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Accelerator System for Spallation Neutron Source

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					                                                            CAS – KEK Accelerator School, Indore, Feb, 2004




                                 General Remarks on

                  Accelerator System
             for Spallation Neutron Source


                                 Isao Yamane
        KEK, High Energy Accelerator Research Organization




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004




                                  CONTENTS

     1, Introduction
     2, General Requirements to Proton Driver for Fruitful Neutron Source
          High beam power (High flux of neutron beam) and Upgradeability
          Reliability (Negligible Failure-Time)
          Maintainability (Easy Maintenance in Acceptable Radioactivity)
     3, Injection Energy
     4, Lattice
          Necessary Straight Section
          Symmetry
          Space Charge Effect
     5, Limit of Acceptable Beam Loss
          KEK 12-GeV PS
          LANL-PSR
          ISIS
     6. Reasonable Upgrade Path to More Powerful Source



KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Fe,2004



                                 1, Introduction


- For this school, lectures are selected only for limited subjects that are
especially crucial for a high intensity proton accelerator as a driver of
spallation neutron source and require alive experience of operating an
actual proton accelerator.
- Subjects such as control, vacuum, and so on are also very important
for accelerator and we will have another chance.
- All lecturers of this school are leading researchers who have enough
experience on the KEK proton synchrotron and development study of
the JPARC accelerator.
- I hope lectures will be a helpful guidance for the Indian project of
proton accelerator for spallation neutron source driver.




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                                           CAS – KEK Accelerator School, Indore, Feb, 2004



                            High Intensity Proton Ring for Spallation Neutron Source


 Machine             Type          Inj. Energy   Ext. Energy    N total          Rep Rate       Qh/Qv           A. H/V
                                      (MeV)        (MeV)       (×1012)             (Hz)                        (p mradm)


Existing Machine
KEK PSB            RCS                 40           500           2.6               20         2.17/2.30        665/109
              Combined function

   IPNS              RCS               50           500           3                 30                         5×10 cm

   ISIS              RCS               70           800           25                50          3.7/4.2         500/400
   PSR             compressor         800           800           31                20          3.2/2.2       5 cm radius
Under Construction
   SNS         Accumulator Ring      1000           1000         200                60       5.82/4.0 -6.0   310 acceptance

 JPARC               RCS              200           3000          50                25          6.8/5.8        Collimators
  3GeV                                                                                                        312pmmmrad
                                                                                                              Dp/p=±0.5%

Planned
AUSTRON              RCS              130           1000          40                50         4.45/4.28          680


   ESS        Two accumulator        1334           1334       234/ ring            50         3.7/4.24         480/480
                     rings




     KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004



                                               ISIS




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004


                                      LANL- PSR




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                              CAS - KEK Accelerator School, Indore, Feb, 2004



                               JPARC 3 GeV Ring




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS - KEK Accelerator School, Indore, Feb, 2004



                                       SNS Layout




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004




              2, General Requirements for a Proton Driver
                    to be a Fruitful Neutron Source


“Utilization of a Neutron Source is usually based on time-sharing
among a large number of small size experiments”

This is definitely different from the accelerator-utilization form of high energy physics
field that is usually based on time-sharing among only limited number of big
experimental programs.

Thus, an accelerator of neutron source driver is required to operate with stable high
intensity beam and along the tight beam schedule with least down time.

Therefore, key requirements are
“High beam power and Upgradeability”,
“Reliability” and
“Maintainability”.



 KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004



                  High beam power and Upgradeability

-High beam power is a fundamental requirement of all neutron source
drivers.
-But a high intensity proton accelerator has a difficulty of accelerator
activation and it is very risky to choose a very high intensity for proton
beam without adequate experience.
-It is wise to choose a 100kW proton driver as a start point, because a
100kW proton driver is a moderate plan and considered to be surely
successful.
- However, user’s demand for beam intensity will soon grow according
to progress of beam utilization and development of scientific interest.
- It is wise for us to keep in mind to upgrade the machine to meet
demand of soon coming next phase.




 KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004




                      Reliability (Negligible Failure-Time)



  -For a neutron source for cooperative utilization, an important
  index of usefulness is the machine failure time. The shorter the
  failure time, the more useful the machine.

  - Although small machine failures are usually unavoidable,
  failure time can be reduced to less than a few % of operation
  time.




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                         CAS – KEK Accelerator School, Indore, Feb, 2004


                         Maintainability
         (Easily Maintainable in Acceptable Radioactivity)

-For a high intensity proton accelerator, somewhat activation of
accelerator components due to beam loss is unavoidable.
- However, beam loss must be reduced as low as possible, and also must
be limited to an acceptable level.
- Limit of acceptable beam loss is considered to be 500W or lower for
hands-on maintenance, as is talked in the next period of this lecture.
- Radiation exposure during maintenance service is the most serious
problem of machine maintenance.
- In order to suppress radiation exposure, maintenance service must be
as easy as possible and thereby the maintenance time must be reduced
as short as possible. Tunnel with enough space and Overhead
travelling crane are very helpful.
- In some case, a very long time may be necessary before maintenance
service in order to cool down the radiation level around the failed
component.


KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                             CAS - KEK Acclerator School, Indore, Feb, 2004


                                         ISIS SP1




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                         CAS – KEK Accelerator School, Indore, Feb, 2004


                                         ISIS SP0




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                         CAS – KEK Accelerator School, Indore, Feb, 2004



                                    Portable Shield




KEK, High Energy Accelerator Research Organization,Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004



                                        ISIS Crane




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004




                              3, Injection Energy
-Higher injection energy may be more desirable, in order to reduce the
space charge effect and thereby the aperture of the accelerator.
-However, the cost of the injector linac will be raised. In addition,
activation of accelerator may be more serious, because somewhat beam loss
is unavoidable with injection and acceleration start of the beam.
-Activation can be suppressed effectively by choosing the injection energy
at an energy lower than 120MeV, the threshold of multiple neutron
production. From this point of view, 100MeV is a good choice of the
injection energy.
- Once injection energy, extraction energy and beam intensity are decided,
the aperture of the synchrotron is determined through discussion about
lattice and space charge limit.



KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                            CAS – KEK Accelerator School, Indore, Feb, 2004




    Threshold of Neutron Multi-Production




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                         CAS – KEK Accelerator School, Indore, Feb, 2004




                                       4, Lattice



                   - Number of straight sections

                   - Symmetry

                   - Space Charge Effect




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS - KEK Accelerator School, Indore, Feb, 2004




        Number of necessary straight section

        Following 4~5m long Straight Sections are necessary

              -Beam Injection                                          1~3

              -Accelerator RF cavities                                 4~5

              -Beam Extraction                                         2

              -Beam Monitors                                           1



KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                             CAS – KEK Accelerator School, Indore, Feb, 2004


                                       PRIME Ring

                         H- Beam



                                              Injection
                                              Bump Magnets                      Halo Collector


                                   RF (for future upgrade)

                                                                  Extraction
                                                                  Kicker Mag.


                              RF                          Extraction
                                                          Septum Mag.

                                     RF                      RF
FODO Lattice
Circumference 131.64m                           RF
Cell Number      12                                                       Extracted
Straight Section 4.6m                                                     Proton Beam


KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS - KEK Accelerator School, Indore, Feb, 2004



                             Straight Section of SNS Ring




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004




                               Lattice Symmetry


      Low Symmetry (2 ~4 fold symmetry)
      - Long straights are advantageous for injection, extraction
      and halo collection at higher energy.

      High Symmetry
      -Density of Structure Resonance with large stop-band and
      thereby possibility of beam loss are reduced.
      - Our case, where injection and extraction energy are not so
      high, high symmetry lattice can be chosen.




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004


                    Example of Low Symmetry Lattice




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004




                        Space Charge Effect

   Tune Shift due to Space Charge Effect
   -Vertical tune should be better chosen as higher than 0.5.
   -Beam loss possibly occurs because vertical tune shift due to
   space charge effect can be as large as 0.3 and tune crosses
   half integer.
   -Stopband correction system. Beam distribution shaping.

                                                         1 rp nt
   -Laslett’s formula                   D  
                                               2p 2 3 B
   - Computer simulation code-----SPACEX



KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004



                   Space Charge Tune Shift : Example of AGS




   To keep the beam, stopband correction system and beam
   distribution shaping methods have to be implemented!
KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004




              5, Limit of Acceptable Beam Loss


     -It is very crucial to realistically estimate the limit of
     the acceptable beam loss, and to take necessary
     measures in advance while designing the accelerator
     and its tunnel.

     - Here is a review on the situation of the existing three
     proton accelerators (KEK12-GeV PS, LANL-PSR
     and ISIS) concerning the beam loss and residual
     activity.




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                                 CAS – KEK Accelerator School, Indore, Feb, 2004



         Table-1. Beam Loss and Residual Activity of Proton Accelerators

                       KEK-PS                      LANL-PSR*                            ISIS

                         0.5-12GeV                    800MeV                        70-800MeV
   Beam            7×1012ppp(2.2s rep.)                70 mA                          200 mA
                  (fast extraction mode)               56kW                           160kW
                           6.1kW
                   Injection (10-20%)           1 st Turn (0.2-0.3%)                RF Capture
 Beam Loss      Extraction(0.5×1012ppp)       Stored Beam (0.3-0.5%)             (~7%, 70 -100MeV)
                                                    Fast (<0.1%)
                         ~400W                         ~400W                          ~1kW**
                30-40mSv/H, extraction       ~200mSv/H, a few points           ~50mSv/H, SP1(hallo
                            section.        ~20mSv/H, Q-mags in 2/3 of               collector)
  Residual      ~10mSv/H, several points         circumference                    6-7mSv/H, SP2
  Activity                with large                                          ~3mSv/H, SP0(injection)
                     dispersion function
                 (3days after beam stop)     (4.5Hours after beam stop)      (1-2days? after beam stop)

* These data show the situation a few years ago when injection was performed in a two-step H0 manner. At
present, the performance has been remarkably improved by replacing the injection system by H - injection.
** It should be noted that beam loss occurs at energy below the threshold of multiple neutron production
at 120 MeV.




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS - KEK Accelerator School, Indore, Feb, 2004


                            KEK 12 GeV PS-Main Ring




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                         CAS – KEK Accelerator School, Indore, Feb, 2004

                                   KEK-PS Booster




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                            CAS – KEK Accelerator School, Indore, Feb, 2004




                                   KEK 12-GeV PS

- In addition to 12 GeV PS, around 500 MeV Booster Synchrotron, a few points
become 20~30 mSv/H.
-Hands-on maintenance. Yearly exposure of several members of the accelerator
maintenance crew exceeds 2 mSv in an ordinary year.
- Experts of accelerator technology, such as the beam-extraction magnets, the
beam monitors or vacuum technology. Especially for the most active members
of those maintenance groups, the yearly exposure is apt to exceed 5 mSv.
- Therefore, at the end of a fiscal year, the accelerator group often receives
notice from the radiation safety administration office to restrict maintenance
work of such persons in the accelerator tunnel. This restriction usually caused
some hindrance to the smooth maintenance of the accelerator.
The desirable target of the beam loss is about 300 W or less in order to keep the
maintenance service smooth. However, beam loss during routine operation is set
slightly higher so as to respond the severe demands of beam users.



KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                      CAS – KEK Accelerator School, Indore, Feb, 2004


                    Beam Performance of LANL-PSR




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                           CAS – KEK Accelerator School, Indore, Feb, 2004



                                          LANL-PSR

      -Hands-on maintenance

      -The maximum personal yearly exposure was ~4 mSv.
      -The beam intensity was limited to about 70 mA because the so-called PSR instability.
      -It is also considered from experience at the KEK12-GeV PS that the situation with
      such a high residual activity should be one of the reasons to keep the beam at about
      70 mA. In order to suppress the beam loss at 300-500 W in total, the beam intensity
      should be kept at this level.

      -At present, the 1st turn loss has been removed by guiding H0 atoms left in excited
      states to a beam dump.
      -The rate of the protons stored in the ring that hit the foil is remarkably reduced,
      because the size of the H− beam can be made much smaller and the necessary foil
      size also reduced.
      -Additional improvements to raise the threshold of the PSR instability.
      -By these improvements, beam power has been increased to 100 mA80 kW.

      - Thus, the beam loss seems to be one of the main factors that limits the beam
      intensity; also the limit of the acceptable beam loss for the LANL-PSR seems to be
      300-500 W.




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS – KEK Accelerator School, Indore, Feb, 2004


                   Induced Activity Distribution of ISIS




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                          CAS - KEK Accelerator School, Indore, Feb, 2004



                                               ISIS

   -Hands-on maintenance.
   -With respect to the beam loss of ISIS, it is mentioned that beam
   loss is assumed to be limited at almost the present level of ISIS in a
   report describing a plan to upgrade the ISIS to 1 MW.
   -Also, the limit of the acceptable beam loss is defined as 500 W per
   ring for ESS (European Spallation Neutron Source using a 5 MW
   proton beam).
   -Because the activation of the accelerator is far more increased at a
   proton energy above the threshold of multiple neutron production
   (~120 MeV), the degree of activation due to the beam loss at ESS is
   expected to be much higher than that of ISIS.
   -Therefore, it is considered that, although the beam loss of ISIS is
   ~1 kW, the limit of the acceptable beam loss is taken as 500 W at
   ESS.


KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                            CAS – KEK Accelerator School, Indore, Feb, 2004



                     On the limit of acceptable beam loss

- Table-1 indicates that the beam loss accepted in each accelerator is not so
much different from each other, although the beam power is as widely
dispersed. The values of the beam loss are in the vicinity of 400 or 500 W.
-The beam loss commonly generates residual activities of several 10 mSv/H
at several points.
-The yearly radiation exposure of a number of key persons becomes several
mSv and, therefore, the residual activity is considered to be at a level near
to the limit to secure safety in the maintenance service.
-This situation is considered to be common for high-intensity proton
accelerators that are maintained in a hands-on manner.
-Thus, the limit of the acceptable beam loss is near to 400 or 500 W when
the beam loss occurs well above 120 MeV. As well, beam loss at energy
below 120 MeV should be better limited about 1kW or lower.



   KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                         CAS – KEK Accelerator School, Indore, Feb, 2004


     5, Reasonable Upgrade Path to More Powerful Source

- Starting accelerator is very moderate and sure to be successful. It is
also expected that user’s scientific activity will grow soon by successful
utilization. Rapidly growing demand for higher power proton beam
will request upgrade of the accelerator.
-100 MeV Linac and (100 MeV-1 GeV)/100 kW Synchrotron with
reasonable surplus for acceptance
- 300 kW by Beam Current Upgrade to 300 mA, by Second Harmonic
RF Cavity
- Add a 3.3 GeV/1 MW Synchrotron or Circular Induction Accelerator
- 1 GeV Linac and 5 MW Synchrotron or Circular Induction
Accelerator




KEK, High Energy Accelerator Research Organization, Isao Yamane
                                                        CAS – KEK Accelerator School, Indore, Feb, 2004



                                 ISIS Upgrade Plan




KEK, High Energy Accelerator Research Organization, Isao Yamane

				
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