Important Parameters of an Electron Beam – Understanding energy (MeV), current (mA) and line speed — and why they matter.

The key parameters to control an electron beam accelerator are the energy, current and line speed of the process. The accelerators used by E-BEAM Services are similar to the old cathode ray tube (CRT) televisions. However, instead of operating at about 25,000 volts, our industrial electron beams can operate at up to 5,000,000 volts. The energy of these beams is stated in MeV (million electron volts) and 5,000,000 volts is 5 MeV. The MeV determines the penetration ability of the beam. Electrons with more energy will penetrate deeper into and through product before stopping.

For more on the penetration capability of electrons, read my post that talks about whether e-beam can penetrate products.

Another key parameter is the current, measured in milliamps (mA), and that is a measure of the number of electrons being produced in a given amount of time. The number of electrons passing through the product directly relates to the “dose” the product receives. Dose is typically measured in kilogray (kGy) or megarads (Mrad) where 10 kGy = 1 Mrad. The dose delivered depends on the current and the line speed – the speed at which the product passes through the ‘shower’ of electrons. The higher the current for a given line speed, the higher the dose delivered.

There is one additional key characteristic of an accelerator – its power capability. The power is measured in kilowatts (kW). Ultimately, the greater the power of an electron accelerator, the proportionally higher the product throughput can be. Usually industrial e-beams have a power from 15 kW to 150 kW. In general, a 150 kW beam has 10 times the throughput capability of a 15 kW beam.

To calculate the power of an accelerator, we can use the following equation:

Power = Current x Energy

Therefore, if an accelerator is operating at 5 MeV, and the maximum current capability is 30 mA, then it is a 150 kW beam. If it is like one of E-BEAM Services’ world-class beams, which can operate at different energy levels, we might choose to operate it at 3 MeV for a given application – and then we could get 50 mA of current! All that current can irradiate a LOT of product, even if a high dose is required!

For a 15 kW beam operating at 10 MeV, there is 1.5 mA of current available. That would mean that the product throughput would be comparatively low. These machines are typically used for medical sterilization, where the dose is low – about 25 kGy.

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