THIS PROJECT WILL INVESTIGATE THE STABILITY OF PROPAGATING SPIRAL WAVES IN PROTOPLANETARY DISKS BY CARRYING OUT THREE-DIMENSIONAL NUMERICAL SIMULATIONS. SPIRAL WAVES IN PROTOPLANETARY DISKS ARE SUBJECT TO RESONANT INTERACTIONS WITH INERTIAL MODES. THIS CAN LEAD TO THE DESTABILIZATION OF THE SPIRAL WAVES INTO SMALL TURBULENT EDDIES BY TRANSFERRING WAVE ENERGY TO INERTIAL MODES -- SPIRAL WAVE INSTABILITY. IMPROVING UPON OUR PRIOR WORK THE PROPOSED PROJECT WILL AIM TO STUDY STABILITY OF THE SPIRAL WAVES EXCITED BY A PLANETARY COMPANION AND TO EXAMINE THE EFFECTS OF DISK THERMODYNAMICS TO THE INSTABILITY. THE NECESSARY CODE ELEMENTS HAVE BEEN IMPLEMENTED IN AND TESTED WITH ASTROPHYSICAL (MAGNETO-)HYDRODYNAMIC CODES FARGO3D ATHENA AND PLUTO BY THE TEAM MEMBERS. USING THE PROPOSED SIMULATIONS WE WILL ASSESS (1) HOW EFFICIENTLY SPIRAL WAVES ARE DESTABILIZED BY THE INSTABILITY; (2) HOW MASS AND ANGULAR MOMENTUM TRANSPORT VIA SPIRAL WAVES CHANGE IN RESPONSE TO THE INSTABILITY; AND (3) HOW DUST DIFFUSES/COLLECTS WITHIN THE TURBULENCE PRODUCED BY THE INSTABILITY. THE RESULTS WILL HAVE POTENTIAL IMPACT IN UNDERSTANDING THE MASS TRANSPORT AND THE FORMATION OF PLANETESIMALS/PLANETS IN THE PROTO-SOLAR NEBULA AS WELL AS IN EXTRASOLAR PROTOPLANETARY SYSTEMS.