Pekka Suominen 2010 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 CO 2 and other molecular beams Ideal extraction for Carbon and Oxygen isotopes High purity (separated as CO 2 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

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 cm coax line Antenna Match- box

Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams” Maxwell-Boltzmann energy distribution Xenon CO 2 breaks Argon Helium Electron energy [eV] Relative e-density CO 2 1st ionization potential

Pekka Suominen: ”Plasma ion sources for radioactive molecular ion beams” Double stage extraction (accel-accel) 0V-potential HV (for example 30 kV)

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 N 2 O (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 Special thanks to: P. Sortais, LPSC-Grenoble, France O. Tarvainen, JYFL, Finland