Suprathermal Ion Mass Spectrometer (SMS) PREFACE The Suprathermal Ion Mass Spectrometer (SMS) instrument on the Akebono (EXOS-D) satellite is a newly developed radio frequency (r.f.) ion mass spectrometer to study the two dimensional thermal (0 - 25.5 eV) and suprathermal (55 eV/q - 4.1 keV/q) ion energy distributions in the satellite spin plane, and is fully described in Whalen et al. [1990]. The instrument is composed of an energy bandpass and aperture selector section, r.f. velocity selector section, and total energy (mass) dispersing section. The instrument has a mass range of 0.9 - 67 amu/q, a programmable mass resolution from 0.06 to 0.20 which is independent of mass or energy, and plasma density dynamic range of 10^-3 to 10^5 cm^-3, sufficient to measure the major and the minor ion energy distribution functions at apogee (~10000 km) as well as at perigee (~300 km) in the low altitude magnetosphere. The instrument has three selectable entrance apertures which view along the satellite spin plane. The three apertures have geometric factor ratios of about 100 : 1 : 0.001 and nominal acceptance angles of about 60 degrees, 30 degrees and 30 degrees out of spin plane for low energy (few eV) ions, respectively. The acceptance angles are energy dependent. In the thermal ion observations for large aperture, the high energy end of the bandpass is approximately 70 eV and the low end is determined by the setting of the retarding potential analyzer (RPA) grid voltage. In the suprathermal ion observations, the instrument has an E/q bandpass of 70 eV and a centre energy E/q range from 150 eV to 4330 eV. The setting RPA grid voltage depends on the SMS observation mode which is included in the header region of SMS data in Science Data Base (SDB). FILE NAME The file name of SMS data in Science Data Base (SDB) is defined by using the start time of each observation pass. The file name is'yymmddhh.sms' where yy is year (-1900), mm is month, dd is day and hh is hour. DATA FORMAT The block size of SMS/SDB is 3661 bytes. The first block is the header where the first 12 bytes show start time of the SMS/SDB file; yymmddhhmmss where last two data of mm and ss are minute and second. Next 3649 bytes have information on SMS observation mode, e-mail addresses, etc. Each data block consists of the block number, SMS attitude and thermal and suprathermal ion data. The format of a data block is as follows, byte (address) 1 block number 2 ram angle in spin plane in degree 3 angle between ram direction and spin plane in degree 4 bit 0-1 aperture: 00 = large 01 = medium 02 = large bit 2-7 minimum pitch angle 5 data flag bit 0 1 2 3 4 5 6 suprathermal mode 7 thermal mode 6~69 thermal H+ for logarithmic couts/sec 70~133 thermal He+ for logarithmic couts/sec 134~197 thermal O+ for logarithmic couts/sec 198~213 suprathermal H+ for logarithmic couts/sec 214~229 suprathermal He+ for logarithmic couts/sec 230~245 suprathermal O+ for logarithmic couts/sec One record of bytes (2~245) is repeated for 15 times; 1 block = 3661 bytes. Bit 0-1 (2 lsb) of byte 4 = 0 for large aperture, 1 for medium aperture, and 2 for small aperture. Bite 2-7 (6 msb) of byte 4 = 0.5 * minimum p. a. For thermal mode SMS data are constucted for 16 spin angles and 4 energy steps. Spin angles vary from 0 to 360 degrees. 0 degree corresponds to minimum pitch angle. The RPA energy is at 3.2, 5.4, 9.1, and 15.3V for '2a' mode which you find in header region but the energy step changes for different mode. You should ask the detailed observation mode by e-mail. For suprathermal mode SMS data are stored for 16 spin angles for integrated flux. The time of i-th data record in the n-th block is calculated as time = (start time) + n*120 (sec) + i*8 (sec). NOTICE (1) You should read the following paper before you use the SMS data in SDB. B.A. Whalen, J.R. Burrows, A.W. Yau, E.E. Budzinski, A.M. Pilon, I. Iwamoto, K. Marubashi, S. Watanabe, H. Mori, and E. Sagawa, The Suprathermal Ion Mass Spectrometer (SMS) onboard the Akebono (EXOS-D) satellite, J. Geomag. Geoelectr., 42, 511-536, 1990. S. Watanabe, B.A. Whalen, A.W. Yau, Thermal Ion Observations of Depletion and Refilling in the Plasmaspheric Trough, J. Geophys. Res., 97, 1081-1096, 1992. (2) If you have question, please contact Andrew W. Yau Department of Physics and Astronomy University of Calgary 2500 University Drive NW, Calgary, Alberta, CANADA T2N 1N4 Phone: 1-403-220-8825 FAX: 1-403-282-5016 e-mail: yau@space.phys.ucalgary.ca Eiichi Sagawa Hiraiso Solar Terrestrial Research Center Communications Research Laboratory 3601 Isozaki, Hitachinaka, Ibaraki 311-12, Japan Phone: 81-292-65-9700 FAX: 81-292-65-9701 e-mail: esagawa@crl.go.jp Takumi Abe College of Science and Engineering Aoyama Gakuin University 6-16-1, Chitosedai, Setagaya-ku Tokyo 157, JAPAN Phone: 81-3-5384-1111 ext.3422 FAX: 81-3-5384-1121 e-mail: abe@ee.aoyama.ac.jp Shigeto Watanabe Department of Astronomy and Geophysics Tohoku University Aoba, Sendai, 980, JAPAN Phone: 81-22-217-6734 FAX: 81-22-217-6739 e-mail: shw@stpp2.geophys.tohoku.ac.jp SAMPLE PROGRAM Following is a sample program for reading SMS/SDB with C language. /* sms_sdb_get.c (94.3.18) by Shigeto Watanabe This program reads SDB/SMS data (see readme.sms). 1 block = 3661 bytes k = 0 for H+ k = 1 for He+ k = 2 for O+ j = 0 to 4 for energy steps of thermal mode but not change for suprathermal mode i is spin angle as i*22.5 degrees */ #include main(argc,argv) int argc; char *argv[]; { FILE *file; int icn,iaper,mfl,dd; char ch1[2],ch2[2],ch3[2]; float ramm,rama,df; int ihs,ims,iss; int ihh,imm,isc; int i,j,k,n; file = fopen(argv[1],"rb"); for(i=0;i<=3660;i++) {dd=getc(file); if(i==6) ch1[0]=dd;if(i==7) ch1[1]=dd; if(i==8) ch2[0]=dd;if(i==9) ch2[1]=dd; if(i==10) ch3[0]=dd;if(i==11) ch3[1]=dd; } ch1[2]='\0';ihs = atoi(ch1); ch2[2]='\0';ims = atoi(ch2); ch3[2]='\0';iss = atoi(ch3); while((icn = getc(file)) != EOF ) { for(n=0;n<=14;n++) { dd = getc(file); ramm = (float)dd; dd = getc(file); rama = (float)dd*2.0; iaper = getc(file); mfl = getc(file); ihh = ihs; isc = iss + icn*120 + n*8; imm = ims + isc/60; if( imm >= 60 ) { ihh=ihh+imm/60; } imm = imm%60; isc = isc%60; if( mfl == 1 ) printf("Thermal ions: %d %d %d %f %f %d %d\n",ihh,imm,isc,ramm,rama,iaper,mfl); if( mfl == 2 ) printf("Suprathermal ions: %d %d %d %f %f %d %d\n",ihh,imm,isc,ramm,rama,iaper,mfl); for(k=0;k<=2;k++) { for(j=0;j<=3;j++) { for(i=0;i<=15;i++) { dd = getc(file); df = ((float)dd)/50.0; if( mfl == 1 ) printf("%5.2f",df); } if( mfl == 1 ) printf("\n"); } } for(k=0;k<=2;k++) { for(i=0;i<=15;i++) { dd = getc(file); df = ((float)dd)/50.0; if( mfl == 2 ) printf("%5.2f",df); } if( mfl == 2 ) printf("\n"); } } } fclose(file); }