Tukaj berem o ionskih črpalkah, kjer med drugim piše:
"Even if some ion pumps can be started at pressures as high as 10 to 20 mtorr, it is not a good idea to do this too often because of the accelerated exhaustion of the cathodes. The cathodes of an ion pump, which are eroded by sputtering, can not be regenerated but must be replaced. This replacement is not a simple matter because the pump will has to be cut, open and then re-welded. The cathode life depends on the amount of gas pumped, on the integral of pressure and time. Typical values for diode pumps are 200 h at a constant pressure of 10-4 torr, 2000 h at 10-5 torr, 20,000 h at 10-6 torr, and so on. Note that at 10-6 torr the life is over 2 years and at 10-3 torr only 20 h!"
Se pravi s časoma katode zmanjka. A kdo ve kakšna je običajno debelina teh katod, da jih tako hitro zmanjka?