LOW-Q DISCHARGE IN FT TOKAMAK
Recently the FT Tokamak has been operating in ohmic regime down to q-L = 2.2. This has been achieved in Deuterium discharges, with B-T +- 40 kG (I-p <= 410 kA) and with a circular stainless steel limiter of 20 cm radius, corresponding to a plasma - wall distance of 3 cm. The main problem has been to overcome the q-L = 3 resonance. The empirical way to break through q-L = 3 is to operate at 1.2 < I-p < 2.4 kA/ms and either by making a strong prefilling of the vacuum chamber or a strong gas puff just after the start up of the discharge. Fig. 1 shows the Hugill plot of FT operation: it appears that there is a narrow window in Murakami parameter (1 < n-eR/B-T < 2 times 10**13 cm-2/Kg) in order to achieve q-L < 3. Figure 2 shows the evolution of T-e profile deduced from 2 omega-ce emission before, during and after the q-L = e-3 crossing; the profile is the narrowest just at q-L = 3 and then broadens again at q-L +- 2.5. Figure 3 shows the corresponding evolution of the MHD instabilities: the poloidal mode number evolves in time from m = 3 to m = 2, m = 1 and m = 0 sawtooth activity (the presence or the onset of such activity is a necessary condition for q-L < 3 operation).
Bibliographic Reference: 11TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, AACHEN (GERMANY), SEPT. 5-9, 1983 IN ENEA REPORT 83.23/CC, PP. 25-29, 1983 WRITE TO ENEA + CENTRO RICERCHE ENERGIA FRASCATI, SERVIZIO STUDI E DOCUMENTAZIONE, C.P. 65 00044 FRASCATI, ROMA (I
Record Number: 1989122052000 / Last updated on: 1987-01-01
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