*[[Cusp trap]] [#s591f9c8]
** Concept of the CUSP trap [#t18ec220]
The CUSP trap consists of the combination of a superconducting anti-Helmholz coil and a stack of ring electrodes.
The CUSP trap provides the minimum '''B''' field configuration but still maintaining axial symmetry.
Due to this symmetry, the CUSP trap realizes stable handlings of both antiprotons and positrons such as trapping, cooling, and mixing.

*** MCEO configuration [#r2d05d5f]
In the MCEO (Magnet Cusp and Electic Octupole fiels) configuration, magnetic cusp 
and electric octupole fields are superimposed. Although a neutral plasma 
confined in the magnetic cusp is hydromagnetically very stable, particles can still escape 
along the magnetic-field lines. In the case of non-neutral plasma, this leakage can be “plugged” 
by applying an electric octupole field, as illustrated in the figure. The MCEO therefore possesses 
advantageous plasma stabilization properties in addition to simply confining the non-neutral
particle plasma, and experiments have already shown that it is well able to confine an electron 
plasma, with confinement time proportional to the square of the magnetic-field strength and 
a plasma density distribution that is nearly parabolic in the central region.


*** Nested well configuration [#jd0d8061]


So-called nested well configuration is also adopted as shown in the above figure. The confinement well for positron plasma is nested in the well for antiproton cloud. This configuration has an advantage to make a spin polarized beam, that is, the polarization of 50K antihydrogen beam amounts to about 30% when they are synthesized near the maximum magnetic field region in the cusp magnetic field. 

** as a polarized antihydrogen beam souce [#yee1b9c5]
Formed antihydrogen atoms in LFS (low field seeking) states are preferentially focused along the axis whereas those in the HFS (high field seeking) states are defocused, resulting in the formation of an intesity enhanced spin-polarized antihydrogen beam.
This is a novel feature of the CUSP trap. By using this antihydrogen beam, we adopt Rabi-technique for the microwave spectroscopy.

*** Experimental setup [#p790e41e]

Cusp trap has been in operation with MUSASHI (antirproton catching) trap, poistoron accumulator, and also Hbar detector. 


***References [#vf7ba472]
- N. Kuroda, S. Ulmer, D.J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, M. Leali, C. Malbrunot, V. Mascagna, K. Michishio, T. Mizutani, A. Mohri, H. Nagahama, M. Ohtsuka, B. Radics, S. Sakurai, C. Sauerzopf, K. Suzuki, M. Tajima, H.A. Torii, L. Venturelli, B. Wünschek, J. Zmeskal, N. Zurlo, H. Higaki, Y. Kanai, E. Lodi Rizzini, Y. Nagashima, Y. Matsuda, E. Widmann, and Y. Yamazaki.
Nat. Commun. 5:3089, Jan. 2014~
'''"A source of antihydrogen for in-fligh hyperfine spectroscopy"'''
- Y. Enomoto, N. Kuroda, K. Michishio, C.H. Kim, H. Higaki, Y. Nagata, Y. Kanai, H.A. Torii, M. Corradini, M. Leali, E. Lodi-Rizzini, V. Mascagna, L. Venturelli, N. Zurlo, K. Fujii, M. Ohtsuka, K. Tanaka, H. Imao, Y. Nagashima, Y. Matsuda, B. Juhász, A. Hohri, and Y. Yamazaki
Phys. Rev. Lett. 105(24)243401, Dec. 2010~
'''"Synthesis of Cold Antihydrogen in a Cusp Trap"''' 
- H. Saitoh, A. Mohri, Y. Enomoto, Y. Kanai, and Y. Yamazaki.~
'''"Radial compression of a non-neutral plasma in a cusp trap for antihydrogen synthesis"'''~
Physical Review A, 77(5):051403(R), May 2008.
- M. Shibata, A. Mohri, Y. Kanai, Y. Enomoto, and Y. Yamazaki.~
'''"Compact cryogenic system with mechanical cryocoolers for antihydrogen synthesis."'''~
Review of Scientific Instruments, 79(1):015112, January 2008.
- T. Pohl, H. R. Sadeghpour, Y. Nagata, and Y. Yamazaki~
'''"Cooling by Spontaneous Decay of Highly Excited Antihydrogen Atoms in Magnetic Traps"''',~
Phys.Rev.Lett. 97 (2006) 213001.
- A. Mohri and Y. Yamazaki.~
'''"A possible new scheme to synthesize antihydrogen and to prepare a polarized antihydrogen beam."'''~
Europhys.Lett., 63(2):207, July 2003.

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