“The RIKEN-RAL Muon Facility”

Document Sample
“The RIKEN-RAL Muon Facility” Powered By Docstoc
					RIKEN Nishina Center
“The RIKEN-RAL Muon Facility”
(International Research Collaboration between RIKEN and
SFTC (Science and Technology Facility Council) in the UK)




                Rutherford Appleton Laboratory (UK)




        RIKEN (Japan)
Introduction
   In Japan, Professor Hideki Yukawa predicted the existence of pions, and
Professor Yoshio Nishina discovered muons in cosmic rays. Nowadays, pions and
muons can be artificially produced with high-energy proton accelerators. In the
nuclear reactions by injecting high-energy proton beam into carbon nuclei, pions are
generated, and then muos are created by the decay of pions.



Muon
   Muons are classified to the electron group in the elementary particles, and have
the mass of 1/9 of proton mass and of 207 times of electron mass. Therefore positive
muons behave like “light proton” and negative muons do like “ heavy electron” in
materials.
  Positive muons have their own spins (magnet needle) with 100% polarization, and
can detect very precisely the local magnetic fields and the fluctuations. The method
to study the characteristic of materials by observing the time dependent change of
muon spin polarization is called “Muon Spin Rotation, Relaxation and Resonance
( SR method), and is applied to condensed matter studies of newly fabricated
materials.
  Negative muons are captured into orbits of nuclei, and form “Muonic Atoms” with
the atomic size of 1/207 compared with ordinary atoms. At the formation of muonic
atoms, the characteristic muoncic X-rays are emitted with higher energies by 207
times compared with X-rays from ordinary atoms. By applying unique features, muon
catalyzed d-t fusion, nuclear physic study on nuclear charge density distributions and
application to non-destructive analysis are in progress.




Muon production and decay                                                     Positive pion
                                                      Carbon target

Pion ( ) production:
                                +/-
Proton + carbon target                + X
                                                Proton beam
                                                                              Negative pion
Pion decay:


(Lifetime: 26 nsec.)

Muon decay
       e     e                                                                       Pion
       e     e                                Superconducting solenoid               Muon
(Lifetime: 2.2 sec.)                          confinement magnet




                                       -1-
International collaboration on muon science between
RIKEN and Rutherford Appleton Laboratory
  RIKEN has concluded an agreement on muon science in September 1990
with Rutherford Appleton Laboratory, entitled by the name of Dr. Rutherford
who experimentally gave proof of the existence of nuclei. RIKEN has
constructed a muon experiment facility producing the highest pulsed muon
beam in the world, and has been promoting muon science open to
researchers of various fields from Japan, UK and the other counties.




Rutherford Appleton Laboratory (RAL)
  Rutherford Appleton Laboratory is located near Oxford city, and is the
largest research institute of basic science in the UK. RAL possesses the ISIS
proton accelerator facility, synchrotron radiation facility (Diamond) and high
intensity laser facility. RAL is carrying forward material science, astrophysics,
space science, high-energy particle physics, earth science, environmental
science and computer science. RAL is also promoting a variety of
international collaboration researches from all over the world.




            The bird’s eye view of Rutherford Appleton Laboratory




                                      -2-
Agreement of international collaboration research on muon science

  RIKEN made an agreement of international collaboration research on muon science with
SERC (Science and Engineering Research Councils) in the UK in September 1990. The
extending second agreement was made in September 2000 between RIKEN and CCLRC
(Council of Central Laboratory Research Councils).
This project was the largest research collaboration project between Japan and the UK, and was
spoken as a good example of successful research projects.
The term of the project is ten years, and the roles of RIKEN and RAL are as follows,
  RIKEN: RIKEN does the construction, operation, maintenance of the RIKEN-RAL Muon
             Facility.
  RAL: RAL supplies a high intensity proton beam from the ISIS accelerator to produce muons
         at the RIKEN-RAL Muon Facility.
In this agreement, RIKEN and RAL have independent PACs (Program Advisory Committee),
and are carrying forward their own muon science researches. This point is a distinguished
feature of the agreement, is not appeared in the other international research collaborations.


History of the RIKEN-RAL Muon Facility
1990 April: Budget Approval by STA (Science and Technology Agency)
1990 September: The first agreement between RIKEN and SERC
1991: Beginning of facility construction
1994 November: Observation of the first muon beam
1995 April: Inauguration of “RIKEN Facility Office at RAL”
            Beginning of condensed matter studies by mSR methods
1996 June: Completion of the RIKEN-RAL Muon Facility
             Beginning of muon catalyzed d-t fusion experiments
2000 September: The 2nd agreement between RIKEN and CCLRC (term: 10 years)
2006 April: Organized in RIKEN Nishina Center for Accelerator-Based Science
2007 November: #1 International Advisory Committee (RAL)
2008 November: #2 International Advisory Committee (RIKEN)




                                               Upper left: The first agreement (Sept. 1990)
                                               Lower left: The second agreement (Sept. 2000)
                                               Right: Inauguration (April 1995)




                                         -3-
High intensity proton accelerator facility of Rutherford Appleton Laboratory
in the UK

                                                                      ISIS accelerator facility




Specification:           MeV,                                       Hz,        pulses
Specification:Energy 800 MeV, Beam current 300 A,Repetition rate 50 Hz, double pulses structure




                                                 RIKEN-
                                             The RIKEN-RAL Muon Faciity
                                             (The highest pulsed muon beam facility in the world)




             Entrance to ISIS facility              Construction of the RIKEN-RAL Muon Facility




                                           -4-
                   Layout of the RIKEN-RAL Muon Facilty

  The proton beam (800 MeV, 300 A) generated by ISIS accelerator is delivered from
left to right along the proton beam line, and penetrates the production target, where pions
are produced by nuclear reactions. The produced pions are collected and momentum-
analyzed in the pion injection system, and are transported into the superconducting
solenoid magnet, where pions decay to muons during the flight. The muons are called
“decay muon”, and have a double-pulsed beam structure due to the proton beam
structure. The double pulsed muon beam is separated into two single pulses with the
pulsed kicker magnet and septum magnet, The two single pulses are transported to port-
1/2 and port-3/4, and two different muon experiments can be performed independently.
The “surface muon” is produced by          decay on the surface of the production target,
and the two single pulses are similarly transported to two experiment ports.


Specification of the RIKEN-RAL Muon Facility
Decay (positive and negative) muon beam and surface muon beam are produced.
Muon momentum range : 20 – 120 MeV/c
Muon beam intensity (200 A proton beam and 10mm thick production target )

 Decay positive muon: 4 x 105 /sec 60 MeV/c
  Decay negative muon: 7 x 104 /sec 60 MeV/c
  Surface muon :         1.5 x 106 /sec 27 MeV/c

Double pulsed muon beam is separated into two single muon pulses.
Two different muon experiments can be performed independently.
Promoting four unique muon experiments at four experiment ports.




                                          -5-
                                                Q1 and Q2 quadrupole magnets
                                                (pion injection system)




                Compressor room




                                              B1 bending magnet (pion injection system)




Helium screw compressor room (ground floor)
RIKEN control room (first floor)                Superconducting solenoid magnet
                                                (   decay section)




       Helium screw compressor                Cold box for helium refrigeration system




                                       -6-
            Pulsed kicker magnet
                                                       Quadrupole triplet and kicker magnet




Kicker magnet (left) and septum magnet (right)




                                                                 Compressor room




  Qadrupole magnet and DC separator




                                                           Muon extraction system




                                                 -7-
        Muon Spin Rotaion, Relaxation, Resonance method
        ( SR method)

Muon production (Muon spin is aligned on the motion axis.)




 Muon decay (asymmetric decay)


                 +



                              e+

       +    e +           +
                      e                               Muon Lifetime: 2.2 sec
                                                           Lifetime




100% spin alignment
                                                      Asymmetry =
                                                 e+   [ NF - NB ] / [ NF + NB ]

   +
                          Sample
S=1/2                                                    Muon spin relaxation
             Forward counter       Backward counter
                   NF                    NB


                                                      Magnitude and fluctuation
                                                      of local magnetic field




                                           -8-
                     Condensed matter physics-1
  Muons have their own spins (magnet needle)        method (10-10-10-12 second) and Nuclear
with 100% polarization, and can detect very         Magnetic Resonance (NMR) (longer than 10-6
precisely the local magnetic fields and their       second). At port-2, the SR experiments on
fluctuations. The method to study the               strong correlated electron system, organic
characteristic of materials by observing the time   molecular system and biological samples are
dependent change of muon spin polarization is       in progress to study the electron structures,
called “Muon Spin Rotation, Relaxation and          superconductivity, magnetism, molecular
Resonance ( SR method), and is applied to           structures and crystal structures.
condensed matter physics studies of newly
fabricated materials. Muons with their own spin
polarization are utilized for condensed matter
studies under an external zero field condition,
for magnetism studies for samples without
nuclear spins, and for observations of muon
spin relaxation changes at a wide temperature
range with the same detection sensitivity. The
detectable time range of local field fluctuations
by SR is 10-6 to 10-11 second, which is a
medium time range between neutron scattering
                                                          SR spectrometer at port-2


             The first observation of dynamical electron transfer
             process between FeII and FeIII sites in charge transfer
             complexes
     Complex showing charge            Longitudinal field SR
     transfer phase transition
                                       Temperaure: 80K
(Phase transition with spin and charge (Dynamic picture)




                                                                 Deternination of charge transfer
                                                                 frequencty from muon spin
                                                                 relaxagtions and magnetic fields
  Charge transfer phase transition                                Electron exchange ( FeII FeIII )
  occurs at 120K by electron       57Fe Mössbauer spectra
  exchange between FeII FeIII
                                   Charge transfer between
  states associated with change of                                Frequency : 120 KHz at 80K
                                   FeII FeIII (Static picture)
  spin states.




                                              -9-
                  Condensed Matter Physic - 2
                                                                                                 spin
                                                                                                 hole
                Mechanism of high temperature superconductor                                     spin
                               (La2-x Srx CuO4)                                                  hole
                                                                                                 spin
                                    Stripe model                                                 hole
                                                                                                 spin

Zero field SR data (left) and
temperature dependence of muon
relaxation rates (right)                                                        Comparison of SR
                                                                                results with electric
                                                                                resistances




                                                    Sr concentration (x)

                                            Coupling between spin and charge

                                            charge                         Suppression of
                                            localization                   spin fluctuation
  time    sec      Temperature (K



                Spin correlation of 2D disordered triangular lattice
                                   X [Pd(dmit)2]2

         Antiferromagnetic transition and long range order           Internal fields determined by
         observed by zero field SR                                   muon spin rotation frequencies
         (CH3)4P[Pd(dmit)2]2         (C2H5)2(CH3)2P[Pd(dmit)2]2




           TN = 39.3 K                        TN = 14.8 K
           anisotropic                   isotropic (frustrated)
           higher TN                     lower TN
                                                                   disorder from 2D triangular lattice




                                          - 10 -
     Ultra slow muon generation and application

 Positive muon beam with thermal energy                                              muonium
is produce by laser irradiation to
muoniums (bound system of + and                                                            slow muon
electron) emitted from the surface of hot
tungsten foil with stopping surface muon
beam. The method enables to generate
the positive muon beam with acceleration
energy from several 100 eV to several keV,               muon beam
a small beam size (a few mm) and good
time resolution (less than 8 nanosecond).
By stopping the ultra slow muon beam in
thin foils, multi-layered materials and
artificial lattices, local magnetic field can                    tungsten film
be measured, and the SR techniques are                                       laser light
applied to surface and interface science.
Since there has been no appropriate probe
to study the surface and interface, the ultra
slow muon beam will open a new area of
surface and interface research field.




    The SR signals were obtained
    by stopping the ultra slow
    muon beam in a test sample
    with 40 nanometer thickness
    at different acceleration
    energies.




                                                - 11 -
                        Muon Catalyzed d-t Fusion
Negative muon stops in deuterium and tritium
mixture to form mounic hydrogen atom (d -,
t -) with small radius (1/207 of ordinary atom
radius). The d - diffuses and converts to t - by
mun transfer. The t - collides with D2 molecule
without any Coulomb repulsive force to
resonantly form dt - molecule. The d-t fusion
reaction occurs in the dt - molecule to produce
a-partcle and neutron. After the d-t fusion,
muon is liberated, and repeats the same
process: Muon Catalyzed Fusion ( CF). With a
slight possibility, muon is captured by -
particle, while there is a chance that muon is
stripped from the       - atom during slowing

down. From a viewpoint of energy production
with applying CF, the effective muon loss in
the process determines the maximum output.
In the experiments, a single muon generates
120 times d-t fusions; the energy production
corresponds to 40% of “scientific breakeven”,
where about 1 million d-t fusions every second
are generated, and the energy generation of
about 3       W is realized. Further basic
experiments are planed to optimize inner and
outer D-T target conditions toward the energy
production with CF.


                   n- spectrum          Neutron Energy
-ray Energy




                                               Time




                                                         Upper:Tritium gas handling system
 d-t CF cycling rate          Muon loss rate at
 at different tritium         different tritium          Lower: CF experiment apparatus
 concentrations               concentrations




                                             - 12 -
                      Muonic X-ray measurement
  Negative muons ( -) are injected to solid
deuterium layer with ion implantation of                     Basic Concept: Solid Deuterium
nuclei (A), and form muonc hydrogen
atoms (d -). The d - atoms diffuse to                                                    A*
collide the implanted nuclei to form muonic
( -A) atoms by muon transfer. At this                   µ−              dµ
formation process, characteristic muonic                                                        A* Ion
X-rays are generated. The muon mass is                                                          Beam
207 times larger than electron mass, and
the muonic atom radius is 1/207 smaller
than ordinary atomic radius. Therefore,           Muon                             µA*
muon orbit is located very close to nuclear       Beam                                        X-Rays
surface, and muonic X-ray energies are
very much influenced by charge density                                D2
distribution (nuclear shape). By measuring
muonic X-ray energies and isotope energy
shifts, precise information on nuclear
charge distribution is obtained.
  The experimental apparatus is equipped
with a surface ionization source, which
produces alkali, alkali-earth and rare-earth
ions to implant to solid deuterium layers.
Recently, successful observations of
muonic X-rays from isotope-separated 86Sr
and 88Sr have been performed. Further
experiments to observe muonic X-rays
from Ba, Sm and Nd isotopes are planed
to study nuclear charge distribution by
obtaining the energies and isotope energy
shifts.


              ~ 1 ppm Ar




                                                        Muonic X-ray energy spectrum of 88Sr and 86Sr
  Muonic X-ray energy spectrum of 40Ar




                                               - 13 -
           Precise measurement of muon lifetime
   Positive muon decays to a positron and two
neutrinos almost 100% by week interaction.
In muon lifetime measurements, time
spectrum of positrons from muon decay were
measured after muon stopping in a target,
and the lifetime was determined by the slops
of time spectra. In order to obtain muon
lifetime, a precise experiments with high
statistics was required. At the RIKEN-RAL, a
new experimental method was developed,
and the muon lifetime measurement was
performed.
   Weak       interaction,     electromagnetic
interaction and muon decay are described by
Weak sector of the Standard Model with
several parameters to be determined by
experiments. One of important parameters is
Fermi coupling constant (GF), which is
described by the following equation, and is
determined by muon lifetime.

    1
        G2
        GFF m 5       me       3 m
                                   2

              3
                  F        1       2
                                     1   r
        192           m        5 MW

In the equation, me, m , mw are masses of
electron, muon and W-boson. The 2nd, 3rd an
4th terms are precisely calculated QED
corrections in the theory, and GF is therefore
determined with the precision of less than
1ppm by precise muon lifetime measurement.
The experiment was conducted at port-2 by
using the apparatus shown in the figure.
Positive muons were stooped in holmium
(Ho) target, and the decay positrons were
detected with Multi Wire Proportional
Counters (MWPC) with 640 channels.




                                                      Muon decay time spectrum of 1011 events was
                                                      analyzed to obtain muon lifetime with high
 Photograph taken from upstream                       precision.
 shows four MWPCs.




                                             - 14 -
Record of the RIKEN-RAL Muon Facility
Published papers: 217 (November 2007)
Proposed experiment proposals to the RIKEN-RAL Muon facility: 363 (2008)

                                   29
Beam time days in 2006: 191 days (29 days for UK researchers)
                                   8
Experiments conducted in 2006: 62 (8 for UK researchers)

Visiting researchers: 500 (August 2008)
Visitors: 394 (August 2008)

Program Advisory Committee of the RIKEN-RAL Muon Facility
(PAC)
The 16th PAC (29 May 2003)
The 17th PAC (10 October 2003)
The 18th PAC (1 October 2004)
The 19th PAC (3 June 2005)
The 20th PAC (27,28 October 2005)
The 21st PAC (1,2 June 2006)
The 1st Program Advisory Committee for Material and Life science at RIKEN
        Nishina Center (ML-PAC) (1 February 2007)
The 2nd ML-PAC (25,27 July 2007)
The 3rd ML-PAC (27,28 March 2008)
The 4th ML-PAC (13,14 January 2009)

Symposium (since 2004)
1. RIKEN Symposium
“The present status and prospect of the RIKENRAL Mon Facility”
held at Okouchi Hall in RIKEN on 27,28 May 2004

2. RIKEN Symposium
“Muon Science at the RIKEN-RAL Muon Facility 2007”
held at RIBF lecture hall on 23,24 July 2007




                                    - 15 -
         Domestic collaborations with RIKEN on muon science 45




        International collaborations with RIKEN on muon science: 13

UK                                     Russia
Oxford University                      MUCATEX                         Canada
Imperial College
                                                                       British Columbia University
Manchester University




 Switzerland
                                                                                         USA
     PSI
                                                                                         University of Columbia
                                                                                         University of California




                    Germany
           University of Stuttgart                             Indonesia
                                           Romania             The Institut Teknologi Bandung
                                     Babes-Bolyai University   Universitas Padjadjaran
                                                               The Institut Teknologi Surabaya




                                                      - 16 -
                             RIKEN Facility Office at RAL in
                             Rutherford Appleton Laboratory




RIKEN Facility Office at RAL
UG-17, R3, Rutherford Appleton Laboratory
Chilton, Didcot, OXON, OX11 0QX, UK
Phone: +44-1235-446802
FAX: +44-1235-446881
Wed site: http://nectar.nd.rl.ac.uk/~rikenral/index.html