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NORMAL CONDUCTING RF CAVITY FOR MICE*
D. Lio, A. DeMello, S. Virostek and M. Zisman, LBNL, Berkeley, CA 94720, U.S.A.
D. Summers, University of Mississippi, Oxford, MS 38677, U.S.A.
Normal conducting RF cavities must be used for the
cooling section of the international Muon Ionization
Cooling Experiment (MICE), currently under
construction at Rutherford Appleton Laboratory (RAL) in
the UK. Eight 201-MHz cavities are needed for the
MICE cooling section; fabrication of the first five cavities
is complete. We report the cavity fabrication status
including cavity design, fabrication techniques and
preliminary low power RF measurements.
The Neutrino Factory (NF) and Muon Collider (MC)
offer great potential physics opportunities, but both are
difficult to build. Intense muon beams are produced with
very large six-dimensional emittance and have short
lifetime (- 2.2 ps at rest). One of the main challenges is
how to effectively manipulate the intense muon beams, in
particular how to reduce their transverse emittance, -
i.e., beam cooling. Ionization cooling is considered to be
the only practical cooling scheme for muons. However, as
yet no one has demonstrated muon ionization cooling
experimentally. MICE is such a demonstration
experiment, in which a section of an actual ionization
cooling channel (based on the US Feasibility Study-II
design) will be built and tested. The experiment is
currently under construction at the Rutherford Appleton
Laboratory (RAL) in the UK . The experiment includes
a dedicated beam line to generate a range of input muon
beam emittance and momentum, with time-of-flight and
Cherenkov detectors to ensure beam purity. The
emittance of the incoming muon beam is measured in an
upstream magnetic spectrometer with a scintillating fiber
tracker. A cooling section will then follow, consisting of
three liquid hydrogen absorbers enclosed in
superconducting focusing coils and two RF-Coupling
Coil Modules; each of these "RFCC" modules comprises
four 201-MHz normal conducting RF cavities surrounded
by a superconducting solenoid magnet. Muon beams lose
energy in the liquid hydrogen absorber and regain the lost
longitudinal energy from the RF cavities, thereby
resulting in a net reduction of transverse emittance. A
second, downstream spectrometer identical to the first one
and an electron-muon identification system provide a
measurement of the outgoing muon-beam emittance.
Figure 1 shows an engineering model of the MICE
Very high gradient normal conducting RF cavities are
required for muon ionization cooling, as the muons decay
*This work was supported by the Director, Office of Science, Office of
High Energy Physics, of the U.S. Department of Energy under Contract
and are confined in strong magnetic fields.
Hardware research & development for muon ionization
cooling has been the main focus of the MuCool program
under the US NFMCC (Neutrino Factory and Muon
Collider Collaboration). MICE RF cavity design is based
on the successful RF cavity built for the MuCool program.
Two RFCC modules
Figure 1: MICE cooling channel: three AFC (Absorber
and Focusing Coil) and two RFCC (RF cavity and
Coupling Coil) modules.
MICE RF cavities will be operated at a 1-Hz repetition
rate, with 1-ms pulse length, at a modest gradient of
8 MV/m, limited by available RF power.
This paper reports recent progress on the fabrication of
MICE RF cavities and low power measurements.
201-MHZ CAVITY FOR MICE
The cavity design, fabrication techniques and post-
processing are based on the successful prototype cavity
for the US MuCool program [2,3]. Unlike the prototype
cavity, MICE cavities will be installed in a vacuum vessel
such that there is differential pressure on neither the
cavity body nor the thin beryllium windows.
Nevertheless, integration of the cavity with its RF tuners,
support structure and superconducting coupling coil
within the vacuum vessel is a challenging task due to tight
Significant progress has been made on RF cavity
fabrication since 2009. The first five MICE cavities are
complete; the next five will be ready soon. Preliminary
low power RF measurements have been conducted.
The MICE cavity design features a round pillbox
profile (similar to that of the MuCool prototype cavity)
with the ratio of peak surface electric field to the
accelerating field on axis being almost one. In addition,
the conventional open beam irises are terminated by
curved 0.38-mm thick, 42-cm diameter beryllium foils
(windows). Muon beams penetrate the beryllium foils
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Li, D.; DeMello, A.; Virostek, S.; Zisman, M. & Summers, D. Normal Conducting RF Cavity for MICE, article, May 23, 2010; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc1013882/m1/1/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.