Baker, C. J.

Charlton, M.

Choi, J. J.

Chung, M.

Clade, P.

Comini, P.

Crepin, P-P

Crivelli, P.

Dalkarov, O.

Debu, P.

Dodd, L.

Douillet, A.

Froehlich, P.

Gafriller, J.

Guellati, S.

Heinrich, J.

Hervieux, P-A

Hilico, L.

Husson, A.

Indelicato, P.

Janka, G.

Jonsell, S.

Karr, J-P

Kim, B. H.

Kim, E-S

Kim, S. K.

Kleyheeg, A.

Ko, Y.

Kosinski, T.

Kuroda, N.

Latacz, B.

Lee, H.

Lee, J.

Leite, A. M. M.

Leveque, K.

Lim, E.

Liszkay, L.

Louvradoux, T.

Lunney, D.

Manfredi, G.

Mansoulie, B.

Matusiak, M.

Mornacchi, G.

Nesvizhevsky, V. V.

Nez, F.

Niang, S.

Nishi, R.

Nourbaksh, S.

Park, K. H.

Paul, N.

Perez, P.

Radics, B.

Regenfus, C.

Reynaud, S.

Rousse, J. Y.

Rubbia, A.

Rzadkiewicz, J.

Sacquin, Y.

Schmidt-Kaler, F.

Staszczak, M.

Tuchming, B.

Vallage, B.

van der Werf, D. P.

Voronin, A.

Welker, A.

Wolf, S.

Won, D.

Wronka, S.

Yamazaki, Y.

Yoo, K. H.

Acta Physica Polonica A

English

International audienceThe GBAR experiment aims to measure the gravitational acceleration of antihydrogen H̅. It will use H̅+ ions formed by the interaction of antiprotons with a dense positronium cloud, which will require about 1010 positrons to produce one H̅+. We present the first results on the positron accumulation, reaching 3.8±0.4×108 e+ collected in 560 s

Niang, S

Charlton, M

Choi, J, J

Chung, M

Cladé, P

Comini, P

Crivelli, P

Crépin, P-P

Dalkarov, O

Debu, P

Dodd, L

Douillet, A

Froehlich, P

Gafriller, J

Guellati, S

Heinrich, J

Hilico, L

Husson, A

Indelicato, P

Janka, G

Jonsell, S

Kim, B, H

Kim, S, K

Kleyheeg, A

Ko, Y

Kosinski, T

Kuroda, N

Latacz, B

Lee, H

Lee, J

Leite, A, M M

Lim, E

Liszkay, L

Louvradoux, T

Lunney, D

Lévêque, K

Manfredi, G

Mansoulié, B

Matusiak, M

Mornacchi, G

Nesvizhevsky, V, V

Nishi, R

Nourbaksh, S

Park, K, H

Paul, N

Pérez, P

Radics, B

Regenfus, C

Reynaud, S

Roussé, J-y

Rubbia, A

Rzadkiewicz, J

Sacquin, Y

Schmidt-Kaler, F

Staszczak, M

Tuchming, B

Vallage, B

van Der Werf, D, P

Voronin, A

Welker, A

Wolf, S

Won, D

Wronka, S

Yamazaki, Y

Yoo, K-H

Baker, C, J

HAL: Hyper Article en Ligne

Accumulation of positrons from a LINAC based source

Choi, J,

Kim, B,

Kim, S,

Leite, A,

Nesvizhevsky, V,

Park, K,

van Der Werf, D,

Baker, C,

Hal-Diderot

Michael Charlton

Liam Dodd

Dirk van der Werf

Christopher Baker

Cronfa at Swansea University

Vol. 137 (2020) ACTA PHYSICA POLONICA A No. 2Proc. of the 15th Int. Workshop on Slow Positron Beam Techniques and Applications, Prague, September 2–6, 2019Accumulation of Positrons from a LINAC Based SourceS. Nianga,∗, M. Charltonb, J.J. Choic, M. Chungd, P. Cladée, P. Cominia, P. Crivellif ,P.-P. Crépine, O. Dalkarovg, P. Debua, L. Doddb, A. Douillete,h, P. Froehlichi,J. Gafrillerj, S. Guellatie, J. Heinriche, P.-A. Hervieuxk, L. Hilicoe,h, A. Hussonl,P. Indelicatoe, G. Jankaf , S. Jonselli, J.-P. Karre,h, B.H. Kimc, E-S. Kimm, S.K. Kimc,A. Kleyheegj, Y. Kon, T. Kosinskio, N. Kurodap, B. Latacza, H. Leec, J. Leen,A.M.M. Leitea, E. Limm, L. Liszkaya, T. Louvradouxe, D. Lunneyl, K. Lévéquek,G. Manfredik, B. Mansouliéa, M. Matusiako, G. Mornacchij, V.V. Nesvizhevskyq,F. Neze, R. Niship, S. Nourbakshj, K.H. Parkc, N. Paule, P. Péreza, B. Radicsf ,C. Regenfusf , S. Reynaude, J.Y. Rousséa, A. Rubbiaf , J. Rzadkiewiczo, Y. Sacquina,F. Schmidt-Kalerr, M. Staszczako, B. Tuchminga, B. Vallagea, D.P. van der Werfb,A. Voroning, A. Welkerj, S. Wolfr, D. Wonc, S. Wronkao, Y. Yamazakis, K.H. Yood(GBAR Collaboration) and C.J. BakerbaIRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, FrancebDepartment of Physics, College of Science, Swansea University, Swansea SA2 8PP, United KingdomcDepartment of Physics and Astronomy, Seoul National University, 1 Gwanak-Ro, Gwanak-gu, Seoul 08826, KoreadDepartment of Physics, Ulsan National Institute of Science and Technology (UNIST),50, UNIST-gil, Ulsan 44919, Republic of KoreaeLaboratoire Kastler Brossel, Sorbonne Université, CNRS, ENS-PSL Research University, Collège de France,Campus Pierre et Marie Curie, 4, pl. Jussieu, F-75005 Paris, Francef Institute for Particle Physics and Astrophysics, ETH Zurich, 8093 Zurich, SwitzerlandgP.N. Lebedev Physical Institute, 53 Leninsky Prospect, 119991 Moscow, RussiahUniversité d’Evry-Val d’Essonne, Université Paris-Saclay, Boulevard François Mitterand, F-91000 Evry, FranceiDepartment of Physics, Stockholm University, SE-10691 Stockholm, SwedenjCERN, 1211 Geneva 23, SwitzerlandkUniversité de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg,UMR 7504, F-67000 Strasbourg, FrancelCSNSM-IN2P3-CNRS, Université de Paris Sud, Orsay, FrancemDepartment of Accelerator Science, Korea University Sejong Campus,Sejong-ro 2511, 30019 Sejong, Republic of KoreanCenter for Underground Physics, Institute for Basic Science,70 Yuseong-daero 1689-gil, Yuseong-gu, Daejeon 34047, KoreaoNational Centre for Nuclear Research (NCBJ), A. Soltana 7, 05-400 Otwock, Swierk, PolandpInstitute of Physics, University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, JapanqInstitut Max von Laue — Paul Langevin (ILL), 71 av. des Martyrs, Grenoble, France, F-38042rQUANTUM, Institut für Physik, Johannes Gutenberg Universität, D-55128 Mainz, GermanysUlmer Fundamental Symmetries Laboratory, RIKEN, 2-1 Hirosawa, Wako, 351-0198, Saitama, JapanThe GBAR experiment aims to measure the gravitational acceleration of antihydrogen H. It will use H+ ionsformed by the interaction of antiprotons with a dense positronium cloud, which will require about 1010 positronsto produce one H+. We present the first results on the positron accumulation, reaching 3.8±0.4×108 e+ collectedin 560 s.DOI: 10.12693/APhysPolA.137.164PACS/topics: positron plasma, positron accumulation, antimatter, Penning–Malmberg trap, Greaves–Surko trap,GBAR∗corresponding author(164)Accumulation of Positrons from a LINAC Based Source 1651. IntroductionThe GBAR collaboration aim is to measure the accel-eration of antihydrogen atoms in the Earth gravitationalfield [1]. In the GBAR scheme, one first produces H+ions [2], which are subsequently sympathetically cooledusing laser cooled Be+ ions [3]. When the anti-ion iscold enough, the extra positron is removed using a laserpulse and the acceleration is derived by timing the sub-sequent annihilation products of the H. The antiprotonsare obtained from the ELENA decelerator at CERN [4],while positronium is produced by implantation of about1010 positrons into a mesoporous silica film at a kineticenergy of 4 keV [5].To obtain the necessary positrons, a 9 MeV LINAC ac-celerates electrons into a tungsten target equipped witha mesh moderator biased at 50 V. The resulting low en-ergy positrons are then accumulated in a buffer gas trap(BGT) and transferred in a high field trap (HFT).The BGT is a Penning–Malmberg trap based on theGreaves–Surko scheme [6], and was developed at CEASaclay [7]. It uses N2 as the trapping gas and CO2 asa cooling gas. The trap is constructed from 3 sets ofelectrodes. In the first stage, inelastic collisions occurunder a typical N2 pressure of 10−3 mbar, whilst thesecond one is used for the accumulation at a typical N2pressure of 10−4 mbar, with the final stage used to storepositrons for a dozens of seconds with a typical N2 pres-sure of 10−6 mbar. The magnetic field in this trap is≈ 0.05 T and an electric potential between −140 V and140 V can be applied to the electrodes, as appropriate.The HFT [8] is a 5 T Penning–Malmberg trap with27 electrodes each able to hold potentials between −1 kVand 1 kV. The base pressure is lower than 10−9 mbar.This trap is used for long time storage.In this article we present the outcome of optimisationstudies to trap a large cloud of positrons. The final goalis to accumulate 1010 positrons in 100 s. The two lastprevious record are 1.2 × 109 in 2.5 h [9] and 4 × 109in 4.5 h [10].2. Studies of the trapping conditionsAfter an accumulation time t in the BGT second stage,using the potential profile shown in Fig. 1a, the positroncloud is axially compressed, and then dumped on a tar-get at the exit of the trap (Fig. 1b,c) after the BGT thirdstage. The positron number is estimated by detectingthe γ rays resulting from their annihilations on the tar-get using a CsI detector. The signal is proportional tothe number of accumulated positrons, which evolves asN(t) = Rτ(1−e− tτ ), whereN is the number of positrons,τ is the lifetime, and R is the trapping rate. Some accu-mulation curves for e+ in the second stage are presentedin Fig. 2a for different N2 pressures as measured at theinjection point of the system. If t  τ , N(t) ≈ Rt, theonly parameter to optimise is then R. For the rest of theFig. 1. On-axis potentials used in the buffer gas trap.(a) Accumulation in the second stage. (b) Axial com-pression of the cloud. (c) Transfer from the second tothe third stage. (d) Re-trapping. (e) Preparation fortransfer/dump. (f) Dump.Fig. 2. (a) Number of e+ as measured by the CsI de-tector, fit with N(t) + c. (b) R vs. N2 pressure. (c)Positron annihilation rate (λ = 1/τ) vs. N2 pressure.Pressures in mbar as measured at the injection point ofthe system.experiment we keep PN2 = 6 mbar, with τ = 0.67±0.01 sand we accumulate for 100 ms before transferring to thethird stage (Fig. 1c,d).Currently, the energy spread in the longitudinal direc-tion of the incoming positrons is σ = 8.8 ± 0.3 eV but aspread of energy smaller than 3 eV [6] would increase Rand therefore the overall efficiency.In the third stage, the e+ lifetime is 16.5(0.5) s, asshown in Fig. 3a, and since this is much greater than100 ms a stacking procedure of the positrons from thesecond stage can be done. Figure 3b shows that, using astatic potential, only 6 stacks can be accumulated in thewell in a linear way, beyond which the stacks are lost.It also shows that by lowering the bottom of the well166 S. Niang, et al.Fig. 3. (a) Lifetime of positrons in the third stage. (b)Measurement of positron signal for different accumu-lation conditions in stage 3 (see text for details). Thebottom of the well is lowered by dV between each stack.Fig. 4. (a) Subsequent on-axis potentials in the HFT.(b) Accumulation signal from HFT, for respectively a1-, 2-, 3- and 4-step sequence.by 0.2 V per stack, a dozen stacks can be accumulatedwithout any loss. Therefore 10 stacks are accumulatedin 1 s (10×100 ms) before being transferred to the HFT.To stack positrons from the BGT third stage in theHFT, one first uses a potential well made of 3 electrodeswith −10 V as bottom of the well as shown in Fig. 4a.Figure 4b shows that the well is saturated after 80 stacks.To accumulate positrons in a linear way, a sequence isused in which the well is enlarged and deepened eachtime we approach a saturation limit. In the first well,50 stacks are accumulated, after which the bottom of thewell is lowered. Then 150 stacks are added, and again thebottom of the well is lowered and then further 200 stacksare added. Finally, we lower the bottom of the well toreach a maximum, so in total, we can accept 560 stacksof e+ from the third stage corresponding to 3.8(0.4) ×108 e+. We are planning to extend this process to trapeven more positrons.With the knowledge that the LINAC based positronsource provides 1.54(0.06) × 105 e+ per pulse at a fre-quency of 200 Hz, the current overall efficiency is 2.3%.3. ConclusionWe succeeded in trapping 3.8(0.4) × 108 e+ in 560 s,which is a first important step for the development of theGBAR experiment. Improvements will be made in thecoming months to reach our next step of 1010 positronsin a few hours, after which the goal will be to decreasethis accumulation time, by increasing the e+ flux at theentrance, and by improving efficiencies at the interfacesof the system.AcknowledgmentsThis research was partially supported by CNES un-der convention No. 5100017115, the French NationalResearch Agency (grant ANR-14-CE33-0008), the SwissNational Science Foundation (grant 20FL21_173597)and the ETH Zurich (grant ETH-46 17-1).References[1] G. Chardin, et al. (GBAR Collaboration), “Proposalto Measure the Gravitational Behaviour of Antihydro-gen at Rest”, CERN-SPSC-2011-029, SPSC-P-342,2011.[2] P. Comini, P.-A Hervieux, F. Biraben Hyperfine In-teract. 228, 159 (2014).[3] J. Walz, T.W. Hänsch, Gen. Relativ. Gravitat. 36,561 (2004).[4] W. Oelert, et al. (ELENA Collaboration), Acta Phys.Pol. B 46, 181 (2015).[5] P. Crivelli, U. Gendotti, A. Rubbia, L. Liszkay,P. Perez, C. Corbel, Phys. Rev. A 81, 052703 (2010).[6] J.R. Danielson, D.H.E. Dubin, R.G. Greaves,C.M. Surko, Rev. Mod. Phys. 87, 247 (2015).[7] A.M.M. Leite, Ph.D. Thesis, Paris-Saclay, 2017.[8] P. Grandemange, Ph.D. Thesis, Université Paris Sud— Paris XI, 2013.[9] L.V. Jørgensen (ATHENA Collaboration), Phys.Rev. Lett. 95, 025002 (2005).[10] D.W. Fitzakerley (ATRAP Collaboration), J. Phys.B 49, 064001 (2016).

Accumulation of Positrons from a LINAC Based Source

HAL-CEA

GBAR Collaboration

Niang, Samuel

Crivelli, Paolo

Janka, Gianluca

Radics, Balint

Regenfus, Christian

Rubbia, André

et al.

Repository for Publications and Research Data

HAL-IN2P3

Choi, J.J.

Crépin, P.P.

Hervieux, P.A.

Husson, Alain

Karr, J.P.

Kim, B.H.

Kim, S.K.

Leite, A.M.M.

Lévéque, K.

Nesvizhevsky, V.V.

Park, K.H.

Pérez, P.

Reynaud, Serge

Roussé, J.Y.

van Der Werf, D.P.

Yoo, K.H.

Baker, C.J.

The GBAR experiment aims to measure the gravitational acceleration of antihydrogen (H) over bar. It will use (H) over bar (+) ions formed by the interaction of antiprotons with a dense positronium cloud, which will require about 1010 positrons to produce one (H) over bar (+). We present the first results on the positron accumulation, reaching 3.8 +/- 0.4x10(8) e(+) collected in 560 s

ScholarWorks@UNIST

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Accumulation of Positrons from a LINAC Based Source

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Cronfa at Swansea University

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Hal-Diderot

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