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Transmission line probes take advantage of larger bore sizes because losses in coaxial lines are minimized with increase in diameters of their conductors and with ability to maintain ratio of these diameters as close to optimal as possible.
This compact TxL circuit design has been described in [1] and is based loosely on traditional transmission line circuits by McKay-Shaefer [2-3] and by Rienstra [3].
A sleeve balun is employed in the 1H channel to electrically balance the sample coil. This prevents wavelength effects at such frequency from degrading RF field homogeneity in the coil.
This probe is built around modified Varian 3.2 mm PencilTM MAS spinner (top picture), which is capable of spinning up to 25 kHz.
Stable spinning is achieved at temperatures as low as 112K. Our automatic refilling station (bottom picture) can maintain constant cryogen levels in the heat exchanger coils for an indefinitely long time.
Perturbations to the actual sample temperature during each filling cycle were brought down to within 0.3 degrees.
(As of January 1, 2007)
| 1H |
B1 = 135 kHz @ 330 W |
20 ms pulses every 2 s |
| X=13C |
B1 > 100 kHz @ 140 W |
10 ms pulses every 2 s |
| X=15N |
B1 = 80 kHz @ 520 W |
2 ms pulses every 2 s |
Nuclei switching is done by replacing a) the chip next to the stator under the probe cap and
b) the tuning component in a long wand threaded through the bottom of the probe:
- Open probe cap and remove the chip under the stator (visible in the top photo). Use the table below to determine replacement value. Insert it in a chip holder from right to left.
- Unscrew the the black knob labeled "X WAND" and slide it out of the probe.
- The tip of the wand has a snap-in component plug — replace it according to tuning table.
- Slide the wand into the probe and screw it in. Do not over-tighten.
| Isotope |
Removeable chip
inside probehead |
Plug for wand
inserted at base |
| 47Ti, 49Ti |
120+120 pF |
150 pF |
| 15N, 35Cl |
82 pF |
39 pF |
| 17O |
68 pF |
6.8 pF |
| 29Si, 207Pb |
12 pF |
6.8 pF |
| 13C |
10 pF |
blank plug |
| 23Na |
6.8 pF |
6.5 turn inductor |
| 11B |
5.6 pF |
6.5 turn inductor |
| 31P |
1.8 pF |
2 turn inductor |
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If your isotope is not in above table, please contact Peter Gor'kov to arrange new tuning plugs.
[1] R.Fu et al., J. Magn. Reson. 177 1-8 (2005) [ read online]
[2] S. M. Holl, R. A. Mckay, T. Gullion, and J. Schaefer, J. Magn. Reson. 89, 620 (1990)
[3] J. Schaefer, R.A. McKay, US Patent: 5,861,748 (1999)
[4] C.M. Rienstra, Thesis, in Chemistry, MIT (1999)
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