Damage to pelletron acceleration tubes

The acceleration tube of the 12UD Pelletron which operated for about 10 years has been disassembled and the damage to the tube electrodes closely inspected. Very slightly melted smooth areas were found only on the anode surfaces. On the other hand, severely, melted areas were observed both on the anode and cathode surfaces. The smoothness of the severely melted areas suggests that there was rather slow process of electrode melting. The hydrogen discharge cleaning technique applied to the tube sections prior to the reinstallation was considered to be effective for the fast recovery of the voltage stability. (orig.)