4.
If the beam is still not in the cor rect po si tion, at tach a fourth shunt bar mag net i cally be hind the one
al ready mounted on the rear of the source.
CAU TION
Do NOT attempt to attach a shunt bar magnetically to the front of the
source. If you do so, the permanent magnet’s field will pull the bar
strongly and rapidly toward the pole piece extensions, possibly
alternating their position and causing minor finger injuries.
Ad justing the Emis sion Cur rent
The emis sion cur rent is the value of the elec tron beam’s high-volt age dc cur rent. Emis sion cur rent con trol
pro vides the only means if vary ing to tal beam power dur ing a run, as the ac cel er a tion volt age value must be
kept con stant to en sure cor rect beam po si tion ing. How ever, this value is not con trolled di rectly but rather by
vary ing the lower-volt age ac cur rent sup plied to the gun’s fil a ment by the e-beam power sup ply. The value of
this cur rent, which is termed the gun cur rent or the fil a ment cur rent, is set via the e-beam power sup ply’s gun
con trol cir cuit. Even if you are ad just ing the fil a ment cur rent, an emis sion cur rent read out should be avail able
on ei ther the HV con trol panel or the gun con trol panel of the e-beam power sup ply.
For in struc tions on ad just ing the emis sion cur rent, and for a more com plete ex pla na tion of the re la tion ship
be tween the emis sion cur rent and the fil a ment cur rent, see the man ual for your e-beam power sup ply.
CAU TION
Never set the emission current so high that the gun’s operating-
power rating of 10 kW is exceeded. Operating above that power level
may result in damage to the crucible or other parts of the source. At
10 kV acceleration voltage, the emission current should be limited to
0.7 A. At 8 kV, the current limit should be 0.875 A.
Operation
STIH-270-2PT
0101-9004-0A
3-3
Figure 3-1. Correct mounting location for shunt bar(s)
Shunt bar(s) bolted
to upper surface of
coil shield
Upper surface
Mounting screw
Mounting screw
Shunt bar(s)
magnetically
attached to
rear of source
