| 研究課題/領域番号 |
15K17638
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| 研究機関 | 東京大学 |
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研究代表者 |
Marti Lluis.M 東京大学, カブリ数物連携宇宙研究機構, 特任研究員 (60706787)
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| 研究期間 (年度) |
2015-04-01 – 2017-03-31
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| キーワード | Gd concentration / Gd susceptibility / Good linearity / AAS no memory effects |
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| 研究実績の概要 |
[Gd magnetic properties.] 3 SQUID measurement campaigns were done:
1st. Experimental setup improvement: better sample containers, good seals, and constant sample volumes were used. The magnetic susceptibility showed a very good correlation with the Gd concentration. A good linear correlation with the Gd concentration, although expected, had not been seen before.
2nd. The goal was to perform a more precise measurement of the susceptibility around the water freezing-point temperature. Problems with containers seen and the data became difficult to use.
3rd. Measurement of the general behaviour of the magnetic susceptibility, χ, following the Curie-Weiss law: χ = K/(T-Tc). Values for K and Tc have been fitted. Supercooling effects are happening here based on the following hints: 1) supercooling happens if there is no crystallisation seed: We are using ultra-pure water and high purity Gd sulphate. 2) during the process of cooling (from 300 K to about 260 K) a different behaviour is seen for different measurements. 3) when going from the solid to the liquid water state the behaviour is always the same.
[Improved measurements with an AAS.] Tantalum (Ta) and tungsten (W) plates were bought. Machining these plates by ourselves proved very difficult. We found a local company that can cut these plates into small pieces with high precision and low cost using electrical discharge machining.
Three different designs have been tested so far. The latest one is still under test but shows no memory effects and good mechanical stability.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
[Gd magnetic properties.] The goals that have been achieved in the last FY are the determination of the following properties with SQUID measurements:
- Due to the Curie-Weiss law lower temperatures are preferable. However, for the sake of experimental simplicity higher temperatures are better. Measurements at temperatures above 273 K seem possible: good linearity has been measured.
- We should avoid the temperature region between 270 and 250 K or make sure the sample is frozen (solid). Samples at dry ice temperature (~194.5 K) would be safe.
- The higher the applied magnetic fields, the better although from 0.5 T measurements already show very good linearity.
These measurements are allowing me to determine the precision requirements for the magnetic susceptibility measurement, sample temperature control and applied magnetic field for the design of the new device for these measurements. According to the plan this should have been already determined but due to the failure of the second SQUID campaign it has been delayed. Since the results seem to be positive I think the project is going well.
[Improved measurements with an AAS.] Three different designs have been tested. The absence of memory effects have been confirmed and the designs are getting closer to our requirements. Although more tests have to be carried out, these results are already promising and pointing to good results. This part of the project is therefore basically on schedule.
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| 今後の研究の推進方策 |
[Gd magnetic properties.] My immediate task is now to analyse the SQUID data and determine the precision requirements for the new device. Once this is complete I will decide upon which option is more adequate.
My preferred option is the construction of a Helmholtz type solenoid for the generation of the magnetic field combined with a pick-up coil and its integrating transducer and signal amplifier. The reason for this preference is that it would allow us for continuous monitoring of the Gd concentration in the detector. Due to limitations of classical Helmholtz coils I expect to at least try with a Gaume-like coil (winding density increasing towards the ends of the coil producing more homogeneous and larger magnetic fields). Another technique that I plan to use in this scenario is a pulsed magnetic field to avoid the destruction of the coil from Joule heat (one of the limiting factors when obtaining stronger fields) and probably some kind of coil cooling. Ideally I can get fields about 2 or 3 T.
Electromagnets could be an option too but due to the difficulties when working with them this would be a less preferred option. If the previous is not possible I plan to study commercially available options.
[Improved measurements with an AAS.] My current plan is to further perform more tests on the current design and confirm the good results I got so far. I envisage at least one more improvement in the design by enlarging the Ta stage. Once I am satisfied with this design I will try using W instead, which may have a better performance and better resistance to high temperatures.
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| 次年度使用額が生じた理由 |
[Gd magnetic properties.] In the original plan I wanted to have by now the specifications/requirements of the new device. However, due to the encountered problems (as described above) the required data for this purpose has been collected recently only and I am currently analysing it. Therefore, the expected expenses for the past FY had to be delayed too.
[Improved measurements with an AAS.] Since the final design is still on test we did not acquire the final mould for the Ta/W stages.
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| 次年度使用額の使用計画 |
[Gd magnetic properties.] Because the data look good and the first results promising I expect to buy the first equipments soon (first half of this FY) which represent most of the grant budget. Basically all the items in the planned budget are still up-to-date.
[Improved measurements with an AAS.] Once the final design is confirmed (within the next months) I will buy the final mould for the Ta/W stages as anticipated on the budget.
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