Studies on the voltage hold off of the SPIDER driver coil at high radio frequency power

SPIDER is the prototype of the ion source of the ITER Heating Neutral Beam Injector presently in operation at the Neutral Beam Test Facility in Padova, Italy, designed to deliver an ion current density of 355 A/m2 in H− (285 A/m2 in D−) and to accelerate the beam of extracted particles up to 100 keV energy. SPIDER is equipped with a plasma source composed of 8 Radio Frequency (RF) drivers of 100kW each to transfer power to the plasma at the frequency of 1 MHz via magnetic inductive coupling. The driver coil, separated from the plasma by a dielectric driver case, works at an estimated pressure of about 0.065 Pa (with a pressure of 0.3 Pa within the source) and reaches a voltage of 12 kV rms at full power. A set of 4 dielectric supports called combs, placed around the driver case, assures the separation of the coil turns. Both the combs and the driver case contribute to the mechanical support of the coil. The design of the SPIDER plasma source, implemented during the procurement of the source, follows the concepts previously developed and proved at IPP Garching. Further studies have proceeded in parallel to SPIDER construction, both at theoretical and experimental level: one important topic analyzed has been the power handling capability of the driver, since the performance in terms of ion current of the beam source increases with the radiofrequency power level, which in turn raises issues related to the voltage hold off of the driver components. The risk of possible breakdowns at the driver coils, already experienced on other devices, has been identified for SPIDER too; the paper reports the present status of the electrical analyses of the SPIDER driver coil region.SPIDER is the prototype of the ion source of the ITER Heating Neutral Beam Injector presently in operation at the Neutral Beam Test Facility in Padova, Italy, designed to deliver an ion current density of 355 A/m2 in H− (285 A/m2 in D−) and to accelerate the beam of extracted particles up to 100 keV energy. SPIDER is equipped with a plasma source composed of 8 Radio Frequency (RF) drivers of 100kW each to transfer power to the plasma at the frequency of 1 MHz via magnetic inductive coupling. The driver coil, separated from the plasma by a dielectric driver case, works at an estimated pressure of about 0.065 Pa (with a pressure of 0.3 Pa within the source) and reaches a voltage of 12 kV rms at full power. A set of 4 dielectric supports called combs, placed around the driver case, assures the separation of the coil turns. Both the combs and the driver case contribute to the mechanical support of the coil. The design of the SPIDER plasma source, implemented during the procurement of the source, follows the c...