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Piegay, N.; Tastevin, Geneviève

doi:10.1023/a:1013791506574

Cited by 8 publications

(19 citation statements)

References 11 publications

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“…Such a study may find applications in the development of cryogenic 3 He magnetometers for experiments where trapping of polarized UCNs is involved as well as in other types of applications where polarized 3 He atoms are employed at low temperatures. At present the feasibility of 3 He magnetometers for UCNs has been studied only at room temperature [12].While a number of experiments [15,16,17,18,19] have reported 3 He longitudinal relaxation times (T 1 ) in mixtures of 3 He-4 He at temperatures similar to our work, the measurements most relevant to ours are [16,18,19] …”

supporting

confidence: 57%

Relaxation of spin polarizedH3ein mixtures ofH3e
Ye
¹
,
Dutta
²
,
H
³

et al. 2008
Phys. Rev. A
7
1
7
0
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We report a first study of the depolarization behavior of spin polarized 3 He in a mixture of 3 He-4 He at a temperature below the 4 He λ point in a deuterated TetraPhenyl Butadiene-doped deuterated PolyStyrene (dTPB-dPS) coated acrylic cell. In our experiment the measured 3 He relaxation time is due to the convolution of the 3 He longitudinal relaxation time, T1, and the diffusion time constant of 3 He in superfluid 4 He since depolarization takes place on the walls. We have obtained a 3 He relaxation time of ∼ 3000 seconds at a temperature around 1.9 K. We have shown that it's possible to achieve values of wall depolarization probability on the order of (1 − 2) × 10 −7 for polarized 3 He in the superfluid 4 He from a dTPB-dPS coated acrylic surface. Hyper-polarized 3 He based on the technique of optical pumping [1,2] has found applications in diverse fields such as in the study of quantum phenomena in low temperature fluids [3] and in the search for violations of fundamental symmetries [4,5,6]. They are also routinely used as polarized neutron spin-filters [7], as effective polarized neutron targets for nuclear and particle physics experiments [8] and for low magnetic field magnetic resonance imaging [9]. All such applications have motivated, as well as benefited from, studies of the relaxation mechanisms of polarized 3 He in gas, liquid and superfluid phases and under different surface conditions. The study of relaxation of polarized 3 He in 3 He -4 He mixtures at low temperatures is, however, of longstanding interest in its own right [10]. The simple atomic structure of 3 He makes a system of 3 He atoms ideal to model correlated fermions.Super-thermal production of Ultra-Cold Neutrons (UCN) from superfluid 4 He has been demonstrated [11] as an efficient way of producing a large number of UCNs. The capability of storing a large number of UCNs following their production is important for experiments studying fundamental properties of the neutron, for example the experiment on the search of the neutron electric dipole moment [6]. In this experiment, the deuterated TetraPhenyl Butadiene-doped deuterated PolyStyrene (dTPB-dPS) coated acrylic surface is chosen for such an application because of the small neutron absorption rate on the surface and its wavelength shifting property. The focus of this work is a first study of polarized 3 He relaxation time in a mixture of 3 He-4 He below the 4 He λ point in a dTPB-dPS coated acrylic cell. Such a study may find applications in the development of cryogenic 3 He magnetometers for experiments where trapping of polarized UCNs is involved as well as in other types of applications where polarized 3 He atoms are employed at low temperatures. At present the feasibility of 3 He magnetometers for UCNs has been studied only at room temperature [12].While a number of experiments [15,16,17,18,19] have reported 3 He longitudinal relaxation times (T 1 ) in mixtures of 3 He-4 He at temperatures similar to our work, the measurements most relevant to ours are [16,18,19]

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supporting

confidence: 57%

Relaxation of spin polarizedH3ein mixtures ofH3e
Ye
¹
,
Dutta
²
,
H
³

et al. 2008
Phys. Rev. A
7
1
7
0
View full text Add to dashboard Cite

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“…3 He gas is continuously injected (at mbar pressures with a flow rate of order 0.1 µmol/s) into a room temperature volume where laser optical pumping is performed, as described elsewhere [6]. It then flows down a narrow tube into a 0.44 cm 3 spheroidal volume partly filled with liquid 4 He at temperature T ≃ 1.15 K. Cs coatings are used to avoid wall relaxation, and bulk dipole-dipole relaxation times reach several hours in our dilute samples ( 3 He molar fractions X = 1-5%) [6].…”

Section: Methodsmentioning

confidence: 99%

“…It then flows down a narrow tube into a 0.44 cm 3 spheroidal volume partly filled with liquid 4 He at temperature T ≃ 1.15 K. Cs coatings are used to avoid wall relaxation, and bulk dipole-dipole relaxation times reach several hours in our dilute samples ( 3 He molar fractions X = 1-5%) [6]. By adjusting the 3 He molar fraction and nuclear polarisation (that can be as high as 40%), we control the magnetisation density M in the sample.…”

Section: Methodsmentioning

confidence: 99%

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

et al. 2007

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Long-range magnetic interactions in highly magnetised liquids (laser-polarised 3 He-4 He dilute mixtures at 1 K in our experiment) introduce a significant non-linear and non-local contribution to the evolution of nuclear magnetisation that leads to instabilities during free precession. We recently demonstrated that a multi-echo NMR sequence, based on the magic sandwich pulse scheme developed for solid-state NMR, can be used to stabilise the magnetisation against the effect of distant dipolar fields. Here, we report investigations of echo attenuation in an applied field gradient that show the potential of this NMR sequence for spin diffusion measurements at high magnetisation densities.

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“…They are based on the use of magic sandwich (MS) pulse sequences [15,16]: continuous bursts of tipping pulses that are appropriately timed and phased so as to refocus spin dynamics associated with dipolar interactions, leading to the formation of echoes. The MS pulse cycle and numerous variants are indispensable tools in the field of solid-state NMR but, to the best of our knowledge, have not been used previously for liquid-state NMR [17].Our samples are confined to a slightly-prolate 0.44 cm 3 spheroidal Pyrex cell treated with Cs metal to suppress wall relaxation [18,19], and are maintained at temperatures T ∼ 1 K. The sample cell communicates with a room temperature metastability-exchange optical pumping cell and various gas reservoirs via a narrow Pyrex tube. The entire apparatus is immersed in a 2.3 mT magnetic field shimmed to ±20 ppm over the sample cell and actively stabilized to ±10 ppm against fluctuations in the background laboratory field.…”

mentioning

confidence: 99%

“…Our samples are confined to a slightly-prolate 0.44 cm 3 spheroidal Pyrex cell treated with Cs metal to suppress wall relaxation [18,19], and are maintained at temperatures T ∼ 1 K. The sample cell communicates with a room temperature metastability-exchange optical pumping cell and various gas reservoirs via a narrow Pyrex tube. The entire apparatus is immersed in a 2.3 mT magnetic field shimmed to ±20 ppm over the sample cell and actively stabilized to ±10 ppm against fluctuations in the background laboratory field.…”

mentioning

confidence: 99%

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics

et al. 2007

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We demonstrate time reversal of nuclear spin dynamics in highly magnetized dilute liquid 3 He-4 He mixtures through effective inversion of long-range dipolar interactions. These experiments, which involve using magic sandwich NMR pulse sequences to generate spin echoes, probe the spatiotemporal development of turbulent spin dynamics and promise to serve as a versatile tool for the study and control of dynamic magnetization instabilities. We also show that a repeated magic sandwich pulse sequence can be used to dynamically stabilize modes of nuclear precession that are otherwise intrinsically unstable. To date, we have extended the effective precession lifetimes of our magnetized samples by more than three orders of magnitude. Elementary treatments of nuclear magnetic resonance (NMR) ignore collective effects. Individual spin dynamics are assumed to be independent of the sample magnetization M, and are thus governed by linear differential equations. This approximation is justified for many -but certainly not all -practical applications. One of the most well known and pervasive counter examples is the phenomenon of radiation damping [1], in which the emf induced in the pickup coil by M drives a current; the magnetic field associated with this current in turn acts on M, driving it into alignment with the static field B 0 in a nonlinear manner. A less common but more insidious problem arises when the magnetic field produced by the magnetized sample becomes large enough to directly influence spin dynamics [2,3,4,5,6]. This leads to a rich variety of nonlinear effects that range from spectral clustering to precession instabilities and spin turbulence. The former arises when small-angle NMR tipping pulses are applied to the sample (generating small angular displacements of M from B 0 ), and is manifest by the spontaneous appearance of long-lived geometrydependent modes of coherent nuclear precession. The latter occurs when large-angle tipping pulses are employed, and involves an exponential growth in the complexity of spatially inhomogeneous magnetization patterns. Far from being mere curiosities, phenomena arising from nonlocal interactions (including the joint action of 'distant dipolar fields' and radiation damping [7,8]) threaten to limit (or profoundly alter) the operation of state-of-the-art highfield high-resolution NMR spectrometers. They are equally important for understanding the dynamics of polarized quantum fluids including Bose-Einstein condensates [9], superfluid 3 He [10, 11], degenerate 3 He-4 He mixtures [12], and two-dimensional H gases [13]. From yet another perspective, the collective effects induced by distant dipolar fields can be used to amplify weak spin precession signals [14] and to enhance the sensitivity of precision searches for CP-violating permanent electric dipole moments [5].Here we describe NMR time reversal experiments that -for the first time -shed light on the extent to which the deleterious effects of spin turbulence can be controlled or suppressed. Moreover, they lay the foundatio...

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Cited by 8 publications

References 11 publications

Relaxation of spin polarizedH3ein mixtures ofH3e
Ye
¹
,
Dutta
²
,
H
³

et al. 2008
Phys. Rev. A
7
1
7
0
View full text Add to dashboard Cite

Relaxation of spin polarizedH3ein mixtures ofH3e
Ye
¹
,
Dutta
²
,
H
³

et al. 2008
Phys. Rev. A
7
1
7
0
View full text Add to dashboard Cite

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics

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Untitled

Cited by 8 publications

References 11 publications

Relaxation of spin polarizedH3ein mixtures ofH3eYe1, Dutta2, H3 et al. 2008Phys. Rev. A7170View full textAdd to dashboardCite

Relaxation of spin polarizedH3ein mixtures ofH3eYe1, Dutta2, H3 et al. 2008Phys. Rev. A7170View full textAdd to dashboardCite

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics

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Product

Resources

About

Relaxation of spin polarizedH3ein mixtures ofH3e
Ye
¹
,
Dutta
²
,
H
³

et al. 2008
Phys. Rev. A
7
1
7
0
View full text Add to dashboard Cite

Relaxation of spin polarizedH3ein mixtures ofH3e
Ye
¹
,
Dutta
²
,
H
³

et al. 2008
Phys. Rev. A
7
1
7
0
View full text Add to dashboard Cite