PAC2013 - List of Authors (Cook, N.M.)

Paper	Title	Page
MOPAC34	Spectral Broadening of Ions Accelerated by a Radiation Pressure Driven Shock	144
	N.M. Cook, P. Shkolnikov Stony Brook University, Stony Brook, New York, USA N. Dover, Z. Najmudin Imperial College of Science and Technology, Department of Physics, London, United Kingdom C. Maharjan SBU, Stony Brook, New York, USA I. Pogorelsky, M.N. Polyanskiy, O. Tresca BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. Laser driven ion acceleration has been the focus of considerable research efforts since multi-MeV energies were first demonstrated. Most experiments use solid state laser pulses focused onto thin foil targets. However, recent progress in CO2 laser technology allows for the creation of intense pulses at λ ~10μm. The longer wavelength permits the use of low density targets. In these conditions ion acceleration is primarily driven by a shock wave due to the radiation pressure of the laser. This acceleration mode has the advantage of producing narrow energy spectra while scaling well with pulse intensity. New improvements to the CO2 laser at the Accelerator Test Facility allow for the unique production of single picoseconds-scale pulses with 1TW peak power. We report on the interaction of an intense CO2 laser pulse with overdense hydrogen and helium gas jets. Using a two pulse optical probe, we are able to obtain real-time density profiles at different times during the interaction, allowing for the characterization of shock wave velocities and peak density conditions. Ion energy spectra are measured using a Thomson spectrometer and scintillating screen. This work has been supported by the United States Department of Energy, Grant DE-FG02-07ER41488.

WEPMA25	Harmonic Ratcheting for Fast Acceleration	1034
	N.M. Cook Stony Brook University, Stony Brook, USA J.M. Brennan, S. Peggs BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. One of the most persistent difficulties in the design of RF cavities for acceleration of charged particles is rapid and efficient acceleration over a large range of frequencies. From medical synchrotrons to accelerator driven systems, there is a need for fast acceleration of protons and light ions to hundreds of MeV. Conventionally, this is a costly undertaking, requiring specially designed ferrite loaded cavities to be tuned over a wide range of frequencies. Ferromagnetic materials allow for the precise adjustment of cavity resonant frequency, but rapid changes in the frequency and operation outside material specific frequency ranges result in significant Q-loss to the cavity. This leads to a considerable increase in power requirements. We introduce an acceleration scheme known as harmonic ratcheting which can be used to reduce the cavity frequency range when accelerating an ion beam in a synchrotron. This scheme addresses the needs of high rep. rate machines for applications such as radiation therapy in which low beam intensity is needed. We demonstrate with simulations the type of ramps achievable using this technique and consider its advantages over h=1 acceleration schemes.

THPAC33	Scintillator Diagnostics for the Detection of Laser Accelerated Ion Beams	1208
	N.M. Cook Stony Brook University, Stony Brook, USA R.S. Lefferts SBUNSL, Stony Brook, New York, USA O. Tresca BNL, Upton, Long Island, New York, USA V. Yakimenko SLAC, Menlo Park, California, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. Radiation pressure acceleration with ultraintense laser pulses presents an exciting new scheme for accelerating ions. One of the advantages conferred by using a gaseous laser and target is the potential for a fast (several Hz) repetition rate. This requires diagnostics which are not only comprehensive for a single shot, but also capable of repeated use. We consider several scintillators as candidates for an imaging diagnostic for protons accelerated to MeV energies by a CO2 laser focused on a gas jet target. We have measured the response of chromium-doped alumina (Chromox), CsI:Tl, and two polyvinyl toluene (PVT) screens to protons in the 2 – 8 MeV range using a CCD camera. We have calibrated the luminescent yield in terms of photons emitted per incident proton for each scintillator. We also discuss how light scattering and material properties affect detector resolution. Furthermore, we consider material damage and the presence of an afterglow under intense exposures. Our analysis reveals a near order of magnitude greater yield from Chromox in response to proton beams at > 5 MeV energies, while scattering effects favor PVT at lower energies. Many thanks are due to M. Babzien, A. Drees, K. Kusche, and A. Lipski for their contributions to this work.

Paper

Title

Page

Spectral Broadening of Ions Accelerated by a Radiation Pressure Driven Shock

144

N.M. Cook, P. Shkolnikov
Stony Brook University, Stony Brook, New York, USA
N. Dover, Z. Najmudin
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
C. Maharjan
SBU, Stony Brook, New York, USA
I. Pogorelsky, M.N. Polyanskiy, O. Tresca
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Laser driven ion acceleration has been the focus of considerable research efforts since multi-MeV energies were first demonstrated. Most experiments use solid state laser pulses focused onto thin foil targets. However, recent progress in CO2 laser technology allows for the creation of intense pulses at λ ~10μm. The longer wavelength permits the use of low density targets. In these conditions ion acceleration is primarily driven by a shock wave due to the radiation pressure of the laser. This acceleration mode has the advantage of producing narrow energy spectra while scaling well with pulse intensity. New improvements to the CO2 laser at the Accelerator Test Facility allow for the unique production of single picoseconds-scale pulses with 1TW peak power. We report on the interaction of an intense CO2 laser pulse with overdense hydrogen and helium gas jets. Using a two pulse optical probe, we are able to obtain real-time density profiles at different times during the interaction, allowing for the characterization of shock wave velocities and peak density conditions. Ion energy spectra are measured using a Thomson spectrometer and scintillating screen.
This work has been supported by the United States Department of Energy, Grant DE-FG02-07ER41488.

WEPMA25

Harmonic Ratcheting for Fast Acceleration

1034

N.M. Cook
Stony Brook University, Stony Brook, USA
J.M. Brennan, S. Peggs
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
One of the most persistent difficulties in the design of RF cavities for acceleration of charged particles is rapid and efficient acceleration over a large range of frequencies. From medical synchrotrons to accelerator driven systems, there is a need for fast acceleration of protons and light ions to hundreds of MeV. Conventionally, this is a costly undertaking, requiring specially designed ferrite loaded cavities to be tuned over a wide range of frequencies. Ferromagnetic materials allow for the precise adjustment of cavity resonant frequency, but rapid changes in the frequency and operation outside material specific frequency ranges result in significant Q-loss to the cavity. This leads to a considerable increase in power requirements. We introduce an acceleration scheme known as harmonic ratcheting which can be used to reduce the cavity frequency range when accelerating an ion beam in a synchrotron. This scheme addresses the needs of high rep. rate machines for applications such as radiation therapy in which low beam intensity is needed. We demonstrate with simulations the type of ramps achievable using this technique and consider its advantages over h=1 acceleration schemes.

THPAC33

Scintillator Diagnostics for the Detection of Laser Accelerated Ion Beams

1208

N.M. Cook
Stony Brook University, Stony Brook, USA
R.S. Lefferts
SBUNSL, Stony Brook, New York, USA
O. Tresca
BNL, Upton, Long Island, New York, USA
V. Yakimenko
SLAC, Menlo Park, California, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Radiation pressure acceleration with ultraintense laser pulses presents an exciting new scheme for accelerating ions. One of the advantages conferred by using a gaseous laser and target is the potential for a fast (several Hz) repetition rate. This requires diagnostics which are not only comprehensive for a single shot, but also capable of repeated use. We consider several scintillators as candidates for an imaging diagnostic for protons accelerated to MeV energies by a CO2 laser focused on a gas jet target. We have measured the response of chromium-doped alumina (Chromox), CsI:Tl, and two polyvinyl toluene (PVT) screens to protons in the 2 – 8 MeV range using a CCD camera. We have calibrated the luminescent yield in terms of photons emitted per incident proton for each scintillator. We also discuss how light scattering and material properties affect detector resolution. Furthermore, we consider material damage and the presence of an afterglow under intense exposures. Our analysis reveals a near order of magnitude greater yield from Chromox in response to proton beams at > 5 MeV energies, while scattering effects favor PVT at lower energies.
Many thanks are due to M. Babzien, A. Drees, K. Kusche, and A. Lipski for their contributions to this work.