Recent Magnetic Measurement Activities at BNL

Transcription

1 Recet Magetic Measuremet Activities at BNL Aimesh Jai (O behalf of the Maget Test Group) Supercoductig Maget Divisio Brookhave Natioal Laboratory Upto, New York , USA 1

2 Itroductio Magetic measuremet activities at BNL ca be geerally classified ito three classes, based o the type of magets measured: (a) Supercoductig Magets (RHIC, LHC, DESY) (b) Covetioal Magets (Spallatio Neutro Source) (c) Isertio Devices (G. Rakowsky, Natioal Sychrotro Light Source at BNL) This talk will focus primarily o the recet developmets carried out i respose to special measuremet eeds i some supercoductig magets. 2

3 Recet Measuremets at BNL i Supercoductig Magets Fast Measuremets for Dyamic Effects (500 µs to 2 sec time resolutio; Time decay, sapback, eddy curret effects.) Helical Dipoles for the RHIC Spi Physics Program (Uusual 3-D field throughout.) Aother talk at IMMW12. Post-RHIC Routie measuremets (HERA upgrade magets, LHC twi aperture dipole prototypes.) Not covered i this talk. 3

4 Fast Measuremets: Dyamic Effects Time decay of allowed harmoics at ijectio, ad sapback o resumig the ramp, are well kow problems i the use of supercoductig magets i accelerators. Typical time decay of harmoics is rather slow several miutes after reachig the ijectio curret. However, the iitial decay is much faster. Sapback occurs very rapidly, typically over a few secods. Rotatig coil systems i routie use at BNL for DC measuremets have a period of ~3.5 sec. ad ca take approx. oe readig every miute. A better time resolutio is clearly eeded to study the dyamic effects. 4

5 Fast Measuremets: Hardware Issues Harmoics are measured durig oe rotatio of the coil. Coil should spi as fast as possible to miimize measuremet time. BNL uses voltmeters, with oe power lie cycle itegratio for oise rejectio. This limits rotatioal speed. No. of agular poits reduced from 128 to 64 (or 32) to gai a factor of 2 (or 4) i speed. Dead time betwee measuremets should be elimiated, thus providig a early cotiuous time map of the harmoics. Modify software to keep acquirig data cotiuously ad storig it i the voltmeters, rather tha trasferig it to the PC. Amout of data limited by 4K memory of timer card, which stores coil speed iformatio. This memory could ot be icreased. 5

6 Coil Rotatio Parameters Two sets of parameters were used: (A) 32 agular positios, 16 time reads per revolutio: Allows T = 0.64 sec. to 1.0 sec. Cotiuous data acquisitio up to 256 revolutios. Foud usatisfactory for higher order terms, but was OK for dodecapole i a quadrupole. (B) 64 agular positios, 32 time reads per revolutio: Allows T = 1.28 sec. to 2.0 sec. Cotiuous data acquisitio up to 128 revolutios. Satisfactory for harmoics measuremets. 6

7 Dyamic Measuremets: Aalysis Issues Certai measuremets, such as eddy curret effects uder rampig coditios, are required to be carried out while the curret i the maget is cotiuously chagig. The covetioal Fourier aalysis, which is used for DC measuremets, ca ot be used to calculate harmoics from the measured coil sigals. I additio to the curret, i geeral, the harmoics are also time depedet (due to time decay, sapback, supercoductor magetizatio, etc.) This makes a geeral treatmet of the aalysis quite difficult. 7

8 Approximate Aalysis of Data A simplified scheme has bee devised to aalyze the data uder the assumptio that the Normalized harmoics are ivariat durig a sigle rotatio of the coil. The absolute values of the harmoics (i Tesla, say) are thus proportioal to the istataeous curret. The assumptio is valid for moderate ramp rates ad faster coil rotatios. The scheme has the advatage of processig data o a rotatio by rotatio basis. The scheme uses Fourier aalysis with some maipulatios of the coil sigal to accout for the chage i curret durig the measuremets. 8

9 Tagetial Coil Sigal i a Varyig Field Field Expasio for the radial compoet: C(,t) = Istataeous amplitude α = phase agle, assumed costat over oe rotatio = referece radius chose for harmoics R ref B r ( r, θ, t) = = 1 Coil Parameters: R c = Radius of the coil = Opeig agle N = No. of Turs L = Legth ω = Agular speed r C(, t) R ref 1 R c si[ θ Y θ ω α ] B r X 9

10 10 Tagetial Coil Sigal i a Varyig Field Flux through a Tagetial Coil: δ = coil agular positio at t = 0 ad θ = ω t + δ. Coil Voltage : Geometric Factor 2 si 2 ) si( ), ( 1 ) ( 1 = = + = Φ = R R NLR G t t C G t ref c ref α δ ω = Φ = = ) si( ), ( 1 ) )cos(, ( ) ( 1 t t t C t t C G dt d t V α δ ω ω α δ ω ω

11 Tagetial Coil Sigal i a Varyig Field Defie: I = Average curret durig oe rotatio of C avg avg R( t) = ( ) = Harmoic stregth correspodig to ( I/ t) = Ramp Rate at time t the coil I avg I terms of these quatities: V ( t) = = 1 G ω C avg I( t) ( ) cos( ωt+ Iavg + I δ α ) R( t) si( ωt+ δ ω avg α) 11

12 Tagetial Coil Sigal i a Varyig Field V ( t) = = 1 G ω C avg I( t) ( ) cos( ωt+ Iavg + I δ α ) R( t) si( ωt+ δ α ) ω V(t), i geeral, is NOT a periodic fuctio of time. Coefficiets of sie ad cosie terms are ot costats. Thus the above expasio is NOT a Fourier series. Goal is to obtai the quatities C avg () ad α from V(t), assumig that the curret ad ramp rate profiles, I(t) ad R(t), are kow. avg 12

13 Iavg V ( t) I( t) Maipulatig the Coil Sigal = 1 G ω C avg ( ) I R( t) si( ωt+ δ ω avg α ) = = 1 G ω C avg ( )cos( ωt+ δ α ) The right had side represets a Fourier series. If the coil sigal, V(t), is modified as expressed o the left had side, a simple Fourier aalysis ca be used to obtai C avg () ad α. Problem is that this maipulatio itself requires the kowledge of C avg () ad α. This problem is solved by usig a iterative procedure. 13

14 Iterative Procedure Iavg V ( t) I( t) = 1 G ω C avg ( ) I R( t) si( ωt+ ω avg δ α ) = = 1 G ω C avg ( )cos( ωt+ δ α ) Approximate values of C avg () ad α are first obtaied by eglectig the secod term o the left had side. The approximate C avg () ad α are the used o the left had side to obtai ew values of C avg () ad α. The process is cotiued util a covergece is reached. Typically, three or four iteratios are sufficiet. 14

15 Curret Ramps Must avoid udershoots ad overshoots. Two types: Quadratic ad Expoetial. Quadratic : Curret Vs time has oly liear ad quadratic segmets. Expoetial : Curret Vs time has liear, quadratic ad expoetial segmets. Dow ramps are always Quadratic. 15

16 Quadratic Curret Ramps Ramp rate varies liearly with time from zero to R max i time t 1, stays costat at R max for time t, the goes liearly to zero i time t 2. Characterized by I mi, I max, R max, f 1 = t 1 /(t 1 +t+t 2 ) ad f 2 = t 2 /(t 1 +t+t 2 ) Typically, f 1 = f 2 = 0.05 to Curret (A) Ramp Rate R max t 2 t Curret Ramp Rate (A/s) t Time (s)

17 Expoetial Curret Ramps Described i LHC Project Report 172, L. Bottura et al. Ramp rate varies liearly with time, the expoetially, the stays costat, the reduces liearly to zero. Characterized by I mi, I max, I s-b, R s-b, R max, I exp-max ad f 4. Parameters eed to be chose carefully to geerate meaigful profiles Curret 30 Curret (A) Ramp Rate Ramp Rate (A/s) Time (s) 17 0

18 RHIC Quadrupole Normal 12-pole (uits at 25 mm) A/s 12-Pole Curret QR7109 T = 0.66 sec 470 A 3500 A 40 A/s Curret (A) Arbitrary Time (sec.) 18

19 RHIC Quadrupole Normal 12-pole (uits at 25 mm) Pole Curret QR7109 T = 0.66 sec Curret (A) Arbitrary Time (sec.) 19

20 RHIC Dipole Normal Sextupole (uits at 25 mm) A/s Sextupole Curret D96525 T = 0.66 sec 470 A 5100 A A/s Curret (A) Arbitrary Time (sec.) 20

21 RHIC Dipole Normal Sextupole (uits at 25 mm) Sextupole Curret D96525 T = 0.66 sec Curret (A) 400 Arbitrary Time (sec.) 21

22 Normal Sextupole (uits at 25 mm) RHIC Dipole D96525: Time decay at 470A; 3500A cycle Data Two Expoetials Fit Log(t) Fit (t > 10s) τ = 45 sec ad 303 sec Time (sec) 22

23 Normal Sextupole (uits at 17 mm) Prototype Twi Aperture Dipole for LHC A/s, with prior quech 25 A/s, o prior quech Curret (1 A/s case) Time resolutio = 2 sec DMP Curret (A) Time sice reachig 300A (sec.) 23

24 Prototype Twi Aperture Dipole for LHC -8.2 Normal Sextupole (uits at 17 mm) DMP402 Decay & Sapback (25A-300A at 1 A/s) Decay & Sapback (25A-300A at 25 A/s) Referece Data (Cotiuous Ramp at 1 A/s) Curret (A) 24

25 Eddy Curret Effects i DMP402 Skew Quadrupole (uit) Up Ramp 1 A/s Up Ramp 10 A/s Up Ramp 25 A/s Curret(A) 25

26 Eddy Curret Effects i DMP402 Normal Sextupole (uit) Up Ramp 1 A/s Up Ramp 10 A/s Up Ramp 25 A/s Curret(A)

27 Eddy Curret Effects at Very High Ramp Rates Focus o Trasfer Fuctio, rather tha harmoics. Measured usig o-rotatig coil. 27

28 Eddy Curret Effects: γ T Quads i RHIC RHIC has ormal quadrupole correctors which are pulsed from +50A to 50A i approx. 30 ms as the beam crosses the trasitio eergy. This amouts to a ramp rate of ~ 3300 A/s. It is importat to kow whether the quadrupole field lags the curret due to eddy curret effects. Difficult to measure harmoics with adequate time resolutio usig rotatig coils. We have measured the quadrupole field stregth usig statioary quadrupole coils with a time resolutio of 0.5 ms (500 µs). 28

29 Curret (A) Gamma-T Jump i CRF132; Ru 41; March 28, Gamma-T Jump from 50A to +50A; Other Supplies at 0 A. Curret Ramp Rate Ramp Rate (A/s) Time (ms) 29

30 Gamma-T Jump i CRF132; Ru 41; March 28, Gamma-T Jump from 50A to +50A; Other Supplies at 0 A Quad-1 Quad-2 Coil Sigal (V) Time (ms) 30

31 Gamma-T Jump i CRF132; Ru 41; March 28, Gamma-T Jump from 50A to +50A; Other Supplies at 0 A. Normal Quadrupole (T at 25 mm) Normal Quad Curret Curret (A) Time (ms)

32 Gamma-T Jump i CRF132; Ru 41; March 28, Gamma-T Jump from 50A to +50A; Other Supplies at 0 A. Normal Quadrupole (T at 25 mm) Normal Quad Liear Fit y = E-03x E Curret (A) 32

33 Magetic Measuremets i Helical Dipoles BNL is producig 48 helical dipoles for Siberia Sakes ad Spi Rotators to be istalled i RHIC uder a joit BNL-RIKEN spi physics program. The dipole field i these magets rotates by 360 degrees over a legth of 2.4 meters, givig a 3-D field throughout. A 51 mm log rotatig coil was built for these measuremets ad the aalysis was modified for the 3-D field. A separate talk at this workshop will give more details. Picture of a helical dipole maget coil 33

34 Covetioal Magets for the SNS Sector dipole magets for the Spallatio Neutro Source are beig assembled at BNL. Productio measuremets will be made usig a 2.49 m log, 164 mm diameter rotatig coil. A rectagular aperture requires measuremets to be made at several horizotal positios of the coil. A built-i horizotal gradiet i the itegral field implies that the coil positio i the maget be accurately determied. The maget ad the rotatig coil have survey targets to determie the coil positio with respect to the maget. I additio to the dipoles, other maget types (quadrupoles ad correctors) of various apertures will also be measured for the SNS. (~ 150 magets total). 34

35 Dipole Maget for the SNS Survey Target 35

36 Magetic Measuremet Facilities at the Natioal Sychrotro Light Source 2.5 m Hall Probe Bech Movig-Wire Itegrated Multipole Bech 2 m Pulsed-Wire Bech Dedicated to measuremet of Isertio Devices ad (warm) beam trasport ad special-purpose magets (More iformatio i a talk by G. Rakowsky ) 36

37 Summary After the completio of RHIC, recet activities at BNL have primarily focussed o the study of dyamic effects ad o productio measuremets of helical magets. New hardware ad aalysis techiques were developed to carry out these measuremets. Stadard measuremets were carried out o magets built at BNL for the HERA lumiosity upgrade project. Productio measuremets o covetioal magets for the SNS ad supercoductig magets for the LHC have just begu. 37