MUCOOL Meeting: 9th July, 1999
In addition to the discussion of the Technical Advisory Group
by Dan Kaplan and Steve Geer, there were two presentations:
Zoira Cruz reported calculations of forces between coils of the
cooling system. These forces are very large because of the high
fields required in the solenoids to produce small beta's, and the
large size of the coils needed to contain the rf cavities.
Forces were calculated using a number of methods, for example directly
from JxB, calculations using mutual inductance, and finally with
OPERA 3D. All the methods gave consistent results and nice graphics.
The force produced was 2.5E7 Newtons. This work will continue to include
the effects of iron and other coil geometriesl
Jim Norem described continuing calculations directed at producing
a design of a bunched beam cooling experiment option. Calculations of
scattering of muons show that they can be collimated neatly, with the
particles either stopping or scattering by vary large (0.1 - 0.3) angles
so they leave the beam phase space. A particularly effective method
seems to be to use cleanup collimators downstream in a FODO line with
a phase advance of 90 degrees between collimators, this effectively
eliminates all spray.
A cooling measurement could be done by putting scintillator hodoscopes
downstream of the cooling system, to look at changes in the phase space
volume determined by the collimators. Variable phase advance down an
FODO channel permits measurements of the beam volume from any phase angle
(phase space tomography).
Other preliminary calculations were presented showing that dE/dx cooling
of muons from 450 to 200 MeV/s in degraders will remove perhaps 95% of
the pions and probably not more. Some low energy decays will be required
to remove the rest of the pions, this may take place automatically in the
cooling channel.
X-rays background in the low pressure TPC's may be a problem. The RF
cavities produce enough 1 MeV X rays to require about a yard of concrete
shielding. The bremsstrahlung spectrum increases at low energy at least
like E^-1, and the cross sections for ionization of all materials increase
like E^-3.3, so the problem is a lot worse at low energies.
The low pressure TPC's are particularly susceptible to x-rays, since
the long drift time (few microseconds) means they will integrate over a
long time, and the signals we are looking for will only be a few ions
per track.
Bunched beam experiments improve these problems by producing much larger
signals (~10^6 more particles), shorter integration times (~0.001) and
perhaps permitting some bends in the line which can avoid line of sight
(or single bounce paths) with the linacs.