MAGNETIC RECONNECTION RESULTS IN RELEASE OF STORED MAGNETIC FIELD ENERGY INTO MANY FORMS INCLUDING PARTICLE ACCELERATION HEATING AND ELECTROMAGNETIC WAVES. DUE TO THEIR LARGER MASS AND ASSOCIATED GYRATION AND INERTIAL LENGTHS HEAVY IONS ARE ENERGIZED DIFFERENTLY FROM THE MORE POPULOUS H+ IONS OR ELECTRONS. THESE HEAVY IONS ARE PRESENT IN THE MAGNETOSPHERE PRIMARILY DUE TO OUTFLOW FROM THE IONOSPHERE DURING STORM TIMES AND DURING AND NEAR SOLAR MAXIMUM DUE TO INCREASED SOLAR EUV. THESE IONS MAY REPRESENT AN IMPORTANT FEEDBACK MECHANISM BETWEEN THE IONOSPHERE AND RECONNECTION REGIONS IN THE MAGNETOTAIL OR AT THE MAGNETOPAUSE. IN ADDITION RECENT STUDIES OF CLUSTER MAGNETOTAIL RECONNECTION EVENTS SHOW THAT THE O+ CAN BE AN IMPORTANT OR EVEN DOMINANT SOURCE OF ENERGY FLUX OUTFLOW FROM THE RECONNECTION REGION. OUR PROPOSED RESEARCH AIMS TO IMPROVE OUR UNDERSTANDING OF THE IMPORTANCE OF HEAVY IONS IN RECONNECTION REGIONS BY ADDRESSING THE FOLLOWING QUESTIONS: (1) HOW DO HEAVY IONS CONTRIBUTE TO PARTITIONING OF ENERGY OUTFLOW FROM THE RECONNECTION REGION? WHAT CONDITIONS AND PROCESSES RESULT IN SIGNIFICANT HEAVY ION CONTRIBUTIONS? (2) HOW DO THE ENERGIZATION MECHANISMS OF HEAVY IONS AND H+ IONS DIFFER? (3) HOW DOES THE PRESENCE OF HEAVY IONS IMPACT ENERGY OUTFLOW DUE TO POYNTING FLUX? THE EFFECT OF HEAVY IONS AND SPECIFICALLY OXYGEN IN RECONNECTION IN THE MAGNETOTAIL IS A QUESTION OF LONGSTANDING INTEREST. OUR PROPOSED RESEARCH WILL MAKE SIGNIFICANT PROGRESS TOWARDS UNDERSTANDING THE ROLE OF HEAVY IONS. DATA AND METHODOLOGY: WE WILL UTILIZE DATA FROM THE THE SET OF MAGNETOTAIL RECONNECTION EVENTS OBTAINED DURING THE 2017 MAGNETOTAIL APOGEE INTERVAL IN ADDITION TO DAYSIDE MAGNETOPAUSE CROSSINGS. WE WILL USE THE FIELDS SUITE TO OBTAIN 3-D ELECTRIC AND MAGNETIC FIELDS BOTH QUASI-STATIC AND WAVEFORM DATA. WE WILL USE OF THE HCPA INSTRUMENT FOR 3D DISTRIBUTION FUNCTIONS OF H+ HE+ HE++ AND O+ IONS AS WELL AS THE FAST PLASMA INSTRUMENTS FOR HIGH-CADENCE DISTRIBUTION FUNCTIONS OF H+ IONS AND ELECTRONS. OUR INITIAL SURVEY HAS IDENTIFIED A SET OF EVENTS CONTAINING A RANGE OF OXYGEN TO HYDROGEN RATIOS SUFFICIENT TO ADDRESS OUR SCIENCE QUESTIONS. IN ORDER TO ADDRESS OUR SCIENCE QUESTIONS WE WILL STUDY MMS MAGNETOTAIL RECONNECTION EVENTS THAT WE HAVE ALREADY IDENTIFIED. CRUCIAL TO THE SUCCESS OF OUR STUDY IS THE SMALL SPATIAL SEPARATION BETWEEN THE SPACECRAFT ALLOWING FOR LOW-ERROR CALCULATION OF THE DIVERGENCE IN THE ELECTRIC FIELD NECESSARY TO DISTINGUISH SCALES OVER WHICH IONS OF DIFFERENT MASSES WILL BE ENERGIZED. IN ADDITION THE 3-DIMENSIONAL ELECTRIC FIELD MEASUREMENTS AND HIGH-CADENCE DATA FOR ELECTRONS AND H+ IONS WILL PROVIDE A MORE COMPLETE VIEW OF THE ENERGY PARTITIONING AT THE RECONNECTION REGION THAN PREVIOUSLY AVAILABLE STUDIES THAT UTILIZED THE CLUSTER 2D ELECTRIC FIELD AND LOWER CADENCE PARTICLE DATA. COMPARISONS WITH SIMULATIONS OF RECONNECTION THAT INCLUDE HEAVY IONS WILL ALSO BE PERFORMED. A SET OF MAGNETOPAUSE RECONNECTION EVENTS WILL ALSO BE STUDIED TO PROVIDE ADDITIONAL COMPLEMENTARY INFORMATION ON SCALE-SIZES OVER WHICH HEAVY ION ENERGIZATION OCCURS AND THE ASSOCIATED OUTFLOWING ENERGY FLUX. RELEVANCE: OUR PROPOSED RESEARCH IS DIRECTLY RELEVANT TO THE GOALS OF THE MMS AND THE MMS GI PROGRAM. WE WILL UTILIZE MMS DATA TO DIRECTLY EXAMINE IMPORTANT PHYSICS ASSOCIATED WITH THE RECONNECTION. THE RESULTS ARE ALSO DIRECTLY RELEVANT TO THE OBJECTIVES IN HELIOSPHERIC DECADAL SURVEY SPECIFICALLY GOAL 3 'DETERMINE THE INTERACTION OF THE SUN WITH THE SOLAR SYSTEM' AND GOAL 4 'DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE.'