![](media/image1.pct){width="5.972222222222222in"
height="0.4583333333333333in"}

13-980720-CLN-01

***TO: DISTRIBUTION***

***FROM: C NEUMEYER***

***SUBJECT: OH GROUND PLANE REWORK AND GROUNDING CONNECTIONS***

**Reference:**

1\) 13-980704-CLN-01, \"OH Ground Plane Behavior\"

2\) 13-980714-CLN-01, \"OH Ground Plane Rework And Grounding
Connections\"

Reference \[1\] provided an analysis of the OH ground plane behavior
based on the ground plane provided by the coil manufacturer, which was
judged therein to be too resistive.

Reference \[2\] described a rework scheme involving the application of a
low resistance paint over the high resistance paint originally applied
by the manufacturer, and suggested a means for making a grounding
connection.

This memo provides revised instructions for reworking the ground plane
and providing connections to ground, and therefore supercedes reference
\[2\].

*Revised Ground Plane Scheme*

In recognition of the fact that voltage is induced in the poloidal, as
well as toroidal, direction, and considering that, with the prior
design, faults could occur which could lead to unacceptably large ground
currents in the poloidal direction, it has been decided to mask off
additional toroidally oriented stripes along the axis of the OH coil.
The prior design called for only one such stripe. The following
spreadsheet indicates the effective resistance and maximum current flow
in the toroidal direction, and poloidal direction, with the proposed
scheme consisting of two stripes opposite one another along the axis of
the OH coil and five circumferential stripes equidistant from one
another along the axis of the OH coil. The \"Low Tol\" column
corresponds to the case where the high resistivity paint exhibits
resistance on the low end of the manufacturer\'s (Ranbar) data sheet
range, and \"Hi Tol\" the high end of the range. The \"Assumed\" column
corresponds to the most likely value of resistivity, based on
measurements made by T. Meighan. It is noted that, with the proposed
design, using 50Ω resistors in the ground connections, the resulting
ground/ground plane resistance is quite similar to that which would have
been obtained using the originally specified (Von Roll/Osola #8003)
100Ω/square paint. Induced currents and energy loss in the conductive
paint layers will be limited to acceptable levels.

  ----------------------- ------------ --------- --------- ----------------
                          Low Tol      Assumed   Hi Tol    

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Coil OD                 12.3                             in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Coil Circumference      38.7                             in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Coil Length             210.0                            in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Length of End Sections  6.0                              in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Ground Plane Length     198.0                            in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Hi R Resistivity        2000.0       2500.0    5500.0    Ω/square

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Lo R Resistivity        1.0          1.5       2.0       Ω/square

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Layer Thickness         0.002                            in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                                                           

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  *TOROIDAL*                                               

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  #Hi R Stripes           2                                

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Hi R Stripe Width       1.00                             in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  R/Hi R Stripe           2000.0                           Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          10.1                             Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  ∑R(Hi R)                4000.0                           Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          20.2                             Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  #Lo R Stripes           2                                

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Lo R Stripe Width       18.4                             in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  R/Lo R Stripe           18.4                             Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          0.1                              Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  ∑R(Lo R)                36.7                             Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          0.2                              Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  ∑R                      4036.7                           Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          20.4                             Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Voltage                 10                               volt

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Current                 0.002                            amp/in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          0.490                            amp

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Power                   6.137                            watt/in\^3

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Time                    0.005                            sec

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Energy                  0.031                            joule/in\^3

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  *POLOIDAL*                                               

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  #Hi R Stripes           5                                

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Hi R Stripe Width       1.00                             in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  R/Hi R Stripe           2000.0                           Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          51.7         64.6      142.1     Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  ∑R(Hi R)                10000.0                          Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          258.3                            Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  #Lo R Stripes           6                                

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Lo R Stripe Width       32.2                             in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  R/Lo R Stripe           32.2                             Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          0.8          1.2       1.7       Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  ∑R(Lo R)                193.0                            Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          5.0                              Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  ∑R                      10193.0                          Ω-in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  R/ground resistor       50.0                             Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Rnet                    363.3                            Ω

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Voltage                 27.8                             volt

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Current                 0.002                            amp/in

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
                          0.076                            amp

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Power                   3.901                            watt/in\^3

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Time                    1.000                            sec

  ----------------------- ------------ --------- --------- ----------------

  ----------------------- ------------ --------- --------- ----------------
  Energy                  3.901                            joule/in\^3

  ----------------------- ------------ --------- --------- ----------------

* Performance of Ground Plane*

As described in \[1\] a model of the transient behavior of the ground
plane was created using PSCAD. The simulation reported in \[1\] was
repeated using the nominal expected value of ground plane resistance
(64.6 Ω per high resistance stripe, 1.2 Ω per low resistance stripe)
with the new proposed design. The results are given in the following
figures.

![](media/image2.pct){width="7.0in" height="2.2916666666666665in"}

Coil/Ground Plane Model

![](media/image3.pct){width="5.597222222222222in"
height="5.013888888888889in"}

Voltages on Ground Plane for Normal Operations

![](media/image4.pct){width="5.333333333333333in"
height="5.013888888888889in"}

Voltages on Ground Plane in Case of Ground Fault

on One Terminal of Coil/Power Supply

The peak voltages of 200V and 500V, respectivly, for the two cases, are
considered acceptable.

*Rework and Grounding of Coil*

Prior to the rework, the condition of the coil is assumed as follows
based on the prior sequence of steps:

• Groundwall of coil covered by Ranbar B-2-135 type semi-conductive
paint (2000-5500 ohms/square) by the manufacturer, Everson Electric;

• Semi-conductive paint covered by polycrylic sealer by PPPL;

• Three 1.25\" wide stripes (two azimuthal, one circumferential) of
semi-conductive paint and sealer were removed by PPPL, down to the
original ground plane surface, as depicted

in the following figure (developed view, outer surface of OH coil).
Azimuthal stripes located at 0o and 180o positions.

![](media/image5.pct){width="4.416666666666667in"
height="6.041666666666667in"}

• Three 1.25\" wide stripes of Glyptal insulating paint applied by PPPL
over the stripes made in the previous step.

*Rework Instructions*

• Prepare the regions of the coil surface still covered by sealer to
accept additional coats of paint by very light sanding.

• Apply Ranbar B-2-135 type semi-conductive paint (2000-5500
ohms/square) over the previously applied stripes of Glyptal insulating
paint as depicted in the following figure.

![](media/image6.pct){width="4.416666666666667in"
height="6.013888888888889in"}

• Mask off seven 1\" wide stripes, two azimuthal and five
circumferential, with azimuthal stripes located at 90o and 270o
positions (180o apart). Five circumferential stripes shall be evenly
spaced in the azimuthal direction. Then overcoat the entire unmasked
area with Tecknit type 73-0025 conducting paint (1 Ω/square) as depicted
in the following figure.

![](media/image7.pct){width="5.527777777777778in"
height="5.986111111111111in"}

*Grounding*

• Apply 2\" wide Kapton tape, approximately 4\" from the two opposite
ends of the ground plane region, in the circumferential direction,
overlapping the regions masked in the prior step (Ranbar B-2-135 type
semi-conductive paint exposed) by 2\" on either side as shown in the
following figure (Kapton pieces 2+1+2 = 5\" long).

![](media/image8.pct){width="5.555555555555555in"
height="5.986111111111111in"}

• Affix, using clamps with dielectric breaks, at each end of the coil,
1\" wide braided copper conductors with soldered ends, such that a 1\"
gap exists at the 90o and 270o positions, per the following figure.

![](media/image9.pct){width="4.430555555555555in"
height="5.986111111111111in"}

• Suggested clamp design is shown in the following figure. Clamp is made
from 2 pieces of thin (e.g. 1/16\") non-magnetic stainless steel, 1\"
wide to cover copper braid. At joints, G-10 spacer block, and G-10
nut/bolt provide dielectric break in toroidal direction. Spring washer
under nut provides for thermal expansion/contraction. Set screw through
nut/bolt provides locking. Wire lug under bolt head at 90 and 270o
postions connect to 10\' long #10 (600V insulated, stranded) conductor.
Subsequent routing of the pair of wires should keep them nested together
(e.g. twisted). Final point of connection of ground wires will be
determined later. Series resistor (e.g. 50Ω) will be introduced in each
path. Prior design, which included \"anti-turn\" of ground wire around
coil, was judged not to be beneficial.

![](media/image10.pct){width="3.0833333333333335in"
height="6.569444444444445in"}

• After installation, measure resistance between all four ground leads:

1-2

1-3

1-4

2-3

2-4

3-4

cc:

J Chrzanowski

P Heitzenroeder

T Meighan

M Ono

S Ramakrishnan

M Williams

NSTX File