3.2 ELEC TRON BEAM CONTROL
The source op er ates in con junc tion with an elec tron beam power sup ply and, op tion ally, with a beam sweep
con trol ler. Var i ous fea tures of these com po nents al low con trol over the fol low ing beam pa ram e ters:
•
to tal beam power
•
the po si tion of the beam spot (i.e., the area where the beam strikes the evaporant ma te rial)
•
the size and shape of the beam spot.
The fea tures that pro vide con trol over these pa ram e ters are:
•
the ac cel er a tion volt age con trol on the e-beam power sup ply
•
the emis sion con trol on the e-beam power sup ply
•
the de flec tion cur rent con trol(s), whether on the e-beam power sup ply or the op tional beam sweep
con trol ler
•
the pole piece ex ten sions on the source it self
The ef fects of ad just ing these con trol fea tures are de scribed be low.
Ad justing the Ac cel er a tion Volt age
The po ten tial at which the dc elec tron beam op er ates is termed the ac cel er a tion volt age. This value is set via
the e-beam power sup ply’s HV con trol cir cuit, which should pro vide a read out of the ac cel er a tion volt age in
kV. To gether with the emis sion cur rent con trol, the ac cel er a tion volt age de ter mines to tal e-beam power.
How ever, the ac cel er a tion volt age value must be kept con stant, as it strongly af fects the lon gi tu di nal po si tion
of the beam spot. Re ducing the ac cel er a tion volt age moves the beam spot to ward the front of the source (i.e.,
to ward the emit ter as sem bly), while in creas ing the ac cel er a tion volt age moves the beam spot to ward the rear
of the source. For in struc tions on set ting the ac cel er a tion volt age, see the man ual for your e-beam power sup -
ply.
Al though the SuperSource2 can be op er ated at any ac cel er a tion volt age be tween 4 kV and 10 kV, the per ma nent
mag net is gaussed for op er a tion at a spe cific ac cel er a tion volt age value. On the stan dard model STIH-270-2PT,
the per ma nent mag net is gaussed so that at 10 kV ac cel er a tion volt age, the beam strikes the tar get ma te rial just in
front of the rear edge of the ex posed pocket. On spe cial ver sions of this source, the per ma nent mag net may be
gaussed so that at 8 kV or 10 kV ac cel er a tion volt age, the beam strikes the ma te rial at or near the pocket cen ter.
In ei ther case, if the source is op er ated at an ac cel er a tion volt age lower than the des ig nated value, the beam will
fall in front of the cor rect po si tion (i.e., far ther to ward the front of the source). In that event, it may be nec es sary
to mount one or more mag netic shunt bars to make the beam strike the cor rect po si tion.
Two shunt bars are sup plied with the source, al though in some cases ad di tional shunt bars may be re quired.
The mount ing po si tions for the shunt bars is shown in Fig ure 3-1. Note, how ever, that the ef fect of the shunt
bars var ies de pend ing on whether they are mounted on the front or the rear of the source. There fore, if mul ti -
ple shunt bars are re quired, it is im por tant to add them in the fol low ing se quence:
1.
Mount the first shunt bar atop the coil shield, as shown in Fig ure 3-1, us ing the socket-head screws
and nuts sup plied with the shunt bars.
2.
If ad di tional shunt ing is re quired, at tach a sec ond shunt bar mag net i cally to the rear of the source, in
the rear ward po si tion shown in Fig ure 3-1.
3.
If a third shunt bar is re quired, mount it above the ini tial shunt bar. Use the mount ing hard ware pro -
vided to hold both shunt bars in place atop the coil shield.
Operation
3-2
0101-9004-0A
STIH-270-2PT
Содержание Temescal SuperSource2 STIH-270-2PT
Страница 54: ...Operation 3 18 0101 9004 0A STIH 270 2PT...
