Status of the LBL/LLL Development Program Page: 3 of 6
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various voltage-current combinations. The initial appli-
cation will be for TFTR 120-kV, 65-A, 0,5-sec modules.
In a year or so, the HVTS will be modified to permit
testing of a negative-ion system at 200 kV, 20A, dc,
Next we describe the operation of a 120-kV, 0.5-sec
injector module which, from an 8- x 10-cm accelerator-
grid array, produces 14A of hydrogen ions or 10 A of
deuterium ions. This module was used to test the design
concep o8of the 10-x 40-cm, 120-kV, 65-A, 0.5-sec TFTR
module which is currently under test.
Injector Module
A cross-section of the 120-kV, 8- x 10-cm injector
module is shown in Fig. 2, The ions are produced in
a high-current low-voltage discharge with no externally
applied magnetic fields. The cathode consists of eighty-
four 0.5-mm-diam, 11-cm-long tungsten filaments; the
anode is a 10- x 10-cm molybdenum plate shown in the
top of the figure. A photograph of the plasma source
is shown in Fig. 3; details on this type of plasma
generator can be found in Ref. 2.
Gag ~ ~ 4,5 inin0~ ti
- - P f n - .w . .
Figure 2. Gross-section of the 120-kV, 0 5-sec source
module with an 8- x 10-cm grid array,I,
Figure 3. Photograph of the plasma source, illustrating
the filament geometry. The flange with the
0-ring was used for plasma-uniformity tests;
it is not part of the structure shown in Fig, 2.A four-grid (three-gap) multiple-slot accelerator
array (a cross section of a single slot of the array
is shown in Fig. 4) is used. Ions are accelerated and
electrostatically focused in the first two gaps; the
third gap has a weak decelerating field to suppress
down-stream electrons. The transparency of the array
is 60%; the scale size was set by the desire to limit
the maximum potential gradient to about 100 kV/cm (our
estimate of the breakdown limit) apd resulted in a design
ion-current densitZ of 0.31 A/cm for a pure D+ beam,
or about 0,25 A/cm for a beam with a realistic mixture
of D+, D2 , and D3 , The desi shown in Fig. 4 was
optimized, using the WOLF code, by varying the shape
of the first, beam-forming, electrode and the potential
of the second, gradient-grid, electrode. The shapes of
all electrodes except the first were chosen to minimize
energy deposition in the structure by secondary particles
created by ionization of the background gas or by secon-
dary emission from grid surfaces.
TFTRO0 0UMP 1,TFTR1127 rSDLUTION=1,ERR0R=0, 03 MAY 7
V - 120000 101000 -2300 0
' SOURCE PLASMA - - .0 CM -- - NEUTRALIZE PLASMA
ION CURRENT DENSITY 0 0.31 A/CW W0+)
TRANSPARENCY = 0,6
BEAM DIVERGENCE ( 09O S) - 0.53 DEGREES
Figure 4. Calculated beam trajectories and equipoten-
tials for a 120-kV accelerator.
The module (Fig. 2) consists of an outer, vacuum-
wall insulator that is sectioned to distribute the po--
tential gradients; to keep these insulators reasonably
short, the outside of this insulator is pressurized with
two atmospheres (absolute) of SF6 gas. The plasma source
and grid assembly are mounted on an inner plug-in struc-
ture (Fig. 5). The tubular insulators to which the grid
assemblies are mounted also carry de-ionized cooling
water to the plates that support the final three grid
arrays; cooling for the first (beam-forming) grid is
obtained from the plasma-source chamber. The 8-cm long
grid rails, arranged in a 10-cm-wide array, are end
cooled. The solid molybdenum rails are brazed to a
fixed support on one end, forming a comb-shaped struc-
ture, and allowed to expand iq 8the long direction to
prevent buckling when heated. The heat is conducted
away in the 1-min interval between pulses.
Figure 5. Photograph of the accelerator plug-in struc-
ture and one of four multi-slot grids.- 2 -
9
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Berkner, K. H.; Ehlers, K. W.; Pyle, R. V. & Hooper, E. B. Jr. Status of the LBL/LLL Development Program, article, November 1, 1977; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1012149/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.