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NMR system for the frozen spin targetto measure the polarisation
Nadja FrömmgenInstitut für Kernphysik
Universität Mainz
CB collaboration meetingUniversity of Edinburgh 2009
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Outline
• Principle of NMR
• Detection of the NMR signal
• NMR signal
• Performance test in July 2009
• Conclusion and Outlook
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Principle of NMR
• Irradiation with a HF field• NMR signal results from the difference between absorbed and emitted energy; voltage is induced in a receiver coil• Signal is proportional to the population difference Polarisation
)31.1062( MHzP
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coil
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How is the NMR signal detected?
Series LC resonant circuit
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Series LC resonant circuit
Resonance frequencyLC
2
1
tuning to the Larmor frequency of nucleus via changing C (varicap)
„Resonance parabola“
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Q-curve of the resonant circuit
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NMR signal
TE
TEDNPDNP AreaUnit
PAreaUnitP
TE: thermal equilibrium
kTB
NNNN
PTE
tanh
Measurement of the TE signal as exactly as possible to minimise the error of the polarisation measurement.
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July 2009
• polarising magnet: 2.507 T• cooled to ~26mK• irradiated with microwaves (15mW) for 3.5 hours
up to ~50% polarisation
Performance test: cryostat, microwave apparatus & NMR system
Successfull measurement: TE signal Polarised NMR signal Polarisation curve Relaxation curve
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TE-Signal
In the meantime the noise on the signal could be reduced.
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Polarised NMR Signal
~ 50% polarisation
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Polarisation curve
2 ¼ hours
Pola
risa
tion
[%
]
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Relaxation curve
30 minutes
Pola
risa
tion
[%
]
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Conclusion and Outlook
NMR-System is working well we expect a polarisation of P>90% and an error in the polarisation measurement of ~1.5%
• system linearity measurement• several stability tests• optimisation of the software by M. Korolija from Zagreb• final test of the frozen spin target in October together with J. Usov, A. Neganov, N. Borisov and A. Lazarev from Dubna
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Thank you for your attention!
