IEEE Aerospace and Electronic Systems Magazine - August 2020 - 33

Credit: SPC-EPFL

contour, which has been previously discussed in [8] with
grounded LDs.
This basic assembly is composed of a central HV ring
of 38 mm diameter separated by two insulating rings from
two conducting LDs of 58 mm diameter, as indicated in
Figure 1. The bias of the two LDs (VLD ) is proportional to
the central ring voltage (VHV ) according to the voltage
divider composed of two resistances R1 and R2 . Since the
physical parameter that determines the breakdown on
short paths between the HV ring and the LDs is their relative voltage (VHV -VLD ), the measured breakdown curves
are identified with the parameter h such that
h¼

R2
VLD
¼
R1 þ R2 VHV

)

VLD ¼ hVHV :

(1)

The values of the resistances must be chosen to find a
tradeoff between two effects. The ratio R1 =R2 must be
high enough to provide a sufficient voltage difference
between VHV and VLD to maintain the Faraday screen
effect, hampering the HV-ring breakdown at low

Figure 1.
Schematic design of the basic assembly with the passively biased
LDs' configuration.

AUGUST 2020

pressures on long paths toward the grounded enclosure.
A value of R1 =R2 ) 1 (h ' 0) tends to the grounded
LDs solution. At the same time, R1 =R2 must result in a
shift to higher values of both VHV and VLD with respect
to the surrounding grounded enclosure before the breakdown of the HV ring occurs. R1 =R2 ( 1 (h ' 1) leads
to VLD ' VHV , therefore losing the Faraday screen
effect and also making the breakdown between the LDs
and the grounded enclosure the dominant process. The
resistances R1 and R2 must be low enough to allow currents larger than the background Townsend currents to
avoid affecting the LDs potential, but high enough to
keep these currents below the current limit threshold of
breakdown detection. This leads to the selection of
resistances of few tens of MV as discussed in the
"Basic Assembly Breakdown Mitigation" section, where
measurements of breakdown curves with the passively
biased configuration are presented.
To reproduce the complex structure of a satellite SRA,
the test-SRA shown in Figure 2 is developed. It is composed of a conducting housing and a central conducting
cylindrical axis on which 36 gold-plated rings of 2 mm
thickness are inserted. Similar to the basic assembly, these
rings are designed to be used in groups of three, arranged
along the stack with a central HV ring of 32 mm enclosed
between two LDs whose diameter progressively increases
from 34 to 56 mm. This allows to test the grounded or passively biased configurations for different size of LDs.
Consecutive conducting rings are separated by 1 mm thick
insulating rings. Gold-plated brushes mounted on the insulating board on top of the housing slip on the corresponding rings, providing electrical continuity. The brushes are
covered with a film of insulator (Kapton), with the exception of the tip in contact with the ring. This is necessary to
avoid the breakdown with the rest of the assembly, since
the brushes extend beyond the volume screened by the
LDs. The printed-circuit board in Figure 2(c) allows to
independently control the potential of each ring. Breakdown measurements of the test-SRA are presented in the
"Test-SRA Breakdown Mitigation" section.

IEEE A&E SYSTEMS MAGAZINE

IEEE Aerospace and Electronic Systems Magazine - August 2020

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