Speakers
Dr
Alexander Smirnov
(Joint Institute for Nuclear Research)Dr
Yury Plis
(JINR)
Description
On the feasibility of using an extracted polarized antiproton beam of the HESR with a solid
polarized target
Yu.A. Plis, A.V. Smirnov et al.
Joint Institute for
Nuclear Research, 141980 Dubna, Russia
It seems real to accelerate and store polarized antiprotons in the high-energy storage
ring (HESR) at FAIR. We accept that all the problems connected with production and
depolarization of the antiproton beam had been solved.
It is known that high-energy protons can be extracted from the beam halo in a
collider (as, for example, it was done at Tevatron FNAL) using channeling in a bent crystal
without interfering in the main experiment.
But for heavy negative particles (antiprotons)
this method of beam deflection
is inefficient due to the fast dechanneling.
At the HESR the planned internal coasting beam could reach $10^{11}$
antiprotons in the momentum range 1.5-15 GeV/c.
One might try to extract halo antiprotons, which can not be
utilised at the PANDA facility by means of
a several meter long electrostatic septum with a field of about 80 kV/cm.
The initial direction of polarization does not matter (probably, it will be longitudinal),
it can be rotated in any direction before
the polarized target.
Then the beam is deflected
by a magnetic field into the solid polarized target.
It should be noted that the halo formation mechanism in the HESR differs from that
in FNAL storage ring, where the in-beam scattering is the main process. In the HESR at the minimal
momentum the main contribution comes from Coulomb scattering, while at the maximal momentum - from
nuclear processes. The beam lifetime for the HESR is about 1 hour, while for FNAL it equals to about 70 hours.
It can be expected, that in the HESR the substantial share of antiprotons lost due to interactions
with pellets comes to the halo.
The simulation has been done with BETACOOL code for PANDA parameters with using the barrier bucket and
electron cooling systems. The longitudinal
acceptance was chosen equal to the effective barrier bucket height. It means that particle will be lost
after interaction with the target pellet if the energy decreasing is larger than the barrier height.
For the cycle duration equal to 1 hour an average intensity will be $\sim10^6 $
antiprotons/s, which, for the typical 10 cm long polarized target, corresponds to the
luminosity $\sim10^{30}$ cm$^{-2}$ s$^{-1}$.
Another possibility is to use the accumulated antiprotons in HESR which are not utilised entirely, and to extract
them slowly at the end of the cycle and send to the polarized target. For example, at slow variation of
the radial betatron oscillation frequency the particles get to the instability region and end up
in the septum due to the resonance build-up of oscillation amplitude.
Primary author
Dr
Yury Plis
(JINR)
