induction technology for free electron laser (FEL) and other applications. It comprises a 1.5 MeV injector with a thermionic cathode which can deliver a high current electron beam (1 to 2 kA) and a 12 cells accelerating block which raises the electron energy up to 3 MeV. The injector has been tested and fully characterized and the accelerator is now being completed. We describe the induction cells and the high voltage generator designed to feed the cells with 150 kV pulses at 1 kHz repetition rate.<<ETX>>

Microwave FEL experiments at CESTA

Abstract At CESTA the EUPHROSYNE pulsed generator was used for Ondine I, our first FEL experiment at 35 GHz. The work was focused on beam creation and propogation first with an oxide cathode and then with a cold cathode. Typically 1 kA at 2.5 MeV was propagated in single shot operation. A lot of calculations have been done on these problems and we have also developed simulation codes on FEL interaction in both Compton and Raman regimes, taking into account 3D wiggler field, guiding field, waveguide modes, and electron beam injection, to obtain trajectories, gain and efficiency. Good agreement with some previous experiments and codes has been found. In the frame of a preliminary superradiant experiment using a bifilar helical wiggler, we obtained an amplification of the spontaneous emission up to 1 MW in the Kα band and 0.2 MW in the 33–36 GHz band. A microwave apparatus has been completed to work in an amplifier configuration: injection magnetron tube (100 kW), amplification line and diagnostics. All these components are compatible of the new Ondine II experiment designed for operation with the LELIA induction linac. This experiment is to start at 0.1 Hz with the induction injector (1.3 MeV, 1 kA, 50 ns) using the same wiggler technology as Ondine 1. In the future we plan to carry out the 35 GHz experiment at 3 MeV by adding an accelerating module to the LELIA injector. An hybrid planar wiggler with parabolic pole faces is being studied for further experiments.