<p>Accurate characterization of plasmas within the discharge chambers of gridded ion engines is essential for their advancement. This study showcases the effectivity of terahertz time-domain spectroscopy (THz-TDS) as a non-invasive technique for profiling low-pressure inductively coupled plasmas, mimicking the conditions of the discharge chamber in a radio-frequency ion thruster. Operating at pressures of 3 - <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44205_2025_106_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">$7\cdot 10^{-3}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>7</mn> <mo>·</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>3</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> mbar inside the discharge chamber and a supply power of the radio frequency generator ranging from 10 - 80 W, THz-TDS reveals electron densities in the range of <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44205_2025_106_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">$2\cdot 10^{16}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>16</mn> </msup> </mrow> </math></EquationSource> </InlineEquation> - <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44205_2025_106_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">$2\cdot 10^{17}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>17</mn> </msup> </mrow> </math></EquationSource> </InlineEquation> m<InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44205_2025_106_Article_IEq4.gif" Format="GIF" Height="11" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">$^{-3}$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mo>-</mo> <mn>3</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation> for xenon, krypton, and argon plasmas. Our results show good agreement with Langmuir probe measurements and global plasma modeling, highlighting the accuracy and reliability of THz-TDS. This validation, conducted under conditions representative of gridded ion engines, demonstrates that THz-TDS is, in principle, suitable for characterizing the electron system of the plasma ignited in such thrusters in operation. This offers great potential of developing a promising additional tool for plasma diagnostics in electric propulsion systems.</p>

Validating THz time-domain spectroscopy as a tool for characterizing low pressure inductively coupled plasmas of ion thrusters

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2025年2月25日

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Kalle Bräumer,
Rodrigo Sandoval Rodriguez,
Markus Stein,
Konstantin Keil,
Kristof Holste,
Felix Becker,
Jana Zorn,
Konrad Wehkamp,
Sangam Chatterjee,
Peter J. Klar

摘要

Accurate characterization of plasmas within the discharge chambers of gridded ion engines is essential for their advancement. This study showcases the effectivity of terahertz time-domain spectroscopy (THz-TDS) as a non-invasive technique for profiling low-pressure inductively coupled plasmas, mimicking the conditions of the discharge chamber in a radio-frequency ion thruster. Operating at pressures of 3 - $7\cdot 10^{-3}$ $7 \cdot 10^{- 3}$ mbar inside the discharge chamber and a supply power of the radio frequency generator ranging from 10 - 80 W, THz-TDS reveals electron densities in the range of $2\cdot 10^{16}$ $2 \cdot 10^{16}$ - $2\cdot 10^{17}$ $2 \cdot 10^{17}$ m $^{-3}$ $^{- 3}$ for xenon, krypton, and argon plasmas. Our results show good agreement with Langmuir probe measurements and global plasma modeling, highlighting the accuracy and reliability of THz-TDS. This validation, conducted under conditions representative of gridded ion engines, demonstrates that THz-TDS is, in principle, suitable for characterizing the electron system of the plasma ignited in such thrusters in operation. This offers great potential of developing a promising additional tool for plasma diagnostics in electric propulsion systems.