Curdy, J.C.

Geller, R.

Jayamanna, K.

Lamy, T.

Olivo, M.

Peaucelle, C.

Schmor, P.

Sole, P.

Sortais, P.

Thuillier, T.

Voulot, D.

Yuan, D.

Hal - Université Grenoble Alpes

Charge breeding method results with the Phoenix booster ECR ion source

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Charge breeding method results with the Phoenixbooster ECR ion sourceT. Lamy, J.C. Curdy, R. Geller, C. Peaucelle, P. Sole, P. Sortais, T. Thuillier,D. Voulot, K. Jayamanna, M. Olivo, et al.To cite this version:T. Lamy, J.C. Curdy, R. Geller, C. Peaucelle, P. Sole, et al.. Charge breeding method resultswith the Phoenix booster ECR ion source. Garvey T. et al. European Particle Accelerator Con-ference 8 EPAC 2002, Jun 2002, Paris, France. Cern, pp.1724-1726, 2002. <in2p3-00012295>HAL Id: in2p3-00012295http://hal.in2p3.fr/in2p3-00012295Submitted on 14 Feb 2003HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.CHARGE BREEDING METHOD RESULTS WITH THE PHOENIXBOOSTER ECR ION SOURCET. Lamy†, J.C. Curdy, R. Geller, C. Peaucelle, P. Sole, P. Sortais, T. Thuillier, D. Voulot, ISN,Grenoble, FranceK. Jayamanna, M. Olivo, P. Schmor, D. Yuan, TRIUMF, Vancouver, CanadaAbstractThe charge breeding method using an ElectronCyclotron Resonance Ion Source (ECRIS) have alreadyshown interesting results when injecting a 1+ ion beaminto the dedicated PHOENIX Booster ion sourcedeveloped at ISN-Grenoble with a 10 GHz RF frequencytransmitter. New results have been obtained with a 14GHz RF frequency and new elements have been studiedto get reliable efficiencies and charge breeding timessuitable for an easy and daily production of multi-chargedRadioactive Ion Beams. The cw regime is suitable forcyclotron acceleration when the Electron CyclotronResonance Ion Trap one, fulfils the requirements ofpulsed accelerators as linacs and synchrotrons. Theafterglow measurements performed give a betterunderstanding of the physical processes involved in theECR-plasma production of highly charged ions and couldlead to improvements of ECRIS efficiencies and thereforeto accelerator ones.1 INTRODUCTIONThe purpose of this publication is to focus on two majorpoints concerning the ability of the ECRIS PHOENIXBooster and its injection system to produce eitherradioactive ion beams (RIB) or metallic ion beamssuitable for an efficient acceleration. The highest primarybeam capture and fast charge breeding time τcbt areexpected. The global efficiency ηG(n,In,I1) is the sum ofthe specific charge efficiency yields ηn, where n and In arerespectively the charge and the intensity of the boostedcharges obtained from the 1+ ion intensity injected I1. ηGincludes three processes: capture, ionization andextraction from the ECR plasma.∑∑ ==nnnnG InI1*ηη2 EXPERIMENTAL SETUP ANDPROCEDURE2.1 Experimental setupThe ISN charge breeding test bench has beenextensively described in many publications [1-4], someimprovements have been carried out concerning thevacuum (increase of the PHOENIX injection sidepumping speed), and the alignment of the 1+ injectionline.n+ Valve1+ Valven+ Faraday Cup1+ FaradayCupInjectionvacuum improvementn+ SourcePHOENIXOptical alignment of the 1+ line (new frame)Figure 1: ISN 1+ → n+ experimental setup. 2.2 Experimental procedureTo prove the reliability of the 1+ → n+ method, 10different ions have been injected in 15 days. The purposeof the experiment was to study the n+ production for A/n≈ 7 ions (A: ion mass in amu) necessary to meet TRIUMFRFQ requirement. The system was tuned to get ηn = 3%and the charge breeding time τcbt (time to reach 90% ofmaximum intensity) was then measured. Concerning theproduction of stable metallic ion beams, the feasibility ofreliable high currents has been studied.3 CHARGE BREEDING OFRADIOACTIVE IONS3.1 New elements injected in PHOENIX Booster14 GHzThe new 1+ ions injected in PHOENIX Booster 14GHz are 20Ne, 23Na, 39K, 64Zn, 69Ga, 85Rb, 88Sr, 90Y, 115In,and 208Pb2+ (due to the magnetic rigidity limitation of the1+ spectrometer). Already studied elements 109Ag and120Sn [3], have been injected too. The efficiency yieldsobtained in routine operation are summarized Table 1.___________________________________________†lamy@isn.in2p3.frTable 1: Efficiency yields obtained for routine operation(one ion per day)Element 1+ Intensity(nA)n+Charge Yield(%)20Ne 1000 4 7.523Na 660 6 1.339K 280 6 6.564Zn 42 10 2.869Ga 460 11 285Rb 90 13 588Sr 470 14 3.790Y 178 14 3.3109Ag 175 17 3115In 130 18 3.3120Sn 167 19 4.1208Pb 700 (2+) 25 6.8The dispersion of the results is due to the experimentalprocedure described above in 2.2. Rare gases ions (i.e.20Ne) when approaching a wall are neutralized, and thencan go back to the plasma where they are still availablefor subsequent ionization. In this situation the 1+ → n+efficiency is always high. However for alkali or metallicions this process does not occur since these ions can stickto the walls, so the radial diffusion is a loss term for theglobal efficiency.3.2 Charge state distributionsMany experiments have been performed to obtain thehighest efficiency on a specific charge. When theparameters are optimized to get the highest capture (ηGmaximized), the ions can be considered as ‘classical’ ionsin the ECR plasma, and thus the charge state distribution(CSD) doesn’t differ from a classical ECRIS [5]. We cannow consider that, for metallic ions with A ≥ 40 amu weget ηn ≈ 6% in standard operation, which means ηG ≈ 40%. Typical CSD’s are shown Fig. 2 and 3 for 39K and115In.0123456783456789101112ChargeEfficiency yield (%)Figure 2: 39K charge breeding efficiency.012345624 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8ChargeEfficiency yield (%)Figure 3: 115In charge breeding efficiency.3.3 Influence of the pressure on the charge statedistributionMany parameters can affect the CSD obtained by the1+ → n+ process: the axial magnetic confinement, the RFpower and the support gas pressure. Let us consider a208Pb2+ injection. After tuning the system to optimize ioncapture, the support gas flux (O2) is varied. Because of theposition of the gauge, located in the injection chamber ofPHOENIX, no significant pressure variation can beobserved. However the effect of this variation on the CSDcan clearly be seen (Fig. 4). Therefore one shouldconsider this parameter as fundamental to get the highestefficiency on the expected charge.0.00.10.20.30.40.50.60.70.80.91.030 29 28 27 26 25 24 23 22 21 20 19 18 17 16chargen+ ion intensity (a.u.) Low gas fluxHigh gas fluxFigure 4: Charge state distribution versus gas flux. 3.4 Charge state dependence of charge breedingtimesThe charge breeding times τcbt strongly depend on thetuning parameters of the source (RF power, magneticfield, pressure). After optimising the 39K charge breeding,we have experimentally measured τcbt for each pure 39Kcharge state (without parasitic ion). The results are plottedFig. 5. t = 0 being the injection time of the 1+ beam, wefirst clearly observe an increasing time shift for theextraction of the different charges, the 11+ appearing 12ms after the 1+ injection. Moreover, the time to reach 90% of the total extracted beam intensity depends linearlyon the charge and is about 10 ms per charge (Fig. 6). Anadditional study should be performed to understand if thisresult is due to the better confinement of the higher chargestates in the ECR plasma.00.10.20.30.40.50.60.70.80.910 25 50 75 100 125Time (ms)Normalized IntensityK4+ K5+K6+ K7+K8+ K9+K11+Figure 5: Potassium charge breeding times τcbt.010203040506070804 5 6 7 8 9 10 11ChargeCharge breeding time (ms)Figure 6: Linearity of the charge breeding time τcbt.4 LEAD PRODUCTIONTo get a more accurate understanding of the PHOENIXbooster ECRIS, charge breeding studies have beenperformed with lead, either in cw mode or in pulsed  one.4.1 continuous working modeIn the context of RIB production, an efficiency of 7%with a CSD peaked in the range (21+ - 27+) has beenobtained with a 500 nA 208Pb2+ injected beam, which isconsistent with the results explained in paragraph 3.2.When the injected current was increased up to 20 eµA theefficiency dropped to 2%, but the 208Pb24+ extracted ionbeam intensity reached 5 eµA. A typical CSD is shown inFig. 7.010002000300040005000100 110 120 130 140 150n+ spectrometer current (A)n+ Ion current (nA)24+22+20+27+Figure 7: Pbn+ 1+ → n+ charge breeding.This result clearly shows that the PHOENIX chargebreeder remains efficient when injecting higher currents.The production of a “low charge-high intensity” ionbeam, and its injection into a low pressure charge boosterwhere the multi-ionization up to high charge states cantake place, can be a very interesting production methodfor metallic ion beams [6]. 4.2 Afterglow modeThe afterglow mode gives a good picture of the ionstrapped in an ECRIS [7, 8] and therefore of itsperformance. When injecting 4 eµA of  Pb2+, we obtainedthe experimental  Pb27+ signal (see Fig. 8) with a 100 µsplateau at 30 µA. In opposition to what we have observedwith MINIMAFIOS, it is possible to tune the timestructure of the signal.051015202530-5 0 5 10 15 20Time (ms)Pb27+  Ion current (µA)Figure 8: Pb27+ Afterglow signal.5 CONCLUSIONA fast tuning of the PHOENIX charge booster gives a3% efficiency yield on a specific charge for metallic ions(A ≥ 40 amu), the use of all the parameters availablepermits to increase this value to 6%. When tuned thebeam extracted is stable at least for hours.The lead production brings up a new method formetallic ion production, and demonstrates that theworking of PHOENIX as a booster is comparable toclassical 14 GHz ECRIS.ACKNOWLEDGMENTSThis work was supported in part by TRIUMF underCS2000/11 and by European Union under HPRI-CT-1999-50003.6 REFERENCES[1] N. Chauvin, thèse de Doctorat Université JosephFourier Grenoble, Juillet 2000.[2] P. Sortais et al., RNB2000 Conference proceedings,Nucl. Phys. A Vol. 701 pp. 537-549 (2002) [3] T. Lamy et al., Rev. Sci. Instrum. Vol.73, nb.2, pp717-719 (2002)[4] T. Lamy et al., Proc. 14th International Workshop onECR Sources, ECRIS99 pp 107-110[5] R. Geller, Electron Cyclotron Resonance Ion Sourcesand ECR Plasmas (IoP, Bristol, 1996)[6] C. Barue et al., Proc. International Workshop on ECRSources, ECRIS99 pp 111-115[7] P. Sortais, Rev. Sci. Instrum. 63, 2801 (1992)[8] N. Chauvin et al., Nucl. Instrum. Methods Phys. Res.A 419, 185 (1998)

Charge breeding method results with the Phoenix booster ECR ion source

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