MD80 DEP FROM CLT IS REQUESTED TO 'TURN OFF THE RWY' TWICE BECAUSE OF ARR SPACING; TWR SUGGESTING FLT CREW'S TKOF ACTIONS WERE TOO SLOW.

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TWR CLRED US FOR TKOF. WE HAD BEEN HOLDING SHORT. I APPLIED NORMAL PWR AND WE MADE THE TURN AND COMPLETED ALL CHKLIST ITEMS AND EXECUTED A NORMAL ROLLING TKOF. AT TKOF PWR; AROUND 60 KTS; TWR CALLED AND ASKED; 'XX XXXX CAN YOU TURN OFF OF THE RWY?' AT THIS CALL; I PULLED THE PWR BACK; WONDERING WHETHER WE HAD INADVERTENTLY BEGUN THE TKOF ROLL WITHOUT CLRNC AND IN CONFLICT WITH LNDG TFC. TWR THEN SENT THE LNDG ACFT AROUND; THEN TOLD US TO CONTINUE. INSTEAD; I TURNED OFF THE RWY AS WE'D USED UP A SIGNIFICANT PART OF THE AVAILABLE RWY AND HAD PWR AT IDLE. I CALLED TWR ONCE WE WERE CLR AND SAID; 'CONFIRM XX XXXX WAS CLRED FOR TKOF.' TWR CONFIRMED WE WERE CLRED; BUT WERE TOO SLOW SO HE WAS ASKING US TO EXIT THE RWY. I EXPECT TO HEAR ONLY 2 THINGS ON THE RWY: EITHER 'CLRED FOR TKOF' OR 'CANCEL TKOF CLRNC; TAXI OFF THE RWY.' 'CAN YOU TURN OFF THE RWY?' IS CONFUSING; AMBIGUOUS AND HAZARDOUS TO NORMAL DECISION-MAKING AT FULL PWR DURING TKOF ROLL. 'ABORT' WOULD HAVE MADE SENSE; BUT WITH TKOF CLRNC; I WOULDN'T EXPECT TO BE TOLD TO ABORT AND CLR THE RWY FOR A LNDG ACFT. WE RE-ENTERED THE TKOF LINE-UP AND THE EXACT SAME THING HAPPENED. WE WERE CLRED FOR TKOF; EXECUTED A ROLLING TKOF AND THE TWR SAID ONCE AGAIN; WHEN WE WERE AT FULL PWR AND ROLLING THROUGH 60 KTS; 'XX XXXX; YOU'RE TOO SLOW; CAN YOU TURN OFF OF THE RWY?' I TOLD THE FO TO NOT ANSWER THE CALL AND TO CONTINUE UNLESS WE WERE INSTRUCTED TO ABORT. THIS CLT INCIDENT -- REPEATED A SECOND TIME -- IS DANGEROUS; NONSTANDARD; AND FRUITFUL GROUND FOR A RWY EXCURSION OR WORSE. I DO NOT UNDERSTAND HOW A TWR CTLR CAN ISSUE SUCH REQUESTS AT A CRUCIAL TIME; PLUS; I QUESTION HIS BASIC OPERATING PREMISES IF ACFT IN POS AND ROLLING CAN BE EXPECTED TO EXIT THE RWY DURING TKOF ROLL IF SEPARATION WITH A LNDG ACFT BECOMES INSUFFICIENT. THAT THIS HAPPENED TWICE IS VERY DISTURBING.