Complete nondestructive diagnostic of nonneutral plasmas based on the detection of electrostatic modes

Amoretti, M.; Bonomi, G.; Bouchta, A.; Bowe, P. D.; Carraro, C.; Cesar, C. L.; Charlton, M.; Doser, M.; Fontana, A.; Fujiwara, M.; Funakoshi, R.; Genova, P.; Hangst, J. S.; Hayano, R.; Jørgensen, L. V.; Lagomarsino, V.; Landua, R.; Rizzini, E. Lodi; Macrı́, M.; Madsen, N.; Manuzio, G.; Testera, G.; Variola, A.; Werf, D. P. van der

doi:10.1063/1.1591187

Cited by 56 publications

(68 citation statements)

References 28 publications

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“…In order to increase the density of the plasma inside the 3 T solenoid, it can be compressed by employing a rotating wall (RW) electric field [14,15]. A nondestructive plasma diagnostic technique has recently been developed using electrostatic mode analysis [16,17] facilitating realtime monitoring of the plasma.…”

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confidence: 99%

“…Extensive surveys were made to optimize the performance in terms of frequency, amplitude, sweep, and duration. During the experiments the plasma parameters were monitored using the mode analysis system; in particular, the (1,0) dipole and (2,0) quadrupole frequencies [17] were used to obtain the plasma density, aspect ratio, and length. The positron number was cross-checked by dumping the positrons on a Faraday cup at the end of each measurement.…”

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confidence: 99%

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New Source of Dense, Cryogenic Positron Plasmas

Jørgensen¹,

Amoretti²,

Bonomi³

et al. 2005

Phys. Rev. Lett.

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We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (10 ÿ9 mbar) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than 10 ÿ13 mbar. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than 1:2 10 9 positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about 20 10 6 positrons were compressed to a density of 2:6 10 10 cm ÿ3 . This is a factor of 6 improvement over earlier measurements.

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confidence: 99%

New Source of Dense, Cryogenic Positron Plasmas

Jørgensen¹,

Amoretti²,

Bonomi³

et al. 2005

Phys. Rev. Lett.

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“…-we used the information we have on the e + plasma shape [13,14] to generate the Pn starting point distributions (in particular, it was found that the e + plasma was approximately a spheroid with radius r p =1 mm and axial half-length z p =16 mm, rotating with a frequency of 300 kHz; i.e. a surface velocity of about 2000 ms −1 ).…”

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Production of slow protonium in vacuum

Zurlo¹,

Rizzini²,

Venturelli³

et al. 2007

TCP 2006

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We describe how protonium, the quasi-stable antiproton-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion H + 2 in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events in the ATHENA experiment, evidence is presented for protonium production with sub-eV kinetic energies in states around n = 70, with low angular momenta. This work provides a new 2-body system for study using laser spectroscopic techniques.

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“…Our model describes the signal induced on an electrode by the coherent oscillations of the dipole mode when an external driving force is applied. In particular we write [16] …”

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“…where m is the positron (or electron) mass [16]. The re- sistance R s characterizes the damping rate of the mode.…”

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Positron Plasma Diagnostics and Temperature Control for Antihydrogen Production

Amsler²,

et al. 2003

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Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss nondestructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed. The antihydrogen was made by mixing low energy antiprotons with a cold, dense positron plasma in a nested Penning trap [4]. A knowledge of the characteristics of the positron plasma is important for several reasons. The most likely antihydrogen formation mechanisms, spontaneous recombination and three body recombination, have different dependences on both the density and the temperature of the positron plasma [5]. Knowing these parameters is crucial in helping to elucidate the antihydrogen formation mechanism. Control and simultaneous monitoring of the positron plasma temperature allow the antihydrogen formation reaction to be effectively turned off while maintaining overlap between antiprotons and positrons. This provides a good measurement of the total background signal for our unique antihydrogen detector [1]. Furthermore, the space charge potential of a * Corresponding author Email address: gemma.testera@ge.infn.it sufficiently dense (10 8 cm −3 ) and extensive (length 3 cm) positron plasma considerably alters the effective electrostatic potential in the positron trap and thus the dynamics of the antiprotons in the nested trap.Harmonically confined one component plasmas at temperatures close to absolute zero are known to form spheroids of constant charge density [6]. In our case the shape is a prolate ellipsoid characterized by the aspect ratio α = z p /r p where z p and r p are the semi-major axis and semi-minor axis respectively [ Fig. 1(a)]. A cold fluid theory [7] relating the frequencies of the low-order plasma modes to the density and the aspect ratio of spheroidal plasmas was confirmed experimentally for laser cooled ion plasmas [8,9] and successfully applied to cold electron plasmas [10]. Work on finite temperature electron plasmas demonstrated that mode detection could be used as a diagnostic of density and aspect ratio and that for a plasma of known density and aspect ratio the frequency of the quadrupole mode is dependent on the plasma temperature [11,12].Here we describe an extension to the above work which provides a non-destructive diagnostic based on measurements of the first two axial modes of a finite temperature positron plasma. The diagnostic has no discernable effect on the normal evolution of the plasma, so it can be used

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Complete nondestructive diagnostic of nonneutral plasmas based on the detection of electrostatic modes

Cited by 56 publications

References 28 publications

New Source of Dense, Cryogenic Positron Plasmas

New Source of Dense, Cryogenic Positron Plasmas

Production of slow protonium in vacuum

Positron Plasma Diagnostics and Temperature Control for Antihydrogen Production

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