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Production of polarized ions in nearly resonant charge-exchange

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Production of polarized ions in nearly resonant charge-exchange Powered By Docstoc
					      Production of polarized ions in nearly resonant
          charge-exchange collisions in plasma


                                        A. S. Belov

              Institute for Nuclear Research of Russian Academy of Sciences
                                      Moscow, Russia




September 10-14, 2007                A.S. Belov, PSTP-2007, BNL, USA          1
• The report is summary of work performed in collaboration with
  several laboratories since 1980th:

• INR, Moscow:
  S. K. Esin, V. E. Kuzik , S. A. Kubalov , L. P. Netchaeva ,
  A. V. Turbabin , G. A. Vasil’ev , V. P. Yakushev
• Novosibirsk Budker Institute of Nuclear Physics
  V. G. Dudnikov
• IUCF, Bloomington
  V. P. Derenchuk




September 10-14, 2007       A.S. Belov, PSTP-2007, BNL, USA       2
    Content:

    • Introduction
    • Nearly resonant charge-exchange reactions, cross-sections
    • Polarized H+/ D+ source
       – with free atomic hydrogen beam
       – with storage cell in a charge-exchange region
    • Source of polarized H/ D ions
    • Scheme of source for polarized 3He ++ ions
    • Pulsed atomic hydrogen beam study
    • Conclusions




September 10-14, 2007          A.S. Belov, PSTP-2007, BNL, USA    3
                           Introduction

• Polarized ions are produced in polarized ion sources via several steps
  process:
   – polarization of neutral atoms (atomic beam method or optical
      pumping)
   – Conversion of polarized neutral atoms into polarized ions
      (ionization by electron impact, electron impact + charge-exchange,
      charge exchange, nearly resonant charge-exchange )

• Nearly resonant charge-exchange processes have large cross sections.
  This is base for high efficiency of polarized atoms conversion into
  polarized ions.


September 10-14, 2007         A.S. Belov, PSTP-2007, BNL, USA              4
• Resonant charge-exchange reaction is charge exchange between atom
  and ion of the same atom:

                               A0 + A+  A+ + A0
              • cross -section is of order of 10-14 cm2 at low collision energy


• Charge-exchange between polarized atoms and ions of isotope relative
  the polarized atoms - to reduce unpolarized background

• W. Haeberli proposed in 1968 an ionizer with colliding beams of ~1-2
  keV D- ions and thermal polarized hydrogen atoms:

                               H0 + D  H + D 0




September 10-14, 2007                A.S. Belov, PSTP-2007, BNL, USA              5
                    Nearly resonant charge-exchange reactions
                    which can be used for polarized ion sources


 H0 + D+  H+ + D 0
 D0 + H+  D+ + H0

  H0 + D  H + D 0
  D0 + H  D + H 0

 3He0  + 4He+  3He+ + 4He 0
  3He0  + 4He++  3He++ + 4He 0



 T+, T-, Li+…




September 10-14, 2007              A.S. Belov, PSTP-2007, BNL, USA   6
                        Cross-section vs collision energy for process
                                    H+ + H0  H0 + H+
                            = 510-15 cm2 at ~10eV collision energy




September 10-14, 2007                   A.S. Belov, PSTP-2007, BNL, USA   7
                        Cross-section vs collision energy for process
                                    H + H0  H0 + H
                             = 10-14 cm2 at ~10eV collision energy




September 10-14, 2007                   A.S. Belov, PSTP-2007, BNL, USA   8
                        Cross-section vs collision energy for process
                                He++ + He0  He0 + He++
                            = 510-16 cm2 at ~10eV collision energy




September 10-14, 2007                   A.S. Belov, PSTP-2007, BNL, USA   9
• Low collision energy is achieved if ions are in plasma with ion
  temperature in eV region.

• Space charge problem for transport of intense ion beam to charge-
  exchange region is eliminated if plasma is used

• V. Nizhegorodtsev and V. Sokolov from IHEP, Russia proposed use
  of plasma from ion source for ionization of polarized atoms in 1971

• INR group in 1984 designed source of polarized protons with nearly
  resonant charge-exchange in plasma : synthesis of ideas of W. Haeberli
  and V. Nizhegorodtsev and V. Sokolov



September 10-14, 2007         A.S. Belov, PSTP-2007, BNL, USA              10
           Scheme of polarized hydrogen ion source with nearly
          resonant charge-exchange plasma ionizer (INR , 1984)




                           
                           
                          D+   H+ Bending/analysing
                                   magnet

                          
polarized                           E                              Deuterium
atomic                                                             plasma
hydrogen                                       Bce
beam



  September 10-14, 2007          A.S. Belov, PSTP-2007, BNL, USA               11
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   12
               Characteristics the INR polarized proton source


• ABS:
   – peak intensity of polarized atomic hydrogen beam is 2 1017at/s
   – most probable velocity is 2 105 cm/s


• Polarized proton beam:
        –    peak current is 6 mA
        –    polarization - 75-90 %
        –    normalized emittance 2 mm mrad
        –    rep. rate up to 10 Hz

• Unpolarized deutron current density - 250 mA/cm2

September 10-14, 2007            A.S. Belov, PSTP-2007, BNL, USA      13
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   14
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   15
             Storage cell in the charge-exchange region

• Storage cell as a donor of polarized electrons in a polarized ion source
  - W. Haeberli, 1966

• Storage cell in a plasma ionizer of polarized ion source -
  V. Nizhegorodtsev and V. Sokolov, 1971

• Storage cell in colliding beam ionizer for polarized H- ion production -
  T. Clegg, 1995




September 10-14, 2007          A.S. Belov, PSTP-2007, BNL, USA               16
                                        Schematic diagram
                        of nearly resonant charge-exchange plasma ionizer
                                        with a storage cell




September 10-14, 2007              A.S. Belov, PSTP-2007, BNL, USA          17
                        The storage cell geometry




September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   18
 •     Intensity of polarized proton beam
       increased ~9 times due to storage
       cell.                            
 •     With 5 mA D+ ion current -
       1 mA of H+ current

 •     With 40 mA unpolarized D+ ion
       current in the storage cell - 8 mA of
       polarized proton current          

 •     50 mA of D+ ion current l - 11 mA
       polarized proton current has been
       obtained




September 10-14, 2007                A.S. Belov, PSTP-2007, BNL, USA   19
• Proton polarization up to 95 %
  was measured with low plasma
  ion flux (5mA D+)         




• Polarization of 80% has been
  recorded for high ion flux in the
  storage cell              




September 10-14, 2007         A.S. Belov, PSTP-2007, BNL, USA   20
  Polarized deutron source for Dubna NUCLOTRON
                      accelerator

                • New source with nearly resonant charge-exchange ionizer is
                  developed
                • Project goal:
                    • 10 mA D+ (Н+)
                    • polarization ~ 90 % from nominal vector polarization
                      + (-) 1 and tensor polarization + 1,-2

                • Parts of CIPIOS source from IUCF (Bloomington, USA) will
                  be used. Collaboration between JINR (Dubna) and INR of
                  RAS (Troitsk).
                • Storage cell is planned to be used to reduce background current
                  of H2+ ions

September 10-14, 2007                A.S. Belov, PSTP-2007, BNL, USA                21
                        Polarized negative hydrogen ion source


• In order to produce polarized negative hydrogen ions it was necessary
  to have deuterium plasma consisting mainly from D+ and D- ions
  because slow polarized H- ions can be easily destroyed in collisions
  with plasma electrons

• Plasma injector producing deuterium plasma enriched by D- ions with
  surface-plasma converter has been developed at INR




September 10-14, 2007                A.S. Belov, PSTP-2007, BNL, USA      22
                         Schematic diagram of the ionizer
                  for polarized negative hydrogen ions production




September 10-14, 2007               A.S. Belov, PSTP-2007, BNL, USA   23
                                                     Magnet for           Section of the
                                                     transversal          ionizer solenoid
                                                     magnetic field

                                  Neutralizer
                                  cone
                             Plasma                                                          High-voltage
                             source coil                                                     screen



                                                                                             Blocker of plasma
                                                                                             electrons
                        Arc-discharge
                        plasma
                        source


                                        Cylinder of the
                                        surface-plasma     Cs oven
                                        converter

                                     Scheme of the injector of deuterium plasma
                                                enriched by D- ions
                                             with two-stage converter




September 10-14, 2007                               A.S. Belov, PSTP-2007, BNL, USA                              24
• Expected H- ion current:
                                      jD 
       I H   eI H 0  (1  exp(          ))
                                       e

• where IH0 = 21017 s-1 is
  intensity of the atomic
  hydrogen beam




September 10-14, 2007                              A.S. Belov, PSTP-2007, BNL, USA   25
                  Destruction of negative hydrogen ions in plasma

•   H + e                 H0 + 2e                          ~ 410-15 cm2
•   H + D+                H0 + D0                          ~ 210-14 cm2
•   H + D0                H0 + D                          ~ 10-14 cm2
•   H + D2                H 0 + D2 + e                      ~ 210-16 cm2
•   H + D0                HD0 + e                           ~ 10-15 cm2




    September 10-14, 2007           A.S. Belov, PSTP-2007, BNL, USA            26
       Oscillograms of polarized H- ion current (vertical scale-
        1mA/div) and unpolarized D- ion current (10mA/div)




September 10-14, 2007         A.S. Belov, PSTP-2007, BNL, USA      27
Characteristics of polarized H- ion beam of the INR source
•     Peak H- ion current                                    4 mA
•     Polarization                                         0.910.03
•     Normalized emittance                                 2  mm mrad
•     Unpolarized D- ion current                         60 mA (~20 mA/cm2)
•     Pulse duration (FWHM)                                    170 s
•     Rep. rate                                               5 Hz
        Source of polarized and unpolarized H-/D- ions of IUCF
•     Peak current of H-/D- ions                              2 mA
•     Polarization                                  up to 0.9 from nominal
•     Normalized emittance                                  1.2  mm mrad
•     Unpolarized H-/D- ion current                           40/30 mA
•     Pulse duration                                      up to 500 s
•     Rep. rate                                                 2 Hz

September 10-14, 2007              A.S. Belov, PSTP-2007, BNL, USA            28
   Schematic diagram of proposed polarized 3He++ ion source
                        3He0    + 4He++  3He++ + 4He 0




September 10-14, 2007              A.S. Belov, PSTP-2007, BNL, USA   29
     Study of polarized pulsed atomic hydrogen beam




                             Schematic layout of the apparatus for
                        study of pulsed polarized atomic hydrogen beam




September 10-14, 2007                   A.S. Belov, PSTP-2007, BNL, USA   30
 Time-of-flight mass-spectrometer with cross-beam
                      ionizer




September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   31
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   32
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   33
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   34
                        Beam-skimmer interference

• Density of pulsed atomic
  hydrogen beam decreases with
  decrease of the nozzle-skimmer
  distance while simulation
  (which does not take into
  account scattering of atoms)
  forecasts increase of density
                           
• Explanation: atomic beam
  forms gas “cloud” inside the
  skimmer and atomic beam
  attenuates due to scattering :
  beam-skimmer intereference

September 10-14, 2007           A.S. Belov, PSTP-2007, BNL, USA   35
                 Beam-skimmer interference simulation

• When atomic beam passes
  through volume with restricted
  conductance - instability can
  arise for formation of gas
  “cloud” and attenuation of the
  beam




September 10-14, 2007         A.S. Belov, PSTP-2007, BNL, USA   36
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   37
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   38
        – Noncomplete cooling of atomic hydrogen in
          nozzle at high gas densities




September 10-14, 2007    A.S. Belov, PSTP-2007, BNL, USA   39
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   40
September 10-14, 2007   A.S. Belov, PSTP-2007, BNL, USA   41
                            Conclusions


• Polarized H+/D+ ion beam with peak current ~ 10 mA as well as H-/D-
  with current 4 mA and polarization of ~90% from nominal have been
  produced by atomic-beam type polarized ion source with nearly
  resonant charge-exchange plasma ionizer.

• Generation of polarized 3He++ with high intensity and polarization
  seems to be possible using similar method.

• Intensity of pulsed polarized atomic hydrogen beam is restricted by
  noncomplete cooling of atoms and scattering of atoms presumably in
  nozzle chamber.


September 10-14, 2007        A.S. Belov, PSTP-2007, BNL, USA            42

				
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