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 pekka.suominen@cern.ch

Special thanks to:P. Sortais, LPSC-Grenoble, FranceO. Tarvainen, JYFL, Finland