plasma ion sources for radioactive molecular ion beams
DESCRIPTION
Plasma ion sources for radioactive molecular ion beams. Pekka Suominen 2010 CERN. Contents. Two new plasma ion sources tested at offline separator COMIC (Compact Microwave and Coaxial) 2.45 GHz coaxial ¼-wave resonator antenna HELICON (miniature RF-source with B-field) - PowerPoint PPT PresentationTRANSCRIPT
Pekka Suominen2010 CERN
Plasma ion sources for radioactive molecular ion beams
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Contents Two new plasma ion sources tested at offline
separator COMIC (Compact Microwave and Coaxial)
2.45 GHz coaxial ¼-wave resonator antenna
HELICON (miniature RF-source with B-field) 100 MHz helical antenna
Technical developments Double stage extraction (accel-accel) Radiation hard coaxial RF power line for frontend 7 (new FE for
GPS)
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Why? Interest for CO2 and other molecular beams
Ideal extraction for Carbon and Oxygen isotopes High purity (separated as CO2 and broken in EBIS)
Main things we aim for High gas efficiency Stable and easy operation Reasonable emittance Compact size & robust construction
(high radiation environment)
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
COMIC”Compact Microwave and Coaxial”
Q-COMIC
”Quartz-COMIC”
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Q-COMIC Developed by P.Sortais / LPSC, Grenoble Plasma ignition with 30 W of 2.45 GHz
Microwaves Quartz plasma chamber developed for ISOLDE
D = 50 mm
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Q-COMIC in ISOLDE target unit
Pictures: (c) P. Sortais
17.8 KV
0.20 mA
LPSC testbench
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Experimental setup at Offline
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Main results for Q-COMIC
Buffer gas CO2 gas efficiency
Argon 0.09 %Krypton 0.12 %Xenon 0.22 %
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
HELICON”A helicon is a low frequency plasma wave
10 kHz(Ignited with RF power of 1 … 100 MHz)”
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
RF source normally has no axial B-field Helicon requires B-field
Introduces low frequency travelling waves in the plasma electrons can ”surf” with the wave and gain energy ionization by electron bombardment
Helicon vs. RF plasma source
(c) Nasa / VASIMR
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
ISOLDE Helicon source
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Matching is difficult due to stray capacitances Normally coaxial line is around 100 pF/m and 200 nH/m
Coaxial line affects strongly to the resonant frequency For long coaxial line one cannot get resonance at the antenna
RF impedance matching
50 cmcoax line
AntennaMatch-box
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Maxwell-Boltzmann energy distribution
Xenon
CO2 breaks
Argon Helium
Electron energy [eV]
Relative e-density
CO2 1st ionization potential
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Double stage extraction (accel-accel)
Puller @ 0V-potential
Base @ HV (for example 30 kV)
Intermediate electrode @ HV - 3kV (27 kV to ground)
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
We need a solution, which can survive 5 years at online
Rad hard RF Coaxial line for FE7
Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams”
Outlook More understanding of the plasma is necessary
Langmuir probing, Beam energy distribution measurements, plasma simulations
New gases to study molecule breaking for example N2O (6.3 eV to break / 12.9 eV to ionize)
COMIC More power
New Solid-state MW-generator 180 W, 2450 MHz +/- 25 MHz Effect of magnetic field at the extraction
HELICON Tests of different antennas Improved RF impedance matching
plate capacitors in vacuum Variable magnetic field (coils) Effect of magnetic field at the extraction
Tests by varying the plasma electrode position
Thank you for your attention !
Do not hesitate to contact me for additional information [email protected]
Special thanks to:P. Sortais, LPSC-Grenoble, FranceO. Tarvainen, JYFL, Finland