Comments on the Review of Neutrino Beam Monitoring

**December 10, 2001**

[Introduction, Summary & Future]{.underline}

[Presenter: S. Kopp]{.underline}

1.  ([Reviewer: B. Bernstein]{.underline}) The environmental variables
    are not well controlled. Measurements need to be made as close as
    possible to the devices, not something 20 feet down the corridor.
    The temperature at the monitor and in the alcoves will vary and
    perhaps I missed it but I believe no data were shown about the
    variation, although the standard equations were trotted out. A
    measurement would be helpful. These will be important particularly
    during start-ups. It is more than likely that these are the times
    when the temperature of the enclosures will vary.

2.  ([Reviewer: A. Marchionni]{.underline}) It was stated that a beam
    position measurement accuracy of 3 cm is needed, but no specific
    design was presented. In particular it was not discussed how well we
    need to know the intercalibration of the different pads to perform
    the measurement.

3.  ([Reviewer: A. Marchionni]{.underline}) In the engineering of the
    muon monitors particular attention should be paid to the humidity
    conditions in the alcoves and to the cabling of the pads, in order
    to avoid the collection of additional ionization outside of the pad
    itself. Some more experimental tests will probably be needed here
    before proceeding to construction.

4.  ([Reviewer: S. Wojcicki]{.underline}) I believe we should do the R&D
    on neutron irradiation up to the levels anticipated.

[Physics Specifications]{.underline}

[Presenter: D. Harris]{.underline}

On the muon system:

1.  ([Reviewer: B. Bernstein]{.underline}) The ties between performance
    and physics goals of the muon system have been well understood.
    Using the different alcoves to test different parts of the flux is a
    good idea and although it is not the final word in accuracy it
    serves a useful purpose for the cost and effort involved.

2.  ([Reviewer: B. Bernstein]{.underline}) The PIC's ought to be able to
    handle the fluxes involved and the group has a convincing plateau
    curve and linearity analysis. Nice work!

3.  ([Reviewer: B. Bernstein]{.underline}) DAH promised to simulate
    damage to the front end of the target. I have personally seen damage
    to the front end of the E616/701 dichromatic target and have a
    picture of it in my desk. I think that is worth doing.

4.  ([Reviewer: B. Bernstein]{.underline}) Although significant progress
    has been made, the physics goals are not as sharply defined as I
    would like. The use of the hadron monitoring to establish initial
    beam position is well thought out but after that I don't see a
    convincing argument.

5.  ([Reviewer: B. Bernstein]{.underline}) The group presents a
    contradictory position on the hadron system. On the one hand the
    device is supposed to be worth building, but on the other it says
    that if something breaks it will not be fixed. Either it is worth
    having or not: if it is then some plan for repair or replacement has
    to be worked out both for the pads and for the readout.

6.  ([Reviewer: J. Hylen]{.underline}) I would like to see the hadron
    monitors be replaceable. I suggest the cost-effective way to do that
    is to have a few small-profile rows sitting in trays or racks, where
    a single row could separately be extracted out the side into a small
    coffin.

7.  ([Reviewer: J. Hylen]{.underline}) As discussed in the general
    comments, a propagation of specification of position accuracy to
    chamber response calibration should be incorporated in the hadron
    monitor specification document. I think this is needed before the
    calibration requirement can be understood for the hadron monitor.

8.  ([Reviewer: A. Marchionni]{.underline}) At this point it is also
    important to quickly finalize the disposition of the PIC muon array,
    which has implications on the engineering of the system. Do we need
    chambers extending outside of the radius of the decay pipe ? It is
    not yet clear to me the role of alcove 1 and 2: the simulation
    results presented at the review showed some discrepancy between the
    fast PBEAM muons and the full GNUMI results for alcove 1.

9.  ([Reviewer: A. Marchionni]{.underline}) The requirement to detect
    overall muon flux changes at the 1% level is useless if the proton
    intensity monitors do not have comparable precision. Anyhow in the
    muon system this comes from free because we are required to detect
    asymmetries at the few percent level. From the physics point of
    view, i.e. to monitor target integrity, how well do we really need
    to monitor the total muon flux ? My feeling is that we need to do a
    little better than what the proton toroids have been specified for.

10. ([Reviewer: S. Wojcicki]{.underline}) I see that the neutron rate in
    DHM is an order of magnitude higher than charged particle rate and
    it appears to come from the absorber. I would suggest investigating
    moving the DHM few meters back (ie shortening decay pipe) and
    putting in neutron absorber (concrete?) with a reentrant hole for
    the beam in it. Just moving it back few meters might gain you some
    factor from the solid angle.

# Chamber Design

[Presenter: D. Naples]{.underline}

1.  ([Reviewer: V. Paolone]{.underline}) The PIC technology will be
    required to work in two different intensity regions: Muon alcoves
    and just downstream of decay pipe. In the muon alcoves information
    was presented to demostrate that the PIC technology is adequate. The
    response of the PIC\'s in the intensity region expected for the muon
    alcoves is linear and well below saturation. While no experimental
    results were directly presented as to the radiation hardness of the
    PIC\'s, a literature search gave no reason to expect that they would
    not survive 10 years in the muon alcoves. In addition the
    calibration scenario presented should allow the tracking of beam
    changes to the few per cent level. The muon monitors using the PIC
    technology should proceed to the engineering design phase. Use of
    the PIC technology for a downstream hadron monitor is a little more
    complicated. The saturation effects I feel are not a problem since
    they can be understood and corrected for. The real issue is the
    radiation hardness of these devices. From the literature search
    discussed above it is not clear they would survive a year in such an
    environment (but nothing was presented that said they wouldn\'t). I
    think some more studies and/or additional literature searches that
    demostrate that the PIC devices could survive for at least \~1 year
    are needed. We expect a useful operating time of \~10 years so an
    engineering effort would also have to be started to allow \"easy\"
    replacement of the DHM\'s during data taking in case failure. After
    demostrating that the a DHM could survive at least a year, I feel
    the DHM design using the PIC technology should proceed to the
    engineering design phase.

2.  ([Reviewer: S. Wojcicki]{.underline}) If pressure and temperature
    variation is a serious concern on might want to consider outting in
    small chambers in the common gas system which would be specifically
    designed to be sensitive to temperature and pressure variation.

# Electronics & Bench Tests

[Presenter: A. Erwin]{.underline}

1.  ([Reviewer: B. Bernstein]{.underline}) The calibration techniques
    seem adequate. Using a press fit is the right answer for the source
    holder.

2.  ([Reviewer: B. Bernstein]{.underline}) The plateau curve for the
    hadron system is not satisfactory. I was not clear as to whether the
    success of the muon group implies that a plateau exists for the
    hadron group since the fluxes are so different. I was unimpressed by
    the argument that Kopp made that a plateau was unimportant.

3.  ([Reviewer: J. Hylen]{.underline}) The dynamic range issue needs to
    be clarified. The current document shows (1) a factor of 40 eaten up
    by variation between pads, which may not leave enough room for
    variation in running conditions, and (2) pads which would fall below
    Albert\'s specification of 10 pC mininum for low intensity running.
    (I believe all is fixable, just not integrated yet).

4.  ([Reviewer: J. Hylen]{.underline}) As discussed in the general
    comments, a propagation of specification of position accuracy to
    chamber response calibration should be incorporated in the hadron
    monitor specification document. I think this is needed before the
    calibration requirement can be understood for the hadron monitor.

5.  ([Reviewer: A. Marchionni]{.underline}) Americium sources mounted on
    each PIC will provide good tracking with time of the response of the
    single pads. The question of the intercalibration of the different
    PIC chambers is still an open one. From construction tolerances,
    variations of 2% and 10% were presented for 5 mm and 1 mm gap PICs,
    respectively. I think it would be nice to support these numbers with
    experimental data on the measured gains of a few different chambers.
    How does the 2% variation affect the possible measurement (by moving
    the target backwards) of alignment of the neutrino beam performed
    with the muon system ? How does this measurement compare with the
    Near Detector one ? How does this uncertainty affect the measurement
    of beam position with the downstream hadron monitors ? I think that
    an intercalibration of all the different pads is worth pursuing only
    if a cheap and easy solution is found.

[Booster Beam Test]{.underline}

[Presenter: R. Zwaska]{.underline}

1.  ([Reviewer: B. Bernstein]{.underline}) The radiation hardness of the
    hadron system is not adequately defined. The group could not come up
    with a consistent statement of either the level required or the
    level achieved. Numbers varied over an order of magnitude from
    roughly a factor of two to twenty better than required but the
    simulations have effects from delta-rays which are only roughly
    approximated. Deltas and soft fuzz are notoriously difficult to
    simulate and I doubt I would believe anything to a factor of two. I
    am told a test at a reactor facility is possible and I believe this
    should be aggressively pursued.

2.  ([Reviewer: B. Bernstein]{.underline}) The differences between PIC1
    and 2 and the linearity analysis were still in a beginning stage.
    The student seems more than capable of doing the analysis but needs
    more time. He has clearly done some nice work. These analyses need
    to be understood at the same level as the ATF analysis.

3.  ([Reviewer: B. Bernstein]{.underline}) I didn\'t follow the
    discussion about how the response with time coupled into the beam
    structure and the ion drift time. Obviously if there is charge
    buildup this could be a big problem so this must be resolved as
    well.

4.  ([Reviewer: J. Hylen]{.underline}) In the tests done so far, the
    chamber center was in the beam but the readout wires were outside
    the beam spot. In actual operation, the readout wire routing will be
    in the beam, so it would be interesting to see what signal the beam
    might induce on that wire and whether mitigation would be needed.

5.  ([Reviewer: A. Marchionni]{.underline}) The tests on the 1 mm gap
    PICs performed at the Booster show that such detectors can cope with
    the downstream hadron monitors intensity. The main question here is
    the one of radiation resistance and in particular the understanding
    of the damage due to neutrons. So irradiation tests with low energy
    neutrons have high priority. Until this question is answered, we
    cannot decide if we keep detectors in all the time or just for
    commissioning/re-commissioning. In any case a mechanical design
    where the system is replaceable is highly preferable.

6.  ([Reviewer: A. Marchionni]{.underline}) I found different numbers
    for the dose expected for the downstream hadron monitors: 2 10\^11
    rad/year in NuMI-B-0785 and 10\^10 rad/year in the presentations. A
    radiation tolerance of 10\^9 rad was presented, but that was
    probably a lower limit.

7.  ([Reviewer: A. Marchionni]{.underline}) I was glad to see that even
    1 mm gap PIC do not need H_2 to work reliably, but pure He is good
    enough. I think that H_2 should be avoided to minimize the signal
    due to neutrons, which would give large signals due to elastic
    scattering on free protons.

8.  ([Reviewer: A. Marchionni]{.underline}) Operating conditions for the
    PICs were suggested at 500 V for a 5 mm gap (muon monitors) and at
    200 V for a 1 mm gap (hadron monitors), with saturation setting in
    for 7 10\^7 part./cm\^2 and 4 10\^10 part/cm\^2, respectively. The
    saturation points do not scale as V/gap\^2, as would be expected for
    a beam in pulsed mode. This is not surprising because in the Booster
    tests the beam spill length is comparable to the drift time of the
    ions (by the way, I do not understand the claim that the ion
    collection time is much less than a musec), so pushing the
    saturation point to higher values. The digitized pulse shapes
    recorded at the Booster test are very useful in order to build a
    realistic model of saturation in the chambers. The test conditions,
    both at the ATF and the Booster, have been harder than what is
    expected for NuMI, with a spill length of 8 μs, so the obtained
    numbers are conservative.

\[Note: M. Messier and D. Michael are also listed as reviewers, but no
comments are available on the [web
page](http://www.hep.utexas.edu/~kopp/minos/beamon/reviews/dec10/).\]