18in Symposium on Fusion Technology, zz-zo. tua-*. t\ain,iuuc

Outline design of a neutral beam injector for ITER EDA J Pamela'1. R. H-mswurihA. J Fei>tb. M Fumelli3, B. Ht-ini-mann°, C Jacquota. F Jaquier3, M Lochterc. S Martinc. M Nightingale, J Sielanko1', A Simonin3, C Sp«.-niakb. E. Spethb. N. Taylord, E. Thompson*". M. Watson' a Association Euratom-CEA. CE Cadarache. 1310S St Paul lez Durance, " Euratom Association, IPP, Garching, c Euratom Association, KFA, Julich, Germany d Euratom Association, UKAEA Government Division, Culham Laboratory, United Kingdom e University of Lublin, Poland f JET Joint Undertaking, Abingdon, United Kingdom

A self consistent physics design for a 50 MW 1 MeV negative-ion based injector has been produced which forms the basis of a preliminary engineering design. Neutronics calculations show that radiation damage to insulators and nuclear heating of cryogenic components does not present any major problem. A detailed report is being issued at NET [1].

1. INTRODUCTION

Detailed studies using an extended version of the code PRETOR [2] have shown that ignition of D-T plasmas in ITER can be 10«cV obtained using 40-50 MW of Neutral Beam pre-accelerator Heating [3]. While the power requirement for ignition is relatively insensitive to the beam energy above 600 keV D°, a beam energy of at least 1 MeV is required in order to maximise the potential for current drive. On SFSfkd last shutter _hi<«eiife»ton this basis, the specification of a neutral beam / / Ine-waax. caJcrimeler—/ water-Jl! I electrical power system for ITER has been chosen, 50 MW of km dunp poww-Jf and 02 lor cryo pumc- neutriber B*»J I It» D-jource D° beam at 1 MeV through 4 ports [4], and a and accelerator flout* door J request was made by ITER EDA to produce system an outline design of this injector (design task D71). The work conducted on this task in Figure 1. Conceptual scheme of an injector is presented here. module

• Electrostatic accelerator : energy 2. BEAM LINE PHYSICS DESIGN Si MeV; SINGAP type [5] (Fig. 2) ; 5 SINGAP beams per source (13 cm pitch) ; The outline design is shown schematically overall beam divergence = 6 mrad ; high in Pig. 1. Its main characteristics are the voltage source configuration. following : 2 • Gas neutralUer : =57 % efficiency at • D- Source : I = 25 A, j = 15 mA cm" , 8 1019 mol/m2 gas target. 1.8 m height, P = 0.6 Pa. • In-Hne electrostatic Qcsuiunt Ton • Beam calorimeter • hypi-rvapotron deflector and dump iRIDD: Fie 3'; peak plate? ; inclination '20° wrt beam axi? : d.c. power densities = 10 to 13 MW/m-'. mean dumping capability : full beam power at power density = 3 M\V/m-. double-sided tOOkeV, neutral beam at 1 MeV. hypervapotrons. • Gas and pumping : cryo pumps ; < 5 x 103 m3/s, differential pumping Isource J 200 calorimeter) • Beam losses = 17 9t (Fig. 4) : stripping 150 •: 10 9c, re-ionisation 7 % ; backstreaming ions 100 <1%. • Tritium accumulation : no problems as 50 regards injector operation. About 300 s of I. 0 continuous injector operation per g of T2 e accumulated in the beamline cryopumps. -50

-100 gas inlet at neutron midpoint -ISO

-200 100 200 300 400 500 Z(mm)

Figure 2. Calculated D" trajectories in a four beamlet columns SINGAP accelerator

SEAMS • •JO tV -*£*- &• 0 V _BL. 2 4 6 8 10 •JOtV pimping speed/ lOW/s ' ^o-- , DO j. -o. 0 V •J^o. \ DO y Figure 4. Stripping and re-ionisation losses -D- , \ •50 *V as a function of the pumping speed

» Hv 3. MAGNETIC SHIELDING Figure 3. Scheme of the Residual Ion Deflector and Dump (RIDD) The ITER magnetic field at the injector level is = 1 kGauss. A reduction to < 1 Gauss • Vertical subdivision of the neutralizer at the source level is obtained by shielding in and RIDD matched to the SINGAP beams, two steps : providing a substantial reduction of the 1. Passive shielding (ordinary steel walls neutralizer gas flow and of the RIDD on both sides of the boxes ; injector shielded deflection voltage (< 50 kV). with a double wall made from a very mild • Beam transmission through the 40 cm steel) ; = 5001 of magnetic material. The wide duct : > 90 % (distance from source to shielding effect is shown on Fig. 5 (3-D Tokamak inner wall : 19.5 m). Calculation). 106

Tiblf I GuiipuU-d nvutr.»n and yanim.i tluvcs

Locaii* r. X. •utr-n flux urn' -S"1! Gamma flux U MA > 1 MeV to:nl i cm - s' i 1 MV insulator? - tup S.Ox 10* 9.7 v 109 1.0 x 1010 9.S x 10s - side 6 5* 104 9.9 x 10s 1.3 x 109 9.6 x 10s - average 2.3 x 10* 3.6 x 109 3.9 x 10s 9.5 x 10s 100 kV insulators 0 1.4 x 109 2.3 x 109 2.8 x 109 Crycpump - near ion dump 0 7.4 x 109 2.4 x 109 3.1 x 109 Transmission line 8.0 x 109 9.8 x 109 1.0 x 1010 1.3 x 109

2. Residual field compensated by actively studies on neutron irradiation are recom­ controlled coils. mended. The use of epoxy insulators cannot The perturbation of the ITER magnetic be recommended without further studies. field is < 2 Gauss. 2. Degradation of the SF6 will occur : a recycling plant is needed. 3. Negligible radiation heating of the cryopumps : < 10 W. magnetic field inside the injector t>ox 4. Activation : one expects no need for remote handling (radiation level < 1 mSv/hr) 30 5 after a decay time of some weeks for 20 :—t=130s z- vertical continuous operating periods of the order of '< 5 10 Lt=80s " • component 10 s. de n \ "• 0 % OODDOODB g OOOOOOQO O

\c -10 5. ENGINEERING DESIGN . » # • racial ft -20 r end of the component OB f neutralzer Two options are considered : fc -an 1. Horizontal vacuum, vessel axis : length 20 22 24 26 28 30 8.1 m, diameter 3.5 m and volume = 72 m3. distance to center (m) 2. Vacuum vessel with vertical axis : height 5 m, diameter 5 m and volume Figure 5. Magnetic field inside the box with = 115m3 (better accessibility, easier main­ shielding (open symbols : t = 80 s ; closed tenance, larger volume, increased pumping symbols : t = 130 s ; squares : vertical area ; but increased weight and complexity of component ; circles : radial component) vessel and shielding). Alignment of injector/duct necessitates flexible isolation between the ITER 4. NEUTRON1CS AND RADIATION secondary containment and the injector cell EFFECTS (vacuum vessel cooldown !). The results of 3D neutronics Monte Carlo Hypervapotron elements on RIDD codes MCNP4 [6] and TRIPOLI3 [7] are (Fig. 6 : double-sided elements) and indicated in Table 1. The expected effects are calorimeter. the following : Actuation of the fast shutter and calorimeter would be achieved via magnetic 1. Radiation induced mechanical defects couplings (non-flexible penetrations ; linear [8], Conductivity (R1C) [9] and Electrical displacement). Degradation (RIED) [10] : no problem for An all metal sealed double gate value is high-quality alumina at < 150°C, for inte­ used to separate the neutral beam injector grated irradiation times > 1 year. Further from the ITER torus (double containment r-cht-m>- in tht* cas-i- -il" rn.unun.i': nf th>.- ACKNOWLEDGEMENTS înjfctiT' This hn^ n> \uih>" ;->d the arcidi-nial oarim-nct/ ol'20 bar Pt •-1. Inpnient Tlv- author- \M^h : .vkn<••••.!«-dirt- th.- is nei'ded pn-euais work uf Mrs A B-.-rlin-Ma^hu a'.'.d ff Mrs J Cousseau in the organisation of meeting* and the edition of the D71 ITER Task report The support of F. Engelmann has also been highly appreciated. This work has been partly performed under NET contracts (ITER Task D71).

REFERENCES

1. J.Paméle et al. "Neutral beams for ITER", NET Report n° 104, 1994 (The NET Team c/o IPP Garching). 2. P.H. Rebut, D.Boucher, D.J. Gambier, B.E. Keen and M.L. Watkins, "The ITER Challenge", Proc. I7lh Symp. on Fusion Technology, Rome (1992), Fusion Engineering and Design 22 (1993) 7. 3. H.P.L. de Esch, D. Stork, CD. Challis and B. T-ubbinj, (^art. II of Ref. [1]). 4. ITER T»*.C4 Meeting documents, ITER­ ERA, San Liego (Jan. 1994). Figure 6. Engineering drawing of the RIDD 5. M. Fumelli et al., ^Proposal for a 1 MeV 0.1 d.c. D' beam acceleration experiment width vertical hypervapotron dump plates th matched to five SINGAP slab beams side by at Cadarache", 6 Intern. Symp. on the side production and neutralization of negative ions Brookhaven, Upton (USA), (November 1992). 6. POWER SUPPLIES 6. J. Briesmeister (Ed), MCNP - "A general Monte Carlo code for neutron and photon The following characteristics are based on transport", LA-7396-M, Rev. 2 (revised a 15 A, 1 MV PS European study [11] : 1991). • accelerator intrinsic capacitive energy 7. J-C. Nimal and T. Vergnaud, "TRIPOLI-3 < 100 J, code de Monte Carlo tridimensionnel • voltage regulation and ripple < 10 %, polycinetique", CEA/DRNVDMT/SERMA • cascade transformer with four stages report, CEA'Saclay. of 250 kV, each having its own rectifier, 8. G.P. Pells, J. Amer. Cerm. Soc. 22 366 • primary power supply : 30 MVA (1994). inverter at 400 Hz to limit the stored energy, 9. G.P. Pells and G.J. Hill, J. Nucl. Materials • switch-off time < 0.1 ms, 14JL142 375 (1986). • HV reapplication time < 100 ms, lO.PellsG.P, J. Nucl. Materials ISA 177 • inductances, resistances and magnetic (1991). snubber included in the transmission line to ll.R.H. Hemsworth, C. Jacquot, Proc. 17th dissipate the PS stored energy (3 kJ), Symposium on Fusion Technology, Rome • auxiliary power at HV : 1.5 to 2 MW. (1992).