A Proof-of-Principal Experiment for a High-Power Target System Page: 3 of 5
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A PROOF-OF-PRINCIPAL EXPERIMENT FOR A HIGH-POWER
H.G Kirk, R. Samulyak, N. Simos, T. Tsang, BNL, Upton, NY 11973, USA
I. Efthymiopoulos, A. Fabich, H. Haseroth, F. Haug, J. Lettry
CERN, CH-1211 Geneve 23, Switzerland
V.B. Graves, P.T. Spampinato, ORNL, Oak Ridge, TN 37831, USA
K.T. McDonald, Princeton University, Princeton, NJ 08544, USA
J.R.J. Bennett, T.R. Edgecock, CCLRC, RAL, Chilton, OX1I IOQX, UK
The MERIT experiment, to be run at CERN in 2007, is
a proof-of-principle test for a target system that converts a
4-MW proton beam into a high-intensity muon beam for
either a neutrino factory complex or a muon collider. The
target system is based on a free mercury jet that intercepts
an intense proton beam inside a 15-T solenoidal magnetic
A muon collider or neutrino factory requires intense
beams of muons, which are obtained from the decay of pi-
ons. Pion production by a proton beam is maximized by
use of a high-Z target such as mercury. A liquid jet target
has the advantages over a solid target that a flowing jet can
readily remove heat and that it is immune to radiation dam-
age. However the proton beam energy disrupts the jet and
the system could be operationally unstable.
Efficient capture of low-energy secondary pions (for
transfer into the subsequent muon accelerator complex) re-
quires that the target system be immersed in a strong mag-
netic field of solenoidal geometry. This magnetic field
should stabilize the mercury flow in regions of nearly uni-
form field, but it perturbs the liquid metal jet as it enters
the field. Hence, the behavior of the mercury jet plus an
intense proton beam inside a strong magnetic field needs to
be understood better before resources are committed to a
larger facility. The MERIT experiment is to be conducted
at CERN in 2007 for this purpose.
Key elements of the target system [11 are: an intense
proton source, copious soft-pion production off a high-Z
target that is replaced every beam pulse, and capture of the
generated low-PL pions in a high-field ( 15 T) solenoidal
magnet, as shown in Fig. 1. An important byproduct of this
approach is that 7w+'s and i-'s are equally produced and
both particle types can be conducted down the solenoidal
Figure 1: Concept of a continuous mercury jet target for
an intense proton beam. The jet and beam are tilted by
100 mrad and 67 mrad, respectively, with respect to a 20-T
solenoid magnet that conducts low-momentum pions into a
Simulations 12] show that maximal pion production oc-
curs for small radii for both the target and the proton beam.
Furthermore, it is advantageous to tilt the target and pro-
ton beam by an angle of 100 mrad to the solenoidal axis
so that soft pions that leave the side of the target are not
reabsorbed after one turn on their helical trajectory.
The proton beam deposits 15% of its energy in the
target, leading to an instantaneous rise in the temperature
of the target, which in turn causes large transient stresses
that can crack a solid target [31. In the case of a liquid
jet target, its dispersal by the beam should not be destruc-
tive to the surrounding target system components. Further-
more, the dispersal of the liquid jet should not reduce the
pion production during subsequent beam pulses (nominally
20 msec apart for 50-Hz operation), or during the various
bunches of a single macropulse. For the liquid jet to present
a new target of two interaction lengths each macropulse, the
mercury velocity must be : 20 m/s.
The mercury target should be in the form of a free jet,
rather than confined in a pipe, since the beam-induced cav-
itation of the liquid metal is extremely destructive to any
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Kirk,H.G.; Samulyak, R.; Simos, N.; Tsang, T.; Efthymiopoulos, I.; Fabich, A. et al. A Proof-of-Principal Experiment for a High-Power Target System, article, June 26, 2006; United States. (digital.library.unt.edu/ark:/67531/metadc926137/m1/3/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.