Data Needs for Low Temperature Plasmas and Accelerator Applications

1. Data Needs for Low Temperature Plasmas and Accelerator Applications Igor Kaganovich Plasma Physics Laboratory Princeton University Princeton, New Jersey, 08543 Presented to Eighth International Conference on Atomic and Molecular Data And Their Applications October 4, 2012

2. Outline • Astrophysics Rotational transitions in molecules in collisions with atoms • Low Temperature Plasmas Double differential cross sections for electron scattering on atoms and molecules • Accelerator Applications Charge-Changing Cross Sections for High Energy Particle Beams

3. Motivation • In applications there is need for approximate data for large range of parameters. • Accuracy can be often sacrificed for wide range applicability • Atomic community used to focus on opposite – accurate calculation of atomic data but within a narrow validity range.

4. 1. Rotational transitions in molecules of asymmetric-top type Water molecules in star-forming regions can undergo a population inversion and emit radiation at about 22.0 GHz, creating the brightest spectral line in the radio universe. To predict maser emission one need to simulate detailed rotational transitions in many different states. My fist Master project – approximate data for 30 pages of Tables for these RT transitions My answer –instead of mindless approximation of tables to derive analytical formulas using approximate (quasi-classical) approach.

6. Outline • Astrophysics Rotational transitions in molecules of asymmetric-top type • Low Temperature Plasmas Double differential cross sections for electron scattering on atoms and molecules • Accelerator Applications Charge-Changing Cross Sections for High Energy Particle Beams

7. Applications of Low Temperature Plasmas Lighting lasers propulsion metallurgy

8. Plasma Etcher: Applied Materials Centura Enabler Plasma etching of dielectric materials for logic contacts and interconnect – 300 mm wafers at the 45 nm node. S. Rauf AMAT

9. Gas discharge lasers • CO2 He-Ne, • Kr-F, O2 - I2 operating at (60-150Torr) pressures of active medium, which is radio-frequency (RF)-pumped at frequencies ranging from tens of MHz to several GHz or by an electron beam. Main issues are instabilities and cooling. http://www.slab-laser.ru/eng-AboutSlab.html

10. Industry Qualified ArF Excimer LaserPhotolithography – Next Generation EUV ArF discharge lasers enable 32 nm photolithography. • Discharge produced plasmas => laser produced plasmas for basis for next generation EUV sources. EUV source is a laser-produced plasma (LPP) generated by a CO2 laser on a tin droplet target. (Source: Cymer) Cymer 100 W EUV demonstration – Semi. Intl., Nov. 2008 200 W for volume manufacturing.

11. Medical applications Plasma Needle • Interactions of plasmas with organic materials and living tissue. • Unclear which species and conditions are beneficial to biological and biologically compatible materials. • Understand the behavior of biologically compatible materials and living tissue in contact with plasmas. • Lessons can be learned from the development of plasmas for semiconductor processing. From NRC “Plasma Science”, 2010.

12. Complex discharge forms at high pressures M. A. Malik, Y. TPS 33, 491 (2005) Courtesy of M. Shneyder

13. 2. Need for improved treatment of electron scattering EVDF anisotropic => good MC model of angular scattering is required, with a probability distribution easy to invert. Actual dσ⁄dΩ is a complicated function of E, θ. Commonly used model [Surendra et al.,1990] has limited applicability: with E is in eV. Rutherford DCS is not reproduced at high energies

14. Model of electron scattering in He for use in Monte Carlo simulations Use model of screened Coulomb potential and allow the screening parameter to be energy-dependent (Fernandez-Varea et al. [1992], Belenguer and Pitchford [1999], Okhrimovsky et al. [2002]): and ξ(E) is found by fitting to the ratio of total-to-transport cross-sections data from experiment or accurate theoretical calculations. This approach automatically uses correct total and transport cross-sections and captures the main features of the actual dσ/dΩat different energies.

15. Proposed model for e-Hescattering For He gas, the solution ξ(E) allowsa 2-pole approximation: The graph shows a comparison of the approximated ratio to the one obtained from the data.The error in is within 1% in the fitting range 0<E<1000 eV, and asymptotic behavior at E→∞, ξ=1-A/E, agrees with the theory. As usual, given a random number 0<R<1, the scattering angle is sampled according to

16. Implication of different models for dσ/dΩ on the scattered particle flux Left - Ratios of the approximated differential cross sections to the Rutherford cross-section. Right - Angular distributions of the scattered particle flux as a function of cosine of scattering angle for all electrons in the discharge plasma with energies above 150 eV.

17. Outline • Astrophysics Rotational transitions in molecules of asymmetric-top type • Low Temperature Plasmas Double differential cross sections for electron scattering on atoms and molecules • Accelerator Applications Charge-Changing Cross Sections for High Energy Particle Beams

18. Heavy Ion Fusion Concept Final Focus Source, Injector Accelerator How Inertial Fusion Target Work

19. 3. Evaluation of Charge-Changing Cross Sections for High Energy Particle Beams Motivation: Ionization of background gases can produce an unwanted electron population, which may lead to the development of collective excitations and two-stream instabilities (e.g., electron cloud instability). Radiative capture, recombination, charge exchange or electron stripping may result in enhanced beam losses.

20. Experiments on TX A&M Cyclotron • Ion beams 3.4-38 MeV/amu • Limited range of Z/M

21. e B A+3 A+ e B+ Extensive Experimental Data Base for Theory Validation Energy 3-38 MeV/amu Kr+7 and Xe+11 in N2; Ar+6 Ar+8 all in He, N2, Ar and Xe. He+ N+6 e Igor D. Kaganovich, et al.,Nuclear Instruments and Methods in Physics Research A 544, 91 (2005). D. Mueller, et al., Laser and Particle Beams 20, 551 (2002); Physics of Plasmas, 8, 1753 (2001). FOR MORE INFO...

22. Average number of electron lost per collision: He 1.45, N 1.57, Ar 1.77, Xe 1.96 Xe nl Ar N He a Electron Loss Cross Sections for 10.2 MeV/amu Ar+6 in Various Gases Multiple electron stripping occurs if number of electrons (Nnl) times one-electron cross section nl is larger than atom size Nnlnl>a2

23. 2 1 Hybrid Method of Cross Sections Calculations • Classical mechanics • Born approximation of quantum mechanics Schematic of atom potential See, I. Kaganovich, et al., Nuclear Instruments and Methods in Physics Research, 544, 91 (2005); Physics of Plasmas 11 1229 (2004).

24. Results of Hybrid Method: N+6 Table. The total electron-loss weighted cross-sections of N+6 on 38MeV/amu compared with the calculated cross sections in units of 10–22 m2. Indicates the valid approximation

25. Classical Trajectory Calculation Works Well If Projectile Velocity is Comparable to the Electron Orbital Velocity for hydrogen

26. Classical Calculation Works Well If Projectile Velocity is Comparable to the Electron Orbital Velocity

27. A new scaling model has been developed that successfully fits the experimental data in a single plot Ionization cross sections of He by ions with charge Zp showing the experimental data: Left - raw data; Right - the scaled data. I. Kaganovich, et al., New Journal of Physics, invited paper submitted (2006); Nuclear Instruments and Methods in Physics Research A 544, 91 (2005). FOR MORE INFO...

28. e B A+3 A+ e B+ nl a How to simulate charge-changing collisions with many electrons? • Classical trajectory method is not possible. • Full quantum computation is too complex. • What else?

29. + + - E>0 - E<0 Radiative electron recombination in electron cooling section (RHIC) • Radiative recombination leads to beam losses. • Rate of radiative recombination determines the beam and cooling section parameters. • "RHIC e-Cooling Collaboration Workshop“ at BNL. Beam pulse Low-emittance electron beam pulse

30. Conclusions • Low temperature plasma applications need data for electron impact elastic and inelastic cross sections for complex gases (halogens, nitrides, etc.). Similarly for radiation transport in complex gases. • Accelerator applications need charge-changing cross sections for complex gases interacting with a variety of projectile targets. • In applications there is need for approximate data for large range of parameters.