Formation and Steady-State Sustainment of a Tokamak by Coaxial Helicity Injection

Jarboe, T.R.

doi:10.13182/fst89-1

Cited by 129 publications

(122 citation statements)

References 14 publications

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“…At high injector flux (85 mWb, corresponding to 9.4 kA in the PF1B coil), no bubble burst was observed even at an injector current level of 20 kA. This is consistent with our understanding of the bubble-burst current magnitude, which states that this current is proportional to the ratio of the injector flux squared divided by the current in the TF coil (3) . Fig.…”

Section: Transient Chisupporting

confidence: 88%

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Solenoid-free Plasma Startup in NSTX using Coaxial Helicity Injection

Raman

Jarboe

Bell

et al. 2005

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The favorable properties of the Spherical Torus (ST) arise from its very small aspect ratio. However, small aspect ratio devices have very restricted space for a substantial central solenoid. Thus methods for initiating the plasma current without relying on induction from a central solenoid are essential for the viability of the ST concept. Coaxial Helicity Injection (CHI) is a promising candidate for solenoid-free plasma startup in a ST. Recent experiments on the HIT-II ST at the University of Washington, have demonstrated the capability of a new method, referred to as transient CHI, to produce a high quality, closed-flux equilibrium that has then been coupled to induction, with a reduced requirement for transformer flux [R. Raman, T.R. Jarboe, B.A. Nelson, et al., Phys. Rev. Lett., 075005-1 (2003)]. An initial test of this method on NSTX has produced about 140 kA of toroidal current. Modifications are now underway to improve capability for transient CHI in NSTX.

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Section: Transient Chisupporting

confidence: 88%

“…The possibility of using CHI in a ST was first proposed in the late 1980's (3) . The first experiments on helicity injection current drive in a ST were conducted on the Current Drive Experiment-Upgrade (CDX-U) at the Princeton Plasma Physics Laboratory (PPPL) (4) .…”

Section: Introductionmentioning

confidence: 99%

Solenoid-free Plasma Startup in NSTX using Coaxial Helicity Injection

Raman

Jarboe

Bell

et al. 2005

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“…CHI [3], a useful method for non-inductive current drive, has been studied in the HIT-II and NSTX STs, in which the compatibility of CHI startup with conventional Ohmic heating and current drive has been verified [4,5]. It is projected that the capability of CHI for current startup would be significantly enhanced if ECH is used to heat the CHI plasma, and this is planned to be tested in NSTX-U for a full non-inductive current start-up and ramp-up scenario [6].…”

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confidence: 99%

Current Start-Up Using the New CHI System

Kuroda

Raman

Hanada

et al. 2017

Plasma and Fusion Research

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Coaxial Helicity Injection (CHI) has now been implemented in QUEST. The goals for the first transient CHI experiments were to establish reliable gas breakdown conditions, and to measure CHI-produced toroidal current generation. Both these objectives were successfully met. Toroidal currents up to 29 kA were measured. Interestingly, these first plasmas on QUEST also suggest the formation of small amounts of closed magnetic flux surfaces. Establishment of methods for solenoid-free plasma current start-up, with robust and stable non-inductive current drive on tokamaks increases the prospects for a compact and low aspect ratio fusion reactor, which has the advantages of lower construction cost and higher plasma beta. QUEST is a mid-size spherical tokamak (ST) device [1], in which plasmas are produced mainly by electron cyclotron heating (ECH), and with minimal use of the central solenoid. Non-inductive toroidal plasma currents up to 70 kA have been achieved on QUEST using 28 GHz microwave injection [2]. We have now implemented coaxial helicity injection (CHI) capability on QUEST. We aim to generate more than 100 kA of initial toroidal plasma current with transient CHI and ramp this seed current noninductively using the high-power 28 GHz microwave system. In this paper we report results from the first CHI experiments on QUEST.CHI [3], a useful method for non-inductive current drive, has been studied in the HIT-II and NSTX STs, in which the compatibility of CHI startup with conventional Ohmic heating and current drive has been verified [4,5]. It is projected that the capability of CHI for current startup would be significantly enhanced if ECH is used to heat the CHI plasma, and this is planned to be tested in NSTX-U for a full non-inductive current start-up and ramp-up scenario [6]. author's e-mail: kuroda@triam.kyushu-u.ac.jpQUEST is equipped with important capabilities that will extend CHI studies to new parameter regimes. The internal vessel walls on QUEST are all metallic; this should be beneficial to CHI as it would reduce the influx of low-Z impurities in to the plasma, which are the prime source of energy loss in low temperature plasmas. The CHI electrode configuration on QUEST is also simpler, and different than the ones on HIT-II and NSTX, and it may be easier to implement this configuration in a fusion reactor [7]. The primary difference is that on NSTX and HIT-II, the insulator is also the vacuum boundary, whereas on QUEST, the insulator is sandwiched between the electrode plate and the divertor plate. However, CHI start-up in this new electrode configuration needs to be demonstrated. This is an important part of the CHI program on QUEST. Figure 1 shows the side view of the QUEST internal structure. The nominal toroidal field at the machine axis (at R 0 = 0.64 m) is 0.25 T at its maximum limit. There are four poloidal field coils above and below the vessel mid-plane; these are normally operated in a series configuration, with two coils connected to a single power supply. As shown in Fig. 1, we installed an e...

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“…[10] Second, the CHI discharge must fill the vessel quickly to keep the required duration of V inj short. This is dependent upon the applied V inj since this determines the rate at which toroidal flux (φ Τ ) crosses the injector and absorber gaps: V inj = dφ Τ /dt.…”

Section: Transient Chimentioning

confidence: 99%