Ion Beam Cocktail Development and ECR Ion Source Plasma Physics Experiments at JYFL

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1 Ion Beam Cocktail Development and ECR Ion Source Plasma Physics Experiments at JYFL Olli Tarvainen 11th International Conference on Heavy Ion Accelerator Technology Venice, Italy 8-12 June 29

2 Outline JYFL accelerator laboratory Heavy ion beam cocktails for component irradiation at JYFL ECRIS plasma physics experiments

3 JYFL accelerator laboratory K-13 cyclotron Two ECR ion sources Negative light ion source Pelletron Injector upgrade in 29 MCC-3 cyclotron (29-21)

4 K-13 cyclotron accelerated ions Accelerated Ions in 22 (All) PROTONS 48 Ca 36 Ar DEUTERIUM 18 O 64 Ni COCKTAIL 86 Kr 16 O 4 Ca 32 S 63 Cu 22 Ne 78 Kr 3 He 14 Ru 4 Ar 65 Cu 5 Ti 28 Si 127 I 3 Si 12 Ru 82 Kr 4 He 15 N Beam time (%) Accelerated Ions in 29 (All) COCKTAIL PROTONS 9 Zr 3 He 4 Ar 4 Ca 84 Kr 36 Ar 4 He 14 N 2 Ne 12 C 48 Ti 12 Ru 14 Ru 17 Ag 11 B 127 I 128 Xe 13 C 13 Xe 131 Xe 132 Xe 136 Xe 139 La 15 N Beam time (%)

5 Heavy ion beam cocktails at JYFL Efficient testing of single event effects: Adequate penetration depth Varying LET-value Fast transition between projectiles

6 9.3 MeV /u high penetration cocktail at JYFL Ion Energy [MeV] Penetration depth [μm] LET [MeV/ (mg/cm 2 )] Δ(m/q) [%] 15 N Si Fe Kr Xe

7 Proposed 1.77 MeV/u beam cocktail Ion Energy [MeV] Penetration depth [μm] LET [MeV/ (mg/cm 2 )] Δ(m/q) [%] 14 N Cl Fe Kr Xe

8 How to reach Xe 38+ routinely? Multiple frequency heating Double frequency heating, factor of 2-5 for high charge states Triple frequency heating 2-4% gain Improved hexapole Radial field from.93 T to 1.7 T (simulation) Only for clean beams, nuclear physics with old chamber (MIVOC, sputtering) Affects the beam allocation procedure due to campaigns Afterglow mode Time structure almost irrelevant for irradiation tests

9 ECRIS plasma physics at JYFL The objective is to understand how and why different ion source parameters and techniques affect the production of highly charged ions Plasma potential measurements Time-resolved bremsstrahlung measurements (PhD Thesis by T. Ropponen in 29-21) Plasma breakdown studies

10 Plasma physics experiments Source parameters studied: Magnetic field Microwave power Neutral gas pressure Bias disc voltage Gas species

11 Plasma potential vs ion mass 7 6 Plasma potential [V] Ion mass [amu]

12 Effect of secondary electrons Normalized ion beam current of O Before a MIVOC-run, plasma potential 24 V After a MIVOC-run, plasma potential 54 V Retarding potential [V]

13 Reaching steady state bremsstrahlung emission Ar plasma, 5 W, 5/5 A, 2.6e-7 mbar 5 Bremsstrahlung count rate Total counts / 2 ms T. Ropponen et al., NIM A, 6, 3, (29), modified Time [ms]

14 What happens in the beginning of the rf pulse? Total counts / 2 ms Total counts / 2 ms Time [ms] mbar mbar mbar Time [ms] 69 W 5 W 3 W T. Ropponen et al. Submitted to IEEE Transactions on Plasma Science

15 Time-resolved ion current the preglow effect Ion current [μa] Counts Ne 3+ Ne 4+ Ne 5+ Ne 6+ Ne 7+ Ne Total counts / 2 ms Ion current [μa] Counts Ne 3+ Ne 4+ Ne 5+ Ne 6+ Ne 7+ Ne Total counts / 2 ms Time [ms] Time [ms]

16 Preglow superadiabatic EEDF Theory: Microwave pulse is applied All free electrons reach stochastic limit (EEDF is superadiabatic) electron density increases power not sufficient to maintain superadiabatic EEDF average energy collapses EEDF becomes the well-known double Maxwellian I.V. Izotov et al. IEEE Transactions on Plasma Science, 36, 4, Part 2, (28), p.1494.

17 Preglow superadiabatic EEDF? Biased disc current [ma] Counts Bias disc current Total counts / 5 μs Time [ms]

18 Plasma breakdown time - theoretical Simple model based on volumetric rate of ionizing collisions dne f = = nenn σ ionv dt t breakdown = ne, ln ne n σ n critical, ion v Plasma breakdown time affected by Neutral gas density Neutral gas species (ionization probability) Density of seed electrons

19 Plasma breakdown time Neutral gas density & species Oxygen, t = 35.7p -.94 Argon, t = 26.3p -.91 Krypton, t = 23.5p Xenon, t = 12.9p Helium, t = 287.1p -.95 Neon, t = 94.5p -1.1 Time [ms] 2 15 Time [ms] Neutral gas pressure [E-7 mbar] Neutral gas pressure [E-7 mbar] O. Tarvainen et al. accepted for publication in Plasma Sources Science and Technology

20 Plasma breakdown time Seed electrons second rf pulse separation 5 second rf pulse separation 1 second rf pulse separation 3 Time [ms] Axial magnetic field [% of maximum] O. Tarvainen et al. accepted for publication in Plasma Sources Science and Technology

21 Plasma breakdown time Seed electrons GHz, 35 W (pulsed) 14 GHz, 35 W (pulsed) GHz, 2.5 W (cw) 14 GHz, 35 W (pulsed) GHz, 5 W (cw) 14 GHz, 35 W (pulsed) GHz, 1 W (cw) 2 14 GHz, 35 W (pulsed) 14 GHz, 35 W (pulsed) GHz, 2.5 W (cw) 14 GHz, 35 W (pulsed) GHz, 5 W (cw) 14 GHz, 35 W (pulsed) GHz, 1 W (cw) He + beam current[μa] He 2+ beam current[μa] Time [ms] Time [ms]

22 Plasma breakdown time Seed electrons Seed electrons shift the preglow CSD towards higher charge states (faster ionization of HCI) Optimize the repetition rate for afterglow? Beam optics seem to affect the shape of the preglow pulse Plasma potential evolves Degree of space charge compensation evolves

23 Future prospects Upgrading the ion beam cocktail at JYFL requires higher charge states than presently available Pulsed operation mode could possibly be utilized for beam cocktails More work is needed to understand the time scales related to HCI production in pulsed mode (to optimize repetition rate)