The shock wave generator in Project 110 is a spherical multipoint initiation system designed to fit inside a nuclear warhead which in turn would be carried in the payload chamber of the Shahab-3 missile nose cone. There is considerable information about this MPI system in the public literature. The IAEA gathered significant information about this system and reported it under the names of MPI system and shock generator. The IAEA summarized its knowledge of this MPI system in its December 2015 report on outstanding issues regarding Iran’s past nuclear program. Much information about this Iranian MPI system also became public in the period of roughly 2008 to 2011.

The basic design of the shock wave generator is a distributed, explosive-filled channel system for initiating hemispherical high-explosive charges. A detonation front initiated at one point via an exploding bridgewire or spark gap is made to arrive simultaneously at a multitude of points on a surface. The assembled system consists of two hemispherical shells and requires only two detonation points, in contrast to the 32 initiation points on the first nuclear weapons built by the United States. Moreover, this system eliminates the need to work with high-explosive lenses and allows for a reduction in the size of the warhead.

In this effort, Iran appears to have had assistance from a foreign expert knowledgeable in nuclear weapons (identified by the Institute in 2011 as Vycheslav V. Danilenko ). According to the IAEA:

Information available to the Agency in 2011 also indicated that Iran could have benefitted from the aforementioned foreign expert, who had knowledge of both MPI technology and experimental diagnostics and had worked for much of his career in the nuclear weapon programme in his country of origin. The foreign expert’s presence in Iran in the period 1996-2001 has been confirmed by Iran, although it stated that his activities were related to the production of nanodiamonds.

U.S. and Russian patents shed light on the principles of such a MPI system. According to a 1969 U.S. patent (filed in 1963 by Richard Stresau) for the U.S. Navy:

This invention relates to explosive devices and more particularly to a new and improved surface-wave generator or detonation wave shaping system wherein a detonation front initiated at one point is made to arrive simultaneously at a plurality of points on a desired surface, the configuration of which may be either plane or curved.

This generator in turn sets off a main charge of high explosives. The device involves a set of channels embedded within a sheet of inert elastomer, also known as an inert polymer.

This U.S. patent design from 1969, of a flat distributor with an adjacent high explosive charge, is illustrated in a 2010 book by Danilenko, whose writings are studied because of his assistance to Iran (see Figure 4). The distributor consists of a layer of inert elastomer with channels or grooves, which are filled with a high explosive, typically a plastic explosive, according to Danilenko. The key idea is that following detonation at one point, the length to any explosive pellet is the same, providing the simultaneity and eliminating the need for multiple detonators. Danilenko notes importantly in his 2010 book that the detonation front in the main charge initiated by the multiple explosive pellets will smooth out as it moves into the explosive charge. He adds that smoothness will be aided by increasing the number of explosive pellets, or points, e.g. decreasing the distance between the points of detonation. However, Danilenko notes that this device is complicated and labor-intensive to make.

There are also at least two Russian patents on similar MPI systems with the same matrix shape as seen in the U.S. patent, although they were filed approximately 20 years after Stresau’s 1969 U.S. patent. It is possible that publication of these patents was delayed due to Russian classification issues. The inventers of both patents list their address at the All-Russian Scientific Research Institute for Experimental Physics (VNIIEF), the Soviet Union’s primary nuclear weapons research and development center. At least one of the inventers, Vladimir K. Chernysev, was an important figure in the development of Soviet nuclear weapons.

Whether similar systems were used in Russian nuclear weapons is unknown. However, the relevance of such systems for nuclear weapons was likely known in the Soviet nuclear weapons complex by the time of Stresau’s patent in the 1960s.

To better understand the MPI system made by Iran, which may have important differences from the systems in the above-mentioned patents, it is useful to review several public media and Institute reports on Iran’s multi-point initiation system derived from the above principles that were published in the period between 2008 and 2011.

In 2008, Jane’s International Defense Review wrote that Iran’s Ministry of Defense had actively pursued a “relatively advanced multipoint initiation (MPI) nuclear implosion detonation technology for some years.” It also reported that Iran had tested this MPI system and found it “good enough” for a nuclear weapon. A schematic in the article (Figure 5), which reportedly shows a portion of the MPI used by Iran, looks very similar to the schematic in Figure 4.

In 2010, Paul-Anton Krüger, a reporter at the Süddeutsche Zeitung, published more detailed information on the shock wave generator, as well as on the role of Danilenko (albeit the report did not provide his real name) in aiding Iran. Krüger reported that the information obtained by the IAEA stated that the Iranian system was composed of two hemispheres with small milled channels and holes uniformly distributed on it and filled with high explosives. On each hemisphere, a single detonator, or exploding bridgewire, sets off the explosives in the channels, and all the small explosive charges in the holes detonate at the same time, igniting the main explosive charge under the shell.

Building on the published media work, the Institute published on this MPI system in 2011, which is summarized in the following several paragraphs. The information provided to the IAEA was that the shock wave generator is comprised of two hemispherical shells connected together. Media reports stated that they were made from aluminum, but this reporting may have reflected information about Iranian models of such systems. In any case, the wall thickness of the shell was one centimeter thick. Many channels, each with dimensions of one-by-one millimeter, were cut into the outer surface of the shell. The channels were filled with the explosive material pentaerythritol tetranitrate (PETN), which was selected because of its moldability and stability when mixed with plasticizers. Each channel terminated in a cylindrical hole, five millimeters in diameter, that was drilled though the shell and contained an explosive pellet. The geometrical pattern formed by channels and holes were arranged in quadrants on the outer hemispheric surface, which allowed a single central point of initiation for each hemisphere and the simultaneous detonation of explosives in all the holes on the hemisphere. This in turn allows the simultaneous initiation by one EBW or spark gap of the high explosives in the main charge located under the hemispheres. EBW initiation would be preferred because Iran could make EBWs but needed to buy spark gaps, at least at that time.

In the IAEA reporting, a full-size version of the Iranian shock wave generator was referred to as the R265 generator, also called a round shock generator, where the number corresponds to the inner diameter of the shell measured in millimeters. The outer radius of the R265 system would be 275 millimeters, or an outer diameter of 550 millimeters, less than the estimated diameter of about 600 millimeters available inside the payload chamber of a Shahab-3.

Both Jane’s and Krüger reported that Iran tested this MPI system. Based on their reporting, prior to the seizure of the archive, the IAEA reportedly had information that Iran conducted a field experiment of a near or actual full-size shock generator with high explosives and a sophisticated diagnostic system, similar to one developed by Danilenko.

This information was confirmed in subsequent IAEA reporting. According to the 2015 IAEA report:

Prior to November 2011, Member States provided the Agency with information that Iran had available to it design information on the explosives technology known as multipoint initiation (MPI) and that it had used this for the initiation of high explosives in hemispherical geometry. The information indicated that Iran had developed of a hemispherical MPI system and conducted at least one large scale experiment in 2003, details of which were technically consistent, both internally and with publications authored by a certain ‘foreign expert’. The Agency has reassessed that this experiment was conducted at a location called “Marivan”, and not conducted in “the region of” Marivan [as previously reported].

An earlier IAEA report from 2011 adds detail about Danilenko:

The Agency has strong indications that the development by Iran of the high explosives initiation system, and its development of the high speed diagnostic configuration used to monitor related experiments, were assisted by the work of a foreign expert who was not only knowledgeable in these technologies, but who, a Member State has informed the Agency, worked for much of his career with this technology in the nuclear weapon programme of the country of his origin.

(It should be noted that the archive contains information about the Marivan site, including photos of it. The archive shows that the Marivan site undertaook work linked to implosion testing. The above test would have fallen under the category of implosion testing.)

According to 2011 Institute reporting, prior to the seizure of the archive, there was publicly available information about this 2003 test. Information from a member state, given to the IAEA several years ago, describes that in this experimental setup, which aimed to measure the time of arrival of the detonation front, 50 kilograms of Composition B explosives in the form of a shell were placed inside a hemispherical shock generator system. The time of arrival of the detonation front at the outer surface of this 50 kilogram shell of explosives was measured by using many hundreds of fiber optic cables drilled into a thin hemispherical shell or holder in close proximity of the inner surface of the explosives. The other end of each of the cables was attached to a fixture or panel. The light signals were transmitted via air to a fast-acting camera with a rotating mirror, likely a framing camera, at a safe distance from the explosion. On firing, the EBW, or spark gap, ignited the PETN explosives in the channels of the shell, setting off the explosive pellets in the holes in the shell, which in turn initiated the outer surface of the Composition B shell. The detonation front traveled through the main charge and on exiting the inner surface produced light, which was transmitted via the fiber optic cables and was captured on the film of the high-speed camera.

This description, with less detail, is in the 2011 IAEA report:

Information provided to the Agency by the same Member State referred to in the previous paragraph [not included here] describes the multipoint initiation concept referred to above as being used by Iran in at least one large scale experiment in 2003 to initiate a high explosive charge in the form of a hemispherical shell. According to that information, during that experiment, the internal hemispherical curved surface of the high explosive charge was monitored using a large number of optical fibre cables, and the light output of the explosive upon detonation was recorded with a high speed streak camera. It should be noted that the dimensions of the initiation system and the explosives used with it were consistent with the dimensions for the new payload which, according to the alleged studies documentation, were given to the engineers who were studying how to integrate the new payload into the chamber of the Shahab 3 missile re-entry vehicle (Project 111).

As noted above, the IAEA recognized that the diagnostic system used in this MPI test is similar to one Danilenko presented in two papers in the early 1990s at a conference on high-speed photography and photonics. In their papers, Danilenko and his colleagues from the Federal Nuclear Center, the All-Russian Institute of Technical Physics (VNIITF), , presented an optical technique in which fiber optic cables are used to capture the time of arrival of an explosive shock wave on a fast camera. VNIITF was created as a back-up facility for the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) and contained expertise in the entire spectrum of work connected with the design and development of nuclear weapons. Figure 6 has two simplified figures from one of their papers that show the basic structure of this system, illustrating it with one fiber cable. In actuality, there would be hundreds. Figure 7 shows a schematic of an experimental arrangement with emphasis on the holder and panel, along with a framing camera with a raster. A raster is a method of displaying multiple channel lines on one screen.

There is one publicly available picture from the archive that apparently shows a model of this experimental system using optical fibers (Figure 8). This model shows a hemispherical object representing the external side of the multi-point initiation system, where inside would be the high explosives and an inner surface, or holder, where the fiber optic cables would connect. The fiber optic cables exiting the hemisphere and the panel can also be seen. (The archive contains many images of actual hemispherical configurations for this type of test as well as other hemispherical high explosive tests related to developing implosion-based nuclear weapons. However, those images, in addition to a considerable amount of other information, were judged as nuclear weapons-sensitive and not made public by Israel.)