Performance characteristics of high power, multiple gun, electrocurtains ®

Abstract

Electron processors are power limited electrically, usually due to the inability of the vacuum window assembly to dissipate the energy absorbed from the primary beam above a certain flux level. This problem is accentuated at low operating voltages typical of selfshielded processors, where the characteristic stopping power of the electron in the window material may be very high. Practical window geometries are discussed which are capable of current ratings of up to 0.4 mA cm 2 at 200 keV. Under these operating conditions, a single window unit can deliver 1 megarad at line speeds of up to 600 m/minute (2000 fpm). For most electron initiated processes, the lowest average dose rate achievable in the process zone is desirable. For products requiring a high treatment level (e.g. dose to cure), it is often desirable to extend the process zone so that the high delivered dose can be achieved without resorting to very high dose rates. A processor geometry is described which incorporates two or more Electrocurtain units in tandem. Typical performance data for these EPZ (Extended Process Zone) units are presented showing depth: dose performance, edge:edge uniformity of ±3%, and dose delivered as a function of output current. For a typical three element processor, 1 megarad can be delivered at 1500 meters/minute at processor voltages in the 150–300 keV range. The behavior of the surface dose fall-off with increasing operating voltage due to stopping power variation is discussed.