TJ-II: Comparison of Beam-wall effects at the beam ducts of NBI

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Experimental campaign

2019 Autumn

Proposal title

TJ-II: Comparison of Beam-wall effects at the beam ducts of NBI#1 (Graphite) and NBI#2 (Stainless Steel)

Name and affiliation of proponent

Macarena Liniers. División de Operación.

Details of contact person at LNF

Macarena Liniers

Description of the activity

Beam-wall interaction gives rise to a number of gas-emission processes that contribute to the pressure rise in the duct area during a beam injection pulse. The magnitude and dynamics of this contribution depend on the wall material and its conditioning status. In TJ-II the protection plates at the final section of the ducts are made of different materials: graphite in NBI#1 and SS in NBI#2. The study of the local pressure behaviour can shed light on the gas desorption and re-emission mechanisms taking place at the beam wall interaction areas. The local duct pressure is measured with Fast Ion gauges, with response times in the order of a few milliseconds. For the comparison to be meaningful the following conditions are necessary: -The two ducts must be “conditioned”: the preliminary degasification after a long period of rest under atmospheric pressure (normally under inert gas atmosphere but also with exposure to air) must have been finalised: the gas dynamics must be dominated by hydrogen adsorption and desorption during the beam operation. -The pumping speed at the calorimeter box, determining the gas flow at the duct, must be similar at the two injectors -The beam power and beam perveance must be similar, so the beam-surface interaction areas are similar. The experiment will run like this: • Conditioning of both beam ducts will be monitored by the FIGs at the two ducts, at the beginning of the campaign • Equal power beams will be injected (check gimbal position) on conditioned ducts with similar pumping at the Calorimeter boxes. o The Pressure traces will be compared o Temperature measurements at the TF plates will be compared. In order to use the fast camera on both ducts these measurements must be made on different days • Comparison of Temperature of the Beam Stop in pulses with/wo Magnetic field will give the total reionization fraction (25 mm lens, BS focus) • Comparison of Temperature of the TF plate in pulses with/wo Magnetic field will give the fraction of the total reionization taking place in the duct section upstream from the TF (12 mm lens, TF focus)

International or National funding project or entity

Proyecto Plan Nacional FIS2017-89326-R

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation: 2 hours+2 hours on different days
  • Essential diagnostic systems:FIGs, IR Thermography, Halpha
  • Type of plasmas (heating configuration): no Plasma. B/noB discharges with NBI injection
  • Specific requirements on wall conditioning if any:same condition for the two experiment days
  • 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:10-02-2020 and 20/03/2020

References

[1] Beamline duct monitoring of the TJ-II neutral beam injectors

M. Liniers, Gilles Wolfers, Jose Antonio Sebastián, Beatriz Rojo, Fernando Martín, Ricardo Carrasco, José Guasp, Félix Martín, Emilio Sánchez, Andrés Jiménez, Guillermo Merino, Marian Ochando, Kieran McCarthy, Enrique Ascasíbar, Bernardo Zurro, Alfonso Soleto y Javier Alonso

Fusion Engineering and Design 88 (2013) 960–963

[2] New infrared imaging diagnostic for the Neutral Beam Heating System at the TJ-II stellarator

M. Liniers, J.A. Quintana, B. Rojo, F. Martín-Díaz, F. Miguel, J.A. Sebastián, R. Carrasco, A. Soleto, E. Sánchez-Sarabia, A. Jiménez-Denche, C. Pastor, C. Rodríguez, J. Guasp, E. de la Cal, K.J. Mc Carthy, I. Pastor and E. Ascasíbar

Journal of Instrumentation, Volume 14, September 2019 3rd European Conference on Plasma Diagnostics (ECPD2019)


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