TJ-II: Combining retarding-field energy analyzer and electrostatic probes measurements, an approach to measure the phase relation between density and temperature fluctuations using RFA?

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Experimental campaign

Spring 2022

Proposal title

Combining retarding-field energy analyzer and electrostatic probes measurements, an approach to measure the phase relation between density and temperature fluctuations using RFA?

Name and affiliation of proponent

Igor Nedzelskiy, Carlos Silva (IST)

Mark Koepke (UWV)

Igor Voldiner, Daniel Carralero, Gregorio Martin, J. L. de Pablos, Carlos Hidalgo (CIEMAT)

HIBP Kurchatov team, Russia

HIBP Kharkov team, Ukraine

Details of contact person at LNF

Igor Voldiner

Description of the activity

Rational. Why is there decoupling between particle and energy transport channels at the transition to improved confinement regimes?. Physics behind uncoupled transport channels is a relevant open question for understanding both ELM control techniques (e.g. using RMP) as part of the ITER base-line scenario and the development of plasma scenarios without ELMs (e.g. I-mode). Interestingly, uncoupled transport channels has been also reported in stellarators. Transport channel decoupling could be driven by any mechanism that leads to a modification of the cross-phase between density and temperature fluctuations caused by changing driving conditions.. The retarding-field energy analyzer (RFA) is a widely used diagnostic tool for ion temperature measurement in the confined-plasma outer boundary. However, temporal resolution in the standard RFA application is restricted to the milliseconds timescale. A new technique has been developed which allows for the measurement of the plasma ion temperature fluctuations [1]. The method is based on measurements of two points on the exponentially decaying region of the I–V characteristic with two differently dc-biased RFEA electrodes. Integrating RFA with electrostatic probes would allow measuring temperature and density fluctuations simultaneously and without phase shift effects.

Goal. We propose to explore the feasibility of measuring the phase relation between density and temperature fluctuations using a combined diagnostic based on Retarting Field Analyzer (RFA) and Langmuir probes that has been recently developed in the TJ-II stellarator.

In addition, the unique capabilities of the dual HIBP system would allow the investigation of density and potential fluctuations in the TJ-II stellarator, from plasma core to plasma edge. Simultaneous, spatially overlapping, measurement of plasma parameters, using HIBP and electrostatic probes, would allow novel probe configurations [i.e. baffled probes [2]] to be tested, and would provide plasma boundary conditions for HIBP calibration.

International or National funding project or entity

Include funding here (grants, national plans)

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2
  • Essential diagnostic systems: RFA, Probes. HIBP operation is also highly desirable.
  • Type of plasmas (heating configuration): ECRH with density ramp-up and ramp-down to include electron-ion root transitions
  • Specific requirements on wall conditioning if any: no
  • External users: need a local computer account for data access: yes/no
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. I. Nedzelskiy et al., Rev. Sci. Instrum. 82 (2011) 043505
  2. V.I. Demidov et al., Contrib. Plasma Phys. 44 (2004) 689

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