Addressing Comments, Questions & Concerns From Prior Proposal ReviewsNSF Proposal Submitted In Year 1998, Ref: AST-9900661(1) Panel Comment: On the basis of its potential scientific
importance, the panel ranked this proposal extremely highly. However,
the panel did not feel competent to judge the likelihood that the
research could or would be completed successfully. The reason for
this is that the proposal is mainly about a laboratory MHD experiment
and no one on the panel has any direct experience with such
experiments. The panel therefore recommends that the NSF program
director seek reviews from several researchers with the relevant
experimental expertise. If they conclude that the experiment is
feasible and likely to be completed successfully by the PI and Co-Is,
then the panel believes this proposal would be among the very best it
has reviewed and should be funded by the NSF.
Reply to (1): The PI has spent his earlier career as an
experimentalist, initially in nuclear weapons testing followed by a
large number of liquid sodium MHD experiments establishing MHD for
fusion plasma confinement. The observation of the tearing in a liquid
sodium fountain led to elucidation of the "tearing mode". Later, many
fusion plasma experiments demonstrated the lack of confinement of
tearing unstable pinches. (This plasma physics of "flux conversion" is
now central to the question of radio lobe evolution. ) However, at
the time there were "pleas" by many theorists to construct and test a
liquid sodium dynamo (particularly Johnny Wheeler). The minimum size
required appeared to be many 10's of meters requiring many thousands
of kW of power. Even for LLNL this was too much. However, in the late
80's with Greg Willette, we recognized the importance of the
rotationally coherent nature of axially displaced plumes in a rotating
frame. This source of coherent helicity has made this experiment
feasible.
Reply to (2): The experimental tradition at NMIMT is
extensive, especially in observational and experimental atmospheric
physics. Please see the NMIMT web site at http://www.nmt.edu/. If it could
have been funded at LANL, it would have cost more than 10 times as
much and take many times longer.
Reply to (3): There is an extensive engineering analysis in
the year 2000 proposal in response to this question. The Couette flow
is only very weakly turbulent, which is why it is chosen. The
pressure curves are now part of this proposal relative to the MRI
investigations, but were known initially for the original design. The
present apparatus is twice the dimension of the size considered in
this first proposal and was chosen on the basis of ease of
construction, lower technology, lower pressures for a given magnetic
Reynolds number.
Reply to (4): The size of the experiment has been doubled
for ease of construction, reduced stresses and technology. NSF Proposal Submitted In Year 1999, Ref: AST-0071070(1) Panel Comment: The external expert referees raise
critical questions about its (the experiment's) safety and engineering
feasibility. We wonder whether this experiment can be realized
without a greatly increased investment in funds, technology and
engineering. Funds might be spent in engineering rather than a Co-I
and graduate student who are not hardware experts.
Reply to (1): The experiment has been designed by physicists
in conjunction with engineering advice. The physics considerations
have been paramount. The original proposal was funded at 100k.
Roughly the same has been spent in addition since then. The apparatus
to test Phase I, the Ω-flow, is nearing completion as shown in
Figs. 1 and 2.
Reply to (2): As discussed in the proposal there are three
sodium dynamo experiments in this country, and two successful ones in
Riga, Latvia and in Karlsruhe, Germany. The later experiments are
up to 10 times the proposed experiment size.
Reply to (3): An extensive safety report is posted on our project web site; please see http://physics.nmt.edu/~dynamo/. A panel member of the 2001 proposal reviewed this with a positive comment; see first reviewer's summary statement, AST-0098474.
Reply to (4): This is discussed in the safety section of our
project's web site: Safety Practices, Procedures and Compliance.
Please see http://physics.nmt.edu/~dynamo/.
Reply to (5): Neither of the two magnetic probe arrays
require emptying and recharging the vessel for service. There are two
magnetic probe arrays associated with the experiment: a 2-D matrix
array and a radially-aligned linear array. The matrix array
is mounted on the external surface of the driven end-wall of the
apparatus, and thus it is directly serviceable. The radially-aligned
linear array is inserted into, and removed from, a radial probe
housing that is itself sealed into the outer cylinder. The radial
probe housing is a hollow aerodynamic "vane", and remains in place
whether the sodium is liquefied or solid. Thus the linear array is
serviceable as required, independent of the sodium.
Reply to (6): The thermal time constant of the sodium when
solid is about 5 minutes. When liquid, the convection time is much
shorter. In addition the external shield can be electrically heated
if necessary.
Reply to (7): 140 kg of liquid sodium sprayed into the
atmosphere at operating pressure and velocity will make a fine
particle cloud that may or may not be able to be ignited at a
temperature of ~110 C. If it burns, it will be about the same as
the equivalent mass of gasoline or jet fuel. This is why the
experiment is performed unconfined outside, not in a building. The
experiment is to be remotely operated.
Reply to (8): The titanium piston itself is guided on its outer surface via the bore of the inner reservoir plenum cylinder and internally by a linear bearing and high-temperature hydraulic seal sliding on the volume-compensating shaft. There is no seal on the piston's outer surface, but the by-pass flow should be negligibly small (clearance area / piston area). The volume-compensating shaft allows for the internal volume of the apparatus to remain constant while the piston extends and retracts in the source and sink reservoirs. The piston rod (hydraulic shaft), titanium also, is guided through linear bearings and high-temperature hydraulic seals. The hydraulic seals are capable of restraining pressures in excess of 3000 psi (~3x actuation and operating pressures) and withstanding temperatures of 150 C.
Reply to (9): These facets are all discussed in the safety
section of our project's web site: Safety Practices, Procedures and
Compliance. Please see physics.nmt.edu/~dynamo/
Reply to (10): The size of the apparatus has been doubled
and the vessel material has become aluminum alloy. The maximum stress
currently expected is 10 ksi compared to a limiting strength of
40 ksi. The vessel will be tested hydrostatically and the apparatus
will have integrity verification measurements performed with mineral
oil under rotational operating conditions.
Reply to (11): See above for discussion of oil immersion of
all seals and bearings; Sec. 1.2, Reply to (8), paragraph 2.
Reply to (12): Experimental runs or tests at or near high speed will be of the order of a few minutes duration. The total time at the near maximum speed will be no more than a few minutes also. The change of temperature during a test will be small, a few degrees at maximum speed (~1 degree per minute at 40kW). The oil circulation can be used as cooling if necessary, but we expect windage heat loss to be larger than internal friction heat gain and therefore have provided the opportunity for heating in the surrounding safety shield. We may require greater power and the current motor can be used to double capacity for the short periods of the experiment.
Reply to (13): Due to the doubling of the apparatus size,
the the outer cylinder assembly, low-speed drive and printed circuit
board (PCB) mount rotate at 30 Hz. The acceleration at the periphery
of the ~30 cm radius apparatus is ~1000 g. The electronics
undergoing this acceleration are the analog devices consisting of Hall
effect detectors, pressure transducers and temperature sensors. The
specific examples of each that have been chosen and purchased can
readily withstand 1000 g in a sustained thermal environment of 150 C.
They are in essence ``off-the-shelf'' items, thus Mil. spec. techniques
were not required. Power and signal communication with these analog
electronics takes place via twisted pairs from the PCB. The PCB
houses the balance of the analog electronics and all the digital
electronics. These consist of amplifiers, multiplexers, A-to-D
converters, and a programmable logic device (PLD). The PCB is
~15 cm in radius, thus the acceleration at its periphery is
~500 g. All components, or component sockets are wave soldered
to the PCB. Being individually low mass, they can readily withstand
500 g. Wiring traces on the PCB are configured such that induced
currents from the magnetic field coils are minimized or nullified.
Power for the electronics are brought on board via conventional carbon
brush slip rings. Bidirectional digital communication with the
electronics takes place via capacitative (air gap) slip rings. The
PCB mounting flange thermally isolates it from the bulk of the
convective and radiative heat such that it should have a saturation
temperature of less than 55 C. The standoff vanes to which the PCB is
physically mounted are configured to pump air behind it when the
apparatus is rotating, and thus force cool it also. When static
heating is taking place, such when charging/emptying of sodium, a fan
and duct will be used to cool the electronics. (The pressure and
temperature electronics will be used to monitor the apparatus during
charging and emptying.) NSF Proposal Submitted In Year 2000, Ref: AST-0098474(1) Panel Comment: The experimental details and the specific
way in which the experiment works were not made optimally clear in the
proposal. For example the schematic diagram was not accompanied by a
step by step outline of how the experiments are performed.
Reply to (1): Additional information is on our web site and
added to this proposal. Please see physics.nmt.edu/~dynamo/
Reply to (2): Howard Beckley is desiring to stay on the
project through its completion. It is intended that he will receive
his Ph.D. at the completion of Phase I, the Ω-Phase of the
experiment. He hopes to continue working on the project as a postdoc
and guide the efforts of other graduate students pursuing their
advanced degrees. He has been responsible for the day-to-day research
guidance of the physics and electrical engineering undergraduate
student's efforts on the dynamo project's instrumentation development
and looks forward to continuing this aspect. All of the requested
funding for this proposal is for Beckley's postdoc salary.
Reply to (3): We will continue to present the experiment at meetings. A paper has been accepted. We are posting more details on our web site. We welcome visitors. The PI obtained his degree in experimental physics with Bob Wilson of Cornell. As an experimentalist he was responsible for the fast diagnostics (neutrons and gammas) for the major thermonuclear weapons tests of LANL and LLNL during the Castle series of 1954, including the 12 megaton equivalent Bravo test. He published more than 50 SRD and open literature reports of plasma physics experiments of the "fusion pinch" program at LLNL. He published more than 40 reports and publications of atmospheric, geophysics, and automated astronomy experiments, 1964 through 1975, while at NMIMT. He continued with a major experimental program at LANL in high explosives and plasma physics.
Reply to (4): We are asking for a more modest 80k per year
for this proposal, primarily to support Howard Beckley as a postdoc.
This level of funding would allow us to complete both phases, I & II,
of the experiment in three years, or just Phase I of the experiment if
funding is for only one year. We expect to have roughly equal funding
available from other funding sources, including DOE Fusion, LANL and a
Frontier Center proposal, and in addition, separate support of the
graduate and undergraduate students.
Reply to (5): The magneto rotational instability (MRI) was
mentioned in a foot note as an obvious first experiment during the
Phase I experiment in the year 1999 and year 2000 proposals. This was
not emphasized because we had not performed the stability analysis in
the presence of the Eckman layer induced turbulence. This analysis is
now a part of this proposal. There were just too few of us spread too
thin. The Rossby vortex mechanism of torque transmission in a
Keplerian disk has the possibility of torque transmission in an
insulating disk and therefore before magnetic fields are generated.
This is not a problem in stellar size disks around compact objects
because the companion star can always supply the flux to the Roche
lobe overflow. The scientific question is whether the MRI can act as
a dynamo and create its own flux. We hope to address this question in
the Phase I & II experiments.
Reply to (6): So far there is no known accepted way to
produce turbulence in a Keplerian disk except the MRI. There are very
many papers that assume it, but none that prove it without the MRI.
This is why the MRI is considered so important. This requires flux
and conductivity. The Rossby vortex mechanism circumvents this
difficulty. (astro-ph/0012479)
Reply to (7): The "turbulence " induced by the Eckman layer
flow stress will indeed be an ensemble of "Taylor columns" . However
the magnetic Reynolds number of these eddies, Rmag / (Rey1/2),
presumably following the law of the walls, or logarithmic profile
distribution, is too low to be significantly affected by the
turbulence.
Reply to (8): Now a major thrust of this proposal.
Reply to (9): We apologize for implying that the α-Ω dynamo might
occur in the accretion disk around compact objects. This may or may
not occur depending upon the effectiveness of the MRI or Rossby vortex
mechanism. To apply the α-Ω dynamo to stars requires a deeper
understanding of convective plumes at the base of the convective zone
than is presently available. One might expect that the diffusive heat
flow, radiation transport transition to convection would truncate the
smaller scales leaving only the large scale convective elements, of
order H to carry the heat. At this scale such plumes would make
effective helicity-generating plumes for the α-Ω dynamo in nearly all
rotating stars.
Reply to (10): We agree that other profiles are of interest.
The profile with maximum stable shear has the best possibility of
making a dynamo with positive gain as demonstrated by the
calculations. Lower shear will create a lower toroidal field (lower
magnetic Reynolds number) and hence less gain for a given helicity.
We will find out in Phase I of the experiment. One simply disconnects
the high-speed drive clutch and monitors the magnetic effects as the
Couette flow profile decays to the solid body profile.
Reply to (11): Separately we have been demonstrating
theoretically and by observations (astro-ph/0106281) that the giant
radio lobes are an indication that the major free energy of BH
formation must be accessed to satisfy the minimum energy requirements,
1061 erg. In addition this must be a coherent, large-scale
production mechanism of magnetic flux. This magnetic energy is 107
greater than the galactic magnetic energy, and 103 greater than the
galactic binding energy. The flux is 104 greater than the galactic
magnetic flux. Only an α-Ω dynamo in the BH accretion
disk has the possibility of accessing this amount of energy and
creating this flux. The helicity generation must then be
non-axisymmetric and episodic by Cowling's theorem.
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