TJ-II: Determination of the spatial periodicity of NBI-driven Alfvén Eigenmodes and study of its magnetic configuration dependence

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Experimental campaign

Spring 2022

Proposal title

Determination of the spatial periodicity of NBI-driven Alfvén Eigenmodes and study of its magnetic configuration dependence.

Name and affiliation of proponent

Álvaro Cappa, CIEMAT. Pedro Pons, CIEMAT. Macarena Liniers, CIEMAT. Enrique Ascasíbar, CIEMAT.

Details of contact person at LNF

Enrique Ascasíbar, CIEMAT.

Description of the activity

MHD activity produced by Alfvén Eigenmodes (AEs) is routinely observed in NBI-heated TJ-II plasmas [1]. The results provided by recently installed sets of helical magnetic coils complement the previous experimental data and, together with advanced analysis tools like the 3D Lomb periodogram [2] allows the determination of the AEs spatial periodicity with an accuracy non reachable so far.

With this goal in mind we propose to study the alfvénic activity produced by both co and counter NBI injectors separately, as well as the one produced by simultaneous, balanced heating with both injectors (compensated plasma current). We plan to perform this study in at least two magnetic configurations, 100_44_64 (edge_iota 1.65) and 100_60_68 (1.77), looking for the expected influence of the configuration on the shear Alfvén spectrum. It time allows we do not discard the possibility of scanning the injector parameters (energy, beam current) to study their influence on the observed AEs.

Since we will be looking for reasonably stationary plasma density conditions to facilitate the mode analysis, we do not discard the use of moderate ECH heating during the NBI plasma phase.

International or National funding project or entity

International: EUROfusion Consortium under grant agreements 633053 (FP8) and 101052200 (FP9).

National: Spanish Ministry of Science and Innovation under grants FIS2017-88892-P and FIS2017-85252-R

Description of required resources

Required resources:

  • Two days of good NBI plasma operation (aprox. 35 discharges each) with reasonably good plasma density control.
  • Essential diagnostic systems: Mirnov coils (helical and poloidal arrays) and CNPA measurements are mandatory. Besides the common shot to shot diagnostics (ECE, Thomson, Interferometry, Radiation), all systems providing edge plasma profiles are needed. If possible, Doppler Reflectometer, HIBP. MSE would also be desirable to evaluate configuration changes induced by non-totally balanced currents. FILD is also desirable to monitor fast ion losses and relate the level of losses to the Alfven activity.
  • Type of plasmas (heating configuration): NBI (both injectors) and ECH.
  • Specific requirements on wall conditioning if any: Good plasma density control usually means that the operation days must be allocated close after the boron/lihium conditioning of the vacuum vessel.
  • External users: need a local computer account for data access: No
  • Any external equipment to be integrated? No

Preferred dates and degree of flexibility

Preferred dates:

If possible, one day in February and another in March


References

  1. A. Cappa et al, Nuclear Fusion, 61(6):066019 (2021), and references therein
  2. S. Zegenhagen, et al., Plasma Physics and Controlled Fusion, 48(9):1333–1346 (2006)

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