MUCOOL Meeting Minutes
28 January, 2000
Scribe: Jocelyn Monroe
1) BNL Design Study Update; R. Fernow
-simulations of 2m Liquid Hydrogen cell surrounded by 2
90cm solenoids of opposite polarity show that angular momentum is
cancelled with 0.1T, 1.2T, 2T magitude B fields, correspoding to 0.5, 1.0,
1.5 Larmor wavelengths respectively (in 2m LH). For this study the
initial beam is monocromatic at 121 MeV, with initial transverse emittance
of 1500 mm-mr.
-to study cooling behavior of this configuration, the magnitude of
the B field was fixed at 2T. With an initial transverse emittance of 2860
mm-mr, (increase over previous study due to introduction of sigma pt = 30
mr) simulation results show final transverse emittance of 2760 mm-mr.
With initial sigma pt of 45mr, initial transverse emittance is 4190 mm-mr,
final transverse emittance is 3510 mm-mr.
-questions were raised as to where to put detectors in this
configuration, and what beam parameters to measure. Suggestions included
using a pencil beam to study the behavior of a small piece of the larger
initial phase space. The question of statistical error was raised with
respect to this suggestion.
2) More Updates; Dan/Don/Gail
-Dan is putting Eun-San Kim's (LBL) DFoFo channel into DPGeant
-Gail is looking at Dan's initial beam and considering measurement
tolerances.
-Don wants to know what the criteria for setting measurement
tolerances of drift chambers (discussed last week) are: are 0.5 MeV/c and
1mr acceptable momentum and angular resolutions?
3) Design Ideas: Kirk McDonald
-Kirk proposes to demonstrate ionization cooling in a prototype
cooling cell with 0.5m Liquid Hydrogen absorber + cryogenics, solenoid +
power supply, TPC detectors, and threshhold Cerenkov counters, for an
initial beam of large emittance, i.e. 10,000 mm-r produced by uranium
diffuser plates of thickness 1-2 radiation lengths. The goal is to
demonstrate 10% transverse cooling of the initial beam, with 1% accuracy.
The question of how to measure longitudinal emittance growth is not
adressed in the proposal.
-Kirk reported that the LASS magnet is available for purchase,
but not on-site use, from LANL.
-Alvin noted that the calculation of beta* is missing a factor of
2. The following numbers in the proposal are ok if the B field is
doubled.
4) Scattering Considerations; Alvin Tollestrop
-Alvin discussed what we need to know about cooling, and how to
measure it.
Heating:
What we need to understand is how multiple scattering and
straggling heat the beam in absorbers, and how to model this, with
emphasis on understanding second moments of the scattering and straggling
distributions, due to the large beam size and small transverse momentum
acceptance in all existing cooling channel designs. The Single
(Rutherford) scattering tail may contribute significantly to particle loss
in cooling channels. Alvin showed that 3-5 out of 1000 particles end up
in this tail after 30cm LH. For perspective, the last published cooling
channel, the DFoFo from LBL, contains something like 40m of absorber.
Straggling has not yet been studied in detail.
Measurement:
Measuring beam heating is more difficult in a solenoid field with
a low energy beam. Beam dynamics are more complicated due to transverse
coupling in solenoidal fields; resulting correlations make precision
measurements of small angles difficult. Without a magnetic field, the
second moment of the multiple scattering distribution is essentially
independent of momentum (it depends on the inverse square of beta),
therefore precision measurements of small angles are easier because they
can be done at energies higher than 200MeV (cooling channel energies).
A constraint on the beam momentum for this measurement comes from the
need to study the contribution of electron-muon scattering to the plural
scattering tail. This process is kinematically limited by the maximum
angle at which an electron can scatter a muon, 5 mr, which sets an upper
limit on the appropriate momentum transfer for studying the electron
contribution.
-A discussion followed on the question of what one needs to test,
simply, to understand optimal configuration (ie. placement of detectors),
beam behavior in, and performance of cooling channels.
Points raised:
1) scattering. Alvin wants to do a precise scattering experiment,
without the complication of the rest of the cooling channel apparatus.
2) engineering tolerances. For this one does need the full monty.
3) beam correlations. How and where to measure them, what is the
appropriate detector technology.
4)long channel. Problems associated with long channels include
misalignment, RF phasing, beam correction and monitoring.
-Steve Geer would like to construct a list of possible problems and
minimal experiments to study these issues. Questions to consider:
-is the basic physics right, and do we need to demonstrate this.
with simulations? with hardware tests?
-what kind of beam do you need to study the basic physics? single
particle or bunched beam?
5) Bunch Experiments; Jim Norem (ANL)
-The concern is that if we propose too modest an experiment, we
won't get funding for anything else (further stages of R&D) for a very
long time. For this reason Jim proposes a high power experiment. The
argument is that to check simulations and test cooling you need the real
beam to adress the question of whether hardware components will work like
the simulations.
What we need:
-momentum analysis, bunching and solenoidal confinement, time
measurements of 1-2 ns, SEM's and/or scintillators for diagnostics, large
i.e. 3x10^12 total protons at 8 GeV.
Proposal:
-3 stages: 1) 1st step, whatever that is
2) cheap setup
3) full test