PST'05 (XIth Workshop on Polarized Source an d Target) 1 Generation of Polarized Generation of Polarized Electrons Electrons by Filed by Filed Emission Emission M. Kuwahara M. Kuwahara A A , T. Nakanishi , T. Nakanishi A A , S. Okumi , S. Okumi A A , M. , M. Yamamoto Yamamoto A A , , M. Miyamoto M. Miyamoto A A , N. Yamamoto , N. Yamamoto A A , K. Yasui , K. Yasui A A , T. Morino , T. Morino A , , R. Sakai R. Sakai A A , K. Tamagaki , K. Tamagaki A A , K. Yamaguchi , K. Yamaguchi B B A: Graduate School of Science, Nagoya University B: Department of Electronic Engineering, The University of Electro-Communications Morning Session II -- Polarized Electron Beam II --
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PST'05 (XIth Workshop on Polarized Source and Target)1 Generation of Polarized Electrons by Filed Emission M. Kuwahara A, T. Nakanishi A, S. Okumi A, M.
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PST'05 (XIth Workshop on Polarized Source and Target) 1
Generation of Polarized Electrons Generation of Polarized Electrons by Filed Emissionby Filed Emission
M. KuwaharaM. Kuwahara A A, T. Nakanishi, T. Nakanishi A A, S. Okumi, S. Okumi A A, M. Yamamoto, M. Yamamoto A A, , M. MiyamotoM. Miyamoto A A, N. Yamamoto, N. Yamamoto A A, K. Yasui, K. Yasui A A, T. Morino, T. Morino A A, ,
R. SakaiR. Sakai A A, K. Tamagaki, K. Tamagaki A A, K. Yamaguchi, K. Yamaguchi B B
A: Graduate School of Science, Nagoya University
B: Department of Electronic Engineering, The University of Electro-Communications
Morning Session II-- Polarized Electron Beam II --
PST'05 (XIth Workshop on Polarized Source and Target) 2
MotivationMotivation
Spin polarized electronsSpin polarized electrons Necessary for high energy physicsNecessary for high energy physics
» Linier collider project (ILC project)Linier collider project (ILC project) Powerful application for material sciencesPowerful application for material sciences
» Spin electron microscopySpin electron microscopy(( SP-LEEM, Spin-SEM, TEM, …SP-LEEM, Spin-SEM, TEM, … ))
» Electron beam holography Electron beam holography considered a spin effect considered a spin effect
Photocathode developmentsPhotocathode developmentsby GaAs-GaAsP strained superlatttice by GaAs-GaAsP strained superlatttice
Few problems are still remainedFew problems are still remained Low emittance and long life time of photocathodeLow emittance and long life time of photocathode
1.1.Low Emittance and High Brightness Polarized eLow Emittance and High Brightness Polarized e-- beam beam2.2.ExtrExtraction of Polarized eaction of Polarized e-- beam without NEA surface problem beam without NEA surface problem
PST'05 (XIth Workshop on Polarized Source and Target) 3
MethodMethod
1.1. Low emittance spin polarized electron Low emittance spin polarized electron
[i] spin polarizing[i] spin polarizing →→ GaAs type semiconductorGaAs type semiconductor
[ii] low emittance[ii] low emittance →→ cross section of beam: very small cross section of beam: very small
Spin relaxation time becomes smaller with rising electron energy Spin relaxation time becomes smaller with rising electron energy
Spin relaxation time 75~85ps Spin relaxation time 75~85ps (( 850to880nm), 850to880nm), BBand-gap and-gap 865nm(1.43eV)865nm(1.43eV)
(( different point between NEA and F.E.different point between NEA and F.E. ))
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Difference of each polarizationDifference of each polarization
Process in extracting into vacuumProcess in extracting into vacuum Tunneling yield is sensitive to the excitation energyTunneling yield is sensitive to the excitation energy
drifting electrondrifting electron ::
Energy dispersion becomes wider in transport process by some scattering.Energy dispersion becomes wider in transport process by some scattering.
Polarization of higher energy part : Polarization of higher energy part : High polarizationHigh polarization
lower energy part : lower energy part : Low polarizationLow polarization (cause by scattering)(cause by scattering)
Surface tunneling is like a filter effect of polarization.
Higher energy part of electrons can be extracted dominantly. : narrow, Pol : high
2/3exp)( ZzT
High energy part is mainly extracted into vacuum. Polarization becomes higher (cut off of depolarization part )
Fig. Generation process of spin polarized electrons with field emission. Blue color density means value of spin polarization.
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ConclusionConclusion
Achievements : Achievements : We demonstrated that F.E. can be used for PES We demonstrated that F.E. can be used for PES as a substitute for using NEA surface.as a substitute for using NEA surface.
Probability of miniaturization, integration and Probability of miniaturization, integration and applications applications for accelerators, microscopy, holography and so on.for accelerators, microscopy, holography and so on.
Extraction of polarized electrons by F.E. : O.K.Extraction of polarized electrons by F.E. : O.K. Electrons extracted by F.E. have higher polarization. Electrons extracted by F.E. have higher polarization.
It is thought that filter effect of tunneling process in surface.It is thought that filter effect of tunneling process in surface. Lifetime Lifetime (( long lifetime compared with NEA surfacelong lifetime compared with NEA surface
Problem Problem :: Work function, fine structure, surface contaminationWork function, fine structure, surface contamination Stability and uniformity of currentStability and uniformity of current Field emission characteristic Field emission characteristic (operation voltage, field enhancement)(operation voltage, field enhancement) Extract more high current Extract more high current
We can confirm that spin polarized electrons can be extracted We can confirm that spin polarized electrons can be extracted by F.E. , and demonstrate the fundamental characteristics.by F.E. , and demonstrate the fundamental characteristics.
PST'05 (XIth Workshop on Polarized Source and Target) 13
Difference from NEA/Bulk-GaAs (2)Difference from NEA/Bulk-GaAs (2)
Depolarization effect of spin polarized electron in a Depolarization effect of spin polarized electron in a GaAs crystal.GaAs crystal.
(( In the case of hot-electronsIn the case of hot-electrons )) DP-process DP-process (( >10>10meVmeV ) )