Wear Testing and Analysis of Ion Engine Discharge Cathode Keeper

Domonkos, Matthew T.; Foster, John E.; Soulas, George C.

doi:10.2514/1.4441

Cited by 11 publications

(15 citation statements)

References 16 publications

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“…Based on measurements, the keeper ion current was 0.225 A during that test. 31 Excellent agreement is seen on the keeper face profile with the profilometry data taken after the 2000 hour wear test. It is expected that with additional time, the region inside the 0.5 radius location will erode faster than the model predicts.…”

mentioning

confidence: 63%

“…28 This model and analysis were completed with some component level testing and prior to any wear test of a NEXT thruster. The assessment determined that the keeper should last a minimum of 375 kg of xenon throughput and possibly up to 844 kg.…”

Section: Keeper Wearmentioning

confidence: 99%

“…6 It is assumed that 0.2 A of ion current is collected by the keeper. 31 The sputter yield values used to produce Figure 6 had a normal value of 2.3x10 -5 atoms/ion, which is 0.27 % the values that are shown in Figure 5. If there were only singly charged xenon ions, this normal sputter yield would correspond to ions with an energy around 20 eV.…”

mentioning

confidence: 99%

“…The effect of the change to graphite on the volumetric wear can be determined based on the equations described in Ref. 28. The change in volumetric wear of the keeper is determined by the ratio of the effective yield of the materials based on singly and doubly charged ions, the keeper's mass, and its density.…”

mentioning

confidence: 99%

“…The ion keeper current was measured for the NEXT thruster over its throttling range and was found to be a strong function of the beam current. 31 The change in keeper lifetime from the discharge voltage was included based on the yield data for C 2 (the sputter yield of the C 2 molecule is greater than the single atom at lower energies). 29 The results of using these ratios for various throttle points are shown in Figure 9.…”

mentioning

confidence: 99%

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Lifetime Assessment of the NEXT Ion Thruster

VanNoord

2007

43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Ion thrusters are low thrust, high specific impulse devices with required operational lifetimes on the order of 10,000-100,000 hours. The NEXT ion thruster is the latest generation of ion thrusters under development. The NEXT ion thruster currently has a qualification level propellant throughput requirement of 450 kg of xenon, which corresponds to roughly 22,000 hours of operation at the highest throttling point. Currently, a NEXT engineering model ion thruster with prototype model ion optics is undergoing a long duration test to determine wear characteristics and establish propellant throughput capability. The NEXT thruster includes many improvements over previous generations of ion thrusters, but two of its component improvements have a larger effect on thruster lifetime. These include the ion optics with tighter tolerances, a masked region and better gap control, and the discharge cathode keeper material change to graphite. Data from the NEXT 2000 hour wear test, the NEXT long duration test, and further analysis is used to determine the expected lifetime of the NEXT ion thruster. This paper will review the predictions for all of the anticipated failure mechanisms. The mechanisms will include wear of the ion optics and cathode's orifice plate and keeper from the plasma, depletion of low work function material in each cathode's insert, and spalling of material in the discharge chamber leading to arcing. Based on the analysis of the NEXT ion thruster, the first failure mode for operation above a specific impulse of 2000 s is expected to be the structural failure of the ion optics at 750 kg of propellant throughput, 1.7 times the qualification requirement. An assessment based on mission analyses for operation below a specific impulse of 2000 s indicates that the NEXT thruster is capable of double the propellant throughput required by these missions.

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mentioning

confidence: 63%

Section: Keeper Wearmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Lifetime Assessment of the NEXT Ion Thruster

VanNoord

2007

43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Analysis of the effect of keeper working conditions on hollow cathode performance

et al. 2023

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Potential fluctuations and energetic ion production in hollow cathode discharges

et al. 2007

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Ions with energies significantly in excess of the applied discharge voltage have been reported for many years in hollow cathode discharges. Models of dc potential hills downstream of the cathode and instabilities in postulated double layers in the cathode orifice have been proposed to explain this, but have not been substantiated. Measurements of the dc and rf plasma density and potential profiles near the exit of hollow cathodes by miniature fast-scanning probes suggests that turbulent ion acoustic fluctuations and ionization instabilities in the cathode plume significantly increase the energy of the ions that flow from this region. Increases in the discharge current and/or decreases in the cathode gas flow enhance the amplitude of the fluctuations and increase the number and energy of the energetic ions, which increases the erosion rate of the cathode electrodes. The transition from the quiescent “spot mode” to the noisy “plume mode” characteristic of these discharges is found to be a gradual transition of increasing fluctuation amplitudes.

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Wear Testing and Analysis of Ion Engine Discharge Cathode Keeper

Cited by 11 publications

References 16 publications

Lifetime Assessment of the NEXT Ion Thruster

Lifetime Assessment of the NEXT Ion Thruster

Analysis of the effect of keeper working conditions on hollow cathode performance

Potential fluctuations and energetic ion production in hollow cathode discharges

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