• G. Serianni, P. Agostinetti, V. Antoni, G. Chitarin, E. Gazza, N. Marconato, N. Pilan, P. Veltri
  Consorzio RFX, Associazione Euratom-ENEA sulla Fusione, Padova
• M. Cavenago
  INFN/LNL, Legnaro (PD)
• G. Fubiani
  GREPHE/LAPLACE, Toulouse

The ther­monu­cle­ar fu­sion ex­per­i­ment ITER, re­quires 33 MW of aux­il­iary heat­ing power from two Neu­tral Beam In­jec­tors (NBI), each of them pro­vid­ing 40 A of neg­a­tive deu­teri­um ions. The EU ac­tiv­i­ties ori­ent­ed to the re­al­i­sa­tion of the elec­tro­stat­ic ac­cel­er­a­tor com­prise the con­struc­tion in Pado­va of SPI­DER, a fa­cil­i­ty de­vot­ed to the op­ti­mi­sa­tion of the beam source. SPI­DER pa­ram­e­ters are: 100 keV ac­cel­er­a­tion, 40/60 A (deu­teri­um/hy­dro­gen) cur­rent. For the op­ti­mised SPI­DER ac­cel­er­a­tor the pre­sent con­tri­bu­tion pro­vides a char­ac­ter­i­sa­tion of sec­ondary par­ti­cles, which in­clude elec­trons pro­duced by im­pact of ions on grid sur­faces, stripped from neg­a­tive ions in­side the ac­cel­er­a­tor, and pro­duced by ion­i­sa­tion of the back­ground gas, and the cor­re­spond­ing pos­i­tive ions. Cur­rents and heat de­posit­ed on the var­i­ous grids and spa­tial dis­tri­bu­tion by sec­on­daries will be de­scribed. It is found that most of the heat loads on the ac­cel­er­a­tor grids is due to elec­trons; more­over the fea­tures of sec­on­daries ex­it­ing the ac­cel­er­a­tor and back-stream­ing to­wards the source will be pre­sent­ed. The re­sults will be com­pared with old in­ves­ti­ga­tions con­cern­ing the NBI 1 MeV ac­cel­er­a­tor.

• M. Cavenago
  INFN/LNL, Legnaro (PD)
• F. Cavaliere, G. Maero, B. Paroli, R. Pozzoli, M. Romé
  Universita' degli Studi di Milano e INFN, Milano

In a Malm­berg'Pen­ning trap like EL­TRAP an elec­tron beam can be stored or prop­a­gat­ed in a space charge dom­i­nat­ed con­di­tion, due to the low ac­cel­er­a­tion volt­age used; in par­tic­u­lar we can test the lon­gi­tu­di­nal ex­pan­sion of the elec­tron bunch with sev­er­al di­ag­nos­tics, in­clud­ing Thom­son scat­ter­ing. Pulsed elec­tron beams pro­duced by an ex­ter­nal pho­to­cath­ode source in the 1'10 keV en­er­gy range and with 4 ns length have been mea­sured also by two elec­tro­stat­ic di­ag­nos­tic sys­tems. A prop­er soft­ware is need­ed to com­pen­sate for the ca­pac­i­tance of the pick­up elec­trodes. Rf can be ap­plied to the sec­tored elec­trode to pro­duce a plas­ma source or to ex­cite or to de­tect ro­ta­tion­al modes; in par­tic­u­lar the use of a new 8 sec­tor elec­trode will allow up to m=3 modes.

• M. Cavenago
  INFN/LNL, Legnaro (PD)

In singly charged pos­i­tive ion sources, the study of beam ex­trac­tion is great­ly sim­pli­fied by the ex­is­tence of a well de­fined place for plas­ma to beam tran­si­tion, given by the well known Bohm cri­te­ri­on, where the ion flow speed equals the speed of sonic per­tur­ba­tion, known as Bohm speed. Most of the ion ex­trac­tion sim­u­la­tion codes are im­plic­i­ty based on the con­cept of quasi neu­tral­i­ty in the plas­ma re­gion, as lim­it­ed by the Bohm cri­te­ri­on. In neg­a­tive ion source the ex­is­tence of an elec­tron co­ex­tract­ed beam and of a mag­net­ic fil­ter makes the rel­e­vant speed less clear. More­over there are sev­er­al scale lengths to be con­sid­ered: the Debye length, that is typ­i­cal­ly 0.01 mm, the elec­tron and ion gy­ro­ra­dius, the H^- scat­ter­ing, ab­sorb­tion and pro­duc­tion length. In the de­vel­op­ment of neg­a­tive ion source for NBI in­jec­tor for ITER, the pro­duc­tion of H^- at wall and the neg­a­tive sheath so gen­er­at­ed is also im­por­tant. A crit­i­cal eval­u­a­tion of these regimes is ob­tained with 1D (one space di­men­sion) mod­els, most­ly re­strict­ed to mag­net­ic fil­ter par­al­lel to the ex­trac­tion wall. Some re­marks on 2D sim­u­la­tion codes is also given.

• M. Cavenago, T. Kulevoy, S. Petrenko
  INFN/LNL, Legnaro (PD)
• V. Antoni, G. Serianni, P. Veltri
  Consorzio RFX, Associazione Euratom-ENEA sulla Fusione, Padova

The de­vel­op­ment of neu­tral beam in­jec­tors (NBI) for toka­mak like the ITER pro­ject and be­yond re­quires high per­for­mance and huge neg­a­tive ion sources (40 A of D- beam re­quired); it was re­cent­ly ac­cept­ed that in­duc­tive plas­ma cou­pled (ICP) ra­diofre­quen­cy sources are the pre­ferred op­tion. It is there­fore use­ful to have a mod­er­ate size source of mod­u­lar de­sign to test and ver­i­fy both con­struc­tion tech­nolo­gies and com­po­nents and sim­u­la­tion codes; here the NIO1 de­sign (60 kV, 9 beam­lets of 15 mA H^- each) and con­struc­tion sta­tus are de­scribed. Source is as­sem­bled from disk shaped mod­ules, for rapid re­place­ment; the beam­lets are ar­ranged in 3 times 3 square ma­trix so that 90 de­gree ro­ta­tion of mod­ules is pos­si­ble and al­lows to cross or to align the mag­net­ic fil­ters used in the source. The 2 MHz rf coil and the rf win­dow are a sim­ply re­place­able mod­ule. Ex­ten­sive rf ab­sorp­tion and mag­net­ic coil sim­u­la­tions were per­formed. Re­lat­ed beam sim­u­la­tion and fast emit­tance scan­ner de­vel­op­ment are de­scribed else­where.