View source for TJ-II:Imaging of pelet cloud dynamics in TJ-II using Halpha and bremsstraahlung filters and a fast-frame camera

== Experimental campaign ==
Spring 2022

== Proposal title ==
'''Imaging of pellet cloud dynamics in TJ-II using Halpha and bremsstrahlung filters and a fast-frame camera '''

== Name and affiliation of proponent ==

[https://orcid.org/0000-0000-0000-0000 Gabor Kocsis], CRC-Budapest and
[https://orcid.org/0000-0000-0000-0000 Tamás Szepesi], CRC-Budapest

== Details of contact person at LNF ==
Kieran J McCarthy

== Description of the activity ==
This aim of this proposal is to investigate the interaction of cryogenic hydrogen and impurity pellets (TESPEL) with stellarator plasma by evaluating fast framing video data. In early 2020, LFS TESPEL and hydrogen pellet injection experiments were conducted on TJ-II but these were cut short by the pandemic. Movies (frame-rates up to 700 kHz) with TOP and TANGENTAL views were recorded using different filters (C I, C III, Hα, Li II). It was seen that the drifting pellet clouds extend broadly along the magnetic field lines. In the case of the impurity pellet, which travels inwardly into the plasma at a constant speed, the C+2 cloud surrounding a TESPEL is small and spherical. In was determined that plasmoids (partialy ionized clouds) are launched frequently (every 5-10µs) - as expected - and drift outwards from the plasma at a speed of approximately 5 km/s. In the case of cryogenic pellets, it was difficult to recognize the individual drifting clouds, despite the 700 kHz frame rate, so perhaps the time resolution was not high enough. Nonetheless, it was concluded that the cloud is hollow around the pellet and drifts outwards. Further experiments are needed in this area to achieve a better understanding of the cloud dynamics. Such information will be compared with cloud dynamics for similar pellets on the stellarator W7-X in order to achieve a more comprehensive understanding.
It is proposed to continue these studies in TJ-II with the W7-X fast camera during 2022 with higher frame rates and with Hα and bremmstrahlung filters. Again, TOP and TANGENTIAL views will be needed and pellets will be injected into both ECRH and NBI plasmas.
The proponents have significant experience in using fast-frame cameras on tokamaks and stellarators. Recently, they studied pellet cloud drifting (cryogenic and TESPEL) on the stellarator W7-X <ref>G. Kocsis et al, Investigation of TESPEL cloud dynamics in Wendelstein 7X stellarator, Nucl Fusion 61 016006 (2021)</ref>. Also, the local team have significant experience with pellet injectiona nd fast frame image analysis <ref>N. Panadero et al, Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II, Nucl Fusion 58 026025 (2018)</ref>.

== 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: 
* Essential diagnostic systems:
* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* 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: March 2022 and May or June 2022

<!-- DO NOT REMOVE THE FOLLOWING LINES -->

== References ==
<references /> 

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals Spring 2022]]