STROFIO The IonSource J A Scheer P Wahlstrm

STROFIO The Ion-Source J. A. Scheer, P. Wahlström, and P. Wurz Physikalisches Institut, University of Bern SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008

SIMION Simulations Neutrals Ions SIMION model of the ion source One-source model because of background suppression (outgassing from satellite) • Simulations and calculations showed that background suppression is critical • Second source would measure mostly outgassing of spacecraft • Background suppression not possible for second source Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 2

SIMION Simulations 120 V Electrons 200 V Ions SIMION model of ionization chamber with extraction electrodes Ionization rate: 0. 0156 per particle s-1 cm-3 Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 3

SIMION Simulations SIMION model of ion source with potential arrays. • Red lines: potential difference 16 V • Yellow lines: potential difference less than 1 V Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 4

SIMION Simulations 400 mm -46 V -123 V -790 V 3 D-view of the SIMION model of the ion source with trajectories of 90000 ions Software optimizer (voltages and geometry) works with full range of ion trajectories and adjustable spot size Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 5

SIMION Simulations 195. 67 V -622 V 99 V -120 V 400 V -70 V -17 V 22 V 120 V -316 V 200 V 198. 95 V SIMION model of ion source with trajectories of 90000 ions -424 V 664 V • Voltages taken from simulation for 976 e. V particles • Grids in ionization chamber to suppress background from spacecraft (i. e. very low-energy ions) Juergen A. Scheer 312 V SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 -65 V -46 V 6

Results of SIMION Simulations The figure shows the effect of different grid voltages in the ionization chamber. Red graph demonstrates suppression of low-energetic background (outgassing) from spacecraft. Settings of red graph were used for all following simulations. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 7

Results of SIMION Simulations Various transmissions simulated for different exit openings with constant particle energy. The trend of higher transmissions for larger openings is clearly seen. The increase of a factor of 2 for the opening diameter results roughly in a factor of 3 higher transmission. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 8

Results of SIMION Simulations Transmissions for different settings of the ion optics, which lead to different particle energies at the exit. The increase of transmission due to increased particle energy at the exit is small but gets more pronounced towards higher initial energies. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 9

Calculations Maxwell-Boltzmann Distributions for various expected components. Particle densities are taken from the ROSETTA mission (black and red lines) to simulate spacecraft gas. Particle densities are taken from Wurz and Lammer (2003) (green lines) for Mercury‘s exosphere. The distributions of H 2 originating from Mercury (green) are shifted according to the satellite‘s velocity of 3000 m/s. Note the overlap of Hydrogen from the spacecraft (black) with Hydrogen from Mercury (green). Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 10

Calculations: H 2 Black lines: Maxwell. Boltzmann distributions. Red and green lines: Fractions of these distributions of detected particles, red line is outgassing from satellite. Result: H 2 can be measured. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 11

Calculations: H Black lines: Maxwell. Boltzmann distributions. Red and green lines: Fractions of these distributions of detected particles, red line is outgassing from satellite. Result: H cannot be measured. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 12

Calculations: Na Particle density of photon-stimulated desorbed Na relative to outgassing of spacecraft. Significant overlap only with light atoms and molecules, i. e. H and H 2. Hydrogen and Na can be easily separated in the detector. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 13

Calculations: Ca Particle density on detector of sputtered calcium => Expected countrate 1 per 8 min Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 14

Particle Densities on Detector Exospheric Species Density [cm-3] cps on detector Outgassing from satellite Density [cm-3] cps on detector Na 1. 05 E+03 8 He 1. 05 E+03 3 Ka 5. 50 E+01 0. 3 H 3. 70 E+01 0. 02 H 8. 60 E+04 2 Ne 2. 05 E+01 0. 2 O 2 5. 60 E+03 36 N 2 1. 20 E+04 84 N 2 2. 10 E+05 4. 6 H 2 7. 50 E+06 8600 H 2 3. 50 E+04 0. 8 H 2 O 9. 00 E+04 766 H 2 O 1. 75 E+06 39 OH 1. 10 E+03 9 OH 2. 90 E+05 6. 5 CO 2 1. 20 E+06 6400 Ar n/a 59 7. 40 E+03 0. 2 45 2. 00 E+05 4. 4 27 2. 30 E+04 0. 5 19 1. 00 E+04 0. 07 Isopropyl alcohol Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 15

The Ion-Source Prototype Filament Ionization chamber with grids and extraction electrodes Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 16

The Ion-Source Prototype Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 17

Calibration Facilities STROFIO: CASYMIR (Calibration System for the Mass spectrometer Instrument Rosina) http: //www. space. unibe. ch/rosina/casymir/cas_SS. html ELENA: MEFISTO (MEsskammer für Flugzeit. In. Strumente und Time-Of-Flight) http: //www. space. unibe. ch/mefisto/ Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 18

STROFIO Calibration: CASYMIR Facility The scope of the CASYMIR project (Calibration System for the mass spectrometer instrument Rosina) is the development of a calibration chamber with the aim of testing and calibrating space mass spectrometers. The spectrometers are part of the ROSINA Instrument package, which is one of the key experiments of the Rosetta mission planed by the European Space Agency ESA. The orbiter will accompany the comet Wirtanen on it's way to the sun. (Launch: 2003, End of mission: 2013). The two mass spectrometers (DFMS and RTOF), which are the main part of the ROSINA instrument package, will analyze the elemental, isotopic and molecular composition of the neutral and ionizes atmosphere of the comet Wirtanen. In order to simulate these conditions of the comet surroundings, CASYMIR consists of a vacuum system with several stages leading to a high vacuum, and a supersonic molecular beam with embedded thermal ions. CASYMIR will be designed and set-up at the Space Research & Planetary Sciences research division at the Physikalisches Institut of the University of Bern, Switzerland. The mass spectrometers will be calibrated in a static as well as in a dynamic mode. In the static calibration mode, a static atmosphere is introduced into chamber V 1 and V 0 in a pressure range of 10 -6 to 10 -10 mbar. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 19

STROFIO Calibration: CASYMIR Facility Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 20

Calibration of Instruments for Detection of Energetic Neutral Atoms (ENA) in Space J. A. Scheer (1), L. Saul (1), P. Wurz (1), E. Moebius (2), E. Hertzberg (3), S. A. Fuselier (3), D. J. Mc. Comas (4), and the IBEX-Team (1) University of Bern, Physikalisches Institut, Sidlerstrasse 5, 3012 Bern, Switzerland (2) University of New Hampshire, Department of Physics and Institute for Study of Earth, Oceans and Space, Durham, New Hampshire 03824, USA (3) Lockheed Research Laboratories, 3251 Hannover Street, Palo Alto, California 94304, USA (4) Southwest Research Institute, San Antonio, Texas 78238, USA corresponding authors: juergen. scheer@space. unibe. ch, peter. wurz@space. unibe. ch The MEFISTO Calibration Facility The Surface Neutralizer MEFISTO is a versatile ion beam calibration facility for characterization of space plasma instrumentation, in particular solar wind and supra-thermal particle instruments. With help of a surface neutralizer or a gas neutralizer, energetic neutral atoms can be produced as well. The IBEX-Lo Instrument The instruments are mounted on a hexapod-table, which allows the instruments to be moved within 5 degrees of freedom. With the alpha-stage (see picture bottom right) the possible movements increase to 6 degrees of freedom. Front view of the MEFISTO calibration facility. Left: instrument chamber, residual gas analyzer (black box). Middle: roughing pump, beam monitor, and gate valve. Right: ion source cabinet and electronics rack. From: [1] The surface neutralizer enables us to produce ENAs in an energy range of 10 e. V up to several ke. V. For details, see the middle part of the poster. For measurements in space, background induced by UV-irradiation is a serious issue. Therefore, MEFISTO has been equipped with a sun-like UV-lamp to calibrate instruments for UV-irradiation. The intensity of the UVlamp is approximately 1015 photons per cm 2 per second at a wavelength of 126 nm Front view of ECR ion source. Left: 2. 45 GHz ECR ion source. Middle: Wien filter. Right: 180° energy analyzer. The whole cabinet can be floated up to 100 k. V. From: [1] View of the inside of the instrument chamber. The grey area is the cryo shroud. The ion beam enters the chamber from the left hand side, the UV-lamp is mounted opposite on the right hand side. In the middle you can see the circular alpha-stage, which allows the instrument to be turned ± 180° around the ion beam axis and thus results in a total of six degrees of freedom for the instrument’s movement. The hoses from above are connected to the cooling (or heating) plate. Juergen A. Scheer This technique requires of course a thorough calibration, especially for the ENA to ion conversion process. Thus, a lot of work has been done to find suitable surfaces [3, 4] and to calibrate them [5]. The Surface Neutralizer described here is already the third version built. Details about the previous versions can be found in [2]. Ions enter the surface neutralizer with a given energy of several ke. V. The desired energy is determined with a voltage applied to the deceleration stage. After passing an electrostatic analyzer the ions hit the neutralization surface, where most of the ions are converted into energetic neutral atoms (ENA). Any ions that survived the scattering process will be deflected by the deflection plates to make sure that only ENAs will leave the surface neutralizer. Setup for calibration of the Surface Neutralizer. Left: Surface Neutralizer Middle: SSL detector Right: homemade highly sensitive pico-ammeter with integrated A/D-converter. The measurement range is 10 n. A to 0. 01 p. A. [3] J. A. Scheer et al, Nucl. Instr. and Meth. B 230 (2005) 330 [4] J. A. Scheer et al, Adv. Space Res. 38 (2006) 664 [5] P. Wahlström, “Calibration of Charge State Conversion Surfaces for Neutral Particle Detectors”, submitted to Journal of Applied Physics The payload of IBEX is extremely simple with only two single pixel sensors and a single Combined Electronics Unit (CEU). The overlap of the energy range between IBEX-Hi (300 e. V – 6 ke. V) and IBEX-Lo (10 e. V – 2 ke. V) maximizes statistics and allows for in-flight cross-calibration, and provides imaging via two completely independent sensors across the most critical energy range for achieving the IBEX science objective. Taken from: http: //www. ibex. swri. edu/index. shtml, for more information please contact Principal Investigator Dave Mc. Comas: dmccomas@swri. org Calibration at the MEFISTO facility of the University of Bern Most of the calibration of IBEX-Lo was done at the University of Bern, with the exception of acoustic tests at IABG in Munich and more UV testing as well as cross-calibration between IBEX-Hi and IBEX-Lo at Sw. RI in San Antonio, TX. Three examples of data derived from the calibration measurements at the University of Bern are shown below: Below and right there are examples of data taken during the calibration of the surface neutralizer. Figures 1 and 2 show horizontal and vertical profiles of a neutral oxygen beam for different distances from the surface neutralizer exit. Figure 3 shows a calibration function for the flux of neutral hydrogen relative to the ion current measured on the neutralization surface. This function got derived from several independent measurement series, labeled as a 1, a 2, … Figure 4 shows this calibration function for three different species, i. e. oxygen, helium, and hydrogen. [2] M. Wieser and P. Wurz, Meas. Sci. Technol. 16 (2005) 2511 Testing of a prototype of the gas neutralizer. Left: gas neutralizer housing including deflection plates to deflect non-ionized particles. Right: : hexapod-table with faraday-cup to monitor the ion beam and SSL-detector to record the distribution of neutral particles. IBEX-Hi IBEX-Lo was designed to sense ENA in an energy range of 10 e. V to 2 ke. V. We found that the only viable technique to do so in space is surface ionization, i. e. incoming neutral particles get ionized upon scattering from a conversion surface and in the following analyzed by the usual mass spectrometric means. The first thing you need to have to calibrate a neutral particle sensing instrument is a neutral particle beam. There are different approaches, such as neutralizing an ion beam with help of a crossing laser beam or neutralizing an ion beam on its way through a gas filled volume via charge exchange with gas atoms but none of these methods were suitable for our purpose. Neutralizing with a laser, for instance, needs a dedicated setup, whereas we were looking for a simple way to extend our already existing facility. And a gas neutralizer works for 200 e. V and higher energies, but we were interested in an energy range of 10 e. V-2 ke. V. Thus, we had to find another solution, and the answer was surface neutralization, which will be explained in the following paragraph. With the prototype of the gas neutralizer (see picture below) energetic neutral atoms (ENA) of hydrogen and oxygen have been successfully produced in an energy of 500 e. V to several ke. V. For the future it is planned to extend this energy range to lower energies. [1] M. Wüest, D. S. Evans, and R. von Steiger (Eds. ), “Calibration of Particle Instruments in Space Physics”, ISSI Scientific Report SR-007 IBEX-Lo The sole, focused science objective of the IBEX mission is to discover the global interaction between the solar wind and the interstellar medium. IBEX achieves this objective by taking a set of global energetic neutral atom (ENA) images. Ions are produced in an homemade Electron-cyclotron resonance ion source and extracted with 3 k. V. With post -acceleration they can reach an energy up to 100 ke. V/q. The ion optic consists of several lenses and deflection plates, a Wien-filter and an electrostatic analyzer. The beam size is adjustable from 0. 1 mm to 8 mm diameter, and the distance from ion beam exit to instrument inlet is about 1 m. The vacuum system is bakeable up to 300°C and the shroud inside the vacuum chamber can be filled with liquid nitrogen. The instrument cooling plate is temperature controlled from -80°C to +150°C. After bakeout, the vacuum chamber reaches a base pressure of 1 x 10 -8 mbar, with use of the cryo shroud the pressure goes down 5 x 10 -9 mbar. The Calibration of IBEX-Lo • The energy range, in which IBEX-Lo works, is divided into 8 discrete Fig. 3 energy bins, which are each separated by a factor of 2. Figure 5 shows the energy response of each energy bin. • An azimuth scan (i. e. rotation within the alpha-stage) is displayed in Fig. 6. Several dips of the efficiency are clearly seen, when the ion beam illuminates spokes or the high-resolution section, which has lower transmission. • During the ENA to ion conversion process some particles are inevitably sputtered from the conversion surfaces and a fraction of these sputtered particles is eventually detected. This fraction is shown in Fig. 7. Left: Surface Neutralizer Middle: IBEX-Lo instrument inside the alpha-stage, which is mounted on the hexapod-table. The instrument has been turned 180° away from the ion beam to face the UV-lamp. Right: housing of UVlamp with black aperture plate. Spokes Lo-res Hi-res SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 Fig. 5 Fig. 1 Fig. 2 Fig. 4 Fig. 6 Fig. 7

Summary and Outlook • One-source design optimal to suppress background. • Up to now, with the exception of H, all expected elements or compounds seem to be measurable with the chosen setup. • Very important: In-flight calibration to identify background! • Design and construction of ion-source prototype finished. Ready for manufacturing. • Input from detector-team essential for progress! • Measurements with ion-source prototype are scheduled for August 2008. Juergen A. Scheer SERENA-HEWG Conference, Santa Fe, May 12 -14, 2008 22