This study extends the applicability of epoxy composites with acid-treated carbon nanotubes (CNTs), previously utilized at 77 K, to 4.2 K, and confirms that the thermal management and operational electrical stability of the filler material are maintained and developed in cryogenic environments. We investigate conduction-cooled NbTi coils impregnated with an acid-treated multi-walled carbon nanotube (MWCNT)/epoxy composite at 4.2 K. The matrix is LOCTITE Stycast 2850 FT with Catalyst 23 LV, and the MWCNTs (outer diameter 6–9 nm) were functionalized using a sulfuric/nitric acid (H2SO4/HNO3) mixture to improve the dispersion and interfacial coupling. SEM confirms uniform dispersion of the treated MWCNTs in the cured matrix. Under conduction cooling at 4.2 K, the composite-impregnated coil cools down faster and has higher minimum quench energy (MQE) across 0.6–0.9 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">${I}_{c}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>I</mi> <mi>c</mi> </msub> </math></EquationSource> </InlineEquation>(energy defined as <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$E={I}^{2}{R}_{\text{heater}}t$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mo>=</mo> <msup> <mrow> <mi>I</mi> </mrow> <mn>2</mn> </msup> <msub> <mi>R</mi> <mtext>heater</mtext> </msub> <mi>t</mi> </mrow> </math></EquationSource> </InlineEquation>), a shorter post-quench re-cooling period, and stable persistent current operation, evidence of the enhanced operational electrical stability of the coil. Transient laser-flash measurements on the composite at 20.7–30.0 °C show a modest increase in through-thickness thermal conductivity, consistent with improved heat spreading. These results demonstrate improved cool-down efficiency, higher MQE, faster post-quench re-cooling, and stable persistent current operation—evidence of enhanced operational electrical stability. In future, we plan to measure the intrinsic low-temperature material properties [<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$k(T)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>,<InlineEquation ID="IEq4"> <EquationSource Format="TEX">${c}_{p}(T)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>c</mi> <mi>p</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, dielectric metrics], together with multi-loading (0–1.0 wt% MWCNTs) testing.

Operational Electrical Stability and Thermal Performance of Conduction-Cooled NbTi Coil with Acid-Treated Multi-Walled CNT/Epoxy Composite at 4.2 K

期刊论文
发表日期：

2025年12月21日

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Hyun Sung Noh,
Dawool Kwon,
Minkyu Sun,
Mtangi Mohamed Mussa,
Haigun Lee

摘要

This study extends the applicability of epoxy composites with acid-treated carbon nanotubes (CNTs), previously utilized at 77 K, to 4.2 K, and confirms that the thermal management and operational electrical stability of the filler material are maintained and developed in cryogenic environments. We investigate conduction-cooled NbTi coils impregnated with an acid-treated multi-walled carbon nanotube (MWCNT)/epoxy composite at 4.2 K. The matrix is LOCTITE Stycast 2850 FT with Catalyst 23 LV, and the MWCNTs (outer diameter 6–9 nm) were functionalized using a sulfuric/nitric acid (H₂SO₄/HNO₃) mixture to improve the dispersion and interfacial coupling. SEM confirms uniform dispersion of the treated MWCNTs in the cured matrix. Under conduction cooling at 4.2 K, the composite-impregnated coil cools down faster and has higher minimum quench energy (MQE) across 0.6–0.9 ${I}_{c}$ $I_{c}$ (energy defined as $E={I}^{2}{R}_{\text{heater}}t$ $E = I^{2} R_{heater} t$ ), a shorter post-quench re-cooling period, and stable persistent current operation, evidence of the enhanced operational electrical stability of the coil. Transient laser-flash measurements on the composite at 20.7–30.0 °C show a modest increase in through-thickness thermal conductivity, consistent with improved heat spreading. These results demonstrate improved cool-down efficiency, higher MQE, faster post-quench re-cooling, and stable persistent current operation—evidence of enhanced operational electrical stability. In future, we plan to measure the intrinsic low-temperature material properties [ $k(T)$ $k (T)$ , ${c}_{p}(T)$ $c_{p} (T)$ , dielectric metrics], together with multi-loading (0–1.0 wt% MWCNTs) testing.