Arc Detection With GUIDAR: First Experimental Tests On MXP Testbed

The GUIDAR technology has been proposed for the detection of electric arcs in the transmission lines for antennas for plasma heating and current drive. After a preliminary study to assess the feasibility of this technique, some experimental tests with real arcs were conducted on the MXP testbed installed at IPP, Garching. The low frequency (25MHz) GUIDAR signal, made of a sequence of short phase-modulated impulses, is up-shifted to around 400MHz and injected into the transmission line by mean of a directional coupler. The echoes are then extracted with another directional coupler and down-shifted again for the processing. The analysis is performed at a pulse repetition frequency of 120-165kHz, enabling an arc detection within 6-8μs. Tests have shown encouraging results to demonstrate the capability of the GUIDAR system to easily detect both high voltage and, most important, low voltage arcs. The possibility of locating the arcs has also been addressed in the testbed with simulated arcs. The insensitivity of the method to slow changes of the line voltage standing wave ratio (mimicking antenna load variations) was also tested.