Electrosurgical instrument with non-liquid thermal transfer

An electrosurgical system comprising:

• an electrosurgical instrument comprising:
• a flexible coaxial transmission line arranged to convey microwave energy;
• a radiating tip portion connected at a distal end of the flexible coaxial transmission line and configured to receive the microwave energy, the radiating tip portion comprising:
• a distal coaxial transmission line for conveying the microwave energy;
• and
• a needle tip mounted at a distal end of the distal coaxial transmission line, the needle tip being arranged to deliver the microwave energy into biological tissue;
• a heat sink mounted at an interface between the flexible coaxial transmission line and radiating tip portion;
• and
• a thermal transfer element disposed along the flexible coaxial transmission line, wherein the thermal transfer element provides a thermal gradient that draws heat energy from the radiating tip portion;
• wherein the heat sink is in thermal communication with a proximal end of the distal coaxial transmission line and configured to draw thermal energy from the radiating tip portion, and
• wherein a maximum outer diameter of the radiating tip portion is smaller than an outer diameter of the flexible coaxial transmission line;
• and
• a cooling device arranged to force cool a proximal portion of the thermal transfer element and the electrosurgical instrument.