Jonathan S. Wurtele

Advanced accelerator concepts

High‐energy accelerators have been physicists’ main tools for exploring the building blocks of matter for more than 60 years. During this time the particle energy has increased exponentially as a result of a combination of improvements in existing machines and the invention of new acceleration techniques. Historically, whenever a given type of accelerator has reached the limit of its performance, an innovative idea for particle manipulation, storage, cooling or acceleration has made possible experiments at ever higher energies. The tremendous increase in the energy of accelerators has not, however, been without an increase in capital costs. The cancellation of the Superconducting Super Collider makes timely an examination of possible alternative concepts for investigating some of the same physics.

A New Estimate of the AverageEarth Surface Land TemperatureSpanning 1753 to 2011

A New Estimate of the Average Earth Surface Land Temperature Spanning 1753 to 2011 We report an estimate of the Earth’s average land surface temperature for the period 1753 to 2011. To address issues of potential station selection bias, we used larger sampling of stations than having prior studies. For the period post 1880, our estimate is similar to those previously reported by other groups, although we report smaller error uncertainties. The land temperature rise from the 1950s decade to the 2000s decade is 0.90 ± 0.05°C (95% confidence).

Confinement of antihydrogen for 1,000 seconds

Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.

Berkeley Earth Temperature Averaging Process

Berkeley Earth Temperature Averaging Process A new mathematical framework is presented for producing maps and large-scale averages of temperature changes from weather station thermometer data for the purposes of climate analysis. The method allows inclusion of short and discontinuous temperature records, so nearly all digitally archived thermometer data can be used. The framework uses the statistical method known as Kriging to interpolate data from stations to arbitrary locations on the Earth.

Resonant quantum transitions in trapped antihydrogen atoms

The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom’s stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and—by comparison with measurements on its antimatter counterpart, antihydrogen—the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.

High-gain free electron lasers using induction linear accelerators

High-power free electron lasers (FELs) can be realized using induction linear accelerators as the source of the electron beam. These accelerators are currently capable of producing intense currents (102-104A) at moderately high energy (1-50 MeV). Experiments using a 500 A, 3.3 MeV beam have produced 80 MW of radiation at 34.6 GHz and are in good agreement with theoretical analysis. Future experiments include a high-gain, high-efficiency FEL operating at 10.6 μm using a 50 MeV beam.

Principles of gyrotron powered electromagnetic wigglers for free-electron lasers

The operation of free-electron lasers (FELs) with axial electron beams and high-power electromagnetic wiggler fields such as those produced by high-power gyrotrons is discussed. The use of short wavelength electromagnetic wigglers in waveguides and resonant cavities can significantly reduce required electron beam voltages, resulting in compact FELs. Gain calculations in the low- and high-gain Compton regime are presented, including the effects of emittance, transverse wiggler gradient, and electron temperature. Optimized scaling laws for the FEL gain and the required electromagnetic wiggler field power are discussed. Several possible configurations for FELs with electro-magnetic wigglers powered by millimeter wavelength gyrotrons are presented. Gyrotron powered wigglers appear promising for operation of compact FELs in the infrared regime using moderate energy (<10 MeV) electron beams.

Laser wake‐field acceleration and optical guiding in a hollow plasma channel

The accelerating and focusing wake fields that can be excited by a short laser pulse in a hollow underdense plasma are examined. The evacuated channel in the plasma serves as an optical fiber to guide the laser pulse over many Rayleigh lengths. Wake fields excited by plasma current at the edge of the channel extend to the center where they may be used for ultrahigh gradient acceleration of particles over long distances. The wake field and equilibrium laser profiles are found analytically and compared to two‐dimensional (2‐D) particle‐in‐cell (PIC) simulations. Laser propagation is simulated over more than ten Rayleigh lengths. The accelerating gradients on the axis of a channel of radius c/ωp are of order of one‐half of the gradients in a uniform plasma. For present high‐power lasers, multi‐GeV/m gradients are predicted.

Laser-driven plasma-based accelerators: Wakefield excitation, channel guiding, and laser triggered particle injection

Plasma-based accelerators are discussed in which high-power short pulse lasers are the power source, suitably tailored plasma structures provide guiding of the laser beam and support large accelerating gradients, and an optical scheme is used to produce time-synchronized ultrashort electron bunches. From scaling laws laser requirements are obtained for development of compact high-energy accelerators. Simulation results of laser guiding and wakefield excitation in plasma channels, as well as laser-based injection of particles into a plasma wake, are presented. Details of the experimental program at Lawrence Berkeley National Laboratory on laser guiding, laser wakefield-based accelerators, and laser triggered injection are given.

Transparency of magnetized plasma at the cyclotron frequency

Electromagnetic radiation is strongly absorbed by a magnetized plasma if the radiation frequency equals the cyclotron frequency of plasma electrons. It is demonstrated that absorption can be completely canceled in the presence of a magnetostatic field of an undulator, or a second radiation beam, resulting in plasma transparency at the cyclotron frequency. This effect is reminiscent of the electromagnetically induced transparency (EIT) of three-level atomic systems, except that it occurs in a completely classical plasma. Unlike the atomic systems, where all the excited levels required for EIT exist in each atom, this classical EIT requires the excitation of nonlocal plasma oscillation. A Lagrangian description was used to elucidate the physics of the plasma transparency and control of group and phase velocity. This control leads to applications for electromagnetic pulse compression and electron/ion acceleration.