A volume-averaged equilibrium β value 〈βeq〉 of 2.14% is achieved in a compact helical system using two neutral beam lines with balanced injection and intense wall conditioning with Ti gettering. This value is the highest β value realized so far in helical systems. Reheat mode, where the stored energy increases after turn-off of a strong gas puff, is employed in the experiment. Discharge conditions are as follows: Bt = 0.61 T; beam power through the port, 1.1 MW (coinjection) and 0.8 MW (counterinjection); line-averaged electron density ne = 6.5 × 1013cm-3. Amplitudes of magnetic fluctuations integrated over the frequency range from 3 kHz to 100 kHz become saturated at 〈βeq〉 higher than 1%. Dominant coherent modes are m n = 2 1 and 1 1 when 〈βeq〉 is lower and higher respectively than 1%. Dependence of the energy confinement time τE on ne (up to 8 × 1013 cm-3) and Bt (from 0.6 to 1.8T) is also studied in this high β experiment. When the density increases τE degrades compared with the LHD scaling; the density dependence exhibits Bohm-like behaviour. On the contrary, τE scales as Bt≈0.75, which is rather close to the LHD scaling (gyro-Bohm-like behaviour).
All Science Journal Classification (ASJC) codes
- Civil and Structural Engineering
- Nuclear Energy and Engineering
- Materials Science(all)
- Mechanical Engineering