SMA LNDG AT YKM; FOLLOWED BY YAK; EXITS RWY WITH MIN INTRAIL SEPARATION. REPORTER INDICATES LACK OF SEPARATION JUDGEMENT BY ATC.

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3 ACFT RADIOED YKM TWR FOR VFR LNDG WITH ATIS INFO; A BONANZA FROM THE SW; MY ACFT FROM THE SW AND A YAK FROM THE E. VMC PREVAILED; LIGHT WINDS FROM THE W; CAVU. ATIS WAS ADVISING RWY 27 IN USE FOR VFR. THE BONANZA WAS CLRED TO LAND ON RWY 9. I WAS INSTRUCTED TO ENTER A R BASE FOR WY 9 BUT REQUESTED RWY 27 OWING TO THE LIGHT WIND FROM THE W. THIS WAS APPROVED AND I WAS INSTRUCTED TO RPT MIDFIELD ON A L DOWNWIND FOR RWY 27 AND THEN CONTINUE ON THE DOWNWIND UNTIL INSTRUCTED TO TURN BASE. THE YAK WAS SEVERAL MI E AND WAS INSTRUCTED TO PERFORM A 360 DEG TURN. I WAS THEN INSTRUCTED TO TURN L BASE AND CLRED TO LAND ON RWY 27. THE BONANZA HAD LANDED ON RWY 9 AND EXITED THE RWY. I WAS IN THE L SEAT AND WAS SOLE OPERATOR OF THE CTLS AND ACFT. MY BEGINNER STUDENT WAS IN THE R SEAT AND HAD XFERRED THE CTLS TO ME PRIOR TO OUR ENTERING THE PATTERN UPON MY REQUEST DUE TO THE PRESENCE OF THE OTHER TFC. AS I TURNED SHORT FINAL; I HEARD THE TWR CLR THE YAK FOR LNDG ON RWY 27. I REQUESTED A LONG LNDG IN ORDER TO MAINTAIN SEPARATION FROM THE YAK COMING UP MY TAIL. THE TWR DENIED THIS REQUEST AND SAID 'I NEED YOU TO EXIT THE RWY WITHOUT DELAY.' I TOUCHED DOWN ON THE NUMBERS AND BRAKED IN TIME TO EXIT AT TXWY C; ONLY A COUPLE OF HUNDRED FT PAST THE THRESHOLD. I SAW THE YAK LAND IMMEDIATELY BEHIND; ESTIMATED AT LESS THAN 30 SECONDS AFTER MY TOUCHDOWN. I WAS SHAKEN AND SO WAS MY STUDENT. ALTHOUGH I WAS CLRED TO LAND IN FRONT OF THE YAK; I KNEW THE APCH SPD OF THE YAK WAS SIGNIFICANTLY IN EXCESS OF MY ACFT'S AND SEPARATION WOULD QUICKLY BE REDUCED. WHEN THE TWR DID NOT INSTRUCT THE YAK TO GO AROUND; I SHOULD HAVE DECLARED AND INITIATED A GAR MYSELF RATHER THAN RISK BEING STRUCK FROM BEHIND. A CONTRIBUTING FACTOR WAS THE MISJUDGEMENT OF ACFT SPDS BY THE TWR.