H-GATE
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Measurement infrastructure
H-gate lines carry bias and microwave signals from room temperature to the mixing chamber. Each run is anchored on the way down so a practical factory build can stay near 10 mK.
Microwave lines
Semi-rigid coax for high-frequency runs. Each stage uses a female-to-female bulkhead. Screw the attenuator onto that bulkhead so the center conductor is heat-sunk as well as the shield. PTFE alone does not thermalize the center pin.
Use 2.19 mm SCuNi only for a few low-loss lines paired with NbTi. In quantity it loads the 4 K stage, and it is not used in high-density RF wiring.
| Property | 2.19 mm SCuNi-CuNi | 0.86 mm SCuNi-CuNi |
|---|---|---|
| Impedance | 50 Ohm | 50 Ohm |
| Dielectric PTFE | 1.67 mm | 0.66 mm |
| Center conductor | CuNi, Ag-plated, 0.51 mm | CuNi, Ag-plated, 0.20 mm |
| Outer conductor | CuNi, 2.19 mm | CuNi, 0.86 mm |
| Attenuation, 300 K | 1.2 dB/m @ 1 GHz · 3.8 dB/m @ 10 GHz | 3.0 dB/m @ 1 GHz · 9.5 dB/m @ 10 GHz |
| Attenuation, 4 K | 0.6 dB/m @ 1 GHz · 1.8 dB/m @ 10 GHz | 1.5 dB/m @ 1 GHz · 4.6 dB/m @ 10 GHz |
| Thermal conductivity, 4 K | 2.2×10⁻⁴ W·cm/K | 7.1×10⁻⁵ W·cm/K |
K / 2.92 mm connectors raise the rating of a high-frequency build to 40 GHz. The cable figures below are the SMA 18 GHz constructions.
| Property | 0.86 mm SCuNi-CuNi | 0.86 mm NbTi-NbTi |
|---|---|---|
| Impedance | 50 Ohm | 50 Ohm |
| Dielectric PTFE | 0.66 mm | 0.66 mm |
| Center conductor | CuNi, Ag-plated, 0.20 mm | NbTi, 0.20 mm |
| Outer conductor | CuNi, 0.86 mm | NbTi, ~0.86 mm |
| Attenuation, 300 K | 3.0 dB/m @ 1 GHz · 9.5 dB/m @ 10 GHz | 9.0 dB/m @ 1 GHz · 30.5 dB/m @ 10 GHz |
| Attenuation, 4 K | 1.5 dB/m @ 1 GHz · 4.6 dB/m @ 10 GHz | < 0.5 dB from DC to 20 GHz |
| Thermal conductivity, 4 K | 7.1×10⁻⁵ W·cm/K | 4.63×10⁻⁶ W·cm/K |
Low-noise readout
Flexible SCuNi with a graphite-coated dielectric and an FEP jacket. The jacket tightens on cooldown so the conductors move less. That cuts triboelectric noise from a contracting PTFE dielectric. Useful when a semi-rigid line would be too microphonic, up to a few gigahertz.
| Property | Published build |
|---|---|
| Impedance | 50 Ohm |
| Dielectric | PTFE, 0.66 mm, graphite-coated |
| Center conductor | CuNi, Ag-plated, 0.20 mm |
| Outer conductor | CuNi braid, 90% shielding |
| Jacket | FEP over the outer conductor |
| Attenuation, 300 K | 5.4 dB/m @ 1 GHz |
| Attenuation, 4 K | 4.3 dB/m @ 1 GHz |
Filtered DC
Sets of six lossy Thermocoax lines from room temperature to the mixing chamber. High frequencies are filtered, leaving a coaxial geometry for DC and low-frequency bias. Lines are 3 m, wound on gold-plated copper bobbins at every stage. A breakout at 4 K is optional.
| Property | RT to MXC | RT to 4 K | 4 K to MXC |
|---|---|---|---|
| Length | 3 m ± 5% | 1.9 m ± 5% | 1.5 m ± 5% |
| Diameter | 0.5 mm ± 5% | 0.5 mm ± 5% | 0.5 mm ± 5% |
| Resistance | 155 Ω ± 5% | 100 Ω ± 5% | 80 Ω ± 5% |
| Capacitance | 562 pF ± 5% | 356 pF ± 5% | 281 pF ± 5% |
DC to 5 GHz
Continuous 0.86 mm CuNi-CuNi lines in sets of six, for DC and low frequency in a coaxial geometry. Less resistive than Thermocoax, with a higher cutoff, but the tight loops inside the bobbins hold the useful band to about 5 GHz. Extra breakouts can be added at the stages you choose.
| Property | Continuous CuNi | Thermocoax |
|---|---|---|
| Useful band | Up to 5 GHz | DC and low frequency |
| Construction | 0.86 mm continuous CuNi-CuNi | 0.5 mm Thermocoax, sets of six |
| Resistance | Lower than Thermocoax | 155 Ω over 3 m, room temperature |
| Anchor | Gold-plated copper bobbins | Gold-plated copper bobbins |
| Warm interface | KF40 breakout, up to 24 SMA lines | KF40 box, 24 lines, or 48 with two boxes |
| Installation | DC installation set | DC installation set |
06
Gold-plated copper bobbins sit on the DC flanges. The set includes a hermetic connector box at room temperature, one aluminium flange, and four copper flanges for 50 K, 4 K, the still, the cold plate, and the mixing chamber. Thermocoax and continuous CuNi use the KF40 port, which takes 3 or 4 feedthroughs.
Semi-rigid and Grapho lines thermalize on female-to-female bulkheads at each stage. The set includes the warm hermetic feedthrough and is sold without cables or attenuators. Screw attenuators onto the bulkheads so the center conductor is heat-sunk with the shield.
07
Thermocoax and continuous CuNi go into a KF40 port with a DC installation set. Grapho and semi-rigid lines need an RF installation set.
Free KF25 or KF40
Free KF40 or ISO-K63
Free KF40 or side-loading port
Free KF40 or side-loading port
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