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					                                           NLC Magnet Systems
                                            2003 Configuration
Author: John Cornuelle
Date: March 3, 2003
Revision: 0

Requirements
        Magnet systems are utilized throughout the NLC beamlines to bend and focus the electron and positron
beams. The specific magnet requirements in each area of the machine are provided by computer codes that take
the beam requirements from the high level accelerator parameters and convert them to a parameter set that is
common to magnets (lengths, bore diameters, and integrated fields). (Systems Engineering frame of reference:
There is no direct mapping (requirements flow-down) between accelerator requirements and the magnets selected
for the machine.) Other design codes convert these parameters to the actual mechanical designs of the magnets.
The power usage of an electromagnet sets the requirements for its power supply. Many alternate designs are
feasible, and the best cost/performance tradeoff is chosen.
        The magnetic field of non-pulsed magnets must be stable over a period of a half-hour. Long-term stability
of the field for both permanent and electromagnets is required. The final alignment of the beam through the
magnets (produced by using the magnet mover to adjust the magnetic center and BPM location relative to the
beam) is produced through a process called beam-based alignment. This alignment process restricts the movement
of the magnetic center of each main linac magnet to less than one micron when the magnetic strength is reduced by
20% from its operating value. In addition, the magnetic center of each magnet must remain stable with respect to
time.
        The magnet systems will have a reliability requirement that is a flow-down from the global NLC reliability
requirement. The NLC global reliability requirement will be allocated out to each machine system in a systematic
manner that includes the relative cost of equipment overhead (redundancy) for that system. This has yet to be done
for the NLC 2003 machine.
        All magnets must be suitably resistant to the radiation produced at their location. The most intense
radiation environment is due to stray particles in the Damping Rings where the average radiation level two inches
from the beam-pipe is 2 Mega-Rads per hour, and the peak level at isolated locations can be as high as 60 Mega-
Rads per hour.

Area Specific Requirements:
    Injector Systems, excluding the Damping Rings, have no special electromagnet/permanent magnet
      requirements. All magnets in the Damping Rings must be capable of tolerating the high radiation
      environment caused by the bends and the wiggler. In general, electromagnets and ferrite permanent
      magnets are relatively immune to radiation. Radiation would activate samarium cobalt permanent magnets
      and weaken neodymium permanent magnets.
    Main Linac diagnostic regions and matching sections into the bypass lines are required to be
      electromagnets. All other magnets are required to be adjustable by 20% to allow for beam-based
      alignment.
    Beam Delivery magnets are required to be all electromagnets to allow for center of mass energy flexibility.
    There are no magnet systems in Conventional Facilities.




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Technical Description:

1. Layouts/Optics Decks
     Magnet optics deck and layout information are available on the NLC website. The Accelerator Physics
       section contains pointers to the optics decks for every beamline in each area of the machine. Accelerator
       Physics also parses this data into Excel sheets called parts lists that provide basic magnet parameters: bore
       diameter, strength, effective length, and the magnet position along the beamline. These parts lists are
       reached in the same way. At the present time detailed layout drawings have not been made because the
       beamline devices have not been designed yet. Although some magnets have been conceptually designed in
       order to understand the features, components, and costs that make up certain styles of magnets.
2. Technical issues
     The main technical issues are beam-based alignment (BBA) using permanent or electromagnets (with
       electromagnets appearing to be much more tractable for BBA), the radiation stability and activation of
       permanent magnets, and the generation of more accurate cost trade-off information between permanent and
       electromagnets. These issues are interconnected with the design assumptions used, making the overall
       permanent or electro evaluation process complex.

3. Magnet Design Features:

Electromagnets will be an enhanced SLAC typical design:
        Solid low-carbon steel cores
        Hollow copper conductors, vacuum-potted coils
        Quadrupole magnetic center stability satisfies beam-based alignment requirement
        Design for low cost and for high reliability (decision on redundant power supplies or other approach by
         Snowmass)
        Power supplies on strings wherever feasible

Permanent magnets will be a similar to FNAL recycler design with steel poles and integrated field strength
adjustability obtained by rotating or sliding segments:
        Solid low-carbon steel cores
        NdFeB, SmCo5/Sm2Co17, or SrFe12O19 permanent magnet material in block form
        Rotating NdFeB elements for buck/boost adjustability. (BBA requirement not yet satisfied.)

4. By Type:
       Permanent – Electromagnet Split: Feb. 2001 Summary (counts will change as feasibilities are scrutinized)
Magnet Type           Permanent               Electromagnet          Total
Dipoles                 336                    522                     858
Quadrupoles           2610                     799                   3409
Sextupoles              270                     82                     352
Total                 3216                    1403                   4619

These magnets are not candidates for permanent magnets:
Magnet type                    Quantity                            Comments
Correctors                      838                                All air-cooled/solid wire
Pulsed magnets                    56
Solenoids                         69
Others                            61                               Wigglers, Septa, Spin
                                                                   Rotators

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5. Changes from Prior Configurations
       Adjustable permanent magnets are replacing electromagnets in ~57% of the machine. (This percentage
         is currently fluid as lattices change; designs are judged for feasibility.)
       Electromagnets have been strung wherever feasible (stringing was limited to some bend magnets in
         May, 1999)
       Power supply volt-amps have been reduced to the minimum required (small number of standard sizes,
         often oversized, used for May, 1999)
       Controlling electronics are in Tunnel Electronics Enclosures (TEE's).
      NLC 2001 and 2003 lattice changes, especially in Beam Delivery, have yet to be included.

6. Notes:
       Which magnets can be permanent or electromagnetic is based on simple technical criteria incorporating
          experience with permanent magnets and the desire to keep their physical size “reasonable”. The major
          work remaining is to demonstrate an acceptable adjustable permanent magnet for the Main Linac, and to
          evaluate the impact of radiation on permanent magnet materials. Restrictions on the types of permanent
          magnetic material (primarily due to radiation) may revert some magnets back to being electromagnets.
       Trims are not included in these figures.
       Trims will disappear if an electromagnet with a trim is changed to a permanent magnet.
       Total magnet count: 5,653 of 123 styles (using June, 2000 lattices/lines)
       Total power supply count: TBD
       Total cable lengths: TBD

Discussion of Configuration Choices
       The magnet styles are highly constrained by the requirements listed in the optics decks. Ongoing
negotiations between area accelerator physicists and magnet engineers aim to reduce the number of styles of
magnets needed. The main configuration choice at the present time is electromagnets versus permanent magnets.
Permanent magnets may have a lower acquisition cost, are less expensive to install and operate, and should be
much more reliable (no water and power connections, no large power supplies). On the other hand, permanent
magnets are not as radiation-resistant, not as adjustable, and may have difficulty meeting the beam-based
alignment requirement in the main linac.
       Another configuration issue, for electromagnets, is how to ensure the reliability of the magnet plus power
supply system. The power supply was identified as the least reliable part of a magnet system, we need to decide
how to improve the power supply reliability, by providing redundant power supplies for example, and if so, how
many and connected how.




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