| dc.description |
Wave damping and plasma heating have been observed for the fast (right -hand polarized ) wave at a frequency equal to 1 ,6 times the ion cyclotron frequency . The waves were launched by a one turn loop around the cylindrical plasma column and damped in a magnetic beach . The current in the one turn loop came from the ringing discharge (Q > 5 , f = 5 MHz ) of an initially charged capacitor (0 .01 yf , 32 kV , 5 J ) into the loop . This current produced a peak , on -axis , vacuum magnetic field of about 0 .04 T , which is approximately 20 % of the background magnetic field (B ) . The plasma was produced from a 10 mTorr initial filling of hydrogen gas by an axial current from a ringing capacitive discharge (Q - 5 , f = 50 kHz ) , At the end of this axial discharge , when the waves were launched , the fully ionized plasma had a temperature of about 2 eV and an electron density of about 3 x 10 20 / m3 , Wave damping measurements are reported in a series of graphs of wave magnitude (b ) versus Bo for two fixed distances from the one turn loop^ and b z versus z for two fixed values of Bo , From these curves , the wave damping is seen to be very strong and very sharp . The wave damping curves correlate well with the plasma heating as shown by graphs of the signal from an unintegrated diamagnetic loop versus B for two fixed positions . The degree of plasma heating as determined by a diamagnetic loop and spectroscopy also agrees with the calculated energy content of the fast wave prior to damping . This damping and heating is believed to be the result of a magnetosonic column resonance . The fast wave is also observed to damp at the second harmonic of the ion cyclotron frequency . |
|