Magnetic multipole induced zero-rotation frequency bounce-resonant loss in a Penning–Malmberg trap used for antihydrogen trapping

Andresen, Gorm Bruun; Bertsche, W.; Bray, C. C.; Butler, E.; Cesar, C. L.; Chapman, S.; Charlton, M.; Fajans, J.; Fujiwara, M.; Gill, D. R.; Hardy, W. N.; Hayano, R.; Hayden, M. E.; Humphries, A. J.; Hydomako, R.; Jørgensen, L. V.; Kerrigan, Sean; Keller, J.; Kurchaninov, L. L.; Lambo, R.; Madsen, N.; Nolan, P.; Olchanski, K.; Olin, A.; Povilus, A.; Pusa, P.; Robicheaux, F.; Sarid, E.; Nasr, S. Seif El; Silveira, D. M.; Storey, J. W.; Thompson, R. I.; Werf, D. P. van der; Wurtele, J. S.; Yamazaki, Y.

doi:10.1063/1.3258840

Cited by 7 publications

(7 citation statements)

References 14 publications

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“…In this case, resonance occurs between harmonics of the magnetron frequency and the axial oscillation frequency. One example of such an effect was identified in ALPHA's nested wells (see section 5.5 and [67]). Empirically, the size of the effect depends on the geometry and density of the plasma, and using the rotating wall technique to prepare plasmas with different parameters, the dependence can be explored.…”

Section: Diffusion and Heatingmentioning

confidence: 95%

Antihydrogen Formation, Trapping and Dynamics

Butler

2011

Preprint

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Antihydrogen, the simplest pure-antimatter atomic system, holds the promise of direct tests of matter-antimatter equivalence and CPT invariance, two of the outstanding unanswered questions in modern physics. Antihydrogen is now routinely produced in charged-particle traps through the combination of plasmas of antiprotons and positrons, but the atoms escape and are destroyed in a minuscule fraction of a second.The focus of this work is the production of a sample of cold antihydrogen atoms in a magnetic atom trap. This poses an extreme challenge, because the state-of-theart atom traps are only approximately 0.5 K deep for ground-state antihydrogen atoms, much shallower than the energies of particles stored in the plasmas. This thesis will outline the main parts of the ALPHA experiment, with an overview of the important physical processes at work. Antihydrogen production techniques will be described, and an analysis of the spatial annihilation distribution to give indications of the temperature and binding energy distribution of the atoms will be presented. Finally, we describe the techniques needed to demonstrate confinement of antihydrogen atoms, apply them to a data taking run and present the results, making a definitive identification of trapped antihydrogen atoms. i Declarations and Statements Declaration

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Section: Diffusion and Heatingmentioning

confidence: 95%

Antihydrogen Formation, Trapping and Dynamics

Butler

2011

Preprint

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“…As mixing progresses, antiproton-antiproton collisions cause additional antiprotons to fall into this side well and into the electrostatic well on the other side of the positron plasma (see figure 4(c)). As there is no direct mechanism to transport these antiprotons radially outward [27] 26 , most will remain at or near their original radius (between 0.4 and 0.8 mm depending on the details of the procedures in use at the time). Approximately 50% of the particles eventually fall into the two side wells, so the number of antiprotons in the side wells eventually approaches the un-mixed antiproton number.…”

Section: Creation During Mixingmentioning

confidence: 99%

“…The strongest electric fields in our trap are found close to the trap wall at the electrode boundaries, and can be as large as E max = 42 V mm −1 . 27 A newly ionized antiproton will be accelerated by these fields, and can pick up perpendicular energy. However, a careful map of the electric and magnetic fields over the entire trap shows that the perpendicular energy gain cannot exceed more than 3 eV before the antiproton settles into its E × B motion, so this process cannot lead to mirror-trapped antiprotons.…”

Section: Creation By Ionization Of Antihydrogenmentioning

confidence: 99%

Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap

et al. 2012

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Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the magnetic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilate. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antiproton and antihydrogen trajectories in this magnetic geometry, and reconstruct the antihydrogen energy distribution from the measured annihilation time history.

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“…[7][8][9][10][11][12][13] Of course, waves and field asymmetries also produce transport in nonneutral plasmas without separate classes of trapped and passing particles, and in these plasmas the dominant transport mechanism is thought to be resonant particle transport. [14][15][16][17][18][19] As described in the abstract, the purpose of this brief communication is to resolve a point of theoretical confusion introduced in the first theoretical papers on the TPDM. 4,5 Using a corrected fluid theory that takes into account the flow of particles back and forth through the separatrix, we show that the fluid description of the trapped particle density perturbation matches that obtained from the kinetic description, and we discuss the consequences of the corrected density perturbation for the mode eigenfunctions.…”

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confidence: 98%

Particle fluxes through the separatrix in the trapped particle diocotron mode

2011

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In the trapped particle diocotron mode, the trapped particles undergo E Â B drift motion in a uniform B field. Since such a flow is incompressible one is tempted to assume that the trapped particle density is constant along a fluid element. However, this is not the case since there is interchange of trapped and passing particles through the separatrix. This paper shows that a corrected fluid analysis, taking into account the particle flux through the separatrix, reproduces the same trapped particle density perturbation as obtained from the kinetic theory, thereby resolving confusion in earlier papers.Electric and magnetic field inhomogeneities in plasma containment devices often cause particles to be trapped in localized regions, and these trapped particles give rise to a class of low frequency modes of oscillation called trapped particle modes 1 and to the important phenomena of neoclassical transport. 2 Recent work using nonneutral plasmas has provided access to the physics of trapped particle modes and neoclassical transport for a simple geometry and quiescent plasma, where well-controlled comparisons of theory and experiment are possible.Trapped particle diocotron modes (TPDM) are routinely excited on nonneutral plasma columns in which there are classes of trapped and passing particles. 3 To create these classes, the usual Malmberg-Penning trap configuration is modified by applying an azimuthally symmetric potential barrier, the squeeze potential, near the axial mid-point of the column. Particles with relatively low axial velocity are trapped on one side or the other of the barrier, while high velocity particles pass back and forth along the axial magnetic field over the full length of the plasma column.The mode dynamics is easy to understand qualitatively. The mode potential has odd parity in the axial coordinate and produces bounce-average E Â B drift oscillations of the trapped particles that are 180 out of phase on the two sides of the barrier, while the passing particles stream back and forth, partially Debye shielding the perturbation in the trapped particle charge density.A theoretical description of the TPDM was obtained using the Poisson's equation and the drift kinetic equation with a Fokker-Planck (FP) collision operator. 4,5 Experiments had observed damping of the TPDM, and the theory explained the damping as resulting from collisional velocity diffusion at the separatrix between trapped and untrapped particles. Associated with the damping is a neoclassical particle transport. The damping and associated transport also were investigated using numerical simulations. 6 Much additional work then explored and generalized the neoclassical damping and transport. 7-13 Of course, waves and field asymmetries also produce transport in nonneutral plasmas without separate classes of trapped and passing particles, and in these plasmas the dominant transport mechanism is thought to be resonant particle transport. [14][15][16][17][18][19] As described in the abstract, the purpose of this brief communication is to...

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Magnetic multipole induced zero-rotation frequency bounce-resonant loss in a Penning–Malmberg trap used for antihydrogen trapping

Cited by 7 publications

References 14 publications

Antihydrogen Formation, Trapping and Dynamics

Antihydrogen Formation, Trapping and Dynamics

Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap

Particle fluxes through the separatrix in the trapped particle diocotron mode

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