D2: Final Layout of Injector. D8 : Multiparticlesimulationsfrom ion source to DTL

Transcription

1 Workof theiap on IFMIFdeliverables D2: Final Layout of Injector and D8 : Multiparticlesimulationsfrom ion source to DTL

2 Need/Motivation : Beam transport in theifmiflebtisdominated bythespace charge forces.beamtransmissionof morethan 90 %isnecessary todeliver + a140 mad beam at the RFQ entrance.emittance growth has to be minimized to avoid particle lossesand activation.therefore the transmission and emittancegrowthas afunctionof beam current, noise and residual gas pressure asmostimportant factorshad to be studied under consideration ofspace charge compensation effects. D2d: "The final layout ofthe injector" Particlelosses induced byinteractionsbetween residualgas and beam ions haveto beconsideredaswell as the results of the ionoptical simulations(d 8a). D8a: "Multiparticlecalculationsfrom sourceto RFQ" Emittance growth inducedby space charge effectsand aberations for different LEBTsystems including space charge compensation effects (correlated bythe pressure withd2d)and sourcenoise(d2b)haveto be studied.

3 Main parameters influencing LowenergybeamTransport forifmif Particle losses: -Chargeexchangereactions withresidualgas -Emittancegrowth Emittance growth : -Aberations due tonon linear fields -Redistributions dueto spacecharge forces -Increaseof the effectiveemittancebytime dependingeffects (noise) Spacecharge forces : -Can bereducedby spacechargecompensation

4 Particle losses byinteraction between beamionsandresiudal gas ion beam residual gas electrons Transmissionasafunctionofresidual gas pressure for an LEBTsystem of1mlength T = n n s = 1m σ loss loss B I = = 1 10 e ( n R G A σ loss s ) 20 m p[hpa]

5 Differential pumping for efficientreduction ofresidual gas pressure (measured values) Pressuremeasurement Aperture r=3/2r beam Ionsource D1 & P1 L1 D2 & P2 L2 D3 & P3 Source LEBT 500l/s Turbopump 500l/s Turbopump 270l/s Turbo pump Farradaycup 10cm Pump1 Pump z[mm]

6 Calculation ofbeamtransmission within the injector Tofullfill theifmif requirements (90%) : 100 The gas pressure 10mmbehind theplasmaelectrodehas tobe -3 below2*10 hpa.(30% losses). Adifferential pumpingsystem reducesfurtherlossesby50% and enhances safetymargin. 90 Afterreductionofthepressure within150 mmonlyminorlosses (<0.1 %/m)occure z[mm]

7 BeamtransportoftheIFMIF beamwithin the injector is dominated byspace charge forces 2 d X 2 dz Beam transportcalculation neglecting collisions and emittancegrowth by useof Envelopequation ε rms, x 2 = 3 + X K 2( X + Y) 2 x k X Drift + D,100 kev,140ma K=0% ε=0.02 K=96% ε=0.6 emittance lenses K=96% ε=0.02 gen.perveance(spacecharge) F U Am I K = = U H G 1 I e K J 3 4πε 2 ζ U 2 0

8 Simulations ofbeamtransport1: Beam extraction and post acceleration For optimizedextraction andlowest beam emittancea postaccelerationfrom extractionvoltagetothe beam energyatrfq injectionis favourable. Therequirements ofifmifcan befullfilled. calculationby IS-WG ε ε rms,calc rms,meas. = πmmmrad =0.062 πmmmrad

9 Simulationsofbeamtransport2: Electrostatic LEBT (RFQ-Tank) 0V 40000V 92500V 0V J Designconsiderations -due tospacecharge as shortas possible(35mm) -topreventhv-breakdown E z,max <7.7kV/mm -fornominalcurrent emittancegrowthapp. 50% -highlysensitvetonoise -effectiveemittancelarger vorseenforifmif. z[mm] RMS-emittance as afunction ofbeam current IGUN-4.016(C)R.Becker, ε Output emittance 100%,rms,n =0,0766 πmmmrad 140 ma An electrostaticlebtsystem doesnot fullfilltheifmifrequirements.

10 Simulations ofbeam transport 3: MagneticLEBTusing soleniods Beam transportcalculations include beamcurrent fluctuations of+/-2% at 100 khz andconservative estimationsabout the compensationdegree: Multiparticlecalculations(n=30000particles) includingfringefields,sourcenoiseandadetailed space chargecompensationscheme. 60% 0% 20% 60% 20% 60% Inthedriftsections 60%, 20 % insidethesolenoids and 0% attherfq entrance. (worstcase scenario!) AmagneticLEBT system consitingof solenoidscan fullfill theifmifrequirements andisatreasonablecosts technicalrealizable. ε 100%,rms,n Solenoid1, B LEBTentrance I=140mA +/- 2% =0,0575π mmmrad ε100%,rms,with noise = πmmmrad (12% ε-growthdue tonoise) max =0.85T z[mm] Solenoid 2,B ε max 100%,rms,n =0.97T LEBTexit I=140mA +/-2% =0,0817π mmmrad ε100%,rms,withoutnoise = πmmmrad (9% ε-growthdueto noise)

11 Ion beam space chargecloud Simulations ofbeam transport 4: Principle ofspacecharge focussing F r Advantages : -strongzylindersymetric focussing -preservationof spacecharge compensation -small externalfields -linearforces -insensitivetonoise z Magneticfieldcoils electrons anode Ion beam setupin Frankfurt Groundelectrodes 10 cm

12 Helmholtz -coils B z,max =0,2T with Gaborlens electrods Simulations ofbeam transport 4: Beam transportusing Gabor Lenses Beam-envelope D + U =100kV I =200mA EX EX ε Initial I=140mA +/- 2% =0,0575π mmmrad Firstlens: B z,max =0,16T =35kV Φ Anode Second lens: B z,max =0,11T =32kV Φ Anode 100%,rms,n ε100%,rms,with noise =0.088 πmmmrad (1-2% ε-growth due to noise) ε100%,rms,with noise = πmmmrad (12% ε-growth due to noise) ε Final I=140mA +/- 2% =0,089π mmmrad 100%,rms,n

13 Finallayout ofinjector PGPlasmagenerator deliveringabeamof140maat55kev PA Postaccerationto 100keV and firstdifferentialpumpingstage D1 Driftsection withdiagnosticsandsecondpumpingstage(l=200mm) S1 Solenoid(l=300mm,B z,max =1.2T) D2 Driftsection withdiagnosticsandpumping(l=200mm) S2 Solenoid(l=300mm,B z,max =1.2T) D2 Driftsection withdiagnosticsandpumping(l=200mm) Total:l=1200mm(costsappr incl.vacuum &diagnostic) Power supply PG PA D1 S1 D2 S2 D3 RFQ Differential pumping P1 &P2 P3 P4 pumping sheme

14 Conclusion: Beam transport in theifmiflebtisdominatedby thespacecharge forces. Beamtransmission of morethan 90 %isnecessary todeliver + a140 mad beam atthe RFQ entrance.the following activities have been successfully performedat theiap: D2d: "Thefinal layout ofthe injector" Detailed studies on beam particle losses byresidual gas interactions. => Requirementson vacuumsystemto fullfill IFMIFdefined. => Magneticsolenoid systemusingspacecharge compensation recomended to fullfillifmifrequirements. => Draftreport written. D8a: "Multiparticle calculations fromsource to RFQ" Detailed particle simulations including fringe fields andnoiseperformed. =>Electrostatic transport systemdoes not fullfillifmifrequirements. =>Magneticsolenoid systemfullfills IFMIF requirements. =>Gabor lenses areable to fullfillifmifrequirements. =>Deliverable report written andaccepted, Deliverable finished.

15 WorkonLEBTin transition year2003 Testinjector 1 Power supply 65 kv IS P S S D RFQ Laser guiding CCD Laser D GL Dipole GL P IS Power supply 20 kv Testinjector2 IS P S D GL Ionsource (diff.)pumpingsystem Solenoid Diagnostic box Gabor ens Exchange of lenssystems between Injector1and 2 to directly compare solenoids andgaborlenses.