ELECTRON ACCELERATOR

The LPR-4 (TESLA) electron accelerator produces an electron beam of 3 to 5 MeV average energy in pulse mode with 200 mA peak current.

Two modes of operation are available:
i)     single pulses
ii)   continuous train of pulses with repetition frequency selectable as 50, 25, 12.5 or 6.25 Hz (about 100 W)

The normal pulse length is 2.6 μs. The pulses can be shortened to about 800 ns by an electrostatic deflection system placed between the electron gun and the accelerator tube. An electromagnetic deflection system is positioning the beam entering the “scanning chamber” and allows scanning with about 1 Hz frequency. The electron beam leaves the chamber through a 0.03 mm thick titanium window of 200 × 18 mm² size.

Using a high-density metal target, such as platinum, strong bremsstrahlung (X-rays) can be produced with a conversion efficiency of a few percent. The high-energy part of the X-ray spectrum can be converted by the relevant (X,n) nuclear reaction to neutrons using deuterium (heavy water) or beryllium placed around or adjacent to the metal target.

It is noted that during operation a strong high frequency electromagnetic field is present around the accelerator that may interfere with electronic devices.

Dosimetry

Physical measurements of beam energy:

The Faraday cup with an electrometer measures the total beam charge. The cage is placed usually besides the target and the electron beam is altering between the cage and the target.

The ferrite core toroidal coil produces a voltage proportional to the beam charge. The coil is placed between the target and the electron source, without intercepting the beam. The method can be calibrated by the Faraday cage or by a chemical dosimeter.