TOWARDS SUB-MICROMETER RESOLUTION OF SINGLE SHOT STRIP LINE BPM

Transcription

1 EUROTe-Report TOWRDS SUB-MICROMETER RESOLUTION OF SINGLE SHOT STRIP LINE BPM alnn January 8, 009 btract hgh reoluton ngle hot BPM et-up egne One of the BPM mofcaton evelope a a trp-lne-pckup-bae fference-um BPM In th BPM, each trp lne gnal converte nto a three-700mhz-wave burt n a tme oman converter The fference an um burt prouce by a hybr juncton are etecte n a par of ynchronou etector The ynchronou etector reference gnal, an DC clock trgger are manufacture from the um burt The et-up an feature of th BPM are preente BPM reoluton etmaton one, contrbuton of varou noe component are conere metho propoe to meaure component nvually The BPM prototype reoluton wa meaure ung a E TF beam For bunch ntenty range 03nC the reoluton ab μm (for BPM ectve aperture /5) Reoluton meaurement reult are cue Wth approprate DC, the BPM can meaure nvual bunche at a rate of up to 50MHz The BPM latency to the DC nput a low a 0n Hgh reoluton an low latency together, make th BPM utable for fat feeback/fee-forwar ytem STFC Darebury Laboratory, Warrngton, W4 4D, U - -

2 EUROTe-Report INTRODUCTION In th paper, ome reult of the evelopment of a ngle hot BPM, bae on an electroe pckup, are ecrbe The evelopment of th evce wa rven by challengng beam agnotc requrement for the ILC, TF [, ], an the EMM [3] accelerator The BPM houl meet the followng requrement: Bunch charge: nc (TF); 00 0nC (EMM) Bunch pacng (gettng-reay-to-the-next-bunch tme): n (TF); 50n (EMM) acuum chamber aperture: 5mm (TF); 40mm (EMM) Beam poton meaurement range: a few mm (TF); a full aperture (EMM) Pckup: trp lne electroe (TF); button electroe (EMM) Reoluton: μm (TF); 50μm (EMM,30pC ) nalog proceng latency: << 50n (TF) n attempt wa mae to evelop a proceng cheme an a correponng et of matchng each other 50Ω crcut that coul be combne nto ome optmal ngle hot BPM that woul meet the requrement above, n partcular, whch woul have hghet reoluton n a full pckup aperture or, wthn a reaonably reuce poton range, a reoluton cloe to the thermal noe reoluton lmt BPM mofcaton for the EMM now uner evelopment Here we focu at a BPM mofcaton that wa meant for the ILC Crab Cavty Tet Bench [] an Fee-Forwar Correcton Sytem [] at the ILC/TF DIFFERENCE-SUM BPM SET-UP In the BPM, each trp lne pckup gnal converte to a flat-top-envelope three-wave burt The fference an um burt from the put of the hybr juncton are amplfe an etecte n a par of ynchronou etector The put of each etector moothe wth a LP flter, the put pule of whch ample at t en flat part by an DC hort burt wth a flat top envelope an mportant feature of the BPM Wth t, three goal are attane: frt, the BPM get a hort gettng-reay-to-the-next-bunch tme; next, t ha a hort latency a the flter put that ample at t en of the ame length a the burt; fnally, wth an envelope flat top an ung an overhot-le Gauan flter, t poble to obtan n a hort burt tme a BPM put pule wth a flat en The flatne at the ample moment gnfcant a t enable to reuce atonal noe generate by DC clock jtter, an to relax the tolerance of ample moment potonng a well n ntal varant of a pckup-gnal-to-flat-top-envelope-burt converter [4] wa bae on a ne-wave rregular-trp-lne coupler ecrbe n [5] coupler wave wa plt nto four wave each of whch wa progrevely elaye an then re-combne The put gnal hown n Fg Fg n put re-combne gnal from a trp-lne-coupler-bae converter The burt 500MHz 5GHz ocllocope TDS754B Beam ntenty ab nc - -

3 EUROTe-Report Later a more compact varant wa evelope a a 50Ω tme oman converter contng of three cacae each of whch a ngle-rectangular-wave coupler mlar to the coupler mentone above The converter mae a a PCB wth a par of couple trp lne between two groun plane To get a flat envelope n a converter of uch kn, t neceary n the egn to ajut the couplng trength n the frt two cacae to have them matche to the lat cacae n put gnal of a converter prototype (no couplng trength ajutment one) hown n Fg Fg Delta functon repone (re) of a cacae-coupler-bae converter prototype The burt 700MHz Network nalyer E507B, a Gauan mpule 5p In th converter, the wave half-pero mae equal to the pacng of the mpule n the trp lne pckup gnal Startng wth the econ half-wave n the burt, the magntue ouble a the wave excte by the pckup oppote polarty mpule are umme wth oppote phae The lat half-wave mlar to the frt half-wave So, the burt envelope ha a trapezoal hape beam gnal of the mentone above converter prototype hown n Fg 3 Fg3 cacae-coupler-bae converter prototype gnal (re) The converter nput gnal (blue, attenuate B) a cm trp lne pckup gnal at the en of a 30m length Helax cable 5GHz ocllocope TDS754B Beam ntenty ab nc - 3 -

4 EUROTe-Report The BPM bae on a (00-)GHz fference-um hybr juncton H-9 from nzac M/- Com In the beam tet, t wa uffcent to balance the BPM prototype nput cable together wth the hybr juncton mply by manual ajutment of a par of nput phae hfter an watchng the fference gnal on ocllocope problem of BPM zero offet tablty an zero offet (remote) ajutment metho an proceure are left beyon the cope of th paper 0B-gan 8GHz-banwth 5B-noe-factor amplfer wa ue bae on a chp RF360 from RFMD a ynchronou etector, a +7Bm-LO (0005-3)GHz mxer SYM-30DHW from Mn- Crcut wa ue The BPM put flter mae a a 50 Ω plexer wth a 6-th orer Gauan LP flter an -n orer HP flter The LP banwth 50MHz, the 0-09 re tme n BPM put buffer amplfer (bae on a chp D8000 from nalog Devce) ha gan +B nto 50Ω an a referre-to-nput noe ab 35μ n the banwth 50MHz The BPM analog put are meaure wth a par of DC Bunch ntenty normalaton uppoe to be one n a gtal pot-proceor Sum of a BPM analog proceng tme, an DC meaurement tme an a normalaton tme amount to a total BPM latency The BPM proceng tme ab 0n Wth a commercal ppelne 00MHz DC, t put avalable after 3 (DS544) or 4 (D6645) clock cycle So, the BPM latency wth normalaton equate to 40 50n In th BPM, an attempt wa mae to make t autonomou It ha an nternal beam-bae ynchronaton The ynchronou etector reference gnal prouce by an nternal crcut from the um burt a a ynchronou burt of regular ampltue nother crcut trggere by the ynchronou burt generate the DC clock DIFFERENCE-SUM BPM RESOLUTION I For the gnal magntue, poton Y calculate a R ( g / g )( / ) where at the fference-um juncton put the beam Y = () R the ectve pckup rau, g an g are the juncton voltage gan for the matchng put loa r For the juncton put thermal noe voltage < u = 4kTB ( r/ ) n the banwth B the reoluton can be wrtten a g < u Y y lmt + ( ) () g R g / g < where mean rm value an Y mean value The expreon () gve a BPM reoluton lower lmt for a poton meaurement range R ( g / g ) The lmt nverely proportonal to beam ntenty an grow wth beam offet (for g = g, up to tme for Y = ) Etmaton of () for R = 9mm, = 0 7 (ee below), Y = 0, r = 50Ω an R B = 50MHz ( < u 8μ ) gve < y = 00nm Wth th lmt, the BPM ultmate range R efne a R = < y / R g / g ) = < u /, R = 99B lmt lmt ( - 4 -

5 EUROTe-Report II ume the gnal, are amplfe an then etecte The amplfer an etector gan an noe factor are repectvely G, at the etector put can be wrtten a < F an G D, F D The thermal noe < y D g G G < u Y D D ( ) y F + F (3) g G R g / g where each total gan G = G G D an each noe factor F = F ) + FD / G The expreon (3) repreent evoluton of the thermal noe However, other kn of noe may appear n the gnal path Coner here one of them umng that for a BPM nput gnal a a ne wave burt, a ynchronou etector ue where the wtche are commutate by a quare wave reference gnal Equatng the etector to a multpler an ntroucng a reference jtter δ t ref << T, where T the pero, one can calculate a etector voltage put a = (a / π )[ π ( δt ref / T )] (4) where for the reference gnal magntue taken equal to, the nput wave ampltue a The frt term the etecte gnal, the econ term wth δ tref ranomly changng from hot to hot an atonal voltage noe Th noe, frt, proportonal to the nput gnal trength, econ, t a non-lnear tranformaton prouct of the reference gnal jtter For Gauan jtter, th noe non-gauan: t ha a DC component, t lmte on one e wth zero an on the other e ha large fluctuaton For an optmal BPM th noe houl not excee the thermal noe For a full aperture BPM wth g = g, takng maxmal beam offet a Y an the etector put range a R F + one can wrte: F ( δ t ref / T (/ π ) R F + F / (5) 3 Etmaton of (5) for R = ( 99)B an F = F = 6 gve δ t / T 0 III Wth a buffer amplfer at the etector put, the noe-to-gnal range at the DC nput can be wrtten a R F + F, where each total noe factor : tot + FD ) / G + ( FB ) tot D F = F ( /G G (6) wth a buffer ectve noe factor taken a F B For an optmal DC, t reoluton n efne a R = α α / ( ) where n the number of bt, an α, α are ome cocent, houl atfy the conton n α α / ( ) R F tot + F tot (7) For R = ( 99)B, F tot = F tot = 5, an α = α = the number of bt n 6 The cocent α ntrouce to take nto account the DC tranton noe The cocent a rm quantty expree wth the LSB unt The cocent α ue to take nto account the DC clock jtter For a flat top BPM put pule the cocent α = ref For a mplet cae of lnear lope = 0[ + ξ( t / mt)], ξ <<, 0 t mt where mt the burt length, an acceptable clock jtter δ / T n a full aperture BPM t clk n δ t / T α / )( / )( m / ξ ) (8) clk ( 0-5 -

6 EUROTe-Report where ± the DC voltage range For, α, n = 6, m = 3 an ξ = 0, δ tclk / T 0 Wth δ t clk / T = 0, the cocent α For a cupola-lke top an wth a ample moment at t apex, the voltage noe generate by the DC clock jtter a non-lnear tranformaton of the latter an ha feature analogou to the feature of the noe generate by ynchronou etector reference jtter I To reuce the contrbuton of the atonal voltage noe component generate n the etector an the DC (an contrbuton of the buffer amplfer noe a well) an to come cloer to the BPM reoluton lower lmt, a common meaure to ncreae the fference channel gan wth reference to the um channel gan: G = G, G = G, ume that n the BPM g = g Ung the gnal at the amplfer put, the beam poton Y can be wrtten a Y = ( R / ) ( / ) (9) ume that the nput voltage range of the etector n both channel are equal whch can be wrtten a max = max In th cae the meaurement range Y max of beam offet hrnk tme wth regar to a full aperture BPM: Y max / Ung (3), the thermal noe can be wrtten a < u Y < y F + F (0) R Wth Ymax / an F ~ F the econ term uner the quare root can be neglecte The thermal noe magntue at the etector nput tme enlarge, whch equvalent to havng contrbuton of the noe n the followng crcut reuce by the ame factor The BPM put thermal noe (0) can be wrtten a < u y F tot / G tot < () where G = /, an the noe factor gven by the expreon (6) : F + + tot ( ) / G + ( F ) / G G F D B D = = F tot Coner a metho that allow a meaurement of the put thermal noe < y an the put total atonal noe <η nvually umng that the atonal noe a well a the thermal noe Gauan, the equaton ytem for two gan G, =, can be wrtten: < y + < η =< r < y + < η =< r where < r are a par of meaure BPM reoluton value Wrte for each gan: = (3) - 6 -

7 EUROTe-Report < r < y < η < < u < υ, < u F tot where < the fference channel total voltage noe, < υ the atonal noe expree alo n olt Note that the latter oe not epen on Comparng value n each par for =, n (4), wrte: F tot < y = < y F tot (5) < η = < η Re-wrte the ytem (3) (nex omtte): < y + < η =< r F tot (6) < y + < =< η r F tot The ytem (6) together wth relaton (5) allow the BPM thermal noe an the BPM atonal noe to be foun for each, =, Th metho can be extene for etmaton of the component of the BPM atonal noe, namely, the noe ue to ynchronou etector reference jtter, an the DC noe, uner the ame aumpton of beng both Gauan gan two BPM reoluton meaurement houl be one, now for two fference channel put buffer amplfer gan G B = G B, GB = k G B, =, For ome wrte: < r < y < j < ρ where k < u k k k < < ϑ < ν F tot < y = < j, (4) (7) y = < y = < the thermal noe, < j = j = < the ynchronou etector noe at the BPM put, < ν - 7 -

8 EUROTe-Report the etector voltage noe at t put, < ρ the DC noe, < ϑ the DC noe expree n olt The equaton ytem rea (nex omtte): < y + < j + < ρ =< r k (8) < y + < j + < =< ρ r k For gven an the thermal noe < y known (that can be meaure by the metho (6) an (5) above), the ytem (8) together wth relaton (7) allow the ynchronou etector noe at the BPM put an the DC noe to be foun BEM-BSED RESOLUTION TEST ummary of the BPM reoluton tet reult wa preente n [6] Below the reult are reconere an cue BPM reoluton tet were one at the E TF Two beam run were ue In the frt run, a ngle BPM wa ue It nput were fe wth the gnal obtane by plttng a gnal of a ngle pckup trp lne The fferental gnal wa cloe to zero an not change wth beam placement The tet wa one for a fxe fference channel gan value G = G an two lower um channel gan value G = G /,, =, In the econ run (three month later), two BPM were ue connecte n parallel (through pltter) to a pckup trp lne par The fferental gnal were correponng to ab 03mm, whch nclue a beam offet a well a a BPM zero offet The um channel gan wa G = G / The BPM prototype wa calbrate agant an TF Extracton Lne BPM, ung a pole teerng col of known trength The pckup ectve rau wa meaure a R 9mm 9 The bunch ntenty wa ab 08nC ( 5 0 e ) For a hybr juncton wth the nput fe rectly from pltter put, the um put burt envelope rm value wa 0 7 I In the frt run, the trp lne pckup gnal were attenuate by ( 7)B for gan value G an by ( 4)B for G That wa equvalent to a vrtual ecreae of the run beam ntenty by up to I = 0 36nC an I = 0 50nC, an a ecreae of the um hybr juncton put by up to = 0 36 an = 0 50 repectvely To get the BPM um put well wthn ynamc range (ab ( 4) agant a peetal et at the buffer amplfer put), the gan were et to G = G / 3 6 ( 0B) an G = G / 5 0 ( 4B) So, the fference channel gan exceee the um channel gan = 3 6 an = 5 0 tme repectvely For G gven, at a hot of number p, the bunch poton wa calculate a p r p (9) p The BPM reoluton wa calculate a a tanar evaton t acro the array (9) Ung (9), wrte: - 8 -

9 EUROTe-Report < r < ( G / ) Rato of meaure tanar evaton t an < r I = = = 4 < r I Wrte the BPM put thermal noe: < u (0) t wa expecte to be equal to the rato: < y F tot (0) Wth R = 9mm an F tot = 5, the expreon (0) yel < y = 03μm for the ntenty I = 0 36nC an < y = 0 3μm for I = 0 50nC The BPM range come to R ~ = 89B an = 9B R ~ II The BPM put gnal were meaure wth a two channel GHz 4bt ± recorer GFT6004 (from cqutek) ume that for nput t ectve reoluton /( 3bt) = 78B For = 0 B the ectve reoluton come to R 88 = B For = 4B the ectve reoluton R = 9B ume here that the recorer ha a tranton noe only whch Gauan an equal to the ectve reoluton above Now the ~ < ρ / R < y, whch ectve tranton noe can be calculate a ( ) yel < ρ = 0 36μm, < ρ = 0 3μm umng that the ynchronou etector noe zero, one can wrte a lower lmt of expecte BPM reoluton a < ρ r lmt = < y + <, whch yel r lmt = 0 48μm () < an < r lmt = 0 33μm The recorer wa free-runnng wth GHz amplng rate an got toppe (wth ome elay) at each hot by the BPM um gnal t clock wa unynchrone wth beam, the BPM pule magntue at each hot wa calculate a a maxmum of a polynomal nterpolaton curve contructe on a maxmum ample an two ajacent ample III For the frt run a poton reang t acro a hot array gave the BPM reoluton The t value for = 0 B are gven n Table, for = 4 B are gven n Table The array length N (number of hot recore) are alo gven Table array N t, μm Table array N t, μm

10 EUROTe-Report The array t ha an tanng value Th a reult of a tep-lke jump n the fference gnal, whch occurre probably ue to ome occaonal movng of the BPM nput cable correponng jump n the poton (ab 5μm) een n a hot-by-hot plot gven n Fg 4, a) The um gnal gven n Fg 4, b) Below, th value exclue from the et a) b) Fg4 The poton (a) an the um gnal (b) v hot number n the array Calculate average value t = ( / N ) N t p for each Table: t = 56μm an p= t = 0 97μm Rato t / t = 6 excee the etmate () above by 5% Each t value ab 3 tme greater than the lower lmt of expecte BPM reoluton that wa etmate above a < r lmt = 0 48μm an < r lmt = 0 33μm repectvely For the cae G = G = G, th BPM woul have t cloe to 5 μm So, the atonal noe of th BPM prototype turne to be gnfcantly larger than the thermal noe etmate above In the econ run, t wa covere that the recorer contrbute ome atonal noe (ee below) The mentone above nterpolaton of the recorer reang may generate ome noe a well Noe ue to ynchronou etector reference jtter houl alo be conere Th BPM prototype wth = 4B ha a bunch ntenty range that exten own to ab 0nC prove the gan G et n nvere proporton to ntenty For that ntenty, the put thermal noe woul equal the atonal noe The BPM beam offet meaurement range / = / 5 of the ectve pckup aperture I For the econ run, the BPM reoluton wa calculate a a ve-by- t acro a poton fference array obtane from the reang of the two BPM t value of one of the array gven n Table 3 Table 3 array 9 N 8 t, μm 5 The t value 5 tme greater than t obtane n the frt run for the ame gan 4 B Whlt ata proceng, t wa covere that ome exceve noe generate by the - 0 -

11 EUROTe-Report recorer, an the larger the recorer nput, the larger th noe So, mot probably, the ncreae of the t above occurre ue to an ncreae of the exceve noe that n t turn occurre ue to eparture of the BPM reang from zero by up to 03mm Invetgaton howe that any array of recorer reang contan a paratc gnal contng of harmonc of 00MHz, an t pectrum beng rregularly changng, generally become broaer wth larger nput The paratc gnal orgnate probably from the recorer nternal clock crcut, a mater generator of whch ha frequency jut 00MHz In Fg 5, two recorer reang pectra are hown They were meaure wth beam for the ynchronou etector OFF The recorer contnuouly meaure put of the BPM buffer amplfer The pectrum a) for zero DC put, the pectrum b) for DC put (a um channel peetal) a) b) Fg5 Spectra of recorer DC nput reang In Fg 5, n the range 0 to 0 bn, a buffer amplfer thermal noe can be een The buffer amplfer noe wa wthn expecte range, ha a contnuou pectrum an n t change wth DC level Th wa confrme ung an ocllocope wth FFT The amplfer put (re) an t pectrum (green) are hown n Fg 6 reference, a pectrum of a 00μ 300MHz ne gnal hown (both blue) Fg6 pectrum of the buffer amplfer put noe - -

12 EUROTe-Report SUMMRY fference-um BPM reoluton etmaton ha been performe Contrbuton of varou noe component are conere metho evelope to meaure nvually the BPM put thermal noe, the ynchronou etector noe, an the DC noe hgh reoluton low latency ngle hot trp lne BPM et up ecrbe For an electron bunch ntenty range 03nC, n a tet at the TF, a BPM prototype reoluton of ab μm ha been acheve, for an ectve pckup aperture of up to /5 The tet reult are cue For completon of BPM reoluton nvetgaton, t neceary to equp the BPM wth t own DC CNOWLEDGEMENTS The work wa upporte by the Common of the European Communte uner 6 th Framework Programme Structurng the European Reearch rea, contract No RIDS- 0899, an by the Scence an Technology Faclte Councl, U I m thankful to Prof PN Burrow for the opportunty to o th work n the frame of the ILC FONT Project I m grateful to my colleague from TF for collaboraton I thank my colleague Dr L Ma for mulaton of flter an converter, an FONT teammate B Contance an C Swnon for help wth reoluton meaurement Reference [] alnn, L Ma, an R J Smth, Beam-Bae Hgh Reoluton Phae Imbalance Meaurement Metho for the ILC Crab Cavte, EPC 06 [] alnn, PN Burrow, Turnaroun Fee-Forwar Correcton at the ILC, PC 07 [3] R Egecock, EMM the Worl Frt Non-Scalng FFG, PC 07 [4] alnn, TF FONT December 05 Run, TF Weekly Meetng, 05 December 005, [5] alnn, Beam-Bae Metho of BPM Center Offet an Reoluton meaurement, EPC 0 [6] alnn, Towar Sub-Mcrometer Reoluton of Sngle Shot Strp Lne BPM, EPC