{"id":3044,"date":"2012-06-10T12:13:11","date_gmt":"2012-06-10T17:13:11","guid":{"rendered":"http:\/\/helian.net\/blog\/?p=3044"},"modified":"2012-06-10T12:13:11","modified_gmt":"2012-06-10T17:13:11","slug":"nuclear-fusion-update","status":"publish","type":"post","link":"https:\/\/helian.net\/blog\/2012\/06\/10\/nuclear-weapons\/nuclear-fusion-update\/","title":{"rendered":"Nuclear Fusion Update"},"content":{"rendered":"

As I mentioned in a previous post <\/a>about fusion progress, signs of life have finally been appearing\u00a0in\u00a0scientific journals from the team working to achieve fusion ignition<\/a> at the National Ignition Facility, or NIF, located at Lawrence Livermore National Laboratory (LLNL)\u00a0in California.\u00a0 At the moment they are “under the gun,” because the National Ignition Campaign (NIC)\u00a0is scheduled to end with the end of the current fiscal year\u00a0on\u00a0September 30.\u00a0 At that point, presumably, work at the facility will be devoted mainly to investigations of nuclear weapon effects and physics, which do not\u00a0necessarily require fusion ignition.\u00a0 Based on a paper\u00a0that recently appeared in Physical Review Letters, chances of reaching the ignition goal before that happens are growing dimmer.<\/p>\n

The problem has to do with a seeming contradiction in the physical requirements for fusion to occur in the inertial confinement approach pursued at LLNL.\u00a0 In the first place, it is necessary for the NIF’s 192 powerful laser beams to compress, or implode,\u00a0a target containing fusion fuel in the form of two heavy isotopes of hydrogen to extremely high densities.\u00a0 It is much easier to compress materials that are cold than those that are hot.\u00a0 Therefore, it is essential to keep the fuel material as cold as possible during the implosion process.\u00a0 In the business, this is referred to as keeping the implosion on a “low adiabat.”\u00a0 However, for fusion ignition to occur, the nuclei of the fuel atoms must come extremely close to each other.\u00a0 Unfortunately, they’re not inclined to do that, because they’re all positively charged, and like charges repel.\u00a0 How to overcome the repulsion?\u00a0 By making the fuel material extremely hot, causing the nuclei to bang into each other at high speed.\u00a0 The whole trick of inertial confinement fusion, then, is to keep the fuel material very cold, and then, in a tiny fraction of a second, while its inertia holds it in place (hence the name, “inertial” confinement fusion),\u00a0raise it, or at least a small bit of it, to\u00a0the extreme temperatures necessary for the fusion process to begin.<\/p>\n

The proposed technique for creating the\u00a0necessary hot spot was always somewhat speculative, and\u00a0more than\u00a0one fusion expert at the national laboratories were dubious that it would succeed.\u00a0 It consisted of creating a train of four shocks\u00a0during the implosion process, which were to overtake one another all at the same time precisely at the moment of maximum compression, thereby creating the necessary hot spot.\u00a0 Four shocks are needed because\u00a0of\u00a0well-known theoretical\u00a0limits on the increase in temperature that can be achieved with a single shock.\u00a0 \u00a0Which brings us back to the paper in Physical Review Letters.<\/p>\n

The paper, entitled Precision Shock Tuning on the National Ignition Facility<\/a><\/em>, describes the status of efforts to get the four shocks to jump through the hoops described above.\u00a0 One cannot help but be impressed by the\u00a0elegant diagnostic tools\u00a0used to observe and measure the shocks.\u00a0 They are capable of peering through materials under the extreme conditions in the NIF target chamber, focusing on the tiny, imploded target core, and measuring the progress of a train of shocks over a period that only lasts for a few billionths of a second!\u00a0 These diagnostics, developed with the help of another team of brilliant scientists at the OMEGA laser facility at the University of Rochester’s Laboratory for Laser Energetics<\/a>, are a triumph of human ingenuity.\u00a0 They reveal that the NIF is close to achieving the ignition goal, but not quite close enough.\u00a0 As noted in the paper, “The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation.”<\/p>\n

It will be a neat trick indeed if the NIF team can overcome this problem before the end of the National Ignition Campaign.\u00a0 In the event that they don’t, one must hope that the current administration is not so short-sighted as to conclude that the facility is a failure, and severely reduce its funding.\u00a0 There is too much at stake.\u00a0 I have always been dubious about the possibility that either the inertial or magnetic approach to fusion will become a\u00a0viable source of energy any time in the foreseeable future.\u00a0 However, I may be wrong, and even if I’m not, achieving inertial fusion ignition in the laboratory may well point the way to as yet undiscovered paths to the fusion energy goal.\u00a0 Ignition in the laboratory will also give us a significant advantage over other nuclear weapons states in maintaining our arsenal without nuclear testing.<\/p>\n

Based on the progress reported to date, there is no basis for the conclusion that ignition is unachievable on the NIF.\u00a0 Even if the central hot spot approach currently being pursued proves too difficult, there are alternatives, such as polar direct drive<\/a> and fast ignition<\/a>.\u00a0 However, pursuing these alternatives will take time and resources.\u00a0 They will become a great deal more difficult to realize if\u00a0funding for\u00a0NIF operations is severely cut.\u00a0 It will also be important to maintain the ancillary capability\u00a0provided by\u00a0the OMEGA laser.\u00a0 OMEGA is much less powerful but also a good deal more flexible and nimble than the gigantic NIF, and has already proved its value in testing and developing diagnostics, investigating novel experimental approaches to fusion, developing advanced target technology, etc.<\/p>\n

We have built world-class facilities.\u00a0 Let us persevere in the quest for fusion.\u00a0 We cannot afford to let this chance slip.<\/p>\n

\n\t\t\t\t\tTweet<\/a>\n\t\t\t\t<\/div><\/div>","protected":false},"excerpt":{"rendered":"

As I mentioned in a previous post about fusion progress, signs of life have finally been appearing\u00a0in\u00a0scientific journals from the team working to achieve fusion ignition at the National Ignition Facility, or NIF, located at Lawrence Livermore National Laboratory (LLNL)\u00a0in California.\u00a0 At the moment they are “under the gun,” because the National Ignition Campaign (NIC)\u00a0is … Continue reading “Nuclear Fusion Update”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[37,43,78,22,23,10],"tags":[],"class_list":["post-3044","post","type-post","status-publish","format-standard","hentry","category-energy","category-environment","category-fusion-energy","category-inertial-confinement-fusion","category-nuclear-energy","category-nuclear-weapons"],"jetpack_publicize_connections":[],"jetpack_shortlink":"https:\/\/wp.me\/pwEq0-N6","jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts\/3044","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/comments?post=3044"}],"version-history":[{"count":2,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts\/3044\/revisions"}],"predecessor-version":[{"id":3046,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts\/3044\/revisions\/3046"}],"wp:attachment":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/media?parent=3044"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/categories?post=3044"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/tags?post=3044"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}