An abrasive fluid jet cutting system, comprising: a high-pressure fluid source; an abrasive material source; an abrasive fluid jet waterjet cutting head configured to generate an abrasive fluid jet from high-pressure water supplied by the high-pressure fluid source and abrasive material supplied by the abrasive material source, the abrasive fluid jet waterjet cutting head including a mixing chamber and an abrasive material input through which the abrasive material is supplied to the mixing chamber of the abrasive fluid jet waterjet cutting head; an abrasive feed passageway in fluid communication with the abrasive material input of the abrasive fluid jet waterjet cutting head, the abrasive feed passageway including an abrasive material feed location through which the abrasive material from the abrasive material source is fed into the abrasive feed passageway for supply to the abrasive fluid jet cutting head; an air flow sensor positioned to measure a volumetric flow rate of air moving through the abrasive feed passageway at a measurement location; an air flow control device configured to control the flow of air moving through the abrasive feed passageway; and a control system communicatively coupled to the air flow sensor and the air flow control device, the control system being configured to continuously or periodically measure, throughout at least a portion of a processing operation during which the abrasive waterjet is discharged from the abrasive fluid jet cutting head, the volumetric flow rate of air moving through the abrasive feed passageway at the measurement location via the air flow sensor, and to adjust the volumetric flow rate of air moving through the abrasive feed passageway via the air flow control device based at least in part on said measurement of the volumetric flow rate of the air moving through the abrasive feed passageway at the measurement location; characterised in that the cutting system further comprises any one of: an air flow booster device coupled to the abrasive feed passageway at an air flow booster location downstream of the abrasive material feed location and upstream of the abrasive material input of the abrasive fluid jet waterjet cutting head; or an air flow suction device coupled to the abrasive feed passageway at a flow dump location downstream of the abrasive material feed location and upstream of the abrasive material input of the abrasive fluid jet waterjet cutting head; or both the air flow booster device and the air flow suction device, wherein the flow dump location is downstream of the flow booster location. a high-pressure fluid source; an abrasive material source; an abrasive fluid jet waterjet cutting head configured to generate an abrasive fluid jet from high-pressure water supplied by the high-pressure fluid source and abrasive material supplied by the abrasive material source, the abrasive fluid jet waterjet cutting head including a mixing chamber and an abrasive material input through which the abrasive material is supplied to the mixing chamber of the abrasive fluid jet waterjet cutting head; an abrasive feed passageway in fluid communication with the abrasive material input of the abrasive fluid jet waterjet cutting head, the abrasive feed passageway including an abrasive material feed location through which the abrasive material from the abrasive material source is fed into the abrasive feed passageway for supply to the abrasive fluid jet cutting head; an air flow sensor positioned to measure a volumetric flow rate of air moving through the abrasive feed passageway at a measurement location; an air flow control device configured to control the flow of air moving through the abrasive feed passageway; and a control system communicatively coupled to the air flow sensor and the air flow control device, the control system being configured to continuously or periodically measure, throughout at least a portion of a processing operation during which the abrasive waterjet is discharged from the abrasive fluid jet cutting head, the volumetric flow rate of air moving through the abrasive feed passageway at the measurement location via the air flow sensor, and to adjust the volumetric flow rate of air moving through the abrasive feed passageway via the air flow control device based at least in part on said measurement of the volumetric flow rate of the air moving through the abrasive feed passageway at the measurement location; an air flow booster device coupled to the abrasive feed passageway at an air flow booster location downstream of the abrasive material feed location and upstream of the abrasive material input of the abrasive fluid jet waterjet cutting head; or an air flow suction device coupled to the abrasive feed passageway at a flow dump location downstream of the abrasive material feed location and upstream of the abrasive material input of the abrasive fluid jet waterjet cutting head; or both the air flow booster device and the air flow suction device, wherein the flow dump location is downstream of the flow booster location.