Travelling-wave tube protection arrangement

A power and protective arrangement for a travelling-wave tube including a cathode, an anode, and a helix, said arrangement comprising:

• cathode current sensing means coupled to said cathode for generating a cathode current signal representative of the cathode current of said travelling-wave tube;
• helix current sensing means coupled to said helix for generating a helix current signal representative of the helix current of said travelling-wave tube;
• controllable voltage generating means including a cathode current control input port and a shut-down input port, and also including output ports coupled to said cathode and said anode of said travelling-wave tube, for coupling between said cathode and said anode of said travelling-wave tube an operating voltage which is controllable in response to a cathode current control signal applied to said cathode current control input port, and which operating voltage is reduced to zero in response to a shut-down signal applied to said shut-down input port;
• shut-down signal generating means coupled to said helix current sensing means and to said shut-down input port of said controllable cathode current generating means, for comparing said helix current signal with a reference signal, and for generating said shut-down signal when said helix current signal exceeds a particular value;
• cathode current reference signal generating means including a control input port, for generating a cathode current reference signal;
• cathode current controlling means coupled to said cathode voltage control input port of said controllable voltage generating means, to said cathode current sensing means, and to said cathode current reference signal generating means, for comparing said cathode current signal with said cathode current reference signal, and for generating a cathode current control error signal representing the difference between said cathode current signal and said cathode current reference signal, and for applying said cathode current control error signal to said cathode current control input port of said controllable cathode voltage generating means with a polarity selected to form a degenerative feedback loop which tends to maintain a constant ratio between said cathode current signal and said cathode current reference signal;
• and
• helix current drive limiting means coupled to said helix current sensing means and to said control input port of said cathode current reference signal generating means, for comparing said helix current signal with a reference value, for generating a cathode current reference threshold adjustment signal, and for coupling said cathode current reference threshold adjustment signal to said control input port of said cathode current reference signal generating means with a polarity selected for forming a degenerative feedback loop which tends to reduce said cathode current when said helix current increases, whereby, in the absence of an arc, the helix current tends to be limited to a value less than said particular value.