The Divertor Tokamak Test (DTT) [1] is planned to be heated through a mix of 45 MW heating power, including 15 MW negative-ion-based Neutral Beam heating (NNBI) which is currently being developed by Consorzio RFX in Padova, Italy [2]. An issue for DTT is that a Toroidal Field (TF) ripple with a maximum value of about ~ 0.42 % (with respect to the on-axis magnetic field B0) is expected on the low-field side (LFS) [3, 4], and this ripple interacts with fast ions through rather well-known phenomena of ripple-precession resonances [5]. In fact, TF ripple breaks the conservation of the fast ion toroidal canonical momentum, expressed as P? = g?k -?p, where g is the covariant toroidal field component in Boozer coordinates, ?k = vk/B and ?p is the poloidal flux which serves as radial coordinate, in such a way that the decrease of the canonical momentum results in the increase of the radial positions of the particles, which are ultimately lost. Regarding the reference DTT configuration [3, 4], and with the parameters of the NNBI project [2], namely energy E = 400 keV and injection angle of ~ 40o w.r.t. the first wall, it is possible to recognize at least four resonances for trapped ions, of the type ?b-nN?d = 0, ?b and ?d being the bounce and precession frequency, respectively, and N the ripple periodicity. Those resonances are characterized by toroidal wavenumbers 3 <= n <= 6. The resonances seem to be well spaced apart, so that the possibility of stochastic overlapping [6] is remote: this is consistent with the calculated contribution of ripple losses in DTT, which are of the order of less than 0.5 % in the standard single-null scenario, as already published in [2]. Acknowledgement: This work is carried out in the frame of the DTT activity. The authors are very grateful to all the colleagues involved in the DTT project for their precious contribution.
Ripple-precession resonance of fast ions in DTT
Spizzo G;Gobbin M;
2020
Abstract
The Divertor Tokamak Test (DTT) [1] is planned to be heated through a mix of 45 MW heating power, including 15 MW negative-ion-based Neutral Beam heating (NNBI) which is currently being developed by Consorzio RFX in Padova, Italy [2]. An issue for DTT is that a Toroidal Field (TF) ripple with a maximum value of about ~ 0.42 % (with respect to the on-axis magnetic field B0) is expected on the low-field side (LFS) [3, 4], and this ripple interacts with fast ions through rather well-known phenomena of ripple-precession resonances [5]. In fact, TF ripple breaks the conservation of the fast ion toroidal canonical momentum, expressed as P? = g?k -?p, where g is the covariant toroidal field component in Boozer coordinates, ?k = vk/B and ?p is the poloidal flux which serves as radial coordinate, in such a way that the decrease of the canonical momentum results in the increase of the radial positions of the particles, which are ultimately lost. Regarding the reference DTT configuration [3, 4], and with the parameters of the NNBI project [2], namely energy E = 400 keV and injection angle of ~ 40o w.r.t. the first wall, it is possible to recognize at least four resonances for trapped ions, of the type ?b-nN?d = 0, ?b and ?d being the bounce and precession frequency, respectively, and N the ripple periodicity. Those resonances are characterized by toroidal wavenumbers 3 <= n <= 6. The resonances seem to be well spaced apart, so that the possibility of stochastic overlapping [6] is remote: this is consistent with the calculated contribution of ripple losses in DTT, which are of the order of less than 0.5 % in the standard single-null scenario, as already published in [2]. Acknowledgement: This work is carried out in the frame of the DTT activity. The authors are very grateful to all the colleagues involved in the DTT project for their precious contribution.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
