with computational models in calculating geometric
Equilibration Ring
inductances in the switch region up to the point when the
Although Figure 2 shows Blumlein strips which are
resistive phase of the gas switch dominates, >100ns,
wider than the beampipe, b > 2r, in general Blumlein
which is not included in the computational model yet.
strips may be of arbitrary size with the inclusion of an
equilibration ring around the beampipe to distribute the
fields. For very fast pulses, the equilibration ring would
need to be impedance matched, however for switch
closure times on the order of a few nanoseconds, it is
sufficient for the equilibration ring width to be 1/3rd the
radius of the beampipe. This is the configuration
commonly used with spiral designs (see Figure 3).
Ez in the middle of the stack in the center line for a 20kV charge voltage
4
3
2
1
0
-1
Figure 3: Spiral designs highlight the need for an
-2
equilibration ring around the beampipe
-3
-4
144
146
148
150
152
154
156
158
160
162
time [nanoseconds]
In gauging the effectiveness of the equilibration ring, a
series of matched monitoring resistors were placed around
the circumference of the beampipe. The overlay of the 8
plots is shown in Figure 4, with the temporal difference
caused by the propagation time around one quarter of the
ring.
10
8
6
4
Figure 5 a-d: comparison with experimental data for a 7-
2
stack in an enclosure with beampipe, Sullivan, et. al. [2]
0
-2
-4
100
-6
80
-8
60
-10
0
10
20
30
5
15
25
35
time (ns)
40
Figure 4: eight waveforms from monitoring resistors
20
placed around the circumference of the equilibration ring
0
-20
EXPERIMENTAL DATA
Mod-4
-40
experimental data
Early experimental data [2] confirming the validity of
the various models in-combination illustrates the benefits
-60
model result
(up to limit of gas
of full wave time domain simulations. These simulations
-80
switch model)
include the switch effects, inductances near the switches,
-100
0
200
400
800
1000
600
transmission line effects, layer-to-layer coupling, coupling
time (ns)
effects around the beampipe, and interactions with the
Figure 6: comparison with experimental data for 20-stack
enclosure (see Figure 5). Subsequent comparisons with
with high inductance gas switch configuration shows
experimental data [3] also showed excellent agreement
excellent agreement, Nunnally, et. al. [3]