154 research outputs found
Wakefield-Induced Ionization injection in beam-driven plasma accelerators
We present a detailed analysis of the features and capabilities of
Wakefield-Induced Ionization (WII) injection in the blowout regime of beam
driven plasma accelerators. This mechanism exploits the electric wakefields to
ionize electrons from a dopant gas and trap them in a well-defined region of
the accelerating and focusing wake phase, leading to the formation of
high-quality witness-bunches [Martinez de la Ossa et al., Phys. Rev. Lett. 111,
245003 (2013)]. The electron-beam drivers must feature high-peak currents
() and a duration comparable to the plasma
wavelength to excite plasma waves in the blowout regime and enable WII
injection. In this regime, the disparity of the magnitude of the electric field
in the driver region and the electric field in the rear of the ion cavity
allows for the selective ionization and subsequent trapping from a narrow phase
interval. The witness bunches generated in this manner feature a short duration
and small values of the normalized transverse emittance (). In addition, we show that the amount of injected
charge can be adjusted by tuning the concentration of the dopant gas species,
which allows for controlled beam loading and leads to a reduction of the total
energy spread of the witness beams. Electron bunches, produced in this way,
fulfil the requirements to drive blowout regime plasma wakes at a higher
density and to trigger WII injection in a second stage. This suggests a
promising new concept of self-similar staging of WII injection in steps with
increasing plasma density, giving rise to the potential of producing electron
beams with unprecedented energy and brilliance from plasma-wakefield
accelerators
Chirp mitigation of plasma-accelerated beams using a modulated plasma density
Plasma-based accelerators offer the possibility to drive future compact light
sources and high-energy physics applications. Achieving good beam quality,
especially a small beam energy spread, is still one of the major challenges.
For stable transport, the beam is located in the focusing region of the
wakefield which covers only the slope of the accelerating field. This, however,
imprints a longitudinal energy correlation (chirp) along the bunch. Here, we
propose an alternating focusing scheme in the plasma to mitigate the
development of this chirp and thus maintain a small energy spread
The FLASHForward Facility at DESY
The FLASHForward project at DESY is a pioneering plasma-wakefield
acceleration experiment that aims to produce, in a few centimetres of ionised
hydrogen, beams with energy of order GeV that are of quality sufficient to be
used in a free-electron laser. The plasma wave will be driven by high-current
density electron beams from the FLASH linear accelerator and will explore both
external and internal witness-beam injection techniques. The plasma is created
by ionising a gas in a gas cell with a multi-TW laser system, which can also be
used to provide optical diagnostics of the plasma and electron beams due to the
<30 fs synchronisation between the laser and the driving electron beam. The
operation parameters of the experiment are discussed, as well as the scientific
program.Comment: 19 pages, 9 figure
The Repeal of the Glass-Steagall Act and the Federal Reserve's Extraordinary Intervention During the Global Financial Crisis
Before the global financial crisis, the assistance of a lender of last resort was traditionally thought to be limited to commercial banks. During the crisis, however, the Federal Reserve created a number of facilities to support brokers and dealers, money market mutual funds, the commercial paper market, the mortgage-backed securities market, the triparty repo market, et cetera. In this paper, we argue that the elimination of specialized banking through the eventual repeal of the Glass-Steagall Act (GSA) has played an important role in the leakage of the public subsidy intended for commercial banks to nonbank financial institutions. In a specialized financial system, which the GSA had helped create, the use of the lender-of-last-resort safety net could be more comfortably limited to commercial banks. However, the elimination of GSA restrictions on bank-permissible activities has contributed to the rise of a financial system where the lines between regulated and protected banks and the so-called shadow banking system have become blurred. The existence of the shadow banking universe, which is directly or indirectly guaranteed by banks, has made it practically impossible to confine the safety to the regulated banking system. In this context, reforming the lender-of-last-resort institution requires fundamental changes within the financial system itself
The Critics of Modern Money Theory (MMT) are Right
Eric Tymoigne and Randall Wray's (T&W, 2013) defense of MMT leaves the MMT emperor even more naked than before (excuse the Yogi Berra-ism). The criticism of MMT is not that it has produced nothing new. The criticism is that MMT is a mix of old and new, the old is correct and well understood, while the new is substantially wrong. Among many failings, T&W fail to provide an explanation of how MMT generates full employment with price stability; lack a credible theory of inflation; and fail to justify the claim that the natural rate of interest is zero. MMT currently has appeal because it is a policy polemic for depressed times. That makes for good politics but, unfortunately, MMT's policy claims are based on unsubstantiated economics
Investigating the potentially contradictory microfoundations of financialization
The existing academic literature on financialization points to multiple instances in which firms attempt to demonstrate the vitality of their stock-market position in ways which ultimately prove to be self-harming. I demonstrate, in the first instance as a matt er of immanent logic, that these actions are linked to the interplay of contradictory tendencies in the microfoundations of financialization. Under conditions of financialization, firms create additional sources of credit to capitalize their productive activities by driving their stock price into greater increases than the market average, thereby generating capital gains. Yet, the more it becomes public knowledge that the financing tricks used to inflate the stock price provide no productive benefit to the firm, the more it would seem to create incentives for fund managers to hold portfolios that replicate the stock market as a whole. In this way, they will minimize their exposure to financial misrepresentation. Such a stance undermines financialized business models, but it does in any case conform to fund managers' basic theoretical training, which revolves around the logical demonstration that an individual stock cannot systematically out-perform the market average. I review the available empirical studies of fund manager decision-making to show that they find against the existence of a simple performativity loop operating between finance theory and fund manager behaviour. However, on many points the empirical evidence does confirm the theoretically derived conclusion concerning the potentially contradictory microfoundations of financialization. Fund managers often do act in a way which is consistent with finance theory's core claim that an index-tracking strategy represents the only equilibrium portfolio, even if this is only rarely as a result of the direct performativity of the theory
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Shadow money and the public money supply: the impact of the 2007-2009 financial crisis on the monetary system
This article explores the effects of the political reactions to the 2007–2009 financial crisis on the monetary system. It chimes in with the view that shadow banks create ‘shadow money’, i.e. private substitutes for bank deposits. The article analyses how the three main forms of shadow money – money market fund shares, overnight repurchase agreements and asset-backed commercial papers – were affected by the short-term government intervention and medium-term regulation during and after the 2007–2009 financial crisis in the United States. The analysis reveals that the measures taken between 2007 and 2014 integrated some shadow money forms in the public money supply. In the year after the Lehman collapse, the initially private shadow money supply was either publicly backstopped or de-monetised as it had broken par to bank deposits. The public backstops took on the form of emergency facilities established by the Federal Reserve and guarantees proclaimed by the Treasury. Those backstops imply that the public institutional framework to protect bank deposits was extended to some forms of shadow money during the crisis. This tendency has continued in post-crisis regulation. Accordingly, the 2007–2009 financial crisis has triggered a paradigmatic change in the monetary system, attributable to the political decisions of US authorities
Hawtreyan 'credit deadlock' or Keynesian 'liquidity trap'? Lessons for Japan from the great depression
This paper outlines the ideas of Ralph Hawtrey and Lauchlin Currie on the need for monetised fiscal deficit spending in 1930s USA to combat the deep depression into which the economy had been allowed to sink. In such exceptional circumstances of 'credit deadlock' in which banks were afraid to lend and households and business afraid to borrow, the deadlock could best be broken through the spending of new money into circulation via large fiscal deficits. This complementarity of fiscal and monetary policy was shown to be essential, and as such indicates the potential power of monetary policy - in contrast to the Keynesian "liquidity trap" view that it is powerless This lesson was not learned by the Japanese authorities in their response to the asset price collapse of 1991-92, resulting in a lost decade as ballooning fiscal deficits were neutralised throughout the 1990s by unhelpfully tight monetary policy with the Bank of Japan refusing to monetise the deficits
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