{"id":210784,"date":"2025-04-07T05:21:53","date_gmt":"2025-04-07T10:21:53","guid":{"rendered":"https:\/\/lifeboat.com\/blog\/2025\/04\/reducing-the-dark-current"},"modified":"2025-04-07T05:21:53","modified_gmt":"2025-04-07T10:21:53","slug":"reducing-the-dark-current","status":"publish","type":"post","link":"https:\/\/lifeboat.com\/blog\/2025\/04\/reducing-the-dark-current","title":{"rendered":"Reducing the Dark Current"},"content":{"rendered":"<p style=\"padding-right: 20px\"><a class=\"aligncenter blog-photo\" href=\"https:\/\/lifeboat.com\/blog.images\/reducing-the-dark-current.jpg\"><\/a><\/p>\n<p>Free-electron lasers (FELs) have an electron problem: a \u201cdark\u201d current that can propagate with the electron beam, limiting the performance of the system. Now Guan Shu of Zhangjiang Laboratory in China and colleagues have developed a method that can reduce the strength of this unwanted dark current by 3 orders of magnitude [<a href=\"https:\/\/physics.aps.org\/articles\/v18\/s40#c1\" class=\"\">1<\/a>]. Because their method requires no structural changes to existing equipment, Shu says it could be easily implemented in existing FELs. Their bright beams of x rays\u2014generated by electrons\u2014are increasingly popular for structural studies.<\/p>\n<p>Most high-repetition-rate free-electron lasers are fed by very-high-frequency (VHF) electron guns. A VHF electron gun contains a photocathode that releases electrons when hit with a laser. These electrons are accelerated by a strong electric field and exit the photocathode as a beam through a port at the front. But the same field generates other electrons by pulling them off the photocathode\u2019s surface and from nearby copper surfaces via the field effect. These so-called dark electrons\u2014they don\u2019t need light to free them\u2014can cause unwanted heating that degrades the main electron beam and damages the beam line.<\/p>\n<p>To weaken the dark current, researchers have typically lowered the gun voltage. But that route reduces the brightness of the main electron beam. Shu and colleagues found an alternative solution: modifying the plug upon which the photocathode material is deposited and grown. The team showed that by pushing the plug around 0.5\u20131 mm deeper than a standard plug, they were able to reduce the intensity of the dark current by nearly 2 orders of magnitude. The over-inserted plug also had another benefit\u2014it defocused the dark current. Rather than propagating downstream to join the main beam, the dark current struck the VHF gun cavity walls before it could leave the photocathode.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Free-electron lasers (FELs) have an electron problem: a \u201cdark\u201d current that can propagate with the electron beam, limiting the performance of the system. Now Guan Shu of Zhangjiang Laboratory in China and colleagues have developed a method that can reduce the strength of this unwanted dark current by 3 orders of magnitude [1]. Because their [\u2026]<\/p>\n","protected":false},"author":427,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1635],"tags":[],"class_list":["post-210784","post","type-post","status-publish","format-standard","hentry","category-materials"],"_links":{"self":[{"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/posts\/210784","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/users\/427"}],"replies":[{"embeddable":true,"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/comments?post=210784"}],"version-history":[{"count":0,"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/posts\/210784\/revisions"}],"wp:attachment":[{"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/media?parent=210784"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/categories?post=210784"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lifeboat.com\/blog\/wp-json\/wp\/v2\/tags?post=210784"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}