10-08-2009, 11:07 PM
Although it was distressing to see the confirmation of the failure of the second stage of the TN device, we must thank Santhanam, Subramaniam and others for lifting the unnecessary veil over the Indian nuclear program. This is what I think was the situation before the 1998 blast:
(1) BARC had built untested fission weapons using the POKHRAN 1 design as a reference. These 20 Kt fission weapons had a fission efficiency of about 15 %. Karnad says that even the cleverest fission weapon is only about 25 % efficient;
(2) BARC also had a simple boosted fission device where they just coated the plutonium with Li D and pumped Tritium gas into the container containing the LID coated plutonium core and the explosive lens.
This design is basically the same as the fission bomb. BARC was sure about the fission part but uncertain about the boosting of fission efficiency that they will get from this design.
(3) BARC had a tentative TN device design but they were themselves uncertain about it. Mahadevan Srinivasan admitted to Karnad about the uncertainty in the minds of the Indian weaponeers about how to concentrate the gamma rays onto the second stage fusion material. Karnad writes that the Indian weaponeers had lots of problems understanding how to focus the gamma rays onto the fusion material.
The situation has changed after the 1998 tests. Now BARC is confident that
(1) their simple fission device will work yielding approximately 20 kts;
(2) their boosted fission design would yield a boosting of fission efficiency of about 4. Karnad specifically mentions a boosting factor of 4 in his book. That means the boosted fission device will get a 60 % fission efficiency unlike the 15 % efficiency fission weapon.
(3) their design to focus the gamma rays on the fusion material is highly inefficient.
What is the implication of these facts regarding weaponisation?
India has simple fission bombs of yields 20 kts with a reliability of greater than say 95 %.
India also has boosted fission bombs in the 60-80 kt range with almost the same degree of reliability. This is because a factor of 4 increase in fission efficiency from the 15 % fission bomb would imply a 60 % fission efficiency and a yield of 4x20 kt or 80 kts. Indian military would have high level of confidence in a 80 kt boosted fission weapon.
India does not have a TN weapon because the confidence level of a BARC design is at say 10-15 % level.
The next question is whether India has a deterrence at a 200 kt level. BARC certainly has the capacity of making a 200 kt boosted fission bomb. They, however, cannot use the blue prints of the 20 kt bomb to do it. They will have to start with a 50 kt fission bomb because they can only get a boosting of factor 4. It is here that uncertainty creeps in because lots of things will have to be redesigned to get a 50 kt fission bomb. Once they have designed a 50 kt bomb, they can coat the plutonium with LiD and immerse the bomb in Tritium gas to get a boosting of 4. It is possible that BARC has designed such a weapon. However, the confidence in such a weapon would be less than the 80 kt boosted fission weapon without tests.
Has BARC modified the TN device design? I think yes from Santhanam and Chidambaram's statements. However this design can not be weaponised without tests.
(1) BARC had built untested fission weapons using the POKHRAN 1 design as a reference. These 20 Kt fission weapons had a fission efficiency of about 15 %. Karnad says that even the cleverest fission weapon is only about 25 % efficient;
(2) BARC also had a simple boosted fission device where they just coated the plutonium with Li D and pumped Tritium gas into the container containing the LID coated plutonium core and the explosive lens.
This design is basically the same as the fission bomb. BARC was sure about the fission part but uncertain about the boosting of fission efficiency that they will get from this design.
(3) BARC had a tentative TN device design but they were themselves uncertain about it. Mahadevan Srinivasan admitted to Karnad about the uncertainty in the minds of the Indian weaponeers about how to concentrate the gamma rays onto the second stage fusion material. Karnad writes that the Indian weaponeers had lots of problems understanding how to focus the gamma rays onto the fusion material.
The situation has changed after the 1998 tests. Now BARC is confident that
(1) their simple fission device will work yielding approximately 20 kts;
(2) their boosted fission design would yield a boosting of fission efficiency of about 4. Karnad specifically mentions a boosting factor of 4 in his book. That means the boosted fission device will get a 60 % fission efficiency unlike the 15 % efficiency fission weapon.
(3) their design to focus the gamma rays on the fusion material is highly inefficient.
What is the implication of these facts regarding weaponisation?
India has simple fission bombs of yields 20 kts with a reliability of greater than say 95 %.
India also has boosted fission bombs in the 60-80 kt range with almost the same degree of reliability. This is because a factor of 4 increase in fission efficiency from the 15 % fission bomb would imply a 60 % fission efficiency and a yield of 4x20 kt or 80 kts. Indian military would have high level of confidence in a 80 kt boosted fission weapon.
India does not have a TN weapon because the confidence level of a BARC design is at say 10-15 % level.
The next question is whether India has a deterrence at a 200 kt level. BARC certainly has the capacity of making a 200 kt boosted fission bomb. They, however, cannot use the blue prints of the 20 kt bomb to do it. They will have to start with a 50 kt fission bomb because they can only get a boosting of factor 4. It is here that uncertainty creeps in because lots of things will have to be redesigned to get a 50 kt fission bomb. Once they have designed a 50 kt bomb, they can coat the plutonium with LiD and immerse the bomb in Tritium gas to get a boosting of 4. It is possible that BARC has designed such a weapon. However, the confidence in such a weapon would be less than the 80 kt boosted fission weapon without tests.
Has BARC modified the TN device design? I think yes from Santhanam and Chidambaram's statements. However this design can not be weaponised without tests.