EDP Sciences : Minimizing plasma temperature for antimatter mixing experiments

Hunter, E.D.; Tajima, M.; Simon, M.C.; Amsler, C.; Costantini, G.; Wolz, T.; Kraxberger, V.; Breuker, H.; Venturelli, L.; Zmeskal, J.; Widmann, E.; Gligorova, A.; Pasino, E.; Ferragut, R.; Higaki, H.; Nowak, L.; Gosta, G.; Kanai, Y.; Nagata, Y.; Ulmer, S.; Mascagna, V.; Matsuda, Y.; Weiser, A.; Kuroda, N.; Leali, M.; Killian, C.; Romé, M.; Murtagh, D.J.; Lanz, A.; Giammarchi, M.; Kletzl, V.; Toso, V.; Chesnevskaya, S.; Maero, G.; Malbrunot, C.; Uggerhøj, U.; Yamazaki, Y.; Mäckel, V.; Migliorati, S.; Nanda, A.

doi:10.1051/epjconf/202226201007

Article
Report number	arXiv:2201.01256
Title	Minimizing plasma temperature for antimatter mixing experiments
Author(s)	Hunter, E.D. (Stefan Meyer Inst. Subatomare Phys.) ; Amsler, C. (Stefan Meyer Inst. Subatomare Phys.) ; Breuker, H. (RIKEN (main)) ; Chesnevskaya, S. (Stefan Meyer Inst. Subatomare Phys.) ; Costantini, G. (Brescia U. ; INFN, Pavia) ; Ferragut, R. (INFN, Milan ; Milan U. ; CERN) ; Giammarchi, M. (INFN, Milan ; CERN) ; Gligorova, A. (Stefan Meyer Inst. Subatomare Phys.) ; Gosta, G. (Brescia U. ; INFN, Pavia) ; Higaki, H. (Hiroshima U.) ; Kanai, Y. (Nishina Ctr., RIKEN) ; Killian, C. (Stefan Meyer Inst. Subatomare Phys.) ; Kletzl, V. (Stefan Meyer Inst. Subatomare Phys.) ; Kraxberger, V. (Stefan Meyer Inst. Subatomare Phys.) ; Kuroda, N. (Tokyo U.) ; Lanz, A. (Stefan Meyer Inst. Subatomare Phys.) ; Leali, M. (Brescia U. ; INFN, Pavia) ; Mäckel, V. (Stefan Meyer Inst. Subatomare Phys.) ; Maero, G. (Milan U.) ; Malbrunot, C. (CERN) ; Mascagna, V. (Brescia U. ; INFN, Pavia) ; Matsuda, Y. (Tokyo U.) ; Migliorati, S. (Brescia U. ; INFN, Pavia) ; Murtagh, D.J. (Stefan Meyer Inst. Subatomare Phys.) ; Nagata, Y. (Tokyo U. of Sci.) ; Nanda, A. (Stefan Meyer Inst. Subatomare Phys.) ; Nowak, L. (CERN) ; Pasino, E. (Milan U.) ; Romé, M. (Milan U.) ; Simon, M.C. (Stefan Meyer Inst. Subatomare Phys.) ; Tajima, M. (Nishina Ctr., RIKEN) ; Toso, V. (INFN, Milan ; Milan U. ; CERN) ; Ulmer, S. (RIKEN (main)) ; Uggerhøj, U. (Aarhus U.) ; Venturelli, L. (Brescia U. ; INFN, Pavia) ; Weiser, A. (Stefan Meyer Inst. Subatomare Phys.) ; Widmann, E. (Stefan Meyer Inst. Subatomare Phys.) ; Wolz, T. (CERN) ; Yamazaki, Y. (RIKEN (main)) ; Zmeskal, J. (Stefan Meyer Inst. Subatomare Phys.)
Publication	2022
Imprint	2022-01-04
Number of pages	7
Note	Proceedings of the Exotic Atoms (EXA) Conference, Vienna, 2021
In:	EPJ Web Conf. 262 (2022) pp.01007
In:	7th International Conference on Exotic Atoms and Related Topics, Online, 13 - 17 Sep 2021, pp.01007
DOI	10.1051/epjconf/202226201007
Subject category	physics.plasm-ph ; Other Fields of Physics
Abstract	The ASACUSA collaboration produces a beam of antihydrogen atoms by mixing pure positron and antiproton plasmas in a strong magnetic field with a double cusp geometry. The positrons cool via cyclotron radiation inside the cryogenic trap. Low positron temperature is essential for increasing the fraction of antihydrogen atoms which reach the ground state prior to exiting the trap. Many experimental groups observe that such plasmas reach equilibrium at a temperature well above the temperature of the surrounding electrodes. This problem is typically attributed to electronic noise and plasma expansion, which heat the plasma. The present work reports anomalous heating far beyond what can be attributed to those two sources. The heating seems to be a result of the axially open trap geometry, which couples the plasma to the external (300 K) environment via microwave radiation.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) CC-BY-4.0

$The Cusp experiment. Positrons and antiprotons are loaded into ``Trap'' from other traps further upstream (left, not shown). The antimatter plasmas are manipulated, cooled, and mixed together to form antihydrogen. The two cusps in the magnetic field $B$ help to focus low energy, low-field-seeking antiatoms into a spin-polarized beam traveling to the right at approximately $1000\,\mathrm{m/s}$. The frequency of the microwaves applied to ``Cavity'' is varied, while monitoring the number of antiatoms that are refocused by ``Sextupole'' onto a scintillator target (right, not shown). When the microwave frequency is close to the hyperfine splitting ($\nu_{HFS}\approx 1.420\,\mathrm{GHz}$), low-field-seeking atoms passing through ``Cavity'' become high-field-seekers. High-field-seekers are defocused by ``Sextupole''. Thus, the transition frequency is detected as a dip in the signal on the scintillator. ``A1'' and ``A2'' are apertures, necessary for admitting particles and letting antiatoms escape from the trap. These apertures also admit room-temperature microwave radiation, which may heat the plasma.$ $Left: Photos of the downstream shield taken through a vacuum window. The shield is open in the top photo, partly open in the middle photo, and closed in the bottom photo. Notice that the shield is still mostly closed in the ``partly open'' configuration; the trap (visible as a small circle in the top photo, having diameter roughly 1/6 the size of the photo) is still completely covered by the shield. Middle: Plasma temperature after cooling with the shield in the three positions shown at the left. Each point gives the mean and standard deviation of $T$ for 15 different plasmas. The numbers next to the points indicate the order in which the data was taken; to further emphasize the ordering, the first three points in the series are black and the last three are red. Right: Plasma temperature as a function of the number of electrons in the plasma. The temperature is $20\,\mathrm{K}$ higher when the downstream shield is open, independent of the number of electrons in the plasma.$ $Left: Photos of the downstream shield taken through a vacuum window. The shield is open in the top photo, partly open in the middle photo, and closed in the bottom photo. Notice that the shield is still mostly closed in the ``partly open'' configuration; the trap (visible as a small circle in the top photo, having diameter roughly 1/6 the size of the photo) is still completely covered by the shield. Middle: Plasma temperature after cooling with the shield in the three positions shown at the left. Each point gives the mean and standard deviation of $T$ for 15 different plasmas. The numbers next to the points indicate the order in which the data was taken; to further emphasize the ordering, the first three points in the series are black and the last three are red. Right: Plasma temperature as a function of the number of electrons in the plasma. The temperature is $20\,\mathrm{K}$ higher when the downstream shield is open, independent of the number of electrons in the plasma.$ Show more plots

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Record created 2022-05-04, last modified 2023-02-10

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