Strofio Status & Calibration

Transcription

1 Strofio Status & Calibration Stefano Livi and Frèdèric Allegrini Southwest Research Institute (210) January nd HEWG Livi - 1

2 Key measurements Sensitivity: > 0.1 (counts/s)/(particles/cm 3 ) for H 2 O (corresponds to 0.1A/torr ion yield and 6% transmission) [ERD_1049] Mass resolution: m/ m 60 [ERD_1035] Mass range: H (1 amu) through Fe (56 amu) [ERD_1028,ERD_1030] FOV ±10, KOZ ±20 [ERD_1061,ERD_1059] Velocity filter: Energy range: 0-10 ev [ERD_1784,ERD_1785] Additional measurements: UV attenuation and light leaks [SEN_614, SEN_615 ] MCP Background noise Maximum rate of 10 4 cts/s [ERD_ 1066] 19 January nd HEWG Livi - 2

3 Strofio Calibration EFFICIENCY 19 January nd HEWG Livi - 3

4 Pressure-Current Law (cross section corrected) 1,00E+08 y = 2.59E+14x 7.84E-01 1,00E+07 Countrate 1,00E+06 All data Power law fit 1,00E+05 1,00E-12 1,00E-11 1,00E-10 1,00E-09 1,00 Pressure (mbar) * Current (A) 19 January nd HEWG Livi - 4

5 Forecast at Mercury Based on this empirical power law and on Anna density forecast, we expect following count rates at Mercury n (1/cm 3 ) P(mbar) (600K) I (A) CR (1/s) E E E E E E E E E E E E E E E+03 Slightly better that the baseline value of 0.14 in units of (cts/s)/(1/cm 3 ) at 1mA, almost a factor of 2 better at maximum emission (1.5mA) 19 January nd HEWG Livi - 5

6 10 Efficiency for Different Masses Efficiency - Ration to Ne efficiency 1 0,1 Beam 2a e- chamber Gate Beam 1a Beam 1b Mefisto 0, Mass 19 January nd HEWG Livi - 6

7 Strofio Calibration MASS RESOLUTION AND RANGE 19 January nd HEWG Livi - 7

8 Mass resolution Determined by spatial resolution on the anode Established by voltage optimization Mass range Mass resolution and range Determined by the length of the path in the reflectron Can be tuned in flight Two ranges Primary (one turn): 1-60 Secondary (two turns) January nd HEWG Livi - 8

9 Including Velocity Filter Effects of the Velocity Filter Countrate 1 Without With VF 0,1 0, Mass (AMU) 19 January nd HEWG Livi - 9

10 Isotopes of Ar (40, 36, 38) Ar: 0.337% 38 Ar: 0.063% 40 Ar: 99.6% 19 January nd HEWG Livi - 10

11 Second Turn H 2 O H H2 He Kr 20 Ne 40 Ar N 2 Kr Ne O 2 36 Ar 19 January nd HEWG Livi - 11

12 Strofio Calibration COUNTING CAPABILITY 19 January nd HEWG Livi - 12

13 Counters (cts/s) 1,00E+07 1,00E+06 1,00E+05 Left and Right Start - Left and right Paired Events 1,00E+04 0, Current (microamp) L+R LP+RP Dead time correction: N N = 1 N τ τ for counter=2.5e-7 τ for event=5.4e-6 (equal to the inverse of the rotation frequency) * * t 19 January nd HEWG Livi - 13

14 Strofio Calibration FIELD OF VIEW 19 January nd HEWG Livi - 14

15 Field-Of-View & Keep-Out-Zone KOZ FOV 19 January nd HEWG Livi - 15

16 Field of View No Velocity Filter Epsilon Scan with Ne Left Right Compensated Epsilon (deg) 19 January nd HEWG Livi - 16

17 Strofio Calibration VELOCITY FILTER 19 January nd HEWG Livi - 17

18 Motivation BepiColombo spacecraft outgassing will limit the capabilities of a mass spectrometer to measure small amounts of the exospheric gas Mercury s exosphere has a total pressure of about mbar at the surface, at most mbar at 400 km altitude Spacecraft background data estimated from data of the Rosetta spacecraft B. Schläppi, K. Altwegg, H. Balsiger, M. Hässig, A. Jäckel, P. Wurz, B. Fiethe, M. Rubin, S. A. Fuselier, J. J. Berthelier, J. De Keyser, H. Rème, and U.Mall, The influence of spacecraft outgassing on the exploration of tenuous atmospheres with in situ mass spectrometry, Jou. Geophys. Res. 115 (2010), A12313, doi: /2010ja January nd HEWG Livi - 18

19 Element/ Molecule Source n at 400km (1/cm 3 ) Rosetta S/C Rosetta S/C Scaled by 40 H a ,000 6,000 H 2 a, c 10,000 20, He a 1,000 1, C c 60 7, N c 10 1, O a 400 1, OH d 30 5, H 2 O h 90,000 15, Ne a, c, i 300 2, Na b, c, i, M Mg c, i, M Al c, i, M3 1 4, N 2 h 25,000 4, Si c, i 50 4, O 2 h 15, S b, c, i K M Ar a, c, e, i Ca M Forecast of Signal Around Mercury Highlighted in blue are the measured species Red are species we will not be able to measure, yellow the ones with S/N small, green the one we will be able to measure An increase of the pressure by a factor of 10 would blind out almost all of the species CO 19 January 2 h 1,500 1, nd HEWG Livi - 19 Fe d, M

20 Summary Requirement Sensitivity 0.1 (cts/sec)/(1/cm 3 ) Performance 0.20 (cts/sec)/(1/cm 3 ) Mass resolution 60 (m/dm) 84 (m/dm) Mass range FOV - KOZ ±10 - ±20 ±10 - ±20 Velocity filter 100 UV attenuation MCP background < 1 Sun 50 cts/s Maximum rate 10 4 cts/s 1.85*10 5 cts/s 19 January nd HEWG Livi - 20