Optimization of the Electron Gun with a Permanent Ion Trap

Transcription

1 Optmzatn f the Electn Gun wth a Pemanent In Tap We Le Xabng Zhang Jn Dng Fe Dpla Technlg R&D CenteSutheat Unvet Nangjng Chna Danel den Engelen Pduct and Pce Develpment(PPD)LG.Phlp Dpla 5600 MD Endhven The Netheland ABSTRACT The mpegnated cathde(i-cathde) n a CRT ae athe entve t n bmbadment than the de cathde. If an I-cathde ubjected t n bmbadment the electn emn can deceae.e. the emn lump. A ndcated n [1] an n tap ntduced t elmnate the dffeence f the n bmbadment between the cente cathde and the de cathde. Unftunatel the electn tajecte ae al nfluenced b the n tap. A eult a few addtnal abeatn ae ntduced and the pt pfle becme we. In th pape the tuctue f the pemanent n tap ptmzed. Afte the ptmzatn degn the pncpal tajecte f bth cente beam and de beam ae almt have the gnal tatu at the entance f the man len. A gd cmpme ha btaned between the n heldng and electn beam fcung. Kewd: pemanent n tap tde fcu INTRODUCTION In tap ae uuall nt appled n the electn gun f CRT nce de cathde ae nt patculal entve t the n bmbadment. On the cnta the mpegnated cathde (I-cathde) ae athe entve t n bmbadment. If an I-cathde ubjected t n bmbadment the electn emn can deceae.e. the emn lump. A ndcated n [1] an n tap ntduced t elmnate the dffeence f the n bmbadment between the cente cathde and the de cathde. Hweve the n tap al enlage the pt ze. Th pape decbe the fcu chaactetc f an electn gun wth an n tap. Sme addtnal abeatn ae geneated b the n tap the pt ze n the ceen becme lage. T btan the mnmum n bmbadment n the cathde and gd fcu pefmance multaneul th pape decbe an ptmzatn f the tuctue f the electn gun wth an n tap. In the ptmzatn the man len kept the ame. The ptn f the apetue f the tde ae mdfed t keep the gnal lpe f pncpal electn taject at the entance f the man len. ADDITION ABERRATIONS CREATED BY THE ION TRAP In a mmetcal electn ptcal tem the cdnate f electn tajecte n the mage plane ae epeed a a pwe ee. Due t the mmetcal chaactetc nl the dd tem ae dffeent fm ze. In th wa the phecal abeatn cma atgmatm dttn etc. f an electn ptcal tem uch a electn gun can be btaned. [] In an electn gun wth an n tap the apetue f G1 electde and the apetue f G electde have a hft n vetcal dectn epectvel[1]. Cnequentl me even tem n the pwe ee al appea. Snce the apetue f G1 and G nl hft n vetcal dectn the electn tajecte n hzntal and n vetcal dectn can be epeed a 197

2 ( ) = m = 0 j= 0 m n ( ) = whee n k = 0 l= 0 c j c kl k j l (1) the cdnate f electn taject n the mage plane and cdnate f electn taject n the bject plane. In the electn gun wth an n tap YOZ plane tll a mmet plane. A eult fllwng lmtatn vald ( ) ( ) = () In the electn gun wth an n tap the electn tajecte have a mall petubatn n Y dectn due t the hftng f apetue. Thu t ncnvenent t appl the vaatnal pncple dectl. Theefe we lke t detemne the abeatn ceffcent dectl fm the cmputatn f the electn tajecte. Ftl a few electn ae emtted fm the cathde wth dffeent ntal cndtn. The Runge-Kutta methd ued t mulate the mvement f electn and the lcatn f thee electn n the mage plane ae btaned. Accdng t the electn tajecte a ee f lnea equatn ae btaned X = [ M]C (3) C the vect f the abeatn ceffcent [ c c.... ] C =. M a m n 1 mat. The tem f the mat ae detemned b the ntal cndtn f the electn tajecte. The can be btaned fm equatn (1). The mla equatn can al be btaned egadng Y cmpnent. In equatn (3) the numbe f equatn lage than that f unknwn vaable. Thu an appach lutn wth mall edual e wth mnmal leat-quae methd. Fg.1 An n tap ntduced b the hftng f G1 G and G3 electde c n The emn cuent et t 0.5mA n the calculatn. The fllwng table hw the cmpan f abeatn ceffcent between the nmal electn gun and the electn gun wth an n tap whee X the cdnate f the electn tajecte [ ] n the mage plane X = m Tab. 1 The electn ptcal paamete n hzntal dectn f the nmal electn gun and the electn gun wth an n tap M Sphecal abeatn Cma Atgmatm Dttn 3 Gun_n Gun_n Whee Gun_n the nmal electn gun Gun_n epeent the electn gun wth an n tap. M the magnfcatn; Sphecal abeatn cma atgmatm and dttn ae abeatn whch ae defned n a mmetcal electn ptcal tem. epeent the abeatn ceffcent whch ae decded b tem 198

3 Tab. The electn ptcal paamete n vetcal dectn f the nmal electn gun and the electn gun wth an n tap M Sphecal abeatn Cma Atgmatm Dttn Gun_n Gun_n Whee Gun_n the nmal electn gun Gun_n epeent the electn gun wth an n tap. M the magnfcatn; Sphecal abeatn cma atgmatm and dttn ae abeatn whch ae defned n a mmetcal electn ptcal tem. epeent the abeatn ceffcent whch ae decded b tem The fllwng cnclun can be dawn (1). Due t the cntuctn f the n tap the pwe f pe-fcu len ha been changed. The magnfcatn f the electn gun wth an n tap dffeent fm that f the nmal electn gun. (). In hzntal dectn the magnfcatn phecal abeatn ceffcent cma ceffcent atgmatm ceffcent and dttn ceffcent d nt nceae gnfcantl afte the ntducng f the n tap. Sme paamete becme even a lghtl malle than that n the nmal electn gun. Thu the n tap wll nt nceae the pt ze n hzntal dectn. (3). Afte ntducng the n tap the vetcal magnfcatn al a lghtl malle than that f the nmal electn gun. Bede th the vetcal phecal abeatn ceffcent the cma ceffcent and the atgmatm ceffcent ae al cle t that f the nmal electn gun. Hweve the dttn f the electn gun wth an n tap lage than that f a nmal electn gun. (4). Afte the cntuctn f an n tap me addtnal abeatn appea. Epecall the abeatn ceffcent egadng 3 and becme patculal lage. Thee abeatn caue the ncement f pt ze n the electn gun wth an n tap. OPTIMIZATION OF THE ELECTRON GUN WITH AN IRON TRAP A dcued n the pevu ectn the n tap can deceae the n bmbadment n the cathde. Hweve me addtnal abeatn appea due t the hftng f the apetue. A cmpme mut be made between the n bmbadment and the pfle f pt. Th acheved b cndeng the n bmbadment the hftng f pt n ceen and the pt ze a element f taget functn. Ftl the value f each vaable gven. The weght fact f dffeent tem ae al chen. The taget functn epeed a q = w d + w + w + w + w p p ( n _ dam n _ dam ) ( hft _ hft _ ) ( hft _ hft _ ) ( pt _ pt _ ) ( pt _ pt _ ) whee w w and w ae the weghted fact d p egadng the n bmbadment the hftng f pt n the ceen and the pt ze. Paamete n _ dam the n bmbadment n the cathde; hft _ and hft _ the hftng dtance f pt n the cente pt _ pt _ f ceen; and the pt ze n hzntal dectn and n vetcal dectn epectvel. Afte mnmum the taget functn the ptmum tuctue f n tap btaned. 199

4 Tab. 3 Cmpan f the nmal electn gun and the electn gun wth an ptmum n tap Shft_gfc1a_ Shft_gfc1a_ In_dam Shft_ Shft_ Spt_ Spt_ Taget functn ( 10 5 mt) Gun_n_cen Gun_n_cen Gun_n_de Gun_n_de Whee Gun_n_cen and Gun_n_de epent the cente beam and de beam f the nmal electn gun epectvel. Gun_n_cen and Gun_n_de ae the de beam f the electn gun wth an n tap. The cepndng electn tajecte and n tajecte ae hwn n Fg. t Fg.3 Fg. The electn tajecte f the cente beam Fg.3 The electn tajecte f the de beam 00

5 The pt pfle f cente beam and de beam Ae hwn n Fg.4 t Fg.7 Fg.4 Pfle f pt f the cente beam Fg.7 The cuent dent f the de beam Fg.5 The cuent dent f the cente beam Fg.6 The pfle f pt f the de beam CONCLUSION In u pevu tud[1] t wa fund that an n tap n a tde pat f an electn gun can deceae the n bmbadment n the cathde. Wth th wa the emn lump f I-cathde can be educed gnfcantl. Hweve n the electn gun wth an n tap the pt ze n vetcal dectn nceae abut 5% due t hftng f the apetue f G1 and G. The electn ptcal ppet f the electn gun wth uch an n tap decbed n th pape. Fm the anal t can be cncluded that addtnal abeatn ae ntduced becaue f the hftng f apetue f the n tap. A cmpme ha t be made between the n bmbadment the hft f pt n the ceen and the pt ze n the ceen. The tuctue f the n tap f bth cente beam and de beam ae ptmzed. In the ptmum tuctue the n bmbadment f the cente beam deceaed b abut 54% and the pt ze nceae b abut 9% and.5% n X and Y dectn epectvel. The n bmbadment f the de beam deceaed abut 1% and the pt ze nceae abut 1.6% and 6% n X and Y dectn epectvel. REFERENCES 1. Xabng Zhang et al. Reducng n bmbadment n I cathde Pceedng f IDW 0 639~ P.W.Hawke E.Kape Pncple f electn ptc Academc Pe