Shiv ji: I read the below in no other way, other than a claim of teller-ulam.
He said — and this astonished me — that based on the 1998 data Indian designers could even design “yield-dialed” weapons by, as Sikka said, simply reducing/increasing the fissile material and changing the mass of chemical explosives to set off the fission implosion in the first stage.
This is because you have convinced yourself that "dial a yield" means a Teller Ulam design. In fact from that fateful day May 8th 1998 the "experts" of BRF instantly stated that what was later called as a fizzle was a Teller Ulam design. I recall being the one and only guy to question this but no one paid any attention. Then the doubts and questions set in and everyone started weeping and beating their breasts howling "All nations have succeeded in first shot of Teller Ulam. India has failed We are useless. We are worthless Chidambaram is a fool. Vajpayee is a liar" - in other words - based on an assumption we started howling and self flagellating
Not even once in the last 19 years have I heard anyone from the nuclear establishment say that a Teller Ulam design was tried. But I digress.
From open source literature I am informed that "dial a yield" works as follows - in a series where the first 3-4 steps are fission and/or boosted fission alone. The last 2 steps can involve a Tellr Ulam design
If you have Pu ball surrounded by explosive lenses and the Pu ball has a "pit" for Tritium boosting, the lowest yield (subkiloton yield) can be obtained by doing a deliberate fizzle in which only one of two onion layers of conventional explosive is set off leading to partial compression and a deliberate subkiloton fizzle
The next step up would be to explode (i.e implode) the whole lens and get adequate compression to get full paisa vasool of fission onlee. No Tritium boosting.
The third step up in yield would be to introduce Tritium gas into the Pu ball core to get boosted fission. The amount of Tritium can be varied - i.e 50% or 100% to get higher but different yields. The small amount of fusion that occurs here makes the fission very effective giving a bigger bang.
Note that so far it is fission and boosted fission alone and just this design can get 100 kilotons or more
Next (as the US does) is to place the above variable yield gizmo inside a Teller Ulam design. A mechanical shield can stop the fusion from working and if fusion is required the shield is removed and you get the thermonuclear part.
Finally if this Teller Ulam thing can be placed in a fissile U 235 tamper (instead of a lead tamper) so that thermonuclear part causes the tamper itself to serve as a fission bomb. Most of the explosive force of a 1 megaton bomb is from fission, Not fusion
Unfortunately lack of some basic physics knowledge will lead to the above being incomprehensible to the person who has never studied or kept in touch with physics. It is no coincidence that the Amreekis call the inner core of their bombs a 'Physics package" - not "rhetoric package" or "history package"
The first "accepted" thermonuclear bomb was a Sloika (not Teller Ulam) design called Joe 4 done by the Soviets which gave 400 kilotons of which about 15% was fusion.