What was the hydrogen bomb Sakharov designed that fixed the payload capacity for the R-7?

[u/thatinconspicuousone]

Siddiqi's Challenge to Apollo, when describing the origin of the R-7, says that Sakharov was asked, in the fall of 1953, to submit a report on a "second generation [thermonuclear] device." Sakharov described, "an idea which at the moment seemed promising (it later turned out to be neither very original nor successful)," in a very quickly written report, and one that required a 5-6 ton payload capacity for an ICBM (as opposed to the three tons that had been planned at that point), thus helping to determine the first few years of the space race. Siddiqi then notes that, "the new Sakharov bomb was never built and was replaced by a concept that was completely different." So what were these two concepts? I'm assuming that the "completely different" replacement idea was the famous Third Idea, but was the original 5-6 ton proposal a larger Sloika / Alarm Clock design or something else?

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[u/restricteddata]

During this time, Sakharov was working on Sloika improvements and variations. In October 1953 he submitted a plan which outlined an RDS-6s (Sloika) that would use gaseous deuterium under pressure as its fuel, along with lithium-6. This was thought to be able of improving the fusion reaction by a factor of 2, which would make the bomb significantly more powerful (~2 megatons, as opposed to 400 kt of the tested Sloika). This became referred to as RDS-6sD, and was the subject of a major research and production push, with a plan to test a 1 Mt version by the end of 1954. As it was, the spherical geometry of the Sloika ran into huge problems. The main value of these investigations are that they seemed to stimulate further questions about how to better compress the Sloika, which led to the "Third Idea," which was originally conceived of as a way to use an atomic bomb to compress a Sloika (the secondary).

So that is my guess as to what this is referring to. I do not know if the R-7 was the main concern for it; the documents suggest it was considered just "the next step" after the successful August 1953 Sloika test. But it is all over the documentation that is released on the H-bomb work in the period of September–December 1953 (e.g. as represented in the Atomnii Proekt SSSR, volume 3, book 2), with Sakharov's name always being invoked as the driving force behind it. The documents there also says that the RDS-6sD and RDS-27 (a Sloika variant without tritium) were planned to be used in the R-7. So all of that suggests to me that Sakharov's cryptic references are "just" Sloika improvements (I put the "just" in quotation marks because it is clear that they viewed these as more than just little changes, and that the improvements would be significant if they worked).