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Retuning and Recovery of Polarized Ammonia Target Magnet for Advanced Microwave Operations

The polarized ammonia target magnet has undergone extensive retuning after 20 years of operation in extreme conditions at UVA, SLAC, and JLab. Diagnosis revealed instability due to coil relaxation, prompting reclamping to original specifications at Oxford Instruments. Post-retuning tests showed stable operation at specified magnetic fields of 5.0T and 5.1T for significant duration. The system is now equipped with efficient microwave sources at 140 GHz and 70 GHz, ready to resume experiments requiring over 90% polarization with sufficient ammonia inventory available for irradiation.

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Retuning and Recovery of Polarized Ammonia Target Magnet for Advanced Microwave Operations

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  1. Polarized Target “Issues” Magnet Microwaves Target Ammonia

  2. UVA/SLAC/JLAB Target

  3. Magnet

  4. After SANE, and operation over 20 years in sometimes extreme conditions, magnet returned to Oxford Instruments for retuning. • Diagnosis was that magnet had become unstable over the years because of relaxation of the clamping of the coils. • At Oxford Instr. Coils reclamped to original specifications. • Magnet retested: • 1) Ramped at higher than original specified rate to 5.1 T Quenched after 15 mins in persistent mode ( training quench)

  5. 2) Ramped at specified rate to 5.0 T Stayed at field in persistent mode for 105 minutes before ramping down • 3) Ramped to 5.1 T at same rate as Test 1 Stayed at field for 105 minutes in persistent mode before ramping down. Ready to operate again in extreme conditions.

  6. Microwaves • 140 GHz/5 T EIO – have several NH3 Polarization > 90% • 70 GHz/2.5 T Carcinotron (have several) or EIO (borrow one from Duke University). EIO has higher power output than Carcinotron. Polarization ~40% Changing EIOs easiest to do – use same power supply.

  7. Microwaves (contd.) • Microwave guides at 70GHz. (Have at UVA) • Frequency and power read-outs at 70 GHz (Have at UVA ) • EIO power supplies ~ four, between UVA and JLab • Carcinotron Power supplies: one at UVA, one somewhere in Germany on way to UVA

  8. NMR • Have all the necessary equipment, many Q –meters, several signal generators and power supplies. • Only need to retune system at 106.5 MHz (2.5 T) from 213 MHz (5 T)

  9. Ammonia Targets • All the polarized material will be irradiated ammonia (14NH3).

  10. Ammonia Targets (contd.) • Ammonia irradiated at the MIRF facility at NIST • Use 19 MeV electrons at 10 – 15 μA • Irradiate to the level of ~1017 e-.cm-2 One irrad. Load ~ 2.5 target loads • Need ~ 18 target loads

  11. Ammonia Targets (contd.) • Current inventory: ~ 16 target loads – checking further. • Unirradiated inventory: 3 target loads – checking further • Previously used material: ???? • Next irradiation (probably June) • Last Irradiation: October 2009

  12. NH3 (2nd Batch)

  13. Participation • Faculty Level Don Crabb, Donal Day, Oscar Rondon • Post Docs HovannesBaghdasaryan, NarbeKalantarians Jonathan Mulholland? • Students • “Stache” Kvaltine, ZihongJi, Mikhail Yurov

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