MAGNETIC RECONNECTION IS AN IMPORTANT PROCESS IN PLASMA PHYSICS WHERE SIGNIFICANT ELECTROMAGNETIC FIELD ENERGY IS DISSIPATED TO ENERGIZE PLASMAS. IN PARTICULAR THE ION THERMAL ENERGY IS SHOWN TO BE THE DOMINANT FORM TO DISSIPATE STORED MAGNETIC ENERGIES. THE CURRENT UNDERSTANDING OF ION HEATING IS MAINLY BASED ON THE INCREASE OF EFFECTIVE TEMPERATURES IN SIMPLIFIED OR 2D LAMINAR RECONNECTION STRUCTURES. THE ACTUAL PROCESS OF ION HEATING FROM THE RECONNECTION INFLOW TO OUTFLOW REGIONS REMAINS AN IMPORTANT OPEN QUESTION PRIMARILY DUE TO THE LACK OF DISTRIBUTION FUNCTION MEASUREMENTS THAT CAN RESOLVE THE EVOLUTION OF ALL POPULATIONS. THE HIGH RESOLUTION PARTICLE MEASUREMENTS BY MMS WILL ENABLE SIGNIFICANT PROGRESS ON THE ION HEATING PROBLEM. WE PROPOSE TO INVESTIGATE ION HEATING IN THE DIFFUSION REGION AND COMPARE IT WITH THE HEATING IN THE FAR EXHAUST. THE OBJECTIVES INCLUDE DETERMINING (1) HEATING OF INDIVIDUAL POPULATIONS IN STRUCTURED DISTRIBUTIONS BY (A) SPATIAL GRADIENTS OF MAGNETIC AND ELECTRIC FIELDS AND (B) WAVES; (2) EFFECTS OF 3D CURRENT SHEET DYNAMICS SUCH AS CURRENT SHEET RIPPLING ON HEATING; (3) HEATING DUE TO ACCELERATION AND THERMALIZATION DURING THE MEANDERING MOTION IN RECONNECTING CURRENT SHEETS. THE PROPOSED STUDY WILL BE BASED ON ANALYSIS OF MMS DATA. THE MMS PHASE 2B DATA (5/4/2017-8/31/2017) WILL BE USED FOR THE PROPOSED RESEARCH. A PRELIMINARY DATABASE OF MORE THAN 70 RECONNECTION EVENTS HAS BEEN CREATED TO ENSURE CLOSURE OF THE PROPOSED PROJECT. THE HEATING PROCESS WILL BE INVESTIGATED BY EXAMINING THE DISTRIBUTION EVOLUTION ALONG WITH THE STRUCTURES OF ELECTRIC AND MAGNETIC FIELDS AND WAVES. WE WILL QUANTIFY THE AMOUNT OF HEATING BY EXTRACTING THE TEMPERATURES OF INDIVIDUAL POPULATIONS. WE WILL CALCULATE GRADIENT SCALES OF ELECTRIC AND MAGNETIC FIELDS ANALYZE WAVE-PARTICLE INTERACTION AND USE ELECTRON AND ELECTROMAGNETIC FIELD DATA IN CONJUNCTION WITH THE ION DISTRIBUTIONS TO INFER THE RECONNECTION STRUCTURE (E.G. SUB-REGIONS) AND 3D CURRENT SHEET ORIENTATIONS. WE WILL STUDY THE ION HEATING IN SIMULATIONS BY ANALYZING DISTRIBUTIONS AND PERFORMING TEST-PARTICLE ANALYSIS TO GUIDE THE INTERPRETATIONS OF MMS OBSERVATIONS. THE PROPOSED RESEARCH IS EXPECTED TO ADVANCE KNOWLEDGE OF MAGNETIC RECONNECTION ION ENERGIZATION IN PARTICULAR WHICH IS DIRECTLY RELEVANT TO THE PRIMARY SCIENCE GOAL OF MMS. THE STUDY IS HIGHLY RELEVANT TO THE DECADAL SURVEY GOALS AS IT HELPS UNDERSTAND RECONNECTION (1) AS A FUNDAMENTAL PROCESS THAT OCCURS THROUGHOUT THE UNIVERSE AND (2) AS A KEY PROCESS THAT AFFECTS THE COUPLING BETWEEN THE SOLAR WIND AND THE EARTHS MAGNETOSPHERE AND IONOSPHERE.