[en] On account of the small depth of penetration of 1-3 MeV electrons, a technique is used for the radiation of large objects--or, rather, large surfaces--whereby the electron beam is moved back and forth, or scanned, over a certain width, at the same time as the surface to be radiated is moved, at a uniform rate, at right angles to the scanning direction. Besides the radiation of a large surface, the scanning and the moving of the table have still another important function, viz., keeping the total energy absorbed locally per time unit low enough to avoid the development of too high temperatures, which would lead to damage to exit window of accelerator and the radiated object

[en] A system for control and stabilization of the IRI 3 MeV Van de Graaff electron accelerator is based on a PI-controller. Parameters are derived from the accelerator open-loop response, and refined by simulation for output of nanosecond multi-ampere pulses and DC current to 1 mA. A switched Anti-Windup Loop (AWL) and variable limiters are incorporated. Long-term voltage stability obtained below the charging belt revolution frequency of 5 Hz is ±0.05%

[en] A passive coaxial pulse shaper has been developed which produces a subnanosecond duration pulse with short rise and decay time from a long pulse with short rise time. The mechanical construction of the pulse shaper is a modified coaxial air line T-section. The pulse shaper has been incorporated in the pulsing circuit of a 3-MV Van de Graaff accelerator. The form of the resulting electron beam pulses was monitored both as the charge collected by a coaxial target and as the Cerenkov light emitted by a quartz plate. In both cases sequential sampling techniques were used. The electron beam pulses were found to have rise and decay tiems of approxiamtely 100 ps and a half-width as short as approximately 200 ps could be obtained. An advantage of this method of producing subnanosecond beam pulses is that it does not interfere with normal nanosecond pulsed operation of the Van de Graaff

[en] An optically isolated electronic trigger system for a pulsed Van de Graaff electron accelerator, producing an external pretrigger pulse 75 ns before arrival of the electron pulse at the target, is described. The total time jitter between trigger signal and electron pulse is 50 ps. The measurement of optical and electrical transients on a subnanosecond time scale with a sequential sampling oscilloscope is demonstrated. The contribution of various parts of the equipment to the total jitter is discussed. Those contributions to the jitter due to the electron transit time fluctuations in the accelerator assuming a constant acceleration voltage gradient and to the shot noise in the photomultiplier detector of the trigger system are calculated to be 5 ps and 12 to 21 ps respectively. Comparison with the experimental results leads to the conclusion that a considerable part of the total jitter may be attributed to acceleration voltage gradient fluctuations, to accelerator vibrations and possibly to density fluctuations in the insulation gas. Possible improvements of the trigger system are discussed. The apparatus is used for pulse radiolysis experiments with subnanosecond time resolution down to 100 ps in combination with subnanosecond time duration electron pulses

[en] Production of electron-beam pulses with a 700-ps FWHM duration, using laser-photoelectron emission from a cold trioxide cathode in a 3-MV Van de Graaff accelerator has been demonstrated. At 70-kW laser power (lambda = 337.2 nm) a current of about 1 mA has been measured which means a cathode quantum efficiency of 10^-7. An electron transit time jitter of about 40 ps has been measured, to be attributed to voltage fluctuations on the accelerator tube electrodes resulting from the charging belt system. The results are discussed with respect to the feasibility to produce short pulses with a 1-nC total charge, taking into account the quantum efficiency of 10^-4 measured in a test setup for the cold trioxide cathode. Larger quantum efficiency for the accelerator cathode and decrease of the transit time jitter are the main goals set for development of the Van de Graaff accelerator as a radiation source for very high time-resolution experiments in radiation chemistry and physics

No abstract available

[en] The shorted air line stub used for subnanosecond pulsing of the grounded-grid cathode gun structure of the IRI 3 MV Van de Graaff electron accelerator is revised. Three-dimensional high-frequency field propagation calculations provide better insight into the performance of different geometrical shapes. Effects on rise- and decay time, and ringing on the output pulses are considered. Practical possibilities for improvement are discussed. Comparison with sampling measurements on several device modifications confirms the reliability of the calculations. The calculation method is subsequently used as design aid for the construction of a '1 ns' device using a quartz loaded shorted stub to fit into the geometry of the existing variable pulse length unit. Capabilities for short pulsing of the accelerator are improved and extended by application of the results obtained