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"Sagan, D"
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Revisiting Hiroshima in Iran
Numerous polls demonstrate that U.S. public approval of President Harry Truman’s decision to drop the atomic bombs on Hiroshima and Nagasaki has declined significantly since 1945. Many scholars and political figures argue that this decline constitutes compelling evidence of the emergence of a “nuclear taboo” or that the principle of noncombatant immunity has become a deeply held norm. An original survey experiment, recreating the situation that the United States faced in 1945 using a hypothetical U.S. war with Iran today, provides little support for the nuclear taboo thesis. In addition, it suggests that the U.S. public’s support for the principle of noncombatant immunity is shallow and easily overcome by the pressures of war. When considering the use of nuclear weapons, the majority of Americans prioritize protecting U.S. troops and achieving American war aims, even when doing so would result in the deliberate killing of millions of foreign noncombatants. A number of individuallevel traits—Republican Party identification, older age, and approval of the death penalty for convicted murderers—significantly increase support for using nuclear weapons against Iran. Women are no less willing (and, in some scenarios, more willing) than men to support nuclear weapons use. These findings highlight the limited extent to which the U.S. public has accepted the principles of just war doctrine and suggest that public opinion is unlikely to be a serious constraint on any president contemplating the use of nuclear weapons in the crucible of war.
Journal Article
Atomic Aversion: Experimental Evidence on Taboos, Traditions, and the Non-Use of Nuclear Weapons
How strong are normative prohibitions on state behavior? We examine this question by analyzing anti-nuclear norms, sometimes called the “nuclear taboo,” using an original survey experiment to evaluate American attitudes regarding nuclear use. We find that the public has only a weak aversion to using nuclear weapons and that this aversion has few characteristics of an “unthinkable” behavior or taboo. Instead, public attitudes about whether to use nuclear weapons are driven largely by consequentialist considerations of military utility. Americans’ willingness to use nuclear weapons increases dramatically when nuclear weapons provide advantages over conventional weapons in destroying critical targets. Americans who oppose the use of nuclear weapons seem to do so primarily for fear of setting a negative precedent that could lead to the use of nuclear weapons by other states against the United States or its allies in the future.
Journal Article
Just and Unjust Nuclear Deterrence
In this essay, I propose five principles to make U.S. nuclear deterrence policy more just and effective in the future: sever the link between the mass killing of innocent civilians and nuclear deterrence by focusing targeting on adversaries’ military power and senior political leadership, not their population; never use or plan to use a nuclear weapon against any target that could be destroyed or neutralized by conventional weapons; reject “belligerent reprisal” threats against civilians even in response to enemy attacks on one's own or allied civilians; replace nuclear “calculated ambiguity” threats against biological or cyberattacks with “deterrence by denial” strategies; and work in good faith toward eventual nuclear disarmament.
Journal Article
Just War and Unjust Soldiers: American Public Opinion on the Moral Equality of Combatants
Traditional just war doctrine holds that political leaders are morally responsible for the decision to initiate war, while individual soldiers should be judged solely by their conduct in war. According to this view, soldiers fighting in an unjust war of aggression and soldiers on the opposing side seeking to defend their country are morally equal as long as each obeys the rules of combat. Revisionist scholars, however, maintain that soldiers who fight for an unjust cause bear at least some responsibility for advancing an immoral end, even if they otherwise fight ethically. This article examines the attitudes of the American public regarding the moral equality of combatants. Utilizing an original survey experiment, we find that the public's moral reasoning is generally more consistent with that of the revisionists than with traditional just war theory. Americans in our study judged soldiers who participate in unjust wars as less ethical than soldiers in just wars, even when their battlefield conduct is identical, and a large proportion supported harsh punishments for soldiers simply for participating in unjust wars. We also find, however, that much of the American public is willing to extend the moral license of just cause significantly further than revisionist scholars advocate: half of the Americans in our survey were willing to allow an unambiguous war crime—a massacre of innocent women and children—to go unpunished when the act was committed by soldiers fighting for a just cause. Our findings suggest that incorporation of revisionist principles into the laws of war would reinforce dangerous moral intuitions encouraging the killing of civilians.
Journal Article
Low-emittance tuning at the Cornell Electron Storage Ring Test Accelerator
In 2008 the Cornell Electron/Positron Storage Ring (CESR) was reconfigured from an electron/positron collider to serve as a test bed for the International Linear Collider damping rings. One of the primary goals of the CESR Test Accelerator (CesrTA) project is to develop a fast low-emittance tuning method which scales well to large rings such as the ILC damping rings, and routinely achieves a vertical emittance of order 10 pm at 2.085 GeV. This paper discusses the tuning methods developed at CesrTA to achieve low-emittance conditions. One iteration of beam-based measurement and correction requires about 10 min. A minimum vertical emittance of 10.3(+3.2/−3.4)sys(±0.2)statpm has been achieved at 2.085 GeV. In various configurations and beam energies the correction technique routinely achieves vertical emittance around 10 pm after correction, with rms coupling <0.5% . The measured vertical dispersion is dominated by beam position monitor systematics. The propagation of uncertainties in the emittance measurement is described in detail. Simulations modeling the effects of magnet misalignments, beam position monitor errors, and the emittance correction algorithm suggest the residual vertical emittance measured at the conclusion of the tuning procedure is dominated by sources other than optics errors and misalignments.
Journal Article
Designing the EIC electron storage ring lattice for a wide energy range
The Electron-Ion Collider (EIC) will collide electrons with hadrons at center-of-mass energies up to 140 GeV (in the case of electron-proton collisions). A 3.8-kilometer electron storage ring is being designed, which will store electrons with a range of energies up to 18 GeV for collisions at one or two interaction points. At energies up to 10 GeV the arcs will be tuned to provide 60 degree phase advance per cell in both planes, whereas at top energy of 18 GeV a 90 degree phase advance per cell will be used, which largely compensates for the horizontal emittance increase with energy. The optics must be matched at three separate energies, and the different phase-advance requirements in both the arc cells and the straight sections make this challenging. Moreover, the spin rotators must fulfill requirements for polarization and spin matching at widely different energies while satisfying technical constraints. In this paper these challenges and proposed solutions are presented and discussed.
Journal Article
Examining mitigation schemes for synchrotron radiation in high-energy hadron colliders
At high proton-beam energies, beam-induced synchrotron radiation is an important source of heating, of beam-related vacuum pressure increase, and of primary photoelectrons, which can give rise to an electron cloud. We use the synrad3d code developed at Cornell to simulate the photon distributions in the arcs of several existing, planned, or proposed highest-energy hadron colliders to analyze the efficiency of several techniques developed, or proposed, to mitigate the negative effects of synchrotron radiation, such as a sawtooth surface and slots in the beam screen.
Journal Article
Simulating synchrotron radiation in accelerators including diffuse and specular reflections
An accurate calculation of the synchrotron radiation flux within the vacuum chamber of an accelerator is needed for a number of applications. These include simulations of electron cloud effects and the design of radiation masking systems. To properly simulate the synchrotron radiation, it is important to include the scattering of the radiation at the vacuum chamber walls. To this end, a program called synrad3d has been developed which simulates the production and propagation of synchrotron radiation using a collection of photons. Photons generated by a charged particle beam are tracked from birth until they strike the vacuum chamber wall where the photon is either absorbed or scattered. Both specular and diffuse scattering is simulated. If a photon is scattered, it is further tracked through multiple encounters with the wall until it is finally absorbed. This paper describes the synrad3d program, with a focus on the details of its scattering model, and presents some examples of the program’s use.
Journal Article