Low voltage Ohmic and electron cyclotron heating assisted startup in DIII-D

摘要: There is considerable interest in the development of low voltage startup scenarios for large tokamaks since it proposed that ITER electric field which will be applied ionization and plasma current ramp-up limited to values E ≤ 0.3 V/m. Studies have been carried out DIII-D with without electron cyclotron preionization preheating. Successful Ohmic has achieved ~ 0.25 V/m by paying careful attention error fields prefill pressure, while heating (ECH) assisted 0.15 demonstrated. ECH gives improved reliability at such permits operation over an extended range pressures magnetic fields. Using ECH, = |B⊥| > 50 G most vessel cross-section Such represents increase more than a factor two highest value was same field. During extreme pressure and/or fields, excessive breakdown delays are observed. The experimental data agree well theoretical predictions based on Townsend avalanche theory. always prompt. primary effect during decrease resistive component loop Vrcs. A significant reduction (~30%) Vres powers (PRF 300-400 kW), but further PRF results only modest additional Vres. not whole phase these experiments produced volt-second consumption up flat-top (Ip 1 MA) 10%. These confirm specified design acceptable demonstrate substantial benefits accrue from use startup.