View source for TJ-II: Injection of TESPELs with compounds or multiple elements of interest for W7-X

== Experimental campaign ==
Spring 2022

== Proposal title ==
'''Injection of TESPELs with compounds or multiple elements of interest for W7-X'''

== Name and affiliation of proponent ==
[https://orcid.org/0000-0002-6408-0922 René Bussiahn], IPP-Greifswald, Germany

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

== Description of the activity ==

=== Motivation and Background ===
Inject TESPELs containing small quantities of either compounds of interest (e.g. Li2CO3) or multiple atomic elements (Al, Ti, Fe Cu, Ni, Mn, and/or W) that are candidates for use in the OP2.1 campaign in W7-X. The principal aims are to identify the strongest emission line from the atomic state of each elements in order to prepare filterscopes for the W7-X TESPEL system and to identify strong emission lines for highly ionized states of the same elements using the VUV spectrometer.

=== Proposal Objectives ===
We will prepare 300 um diameter TESPELs at the Ciemat TESPEL laboratory and fill these will small known quantities of the different tracers of interest. These will be injected into NBI heated phase of plasmas in TJ-II, if available. Otherwise they can be injected into the final 10's of milliseconds of the ECRH phase. It is intended that the TESPEL will reach the plasma core at which point the tracers will be exposed to the plasma. Once exposed to the hot plasma, spectral line emissions for the atomic state will be recorded using a compact UV-visible spectrometer located in the same TJ-II sector as the TESPEL injector. Strong spectral lines for highly ionized states of the same elements will be recorded using a VUV spectrometer located 180º away toroidally.

=== Approach and Methodology ===
NBI heated plasmas are best for this as the plasma is not affected by a density cut-off limit, as can occur for injections into ECRH plasmas. The standard magnetic configuration with one or both NBI heaters working will be employed. Frequent entries into the TJ-II experimental hall to change the TESPEL revolver position are required. Given the need to minimize such entries the number of TESPELs to be injected will be limited. Thus experiment can be run in conjunction with pellet or LBO experiments.

== International or National funding project or entity ==
Include funding here (grants, national plans)
Studies of fuelling and impurity control in the stellarators TJ-II and W7-X through the use of cryogenic and TESPEl pellets (Estudios de abastacimiento y control de impurezas en los stellarators mediante el uso de perdigones criogenicos y TESPEL", Ref: PID2020-116599RB-I00

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation: 2 days
* Essential diagnostic systems (without which, the proposal cannot be conducted): TESPEL injector and UV-visible spectrometer
* Other diagnostic system of special interest: Thomson scattering, VUV spectrometer
* Type of plasmas (heating and magnetic configuration): NBI (balanced or unbalanced) and 100_44_64
* Specific requirements on wall conditioning if any: none
* External users: need a local computer account for data access: no
* Any external equipment to be integrated? W7-X fast-frame imaging camera (has been done previously)

== Preferred dates and degree of flexibility ==
Preferred dates: mid-May to mid-June

(If remote participation is required or preferred, please, indicate it here. A Zoom connection with the local contact person will be arranged on the day of experiments.)

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== References ==
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