A plasma compressing system, the system comprising: a plasma generator (110, 110a) configured to generate plasma and having a discharge outlet for discharging the generated plasma; a plasma compression chamber having an outside wall defining an inner cavity of the chamber and having an opening (185, 185a), the inner cavity of the chamber being partially filled with a liquid medium, the discharge outlet of the plasma generator (110. 110a) being in fluid communication with the inner cavity of the compression chamber via the opening (185, 185a), such that the generated plasma can be discharged into the plasma compression chamber; a pressure wave generator comprising a plurality of pistons arranged around the chamber, the pistons being configured to generate a converging pressure wave into the liquid medium; a cavity generating means for generating an elongated empty cavity into the liquid medium, the cavity having a first end and a second end, the first end being aligned at least partially with the discharge outlet of the plasma generator (110, 110a) such that the plasma discharged by the plasma generator (110, 110a) enters the elongated cavity, and wherein the converging pressure wave reaching a cavity interface collapses the cavity enveloping the plasma; characterized in that said system further comprises a jet control device (10, 200) comprising: means for injecting a jet deflector material (12, 210, 300) in communication with a jet deflector material source (11, 220, 310) and having a discharge end (17, 207) directed at a jet formation location in the cavity, the means for injecting configured to inject the jet deflector material (12, 210, 300) into the cavity such that a fluid jet (18, 180) formed at the jet formation location is disrupted or deflected away from the plasma generator (110, 110a). a plasma generator (110, 110a) configured to generate plasma and having a discharge outlet for discharging the generated plasma; a plasma compression chamber having an outside wall defining an inner cavity of the chamber and having an opening (185, 185a), the inner cavity of the chamber being partially filled with a liquid medium, the discharge outlet of the plasma generator (110. 110a) being in fluid communication with the inner cavity of the compression chamber via the opening (185, 185a), such that the generated plasma can be discharged into the plasma compression chamber; a pressure wave generator comprising a plurality of pistons arranged around the chamber, the pistons being configured to generate a converging pressure wave into the liquid medium; a cavity generating means for generating an elongated empty cavity into the liquid medium, the cavity having a first end and a second end, the first end being aligned at least partially with the discharge outlet of the plasma generator (110, 110a) such that the plasma discharged by the plasma generator (110, 110a) enters the elongated cavity, and wherein the converging pressure wave reaching a cavity interface collapses the cavity enveloping the plasma; characterized in that said system further comprises a jet control device (10, 200) comprising: means for injecting a jet deflector material (12, 210, 300) in communication with a jet deflector material source (11, 220, 310) and having a discharge end (17, 207) directed at a jet formation location in the cavity, the means for injecting configured to inject the jet deflector material (12, 210, 300) into the cavity such that a fluid jet (18, 180) formed at the jet formation location is disrupted or deflected away from the plasma generator (110, 110a).