A%20selection%20of%20slides%20for%20Jim%20Volk%20to%20consider%20for%20his%20talk%20to%20MAC%20(May%2002),%20covering%20recent%20work%20at%20SLAC%20and%20LBNL.%20People%20to%20be%20credited:%20Jose%20Alonso,%20Jin-Young%20Jung,%20Seung%20Rhee,%20Cherrill%20Spencer,%20Jim%20Spencer,%20SLAC%20Magnetic%20Measurements%20Group.

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A selection of slides for Jim Volk to consider
for his talk to MAC (May 02), covering recent
work at SLAC and LBNL.People to be credited
Jose Alonso, Jin-Young Jung, Seung Rhee,
Cherrill Spencer, Jim Spencer, SLAC Magnetic
Measurements Group.
NLC - The Next Linear Collider Project

• From Cherrill Spencer

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Recent Work at SLAC on measuring radiation fields
how they effect pm materials.

• In order to establish if pm magnets can be used
  in the NLC we must first predict how much
  radiation of what types will be produced in
  various NLC beamlines in the vicinity of the
  magnets. Only when these predictions are
  believeable can we proceed to testing candidate
  pm materials with appropriate types and levels of
  radiation.
• We have looked at old measurements of radiation
  levels in the SLC linac and damping rings and
  tried to relate this data to supposed lost beam
  power. Could not make the so-called data from the
  2 beamlines match in terms of rads produced per
  watt of beam lost.
• Further analysis of data showed them to to be
  generated from a few measurements with many
  artificial assumptions and calculations
  sufficient to lead to large enough errors in the
  data to be of little use to extrapolating to NLC
  conditions.
• Furthermore the radiation measurements were made
  with detectors that did not distinguish between
  gammas, electrons, neutrons and protons.

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Why it is important that we can accurately
predict how much radiation will occur in NLC

• We know that permanent magnet materials will lose
  some of their magnetization if exposed to
  some radiation types at some level we need
  to quantify all these somes in order to make
  the technology decision for the NLC magnets
  electromagnets or permanent magnets (pms).
• The result of this decision may be different in
  different areas of the NLC because the expected
  radiation levels vary by orders of magnitude from
  beamline to beamline and within beamlines,
  according to our current (but faulty) data.
  Plus, the types of radiation produced vary within
  beamlines.
• Accurately predicting radiation levels and types
  is only half the story published data on the
  effect of various types of radiation on various
  types of pms show sufficient variation in loss of
  magnetization for apparent similar radiation
  conditions that we are not confident in the
  applicability of many of the published
  experiments to the ( roughly predicted) NLC
  conditions.
• Virtually all materials that will be used in the
  NLC tunnels will be affected by radiation at some
  level- important that we can accurately estimate
  it.

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What we do know about radiation effects on some
up to date pm materials.

• Different radiation types have vastly different
  effects- summarizing data from best papers
• To cause a given effect, (e.g. 20 loss of Br
  for certain type of NdFeB) requires
• Ö 1 kGray protons (200 MeV Ito et al)
• Ö 10 kGray neutrons (fast Cost, Brown)
• Ö 5 MGray electrons (17 MeV Okuda et al)
• gtgt 10 MGray photons (60 Co several authors)
•   1 Gray 100 rads
• So simple measurement of DOSE is INADEQUATE to
  assess likely radiation-induced effects. But that
  is all we have for radiation in our best role
  model for the NLC the SLAC Linear Collider
  (SLC).

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More of what we do know about radiation effects
on pm materials.

• Different magnetic materials have very different
  responses to radiation 
• Measurements show SmCo to be significantly more
  resistant than NdFeB in exposures to several
  different radiation types
• - Factors of 103 are typical (similar effects
  for 103 times more dose on SmCo)
• BUT (compared to NdFeB)
• SmCo is significantly more expensive (Ö x 10)
• SmCo has long-lived activation products (worst
  offender 71-day 58 Co)
•  
• Measurements in NdFeB show significant
  variations depending on
• Metalurgical properties Higher coercivity can
  have Ö x 10 effect
• Macroscopic environment Optimizing
  permeance can have Ö x 10 effect
• - Brick geometry (Thick blocks better than
  thin disks) 
• Remagnetization restores full Br, even if
  material suffers gt80 radiation-induced
  demagnetization

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Radiation-Induced Demagnetization(Japanese
experience with 200 MeV protons)

• Material Type has large impact
• Red N48 High Br (1.4T) Low Hc (1.15 MA/m)
• Blue N32Z Lower Br (1.14 T) Higher Hc (2.5
  MA/m)
• High coercivity material almost 30 times more
  resistant
• Material Shape has large impact
• (All samples are discs 10 mm dia)
• Circle thickness 2 mm (Pc 0.5)
• Triangle thickness 4 mm (Pc 1.0)
• Square thickness 7 mm (Pc 2.0)
• - Higher Permeance coefficient
• increases resistance (x 10)
• SmCo is much more resistant than NdFeB

Would not put a Neo magnet anywhere close to 200
MeV protons, but will the electrons escaping from
any NLC beampipe produce any 200 MeV protons
? This is the kind of detail we need to establish
in order to choose between electromagnets and
permanent magnets.
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At SLAC/LNBL we have started a 3 pronged
approach to answer the questions about radiation
levels and their effects on permanent magnet
bricks

• I. Field characterization Careful systematic
  measurements with appropriate detectors 
• A. Identify dosimeters capable of
  differentiating radiation types 
• Currently testing dual silicon-based devices
  MOSFET (ionizing-radiation (x-ray) sensitive) and
  Pin Diode (displacement-damage (neutron)
  sensitive)
• - Promising first results in SLC DR where we
  have had 3 dosimeters taking data for last 6
  months , but
• - Encountering calibration and normalization
  difficulties and the DR is a mixed source and
  levels vary dramatically from place to place 
• - Using a Californium source to calibrate
  dosimeters and irradiate samples
• Continue searching for other dosimeters
  (talking to experts at LBNL for e.g.)
• - Inexpensive, for simultaneous measurements
  at many sites around DR
• - Capable of differentiating different
  radiation-types
• - Good lifetimes in very high fields

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Second prong of SLAC/LBNL effort to understand
radiation effects on permanent magnets II A
Subject pm samples to known radiation sources.

• Have subjected Sm Co5 and NdFeB bricks from
  Vacuumschmelze to successive irradiations with a
  pure, well-calibrated Co 60 ? source, in between
  have measured their magnetization in 3 axes in a
  SLAC Helmholtz coil set-up no deterioration
  after 277 KGray.
• Placed same 2 bricks, attached to a piece of
  steel, in the SLC DR near the extraction Y where
  we understood the radiation levels would be
  high, left them for 70 days, then took them out
  and remeasured them no deterioration, but have
  not yet characterized the radiation.
• Then placed same 2 bricks within a few inches of
  a Californium source emitting just 2.2MeV
  neutrons also measuring radiation with the Pin
  Diode detector. Will take them out after 1
  month has passed.
• Will continue to expose bricks to radiation in
  pure sources and in the SLC DR, and to try to
  understand the calibration of the new detectors.

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More on second prong of SLAC effort to understand
radiation effects on pms

• II continued
• B. Develop techniques for measuring very small
  changes in magnetization 
• Available sources of pure radiation not
  strong enough to simulate many years exposure,
  will most likely have to extrapolate from very
  small effects 
• C Network with research community engaged in
  this field 
• Jyvaskyla Finland (alphas, protons)
• Wakasa-Bay Japan (protons) ( first visit
  already made)
• Osaka University (electrons) (first visit
  already made)
• Oak Ridge (neutrons)
• MSU (neutrons, gammas, deuterons) 
• D Develop understanding of mechanism for
  radiation-induced demagnetization
•   Select most radiation-resistant material
• Develop magnet designs with greatest potential
  for demagnetization resistance

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Third prong in SLAC/LBNL effort to understand
radiation effects in the NLC

• III Model with a well-used computer modelling
  program, FLUKA, the shower of particles and gamma
  rays initiated by a single electron of known
  energy leaving a bunch at a known angle and
  passing through a specified vacuum pipe ( in the
  first case conforming to an already designed
  copper vacuum pipe in the wiggler of the main
  DR), through a specified length of air and then
  passing through representative pieces of magnet
  material steel and Neo. Validate program by
  modelling an exisiting beampipe in SLACs damping
  rings and comparing to new measurements.
• Using predictions of NLC beam loss percentages,
  extrapolate above FLUKA results to predict
  radiation levels and types in various NLC
  beamlines.
• Judge if commercial pm materials will withstand
  the predicted NLC radiation types at predicted
  levels.

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New data on the electromagnetic quad with
improved magnetic measuring set-up.
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Developing Methodologies to Estimate Overall
Magnet Costs- including repair costs
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Magnet Failures at SLAC Jan. 97 Dec. 2001
SLAC Downtime (Avg)
30
25
20
Downtime (hr)
15
10
5
0
Small
Medium
Large
Magnet Size
SLAC Downtime
200
180
160
140
120
Hours
100
80
60
40
20
0
Small
Medium
Large
Magnet Size
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SLAC Downtime by Failure
180
40
35
30
25
Downtime (hr)
20
15
10
5
0
Insulation
Water Leak
Water
Human Error
Connector
Other
Blockage
Failure Type
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Water Cooled Magnets (Med Large) Failures
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LBNL SLAC work on designing magnets (pms and
ems) for the damping rings.

• RECALL Main Damping Ring lattices have been
  published with detailed requirements on all
  magnets, including field quality and distances
  between adjacent magnets.
• Prior to last MAC meeting we designed permanent
  magnet versions of DR quadrupoles and transport
  line dipoles using 2-D PANDIRA code. The NdFeB
  (Neo) style magnets were of reasonable size so
  since that meeting we have investigated the Neo
  quads, with rotating rods to generate the /-10
  adjustability, in more detail to see if they
  could meet all the requirements.
• LBNL employee Jin-Young Jung learnt how to model
  magnets in 3-D using the well-known TOSCA code so
  we could estimate the loss of integrated field
  strength through any end effects of these magnets.

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PANDIRA 2-D model prediction of the torque needed
to turn one tuning rod in a DR quad.
Very high torques were predicted, 200 lb-in.
Modelling process was validated by modelling the
main linac wedge quad prototype and comparing
predicted torques with measured ones good
agreement. These much higher torques needed in
the larger aperture DR quads, plus the concern
about radiation damage to the pm material led us
to, temporarily, abandon the pm magnets for the
DR and revert to designing electromagnets.
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NLC DR quad as an electromagnetTOSCA model
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NLC DR Gradient Dipole POISSON design
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NLC DR Gradient Dipole TOSCA design. Studying
end effects and fringe fields.
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Latest data on the wedge-style pm quadrupole from
the SLAC rotating coil measurement set-up
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Photo of the wedge01-6 on the SLAC measuring
set-up.
Wedge magnet, secured to V block
Rotating coil read-out
Cooling fan for readout stand
Aluminium V block, secured to granite table
Tuning rods rotation mechanism. One rod only
connected. Smaller gear wheel turned with wrench.
Heidenhain 0.5µm indicator
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