Speaker
Description
Mitigation of disruption electro-magnetic load with SPI on JET-ILW
The disruption mitigation system at ITER consists of shattered pellet injectors (SPI) that can inject up to 24 pellets from three different equatorial port plugs, which will be dedicated to the mitigation of electro-magnetic loads (EML), thermal loads and the avoidance and suppression of runaway electrons. Recently the JETILW was equipped with an SPI with a wide capability. Specifically: pellet diameter d = [4.57, 8.1, 12.5] mm and effective length/d ratio = [1.4, 1.6, 1.54]; pellet compositions of D2, Ne with D2 shell, D2+Ne mixture and Ar; propellant gas or mechanical punch to release the pellets.
The experiment was performed with ohmic plasma with Ip = 1.1-2.9 MA and D2+Ne pellet composition. The current quench (CQ) time, τ80-20, is the key characteristic of mitigation effectiveness. This study reveals (a) a marginal effect of pellet integrity prior to shattering and pellet size on τ8020; (b) strong dependence of τ80-20 on Ne fraction; (c) SPI efficacy, in terms of τ80-20, does not depend on pre-disruptive Ip (in another words on the poloidal magnetic energy) for middle-sized pellets. The SPI was applied on plasmas with various statuses: normal (“healthy”) plasma i.e., not prone to disruption and post-disruptive plasma. However, efficacy SPI on off-normal (e.g. affected by Locked mode) pre-disruptive plasma has not been studied yet. The preliminary results from the first study show that SPI effectiveness does not depend on plasma status. One of the results of the experiment was prevention of asymmetrical vertical displacement events (AVDEs) by SPI, which increases the safety factor q95 and, presumably, eliminates the excitation of the m=1, n=1 kink mode, responsible for AVDE. In this regard, SPI is similar to the effect of Massive Gas Injection.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053 and from the RCUK Energy Programme [EP/T012250/1]. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
| Member State or International Organization | United Kingdom |
|---|---|
| Affiliation | UKAEA/CCFE |
