NASA Technical Memorandum 102 124 

AIAA-89-2719 

Structural and Thermal Response of 30 cm 

Diameter Ion Thruster Optics 

G.S. MacRae, R.J. Zavesky, and S.T. Gooder 

Lewis Research Center 

Cleveland, Ohio 

Prepared for the 

25th Joint Propulsion Conference 

cosponsored by the AIAA, ASME, SAE, and ASEE 

L Monterey, California, July 10-12, 1989 

(1ASA-w10212U) STRUCTURAL AND THEBWAL N 89- 273 03 

BESPOBSE OF 30-cr DIBMETEB ION THRUSTER 

OPTICS (NASA., Lewis Research Center) 29 p CSCL 21c Unclas 

G3/20 0225957 
STRUCTURAL AND THERMAL RESPONSE OF 30 CM 

DIAMETER ION THRUSTER OPTICS 

G. S. MacRae, R. J. Zavesky and S. T. Gooder 

National Aeronautics and Space Adminiswition 

Lewis Research Center 

Cleveland, Ohio 

ABSTRACT 

This paper presents tabular and graphical data intended for use in calibrating and validating 

structural and thermal models of ion thruster optics. A 30 cm diameter, two electrode, mercury 

ion thruster was operated using two different electrode assembly designs. With no beam 

extraction, the transient and steady state temperature profiles and center electrode gaps were 

measured for three discharge powers. The data showed that the electrode mount design had 

little effect on the temperatures, but significantly impacted the motion of the electrode center. 

Equilibrium electrode gaps increased with one design and decreased with the other. 

Equilibrium displacements in excess of 0.5 mm and gap changes of 0.08 mm were measured at 

450 W dscharge power. Variations in equilibrium gaps were also found among assemblies of 

the same design. The presented data illustrate the necessity for high fidelity ion optics models 

and development of experimental techniques to allow their validation. 

INTRODUCTION 

Ion thrusters can deliver specific impulses from 2000 to 5000 seconds which makes them an 

attractive alternative to chemical rocket systems for orbit transfers, interplanetary missions, and 

other roles not requiring or not desiring high thrust levels.' Development efforts have 

increased and continue to increase the thrust delivered by ion thrusters. Space Electric Rocket 

Test I (SERT I) thrusters produced 25 mN thrust with a 10 cm ion extraction diameter or about 

3 N/m2.2 SERT I1 thrusters produced 27 mN with a 14 cm ion extraction diameter, or 2 

N/m2.3 Today's 30 cm diameter, xenon thrusters produce 500 mN thrust or 7 N/m2! 

These increases in thrust per unit area and thruster area are largely due to advances in ion optics 

design. The early electrodes (ion optics) used on SERT I and SERT I1 were flat and subject to 

severe, uncontrolled buckling when the radial temperature gradient became large. These 

factors limited the ability to scale the planar electrodes to large diameters and high thrust levels. 

By dishing the electrode^,^ the first buckling mode can be controlled, allowing reductions in 

electrode gap and thickness.6 Because the beam extraction is space charge gap and 

grid thickness reductions translate into higher thrust per unit area as shown by Rawling (Fig. 

1). Greater control over the buckling and gap size also allows larger electrodes and higher thrusts to be achieved. 

These advances were made with minimal computer aided structural analysis, and even less 

experimental measurement of deformations. Hughes Aircraft Company lo and Lord ElectroOptic Systems (EOS)11 both developed finite element structural models of two and three 

electrode ion optics systems. Lord EOS also made displacement measurements of electrode 

gaps using an optical system." Unfortunately, the uncertainty associated with those 

nieasurenients was unquantified. With large circular and non-circular electrodes now under 

consideration, computer modeling is both an economical and essential step in advancing ion 

thruster design. The difficulty with most of these models is calibration and verification of the 

1 
predictions. The primary objective of this paper is to report experimental data to facilitate 

inodeling efforts. 

for two different electrode assembly designs. 

Three electrode assemblies of two different designs were used in the tests. The electrode 

assemblies consisted of two electrodes, insulators, and a mounting ring. The inner (screen) 

electrode was maintained at the cathode potential and the outer (accelerator) electrode was 

usually held a few hundred volts negative of the neutralizer potential. The insulators provided 

electrical isolation between the electrodes and the mounting ring fixed the cold electrode gap. 

Four major design iterations were made in the development of a 3 kW mercury ion thruster for 

planetary propulsion applications.1~13~14 The 900-series and J-series, which were fabricated 

in the late 70s, were the last two. Both assemblies used identical electrodes and insulators 

with different mounting and stiffening rings. Because of an effort to reduce mass, the 900 

series mounting ring was all titanium, and the screen electrode was mounted directly with 

screws. (Figs. 2 and 3). A thin molybdenum stiffening ring provided the interface between 

the accelerator electrode and the titanium portion of the mounting ring. The J-series design 

added a thick molybdenum stiffening ring to the screen electrode and increased the size of the 

stiffening ring on the accelerator electrode interface. The J-series molybdenum stiffening rings 

were attached to the electrodes with rivets and to the titanium ring with screws (Figs. 4 and 5). 

The titanium ring was redesigned for manufacturing ease and slotted to reduce the stiffness. 

A three step process was used to manufacture the electrodes. First, a photoresist pattern was 

applied to the molybdenum sheets and the patterned sheets were then dished hydrostatically to a 

depth of 22 mm to control buckling. Then, circular ion extraction holes were chemically etched 

in the dished sheets.5J5 All electrode dimensions are shown in Table I. The screen electrode 

open area was high, 67 percent, to maximize ion extraction, while the accelerator open area 

was lower, 24 percent, to minimize neutral particle losses. The screen electrode hole pattern 

was sized down by 0.35 percent to intentionally misalign the screen and accelerator holes. 

This misalignment was intended to compensate for misalignments caused by the dishing 

procedure and to steer the beamlets to reduce beam divergence.16 

PROCEDURE 

I A 30 cm diameter, divergent field, mercury ion thruster was operated in a 21 m long, 7.6 m 

diameter diffusion pumped vacuum chamber at NASA Lewis Research Center. Current 

regulated supplies were used to maintain the discharge, and there was no beam extraction. 

After preheating the mercury vaporizers on the cathode, neutralizer, and main flow systems, 

the discharge was initiated and the anode current, Jd, was fixed at a value determined by the 

beam current, Jb, being modeled. The mercury flow through the cathode was then adjusted to 

bring the discharge voltage, Vd, to 32 V. Only about 5 percent of the mercury vapor flowed 

through the cathode as the main portion was injected directly into the discharge chamber. The 

main mercury flow rate was fixed at approximately the values that would be required to achieve 

the beam current that corresponds to the anode current used. With ion beam extraction, the 

discharge power, Pd, is the product of the discharge voltage and the difference between the 

anode current and beam current. Because no beam was extracted during the testing, the 

formula for discharge power was simply: 

, 

2 
For a more complete description of ion thruster techniques, set points, and logic, see Ref. 14. 

Two electrode assemblies, the 900-series (SN813) and the J-series (SN842), were configured 

with 10 chromel-alumel thermocouples, of which three were attached to each of the electrodes 

and four to the mounting rings (Figs. 6 and 7 for the 900 and J-series respectively). The 

thermocouples were located at the same radial positions to simplify comparisons of the 900 and 

J-series assemblies. Transient and steady state temperatures were measured at three power 

levels for both assemblies. For all tests, the same 30 cm diameter discharge chamber was 

used. 

Data could not be taken continuously, so the exact times required to reach equilibrium 

temperatures were not always available. The data presented, therefore, employ two artificial 

time constants. The time constant definitions were based on the assumption that an exponential 

equation of the form: 

T = AT (1 - e-flc) + Ti (2) 

governed the temperature change, where T was the temperature at time t, AT was the difference 

between the equilibrium temperature and the temperature at cathode ignition, Ti, and T, was the 

time constant. The 63.2% time constant was defined exactly as in Eq. 2, and was the time 

required for the temperature to reach 63.2 percent of the difference between the equilibrium and 

cathode ignition temperatures. The 95% time constant was the time required to reach 95 

percent of the temperature difference. The 95% time constant would be three times the 63.2% 

time constant if Eq. 2 described the temperature function exactly. The distribution of the data 

made the 95% time constant more accurate than the 65% time constant. 

All transient data were referenced to cathode ignition time, for two reasons. It was explicitly 

known for all of the test runs, while the preheat times, wherein the mercury vaporizers heated, 

varied for the tests. In addition, the presence of the discharge was the dominant factor in 

determining the temperatures of the ion optics. 

ent Measurements 

Thermally induced displacements were measured for three electrode assemblies. Two of these, 

the 900-series (SN813) and J-series (SN842) assemblies, were instrumented with 

thermocouples for simultaneous measurement of the temperature profiles. The last assembly, 

J-series (SN903), was tested without thermocouples. It was chosen for tests because it 

demonstrated the most efficient beam extraction capability of the J-series assemblies available. 

Displacements were measured using a stepper motor driven probe that contacted either the 

accelerator electrode or a post extending from the screen electrode (Figs. 8 and 9). The 

measuring system was rigidly attached to the discharge chamber, as shown in Figure 10. The 

motion of the reference location of the measuring system was uncompensated and unknown. 

Thus, to remove any error introduced by motion of the reference position, the gap, or 

difference between the measurements of the screen and accelerator electrode locations, was 

used to compare displacements for different designs and discharge powers. 

The probe was a 7.9 thread per cm jack screw actuator driven by a variable reluctance, 15'/step 

stepper motor with a 97:l gear box. Probe contact was confirmed when an electrical circuit 

3 
between the electrode and the probe was closed. Each actuator had a sensitivity of 47 pulses 

per 0.0025 cm of motion. A hysteresis or dead band occurred when the motion was reversed. 

The screen and accelerator actuators had dead bands of 110 and 1 15 pulses, respectively. The 

dead bands were calibrated using a dial indicator accurate to 0.0013 cm. Displacement 

measurements were made at the electrode centers on the thruster axis. The actuator controller 

drove both stepper motors independently and simultaneously, The total uncertainty of the 

centerline gap measurement was about 0.0025 cm. 

I No ion beam was extracted because it would have had detrimental effects on the displacement 

measuring equipment which was installed in the center of the beam path. 

RESULTS 

The data presented are intended for use in calibrating and verifying models used to predict 

electrode response. For that reason, data are presented in figure and tabular form. Some of the 

data are omitted from certain figures to improve clarity. All of the data were taken without ion 

beam extraction to provide direct comparison for the temperatures and electrode gap 

measurements for use in modeling efforts. 

Table I1 shows transient temperature profiles measured at discharge powers of 210, 350, and 

493 W for the 900-series assembly. Figures 11 through 13 show the tempentures measured at 

selected thermocouples. All times were normalized to cathode ignition at 0 minutes in order to 

provide a consistent, accurate reference for comparisons. The heating before the cathode was 

ignited was due to the vaporizer heaters. After ignition, the temperatures rose exponentially 

towards their equilibrium values. 65% and 95% time constants were extracted for each of the 

thermocouples on the 900 series electrode (Table 111). Figure 14 shows the 95% time 

constants for two discharge powers. The time constants increased monotonically from the 

center to the edge of the screen electrode with a variation of more than a factor of 2.5. Across 

the mounts, the fractional variation in time constants was smaller but all were higher than the 

electrode constants. Again time constants increased monotonically with radial location. The 

time constants from the accelerator electrode were close to, but slightly higher than those of the 

screen electrode. As will be discussed later, these results strongly affected the transient 

electrode spacing. 

The J-series design showed similar transient thermal characteristics. Transient temperatures are 

+own in Table IV and Figure 15 for a 210 W discharge. The 95% time constants are given in 

Table V and compared with values from the 900-series electrode in Figure 16. The J-series 

assembly demonstrated a smaller spread of time constants than the 900-series. This was likely 

due to the higher initial temperatures for the J-series test. The discharge was initiated about 20 

minutes earlier than shown in figure 16 but, was held at a low power until the indicated cathode 

ignition time. Again, if the accelerator and screen electrode locations are treated separately, the 

time constants increased monotonically with the radius. 

The temperature measurements described above were taken without displacement 

measurements. This allowed documentation of the transient temperatures at all of the 

thermocouple locations. The following temperature measurements were taken concurrently 

with displacement measurements, using the same electrode assemblies. The labor intensive 

method of controlling the displacement measurement interfered with temperature measurement 

records so transient temperatures were measured only on tne electrode cen terlines. 

Comparisons of the transient centerline temperature measurements in Tables VI and VII show 

good agreement with the equivalent temperatures shown in Tables 11 an IV. When equilibrium 

I was reached, temperatures were recorded for all of the thermocouples. Of the data presented, 

I 4 
the data from Table VIII provide the highest fidelity and should be used for steady state values 

to compare model predictions with displacement measurements. 

Transient temperature data on the --series (SN813) and J-series (SN842) assembly 

centerlines are shown in Tables VI and VI1 and Figures 17 and 18. Again, the transient 

response is almost identical for the two designs. For all discharge powers and designs tested, 

the electrode assemblies heated to their equilibrium temperatures within 100 minutes of 

initiating a discharge. 

Steady state temperatures for the two assemblies are shown in Table VI11 and figure 19 for 

discharge powers from 210 to 450 W. The figures show that, for a given power level, the 

only significant difference in temperatures occurred near the transition from molybdenum to 

titanium on the mounting ring. The molybdenum support ring on the J-series design 

maintained a higher temperature than the equivalent position on the titanium mounting ring of 

the 900-series design. 

Transient electrode motion and spacing changes are shown in Tables VI and VI1 and Figures 

20 and 21. The electrode gap was reduced initially for both the 900 and J-series assemblies, 

then the gap opened to the equilibrium value. Transient displacements of the screen electrode 

of more than 0.8 mm and transient gap reductions of more than 0.25 mm were measured. 

Both the rate and magnitude of the gap changes were complex. The initial gap reduction was 

due to rapid heating of the screen electrode. With the 900-series assembly, the magnitude of 

the initial gap change varied inversely with discharge power. The magnitude of the initial gap 

change of the J-series assembly did not vary monotonically discharge power. The time required 

for the minimum gap to be reached, for both assemblies, seemed to increase with discharge 

power increases. The complex response characteristics were probably due to the variations in 

thermal equilibration times for points at different radii on the assemblies. 

Equilibrium gap changes are reported in Table IX for a 900 and two J-series assemblies. The 

equilibrium gap is plotted in Figure 22 for the same conditions. The equilibrium gaps for a 

given assembly were reproducible to within the accuracy of the measuring system for all power 

levels tested. The 900 and J-series assemblies had distinctly different responses. The 900- 

series gap increased at all power levels between 200 and 450 W and the J-series gaps all 

decreased at those power levels. This appears to be due to design differences, specifically, the 

addition of a molybdenum support ring and weakening of the titanium ring on the J-series 

design. With its higher expansion coefficient, the 900-series titanium mounting ring put the 

screen electrode under tension at the edge, which reduced the absolute motion of the electrode 

center. 

It is difficult to account for the differences in the responses of the two J-series assemblies. 

While the first J-series assembly demonstrated a monotonic response to discharge power, the 

second did not. The gap change of the second assembly was greater than that of the first and 

nearly constant. This suggests that the initial states of the electrodes were different. 

CONCLUSIONS 

The electrode designs under consideration for future ion thrusters make computer modeling 

both an economical and essential step in advancing the state of the art. The largest road block 

to these efforts is the scarcity of experimental data to calibrate and validate the models. This 

paper presented transient and steady state thermal and displacement data from tests of a 30 cm 

diameter, mercury ion thruster operated without beam extraction. The fidelity of the steady 

state data was ensured by recording the displacement and thermal data simultaneously. The 

5 
I ~ 

~ measurements. 

transient centerline temperatures measured concurrently with displacement measurements 

closely matches the transient thermal data recorded independently of the displacement 

Experimental data to calibrate and validate finite element models of ion thruster optics systems 

are presented. Except for one thermocouple location on the mounting rings, the temperature 

measurements show little difference between the equilibrium or transient temperatures of the 

two electrode assembly designs tested. Across the radius of the assembly, the time constants 

vary by as much as a factor of four, increasing monotonically with the radius. The highest 

95% time constants were less than 100 minutes for all assemblies and power levels tested and 

increasing the discharge power reduced the time constants. 

Transient electrode motions were found to be very complex. The general pattern was for the 

gap to decrease a large amount initially and then approach the equilibrium gap which could be 

larger or smaller than the initial gap depending on the electrode design. Transient 

displacements as high as 0.8 mm for the screen electrode and transient gap reductions as high 

as 0.25 mm were measured. Steady state gap changes as large as 0.08 mm and motions of 0.5 

mm were measured. 

The equilibrium electrode motions were very different for the two designs. The electrode gap 

increased from the cold gap at operating temperatures in one design while the gap decreased 

with the other design. The equilibrium gap was also found to vary significantly among 

assemblies of the same design. The difference in responses of the two designs should be 

predictable with modeling. The variation within a design may be due to the initial states of the 

hardware which most likely must be addressed by improved controls on manufacturing, 

assembly, and handling processes. The data of this report indicate the necessity of high fidelity 

ion optics models and further development of experimental techniques to allow their validation. 

REFERENCES 

1 

2 

3 

4 

5 i 

6 

Stone, J. R., Byers, D. C. and King D. Q., "The NASA Electric Propulsion 

Program," Proceedings: 20th International Electric Propulsion Conference, October 

Cybulski, R. J., "Results from SERT I Ion Rocket Flight Test," NASA TN D-2718, 

March 1965. 

1988, pp. 17-25. 

Kerslake, W. R., Byers, D. C. and Staggs, J. R., "SERT I1 Experimental Thrustor 

System," AIAA Paper 67-700, September 1967. 

Patterson, M. J. and Rawlin, V. K., "Performance of 10 kW Class Xenon Ion 

Thrusters," AIAA Paper 88-2914, July 1988. 

Rawlin, V. K.; Banks, B. A. and Byers, D. C., "Design, Fabrication, and Operation 

of Dished Accelerator Grids on a 30 cm Ion Thruster," Journal of SDacecraft and 

Rockets, Vol. 10, No. 1, January 1973. 

Rawlin, V. K., "Studies of Dished Accelerator Grids for 30 cm Ion Thrusters," AIAA 

Paper 73-1086, October 1973. 

6 
10 

ELECTRODE ASSEMBLY 

SERIES SERIAL 

NUMBER 

900 813 

J 842 

J 903 

11 

HOLE DIAMETER, MM ELECTRODE THICKNESS, OPEN AREA FRACTION COMPEN- RAT0 OF 

MM SATION. DISH DEPTH 

SCREEN ACCELERATOR SCREEN ACCELERATOR SCREEN ACCELERATOR STRAIN% TODIAMETER 

1.91 1.14 0.38 0.38 0.67 0.24 0.35 0.075 

1.91 1 .14 0.38 0.38 0.67 0.24 0.35 0.075 

1.91 1.14 0.38 0.38 0.67 0.24 0.35 0.075 

12 

13 

14 

15 

16 

Kaufman, H. R., "Technology of Electron-Bombardment Ion Thrusters," Advances in 

Electronics and Electron Phvsics, Vol. 36, Academic Press, New York, 1974. 

Rawlin, V. K., "Sensitivity of 30 cm Mercury Bombardment Ion Thruster 

Characteristics to Accelerator Grid Design," AIAA Paper 78-688, April 1978. 

Rawlin, V. K., "Studies of Dished Accelerator Grids for 30 cm Ion Thrusters," AIAA 

Paper 73-1086, October, 1973. 

Poeschel, R. L. and Kami, S., "Analysis and Design of Ion Thrusters for Large Space 

Systems," NASA CR-165140, September 1980. 

James, E. L.. et al, "Advanced Inert Gas Ion Thrusters," NASA CR-168192, July 

1984. 

Poeschel, R. L., "Retrofit and Acceptance Test of 30 cm Ion Thrusters," NASA 

NAS3-21357, June 1981. 

"30 cm Ion Thruster Subsystem Design Manual," NASA TM-79191, June 1979. 

Schnelker, D. E., Collet, C. R., Kami, S. and Poeschel, R. L., "Characteristics of the 

NASA/Hughes J-Series 30 cm Engineering Model Thruster," AIAA Paper 79-2077, 

October 1979. 

Collet, C. R., "Fabrication and Verification Testing of ETM 30 cm Diameter Ion 

Thrusters," NASA CR-135193, April 1977. 

Danilowicz, R. L., Rawlin, V. K., Banks, B. A. and Wintucky, E. G., "Measurement 

of Beam Divergence of 30 cm Diameter Dished Grids," AIAA Paper 73-1051, October 

1973. 

7 
TABLE II. - TRANSIENT TEMPERATURE OF THE 900-SERIES SN813 ASSEMBLY. 

A. - 210 W DISCHARGE POWER. 

THERMOCOUPLE LOCATIONS REFERENCED TO FIG. 6 

RADIAL POSITION, CM 

14.4 I 15.8 16.9 18.3 15.8 

22 22 22 22 22 

-16 26 24 23 22 24 

- 

5.0 

22 

- 

- 

0.0 - 

22 

- 

5.0 

22 

31 

52 

63 

166 

209 

233 

246 

256 

261 

268 

270 

269 

- 

- 

- 

14.4 

22 

25 

36 

42 

62 

91 

123 

141 

153 

161 

174 

178 

- 178 

28 

46 

55 

108 

152 

182 

198 

207 

21 3 

223 

225 

- 226 

29 

49 

59 

121 

169 

198 

21 6 

223 

227 

235 

238 

- 238 

-6 

-1 

2 

6 

14 

24 

34 

44 

89 

194 

- 284 

27 

31 

36 

52 

85 

112 

131 

145 

168 

173 

173 

55 

67 

190 

230 

252 

271 

276 

279 

284 

284 

284 

121 

79 117 

101 129 

117 139 

145 154 

151 158 

152 158 

B. - 350 W DISCHARGE POWER. 

- 

TIME, 

MIN 

-27 

-1 7 

-7 

-2 

1 

3 

6 

10 

16 

23 

33 

48 

98 

133 

233 

- 

- 

a 

5 

16.9 

26 

26 

31 

34 

38 

51 

71 

97 

135 

163 

187 

207 

224 

225 

231 

,oaTI 

- 

- 

THERMOC 

11 213 4 

15.8 

26 

27 

34 

39 

46 

66 

97 

133 

179 

204 

224 

241 

255 

256 

257 

- 

- 

- 

- 

14.4 

26 

30 

42 

50 

98 

138 

162 

200 

231 

249 

263 

274 

284 

285 

- 286 

- 

0.0 

26 

33 

52 

63 

134 

207 

229 

263 

284 

291 

297 

302 

308 

309 

309 

- 

- 

- 

0.0 

26 

34 

57 

71 

227 

283 

291 

328 

345 

349 

354 

358 

362 

363 

361 

- 

- 

- 

5.0 

26 

34 

55 

67 

203 

256 

267 

310 

322 

333 

338 

343 

347 

348 

348 

- 

- 

- 

15.8 

26 

27 

34 

39 

47 

67 

91 

114 

141 

157 

173 

186 

197 

198 

199 

- 

- 

- 

14.4 

26 

29 

39 

45 

66 

98 

124 

153 

178 

194 

207 

217 

227 

228 

229 

- 

- 

- 5.0 

26 

32 

49 

59 

124 

186 

207 

244 

265 

276 

283 

290 

297 

297 

- 298 

26 

27 

29 

31 

33 

41 

55 

83 

113 

144 

170 

192 

193 

- 194 

C. - 493 W DISCHARGE POWER. 

- 

PER, 

5 

16.: 

23 

24 

26 

28 

32 

36 

39 

51 

81 

127 

169 

204 

222 

233 

239 

243 

248 

249 

249 

cATI( 

- 

- 

RES, "C 

L REFERENCED TO FIG. 6 

6 17 1 8 1 9 I10 

- 

UPLE 

4 

15.8 

23 

25 

28 

32 

37 

42 

47 

67 

116 

178 

21 8 

247 

262 

270 

275 

278 

283 

284 

284 

- 

- 

- 

- 

THERM 

'WE, 11 213 

MIN 

-32 

-22 

-17 

-12 

-7 

-2 

1 

3 

6 

11 

18 

28 

38 

48 

58 

68 

116 

190 

248 

- 

- 

- 

5.0 

23 

- 

- 

0.0 - 

23 

- 

15.8 

23 

25 

28 

33 

37 

42 

47 

68 

104 

138 

163 

185 

197 

204 

208 

21 1 

21 5 

21 6 

216 

- 

14.4 

23 

26 

31 

37 

43 

49 

62 

104 

148 

184 

207 

226 

235 

241 

244 

247 

251 

251 

251 

- 

- 

18.3 

23 

- 

32 

43 

55 

68 

78 

100 

321 

349 

371 

383 

391 

395 

397 

398 

399 

402 

32 

42 

54 

64 

74 

173 

286 

323 

349 

361 

370 

375 

377 

379 

381 

383 

27 

33 

41 

47 

54 

06 

151 

197 

243 

269 

289 

299 

304 

308 

31 1 

31 4 

23 

23 

25 

27 

29 

32 

34 

42 

68 

108 

152 

176 

191 

199 

204 

21 2 

21 3 

- 21 4 

30 

38 

48 

56 

64 

104 

208 

256 

288 

304 

31 5 

32 1 

324 

326 

328 

331 

331 

- 33 1 

31 

40 

51 

61 

69 

109 

232 

279 

307 

322 

332 

337 

339 

34 1 

343 

345 

346 

346 

8 
TABLE 111. - 62.3% AND 95% TIME CONSTANTS FOR A 900-SERIES ELECTRODE ASSEMBLY. 

63.2% 

I THERMOCOUPLE I I TIME TO REACH 63.2% OF I TIME TO REACH 95% OF 

9 5 % 

LCCATIONS 

REFERENCED 

TO FIG. 6 

1 

2 

3 

4 

5 

6 

7 

8 

9 

RADIAL 

POSITION, CM 

0.0 

5.0 

14.4 

15.8 

16.9 

18.3 

15.8 

14.4 

5.0 

0.0 

4 

14 

23 

29 

36 

22 

17 

9 

3 

10 

16 

22 

30 

16 

11 

6 

2 

8 

14 

18 

26 

15 

10 

4 

97 85 

83 70 

78 60 

65 38 

57 33 28 

TABLE IV. - J-SERIES TRANSIENT TEMPGRATURE PROFILES AT 210 W DISCHARGE POWER. 

- 

TIME, 

MIN 

-57 

-47 

-37 

-27 

-17 

-1 1 

1 

5 

9 

22 

50 

77 

95 

359 

- 

1279 

- 

0.0 

23 

34 

59 

83 

101 

109 

119 

206 

229 

254 

268 

271 

269 

269 

269 

- 

5.0 

23 

32 

54 

78 

94 

103 

114 

194 

21 7 

246 

259 

262 

263 

263 

262 

TI 

THERMOCOUPLE I 

11 21314 

83 

97 

118 112 

146 139 

197 192 

223 221 

229 226 

232 229 

232 229 

232 229 

- PERA' 

5 

16.9 

23 

23 

26 

32 

39 

46 

57 

61 

71 

109 

150 

161 

166 

166 

166 

23 

25 

31 

38 

44 

54 

57 

64 

96 

138 

149 

154 

155 

- 155 

- 

15.8 

23 

25 

33 

44 

56 

62 

72 

86 

105 

140 

169 

176 

179 

180 

180 

RES, "C 

; REFERENCED TO FIG. 6 

6 17 1 8 1 9 I10 

p!J 

18.3 

22 

- 

TABLE V. - J-SERIES TIMES TO TEMPERATURES 

FOR A 210 W DISCHARGE POWER. 

THERMOCOUPLE 

LOCATIONS 

REFERENCED 

TO FIG. 6 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

RADIAL 

POSITION, CM 

0.0 

5.0 

14.4 

15.8 

16.9 

18.3 

15.8 

14.4 

5.0 

0.0 

49 

46 

- 

0.0 

23 

32 

51 

72 

87 

95 

105 

172 

193 

21 6 

227 

229 

230 

231 

230 

9 
TABLE VI. - 900-SERIES SN813 ELECTRODE TRANSIENT DEFORMATIONS AND TEMPERATURES. 

A. - 210 W DISCHARGE POWER. 

0.51 

- 

TIME, 

MIN. 

30.8 

28.7 

21.3 

16.5 

11.8 

-6.7 

0.0 

0.8 

1 .o 

1.3 

1.5 

2.0 

2.2 

2.5 

3.2 

4.1 

4.3 

5.3 

8.3 

11.1 

13.2 

15.7 

20.4 

27.7 

29.0 

32.6 

121 

166 

250 

- 

3.8 

1196 

PREHEAT 

CATHODE IGNITION 

210 W DISCHARGE EQUlLlBRlUl 

-EMPERA 

SCREW 

CBil-EFl 

19 

48 

74 

225 

223 

279 

286 

285 

IRES,"C 

ACCEL 

e 

19 

42 

63 

161 

224 

226 

238 

238 

iLECTRODl 

SCREEN 

0.00 

0.03 

0.05 

0.08 

0.10 

0.13 

0.13 

0.28 

0.33 

0.38 

0.41 

0.48 

0.48 

0.51 

0.53 

0.53 

0.56 

0.56 

0.56 

0.56 

0.51 

0.48 

0.46 

0.43 

0.43 

0.41 

0.38 

0.36 

0.33 

0.33 

0.33 

MITION, MM 

KCa 

0.00 

0.03 

0.01 

0.08 

0.10 

0.13 

0.15 

0.20 

0.23 

0.25 

0.28 

0.31 

0.33 

0.33 

0.36 

0.38 

0.38 

0.41 

0.43 

0.46 

0.48 

0.48 

0.46 

0.46 

0.43 

0.43 

0.41 

0.38 

0.36 

0.36 

0.36 

0.51 

0.51 

0.51 

0.51 

0.51 

0.51 

0.53 

0.43 

0.41 

0.38 

0.38 

0.33 

0.36 

0.33 

0.33 

0.36 

0.33 

0.36 

0.38 

0.41 

0.48 

0.51 

0.51 

0.53 

0.51 

0.53 

0.53 

0.53 

0.53 

0.53 

PREHEAT 

CATHODE IGNITION 

210 W DISCHARGE EQUlLlBRlUl 

10 
TABLE VI. -CONCLUDED. 

B. - 350 W DISCHARGE POWER 

'EMPERATURES, 

SCREEN 

cENlEFlc€NTER 

22 

70 

292 

337 

354 

- 

TIME, 

MIN. 

25.7 

21.6 

.15.4 

10.4 

-5.2 

0.0 

2.5 

3.0 

3.5 

4.0 

4.8 

5.5 

6.1 

6.7 

10.3 

11.1 

12.4 

14.3 

19.3 

25.2 

35.8 

37.6 

1235 

- 

"C 

PCCEL 

22 

61 

216 

278 

303 

- 

TIME, 

MIN. 

29.t 

25.5 

17.E 

-9.9 

0.0 

18.3 

20.1 

21.9 

23.3 

24.4 

25.0 

26.1 

26.6 

27.1 

30.4 

52.8 

59.4 

60.3 

- 

1045 

0.00 

0.03 

0.05 

0.08 

0.10 

0.1 3 

0.25 

0.38 

0.51 

0.66 

0.74 

0.74 

0.76 

0.76 

0.64 

0.61 

0.58 

0.56 

0.53 

0.51 

0.51 

0.48 

0.38 

0.00 

0.03 

0.05 

0.08 

0.10 

0.13 

0.18 

0.25 

0.28 

0.41 

0.53 

0.61 

0.64 

0.66 

0.69 

0.69 

0.69 

0.69 

0.66 

0.66 

0.64 

0.64 

0.53 

62 

dOTION,MM UEcTRoOE 

KXXL GAP,MM 

353 

EVENT 

39 1 

396 

0.00 

0.03 

0.05 

0.08 

0.10 

0.36 

0.61 

0.69 

0.71 

0.71 

0.74 

0.74 

0.74 

0.74 

0.69 

0.69 

0.69 

0.69 

0.58 

0.51 PREHEAT 

0.51 

0.51 

0.51 

0.5 1 CATHODE IGNITION 

0.48 

0.41 

0.38 

0.41 

0.43 

0.53 

0.56 

0.56 

0.64 

0.64 

0.66 

0.69 

0.69 

0.69 450 W DISCHARGE EQUlLlBRlUb 

ELECTROO€ 

GAP, MM 

0.51 

0.51 

0.51 

0.51 

0.51 

0.51 

0.43 

0.38 

0.28 

0.25 

0.30 

0.38 

0.38 

0.41 

0.56 

0.61 

0.61 

0.61 

0.64 

0.66 

0.64 

0.66 

0.66 

56 

282 

334 

343 

C. - 450 W DISCHARGE POWER. 

0.03 

0.05 

0.08 

0.1 0 

0.38 

0.76 

0.81 

0.81 

0.79 

0.71 

0.69 

0.64 

0.61 

0.56 

0.53 

0.51 

0.51 

0.41 

YEW 

'REHEAT 

:ATHOD€ IGNITION 

W DISCHARGE EQUlLlBRlUN 

11 
TABLE VII. - J-SERIES SN842 ASSEMBLY TRANSIENT DEFORMATIONS AND TEMPERATURES. 

A. - 21 0 W DISCHARGE POWER 

- 

TIME, 

MIN. 

25.6 

23.2 

17.6 

13.7 

-9.5 

-6.5 

-5.6 

-1.1 

0.0 

3.7 

4.0 

4.2 

4.4 

4.7 

5.0 

5.4 

5.8 

6.2 

6.8 

7.0 

8.1 

9.5 

11.3 

11.9 

12.4 

13.0 

15.5 

17.1 

20.8 

21.4 

25.4 

33.2 

40.7 

116 

202 

334 

- 

264 

'EMPER/ 

SCREEN 

CENTER 

23 

72 

180 

240 

267 

281 

287 

200 

288 

- 283 

IRES,"C 

Acca 

23 

47 

87 

152 

178 

200 

219 

221 

221 

- 216 

LECTROC 

SCFIEDJ 

0.00 

0.03 

0.05 

0.08 

0.10 

0.1 0 

0.13 

0.15 

0.10 

0.23 

0.28 

0.30 

0.38 

0.43 

0.46 

0.48 

0.51 

0.53 

0.53 

0.56 

0.56 

0.56 

0.51 

0.51 

0.48 

0.46 

0.46 

0.43 

0.43 

0.43 

0.41 

0.38 

0.36 

0.33 

0.30 

0.30 

0.30 

AOTION. MM 

Acca 

0.00 

0.03 

0.03 

0.05 

0.05 

0.08 

0.08 

0.08 

0.10 

0.13 

0.13 

0.15 

0.18 

0.20 

0.20 

0.23 

0.25 

0.28 

0.30 

0.33 

0.36 

0.38 

0.41 

0.41 

0.41 

0.41 

0.43 

0.43 

0.41 

0.41 

0.41 

0.41 

0.38 

0.30 

0.28 

0.28 

0.28 

iiz7EE 

GAP, MM 

0.51 

0.51 

0.48 

0.48 

0.46 

0.48 

0.46 

0.43 

0.51 

0.41 

0.36 

0.36 

0.30 

0.28 

0.25 

0.25 

0.25 

0.25 

0.28 

0.28 

0.30 

0.33 

0.41 

0.41 

0.43 

0.46 

0.48 

0.51 

0.48 

0.48 

0.51 

0.53 

0.53 

0.48 

0.48 

0.48 

0.48 

ATHODE IGNITION 

10 W DISCHARGE EQUlLlBRlUN 

12 
- 

TIME, 

MIN. 

- 

-26.3 

-22.6 

-1 5.5 

-1 2.2 

-7.5 

0.0 

2.7 

4.1 

4.2 

4.4 

4.7 

5.0 

5.4 

6.0 

6.3 

6.9 

7.7 

8.7 

10.8 

11.5 

13.4 

18.5 

21.3 

23.7 

27.4 

35.3 

45.0 

50.7 

1219 

rEMPERA 

SCREB] 

CamR 

26 

75 

231 

279 

296 

327 

343 

353 

IRES,"( 

pccn 

26 

ELF! 

49 

104 

171 

201 

240 

269 

292 

TABLE VII. - CONTINUED. 

B. - 350 W DISCHARGE POWER 

LECTRODI 

SCREEN 

0.00 

0.03 

0.05 

0.08 

0.1 0 

0.28 

0.23 

0.58 

0.61 

0.64 

0.66 

0.66 

0.69 

0.69 

0.69 

0.69 

0.69 

0.69 

0.69 

0.61 

0.58 

0.56 

0.53 

0.53 

0.51 

0.51 

0.51 

0.51 

0.46 

AOTION, MM 

KCEL 

0.00 

0.03 

0.05 

0.05 

0.08 

0.10 

0.13 

0.28 

0.30 

0.33 

0.36 

0.38 

0.41 

0.43 

0.46 

0.48 

0.51 

0.53 

0.56 

0.56 

0.56 

0.58 

0.56 

0.48 

0.53 

0.51 

0.48 

0.41 

0.48 

GAP, MM 

0.51 

0.51 

0.51 

0.48 

0.48 

0.33 

0.36 

0.20 

0.20 

0.20 

0.20 

0.23 

0.23 

0.25 

0.28 

0.41 

0.33 

0.36 

0.38 

0.46 

0.48 

0.48 

0.48 

0.51 

0.53 

0.51 

0.48 

0.48 

0.46 

ATATHOOE KWITION 

50 W DISCHARGE EQUlLlBRlUh 

13 
0.43 

TABLE VII. -CONCLUDED. 

C. - 450 W DISCHARGE POWER 

1450 W DISCHARGE EQUIUBRIU) 

IRES, "CI ELECTRODE MOTION, MN 

mELlSy;REENI AMXL 

TIME, 

MIN. 

29.6 

25.6 

16.9 

-9.4 

-1.2 

0.0 

6.0 

6.7 

7.5 

8.3 

8.6 

8.8 

9.4 

9.8 

10.5 

11.8 

13.8 

15.7 

17.0 

17.6 

20.8 

21.4 

27.8 

31.9 

32.9 

37.4 

52.4 

92.4 

136 

1302 

>ENTER I I 

23 1 0.00 I 0.00 

TEMPERA 

SCREEN 

CENTER 

23 

86 

324 

381 

391 

392 

394 

397 

54 

224 

303 

313 

319 

325 

327 

0.03 

0.05 

0.10 

0.13 

0.15 

0.41 

0.58 

0.74 

0.79 

0.79 

0.81 

0.81 

0.81 

0.81 

0.81 

0.81 

0.71 

0.69 

0.66 

0.64 

0.64 

0.61 

0.61 

0.58 

0.58 

0.58 

0.56 

0.56 

0.53 

0.03 

0.05 

0.08 

0.10 

0.10 

0.36 

0.36 

0.38 

0.48 

0.51 

0.53 

0.56 

0.58 

0.61 

0.64 

0.66 

0.69 

0.69 

0.69 

0.66 

0.66 

0.64 

0.61 

0.61 

0.58 

0.53 

0.48 

0.46 

0.46 

m 

GAP, MM 

0.51 

0.51 

0.51 

0.48 

0.48 

0.46 

0.46 

0.28 

0.15 

0.20 

0.23 

0.23 

0.25 

0.28 

0.30 

0.33 

0.36 

0.48 

0.51 

0.53 

0.53 

0.53 

0.53 

0.51 

0.53 

0.51 

0.46 

0.43 

0.41 

MM 

'REHEAT 

ATHODE IGNITION 

14 
KXXLEMTCR 

4 

9 5.0 189 276 31 0 225 287 327 

10 0.0 209 292 327 238 303 343 

3 

ELECTRODE ASSEMBLY 

SERIES SERIAL 

NUMBER 

900 I 813 

1 

ABWLUTE GAP CHANGE, MM 

DISCHARGE POWER, W 

210 I 350 I 450 

0.025 I 0.15 I 0.18 

TABLE IX. - EQUILIBRIUM ELECTRODE GAP CHANGE. 

J 

J 

5 % 30% 35% 

842 -0.025 -0.051 -0.076 

-5% -10% -15% 

903 -0.18 -0.18 -0.15 

-35% -35% -30% 

1 I 

-. 

500 

,.... 

1000 1500 

INITIAL 

ELECTROM 

SPACING, MM 

+ 0.56 

Y 0.86 I+ 0.99 I 

MINIMUM TOTAL ACCELERATING VOLTAGE, V 

FIGURE 1. - BEAM EXTRACTION SENSITIVITY TO ELECTRODE SPACING, REF. 9. 

15 
7 MOLYBDENUM 

ACCELERATOR 

MOLYBDENUM 

SCREEN 

2 

ELECTRODE 

TITANIUM TITANIUM 

RING GUSSET 

STAINLESS STEEL 

ALUMINA 

INSULATOR 

FIGURE 2. - 900-SERIES ELECTRODE ASSEMBLY. 

FIGURE 3. - 900-SERIES ELECTRODE ASSEMBLY. 

16 
/RIVETS 

SCREEN 

ELECTRODE 

2 

MOLYBDENUM 

STIFFENING RINGS 

MACHINE SCREWS 

STAINLESS STEEL 

MOLYBDENUM 

ACCELERATOR 

MOLYBDENUM 

ALUMINA 

INSULATOR 

I / i 

TITAN I U M 

RING 

FIGURE 4. - J-SERIES ELECTRODE ASSEMBLY. 

FIGURE 5. - J-SERIES ELECTRODE ASSEMBLY COMPONENTS. 

17 
I 

r 

0 

z 

FIGURE 6. - THERMOCOUPLE LOCATIONS ON THE 900-SERIES SN813 ASSEMBLY. 

I I ,TC10 

/Tc9 ica 

r 

0 

s 

Ill I 

FIGURE 7. - THERMOCOUPLE LOCATIONS ON THE J-SERIES SN842 ASSEMBLY. 

18 
.. ~~ 

ELECTRODE 

/ 

POST 

" STEPPER MOTOR 

ACCELERATOR 

ELECTRODE 

FIGURE 8. - SCREEN ELECTRODE MEASURING SYSTEM SCHEMATIC. 

FIGURE 9. - DISPLACEMENT MEASUREMENT PROBE ASSEMBLY. 

19 
FIGURE 10. - DISPLACEMENT MEASUREMENT ASSEMBLY. 

SyMBOLs 

OPEN - SCREEN LOCATIONS 

SOUD- MOUNTING RING 

LOCATIONS 

HALF-ACCELERATOR 

LOCATIONS 50

400 

THERMOCOUPLE 

300 2ool 100 

-50 0 50 100 150 200 250 300 

LOCATIONS 

FROM FIG. 6 

-9 - 10 

TIME, MIN 

FIGURE 11. - 900-SERIES ASSEMBLY TRANSIENT TEMPERATURES 

AT 210 W DISCHARGE POWER. 

20 
mMBoLs 

WEN - SCREEN LocATlONS 

SOLID- MOUNTING RING 

HALF - ACCELERATOR 

LOCATIONS 

400 

300 

200 

100 

LOCATIONS 

THERMOCOUW 

LOCATIONS 

FROM FIG. 6 

-1 

*2 

*3 

+4 

-6 

+ 

-9 

10 

+a 

-50 0 50 100 150 200 250 300 

TIME, MIN 

FIGURE 12. - 900-SERIES ASSEMBLY TRANSIENT TEMPERATURES 

AT 350 W DISCHARGE POWER. 

500 

mMBoLs 

OPEN - SCREEN LOCATIONS 

SOLID- MOUNTING RING 400 LOCATIONS 

v LOCATIONS wa: 300 

HALF - ACCELERATOR 

MERMOCOCRLE 

LOCAllONs 

FROM FIG. 6 

3 

4 

w 

a 

I 200 P 

-50 0 50 100 150 200 250 300 

0 

TIME, MIN 

10 

100 

FIGURE 13. - 900-SERIES ASSEMBLY TRANSIENT TEMPERATURES 

AT 493 W DISCHARGE POWER. 

21 
100 b 

60 

z 

I 

I-- 

2 5 60 

cn 

z 

s 

E 

w 40 

6 9 10 

MOUNTING PMXLERATOR 

45671 RING ELECTRODE 

12 

ELECTRODE 

SCREW I 

MSCHARGE 

POWER, W 

FIGURE 14. - 95% TIME CONSTANT FOR A 900-SERIES ASSEMBLY 

(THERMOCOUPLE LOCATION FROM FIGURE 6). 

w a 

w 

II 200 

100 

sEd3QLs 

OPEN - SCREEN LOCATIONS 

SOUD- MOUNTING RING 

HALF - ACCELERATOR 

LCCATIONS 

LOCATIONS 

THERMocouPLE 

LOCATKNS 

FROM FIG. 7 

Y 

Y 

I I 1 I I I 1 0' 

-50 0 50 100 150 200 250 300 

TIME, MIN 

FIGURE 15. - TRANSIENT TEMPERATURES OF A J-SERIES ASSEMBLY AT 210 W. 

22 
12 8 9 10 

MOUKTING MxaER4m 

- ELECTRODE SCREEN314 RING '1 ELECTROM 

FIGURE 16. - COMPARISON OF 95% TIME CONSTANTS FOR A 900 AND J-SERIES 

ASSEMBLY AT 210 W (THERMOCOUPLE NUMBER FROM FIGS. 6 AND 7). 

400 

v 

a 

J 300 

OPEN - 210 W DISCHARGE 

SOLID - 450 W DISCHARGE 

L p 200 

; 100 

W 

2 

i 

CT w 

0 

0 

0 1000 2000 

TIME, MIN 

FIGURE 17. - COMPARISON OF TRANSIENT SCREEN ELECTRODE CENTERLINE 

TEMPERATURES FOR 900 AND J-SERIES. 

23 
z 100 -I 

OPEN - 210 W DISCHARGE 

SOLID- 450 W DISCHARGE 

I I 

2000 0’ 

0 1000 

TIME, MIN 

FIGURE 18. - COMPARISON OF TRANSIENT ACCELERATOR ELECTRODE CENTERLINE 

TEMPERATURES FOR 900 AND J-SERIES. 

DLSCHARGE 

POWER, W 

10 20 0 

0 

RADIAL POSITION, CM 

A. - SCREEN ELECTRODE TEMPERATURES 

FIGURE 19. 

OPEN - 900-SERIES 

loot 

0 10 20 

RADIAL POSITION, CM 

B. - ACCELERATOR ELECTRODE LOCATKXJS. 

’ EQUILIBRIUM TEMPERATURE PROFILES. 

24 
I. 

0.5 - 

0.4 - 

0.3 - 

0.1 ::$ 

"._ , 

0 1000 21 

TIME, MIN 

A. - LONG TERM EOUlLlBRATlON TRANSIENT 

0.6 O''5 

0.1 o'21 

DISCHARGE 

POWER, W 

* 450 

0 

DlscHARGE 

POWER, W 

-50 0 50 100 150 

TIME, MIN 

6. - SHORT TERM HEATING TRANSIENT 

FIGURE 20. - 900-SERIES SN813 TRANSIENT ELECTRODE GAP 

25 
O''> 0.6 

0.0 

0.5 

0.4 

0.3 

0.2 

, 

Y 

0.1 

0.0 ! 

0 1000 2 

TIME, MIN 

A. - LONG TERM EQUILIBRATION TRANSIENT. 

0.7 

0.6 

0.5 

0.4 

03 

0.2 

0.1 

DISCl-L4RGE 

POWER, W 

%f * 

0 

26 
0.8 

0.6 

€ 

?i 

E 0 0'4 

0.2 

0.0 

COLD 

WP 

c ELH;TRoDE 

ASSEMBLY 

DESIGN 

900-SN813 

H J-SN842 

El J-SN903 

21 0 350 450 

DISCHARGE POUIER, W 

FIGURE 22. - EQUILIBRIUM ELECTRODE GAP FOR THREE ASSEMBLIES. 

27 
Im 

7. Key Words (Suggested by Authoqs)) 

Ion engine 

Ion optics 

Structural analysis 

Finite element analysis 

Report Documentation Page 

18. Distribution Statement 

Unclassified - Unlimited 

Subject Category 20 

2. Government Accession No. NASA TM-102124 

AIAA-89-2719 

1. Report No. 

4. Title and Subtitle 

Structural and Thermal Response of 30 cm 

Diameter Ion Thruster Optics 

3. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No of pages _- Unclassified Unclassified 28 

7. Author(s) 

G.S. MacRae, R.J. Zavesky, and S.T. Gooder 

22. Price' 

A03 

9. Performing Organization Name and Address 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135-3191 

12. Sponsoring Agency Name and Address 

National Aeronautics and Space Administration 

Washington, D.C. 20546-0001 

3. Recipient's Catalog No. 

5. Report Date 

6. Performing Organization Code 

8TPerforming Organization Report No. 

E-4904 

10. Work Unit No. 

506-42-3 1 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

Technical Memorandum 

14. Sponsoring Agency Code 

5. Supplementary Notes 

Prepared for the 25th Joint Propulsion Conference cosponsored by the AIAA, ASME, SAE, and ASEE, 

Monterey, California. July 10-12, 1989. 

6. Abstract 

This paper presents tabular and graphical data intended for use in calibrating and validating structural and thermal 

models of ion thruster optics. A 30 cm diameter, two electrode, mercury ion thruster was operated using two 

different electrode assembly designs. With no beam extraction, the transient and steady state temperature profiles 

and center electrode gaps were measured for three discharge powers. The data showed that the electrode mount 

design had little effect on the temperatures, but significantly impacted the motion of the electrode center. 

Equilibrium electrode gaps increased with one design and decreased with the other. Equilibrium displacements in 

excess of 0.5 mm and gap changes of 0.08 mm were measured at 450 W discharge power. Variations in 

equilibrium gaps were also found among assemblies of the same design. The presented data illustrate the 

necessity for high fidelity ion optics models and development of experimental techniques to allow their validation. 

'For sale by the National Technical Information Service, Springfield, Virginia 221 61 SA FORM 1616 OCT 86