A Proof-of-Principal Experiment for a High-Power Target System Page: 4 of 5
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solid wall in the immediate vicinity of the interaction re-
The operation of a liquid metal jet inside a strong mag-
netic field raises several magnetohydrodynamic issues as
to possible deformation of the jet's shape and trajectory, as
well as the effect of the magnetic field on the beam-induced
dispersal of the jet.
Initial tests involving the interaction of proton beams on
mercury targets were performed at the BNL AGS Gradient
Synchrotron , and continued at the CERN ISOLDE fa-
cility (61. The BNL tests featured a 24-GeV proton beam
interacting with a free mercury jet with a diameter of 1 cm
and velocity of 2.5 m/s. Proton bunch intensities of 2-
/ x 1012 (2-4 TP) protons were delivered into a spot size
of a, = 0.3 nm and o- = 0.9 mm and 100 ns duration.
This resulted in a peak energy deposition of 80 J/g, which
is comparable to that expected from a 4-MW proton driver
delivering a 24-GeV proton beam at 15 Hz. These initial
tests did not have a magnetic field on the target.
Figure 2: A 1-cm-diameter, 2.5-m/s Hg jet at 0, 0.75, 10,
and 18 ms after interaction with 3.8 x 1012 24-GeV protons.
This experiment had several key observations:
" The dispersal velocity of Hg droplets with 4 TP on
target, seen in Fig. 2 was on the order of 10 m/s.
* The Hg dispersal was largely confined to the trans-
verse direction and did not extend outside the region
of overlap with the proton beam.
* The visible manifestation of Hg dispersal occurred
40 ps after arrival of the proton beam pulse.
" The Hg jet showed surface-tension instabilities; its di-
ameter varied from 0.5 to 1.5 cm.
These results validate numerical simulations  that in-
clude cavitation in the interior of the jet by the proton beam,
and the formation of filamentary instabilities on the surface
of the jet, as shown in Fig. 3.
A parallel effort was undertaken to study the effects
of high-velocity mercury jets in the presence of high-
magnetic fields , but with no proton beam. The Hg jet
had a diameter of 4 mm and a velocity of 12 m/s. Magnetic
fields up to 20 T were utilized. The main result was the
observation of jet stabilization (damping of surface tension
waves) as the magnetic field was increased, as shown in
Fig. 4. No perturbation of the jet on scales larger than 1 mm
Figure 3: Numerical simulation of the evolution of a free
mercury jet after exposure to an intense proton beam .
Left: Growth of surface filaments. Right: Growth of cavi-
tation bubbles inside the jet.
were observed when the jet was introduced into magnetic
fields of [0-20 T at an angle of 100 mrad to the solenoid
Figure 4: The Rayleigh instability of a mercury jet (4-mm
diameter and 12-rn/s velocity) is suppressed by high mag-
netic fields .
THE MERIT EXPERIMENT
We have proposed  and been approved to perform a
proof-of-principle experiment at the CERN Proton Syn-
chrotron (PS) that will combine a free mercury jet target
with a 15-T solenoid magnet and a 24-GeV primary proton
The PS will run in a harmonic-16 mode and we will be
able to till 1-8 of the 16 rf buckets with 2.5-3 x 10 2 pro-
tons/bunch at our discretion. The achievable spot size at the
experiment will be r > 1.2 mm (rms). This will allow us to
place up to 30 x 1012 protons on the mercury target within
a 2-ps spill, thus generating a peak energy deposition of
The experiment will be performed in the TT2A tunnel
at CERN (also used for the nToF beamline), as sketched in
For this experiment, we have designed and built a high-
field pulsed solenoid with a warm bore of 15 cm [81. This
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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/m1/4/: accessed January 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.