MIDAS-NA: MInimization of Destructive plasma processes in ECR ion source

Transcription

1 MIDAS-NA: MInimization of Destructive plasma processes in ECR ion source H. Koivisto, ENSAR Town Meeting, th April 2018, Groningen, The Netherlands Partners: JYFL ATOMKI CERN GANIL GSI KVI LPSC UCLM AVS Pantechnik Task 1: Coordination of scientific activities and dissemination of know-how and good practices subtask: organise an open database ( Task 2: Annual collaboration workshops platform for open discussion, problem solving and planning of future R&D Task 3: Hands-on-training transfer of most useful methods and practices among the partners

2 Hands-on-training Hands-on training is for the transfer of the best practises and useful methods between the participating institutes 10 hands-on-trainings have been organised and 40 participants trained: Evaporation ovens for metal ion beams (1 x GANIL) MIVOC method for metal ion beams (2 x JYFL) Plasma diagnostics (2 x JYFL) Langmuir probes (1 x ATOMKI) Microwave components (2 x GSI) Charge breeders + emittance scanner (1 x LPSC) Evaporation ovens for metal ion beams (1 x GSI) 5 hands-on-trainings will be organised by the end of 2018: 2 nd training for Langmuir probes (ATOMKI) 1 st and 2 nd training for LT plasma diagnostics (UCLM) 1 st and 2 nd training for low energy beam transport and emittance measurements (KVI) JYFL training: Setting up plasma diagnostics GSI training: Network analyzer was used to measure the properties of different microwave components. For further information visit MIDAS website:

3 Outcome of hands-on-training Hands-on-training has had a very active role in MIDAS NA: Feedback has been very positive. Risto Kronholm (PhD student at JYFL) will have a presentation about his experience as a trainee and trainer. As a result of wide hands-on-training we have now better idea: - what can be done - what should be done in collaboration for having more efficient R&D! second half of ENSAR2: focus will be moved from trainings to R&D collaboration.

4 Background of MIDAS: MInimization of Destructive plasma processes in ECR ion source source Hypothesis: We can increase the intensity of highly charged ions if we minimize the destructive plasma reactions and maximize the volume favorable for the creation of highly charged ions. Testing of hypothesis has been a crucial part of our research. The processes regarding each charge state can be described by balance equation: Creation Destruction Ionization rate to charge state q This has been the main focus of ECRIS development A A: Charge exchange rate from q to q-1 Presentation by R. Kronholm B: Other losses caused for example by plasma instabilities B n e = electron density, n i = ion density, n 0 = neutral density, τ i = confinement time

5 Destructive process: Plasma instabilities Creation Destruction A B Sequence: Too efficient electron heating results in anisotropic EEDF. This triggers plasma microwave emission induced burst of electrons Increases quickly positive plasma potential induced burst of ions drop in ion beam intensity recovery new instability event. Notice the time scale of different events! Instability frequency: varies between khz depending on tuning. Decreases confinement time enough time for high q! H. Koivisto, ENSAR Town Meeting, th April 2018, Groningen, The Netherlands f 0.2 khz

6 What affects plasma instabilities? Ion source tuning and magnetic field configuration affects the instability rate and amplitude Repetition rate of instability Factors affecting instabilities and rep. rate: - Minimum B-field value (linked to gradb) - Microwave power - Gas feed rate (linked to plasma density) Magnetic field on resonance seems to be a key factor. Try to avoid low gradb at ECR resonance (design goal), which induces plasma instabilities!

7 Magic knob to make plasma more stable: multiple frequency heating Small amount of secondary frequency decreases kinetic instabilities losses of highly charged ions decreases

8 Charge breeder vs kinetic instabilites (EMERGENCE project) Impurities in the extracted ion beam is a major drawback of ECRIS charge breeders Impurities Impurities Impurities We run LPSC charge breeder in stable and unstable mode. Remarkable increase of unwanted elements in unstable operation mode (see A/Q spectrum). Instability event explodes the plasma wall material is sputtered by energetic ions Unstable operation is associated with low gradb ( high B min /B ECR ).

9 HIISI 18 GHz ECRIS at JYFL Requirement: Intensity of medium charge states (M/q 5) have to be increased by factor of >5. Earlier-mentioned hypothesis has been used as design guideline of HIISI: minimize destructive plasma reactions. HIISI specifications: Even 4 freq. heating possible! Strongest PM ECRIS hexapole Frequency 18 GHz + 14 GHz B inj 2.8 T Klystron power 2 kw + 2 kw B ext (1.5) T TWTA 8-18 GHz P max : 250 W L (plasma) mm 2 tunable oscillators B rad (24-segm) 1.3 T L plasma chamber 400 mm B rad (36-segm) 1.45 T D plasma chamber 100 mm gradb on axial resonance > 5 T/m. Based on experience with JYFL 14 GHz ECRIS (stable vs unstable operation) Strongest RT axial field Largest RT ECRIS plasma Refrigerated and vacuum insulated hexapole for improved properties of permanent magnets. Cooling down to -20 C

10 Preliminary HIISI results with 24 segment hexapole ( 1.3 T) HIISI has been tested with oxygen, argon, krypton and xenon JYFL 14 Ghz ECRIS HIISI clearly outperforms the JYFL 14 GHz ECRIS 36-segment hexapole ( 1.45 T) will be tested during the spring 2018.

11 Extraction of 0.25µA of 129 Xe 32+ beam from the KVI- CART AECR-ion source used for the AGOR accelerator Installation of a new hexapole Pole tip field 0.86 Tesla T = C

12 GANIL GTS ECRIS upgrade Improve beam capabilities for low energy interdisciplinary research (ARIBE facility) Establish good performance for GTS to serve as a beams R&D platform for GANIL Extraction improvement Improved optics Improved operational flexibility Improved vacuum Improved HCI beam currents (3x so far) Improved temporal beam stability Extended range of available beam energies Injection redesign Two wave guides GTS for GHz GHz ECR double Ion frequency Source operation Compatible Improved with operational metal beam flexibility production (oven/mivoc) Availability of 2 frequency heating H. Koivisto, ENSAR Town Meeting, th April 2018, Groningen, The Netherlands Enhanced plasma confinement New middle coil installed Injection plug redesign to increase axial B field maximum Improved confinement and B field control 12

13 Recent low temperature plasma research at UCLM Time resolved measurements of hydrogen ion energy distributions in a pulsed 2.45 GHz microwave plasma A. Megía-Macías, O. D. Cortázar, O. Tarvainen, and H. Koivisto. Physics of Plasmas 24, (2017). Experiment IEDFs time evolution for H +, H 2 + and H 3 + Ion temperatures evolutions

14 Summary Hands-on-training has been an excellent concept to improve and develop networking and collaboration MIDAS community has done a lot of R&D in the spirit of the original MIDAS plan. We have created vast amount of new information and new developments. R&D for plasma instabilities R&D for charge exchange and other plasma processes ECRIS development: HIISI, upgrade of GANIL GTS, upgrade of KVI-CART ECRIS, R&D on 60 GHz ECRIS project at LPSC/LNCMI Next MIDAS annual meeting will be held in Toledo (23-24th May, 2018). Main focus will be on development of R&D collaboration and problem solving.

15 Extra slide if time LPSC 60 GHz ECRIS: test stand for European ECRIS community? 3 laboratories have collaborated since 2006 to pave a way for 60 GHz ECRIS (LPSC, LNCMI, IAP-RAS) An axi-symmetrical RT ion source operated at 60 GHz was designed and tested at LNCMI (using polyhelix technology) Record current densities up to 1 ma/cm 2 for medium charge states have been reached Next step: RT hexapole allowing ECRIS operation at 60 GHz. LPSC will open discussion about the possibility of larger (EU) collaboration (MIDAS annual meeting in Toledo, May, 2018 ). Note: high power consumption not for daily operation. BUT Could be used as a test stand for european ECRIS community: Study ECR plasma physics (@60 GHz) Study high intensity (HCI) beam extraction and transport Solve the problems which we cannot yet anticipate Can we be prepared when superconducting technology would (safely) allow the construction of 60 GHz ECRIS? 1m e.g. Iofee coil design (flesh) and axial SC cooils (red)