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Engineering Note DocumentTest Results of LCLS-II Cryomodule Magnet SPQA103Document Number: LCLSII-4.5-EN-NNNN of 20

Test Results of LCLS-II Cryomodule Magnet SPQA103J. DiMarco, V. Kashikhin, T. Strauss, M. Tartaglia

I. IntroductionHE production magnet SPQA103 for LCLS-II Linear Accelerator [1] was built by Milhous and tested at Fermilab. The magnet package is conductively cooled by LHe inside the Cryomodule, and has a splittable in

the vertical plane configuration (see Fig.1). The magnet was built in an agreement with the magnet physical requirements LCLSII-2.4-PR-0081-R0, and the specification LCLSII-4.5-ES-0355-R0. The magnet design, and previously tested magnets are described in [2] – [10].

T Two prototype magnets SPQA01 and SPQA02 were built for testing the verification of the magnet design and the conduction cooling (See LCLSII-EN-0612). This note describes the bath cooling test results of SPQA103 magnet including high precision magnetic measurements by a rotational coil system. The magnet view inside SCRF Cryomodule is shown in Fig. 1.

Fig. 1. Magnet package inside the LCLS-II SCRF Cryomodule.

The main goal of the magnet test at FNAL Technical Division Stand 3 is to test magnets in the bath cooling mode, and prove their magnetic performance in the wide range of operating currents and operating scenarios. One of the most critical magnet specifications is to provide quadrupole, and dipole corrector field reproducibility in the range of ±1 %. Most of uncertainty in the magnet strength is caused by the iron core hysteresis effects which substantially increase at low field levels. To reduce these effects, degaussing and standardization procedures were used. All three magnet power supplies are bipolar and provide the full current operational range of ± 20 A for each magnet circuit, which allows up to 2.5 T integrated quadrupole field gradient. Bipolar cycling will be used for magnet degaussing. During operation the quadrupole magnet will not change in polarity, except possibly the first magnet, QCM01, and unipolar full or partial cycling will be used for the quadrupole standardization procedure. The test results were used to formulate the magnet operation procedures in the accelerator to obtain reproducible magnet strength vs. current variations for quadrupole and dipole magnets.

The main magnet parameters shown in Table 1, and the magnet cold mass in Fig. 2. The magnet test plan described in LCLSII-4.5-PP-0731-R0.

The only official copy of this file is located in the LCLS-II Controlled Document Site. Before using a printed/electronic copy, verify that it is the most current version.


TABLE ILCLS-II MAGNET PACKAGE PARAMETERS

Parameter Units ValueIntegrated peak gradient at 10 GeV T 2.0Integrated peak gradient at 0.4 GeV T 0.05Clear bore aperture mm ≥78Ferromagnetic pole tip bore diameter mm 90Effective length mm 230Peak quadrupole gradient T/m 8.67Quadrupole field harmonics at 10 mm radius % ≤1.0Quadrupole magnet inductance (DC) H 0.66Number of superconducting coil packages 4Number of superconducting sections in the coil package 3Number of turns in the quadrupole section 426Number of turns in vertical/horizontal dipole sections 39Peak superconductor current A ≤20NbTi superconductor diameter mm 0.5Superconductor filament size µm 3.7Dipole corrector integrated strength T-m 0.005Max magnetic center offset in Cryomodule mm ≤0.5Magnet physical length mm 340Magnet width/height mm 322/220Quantity required 35

Fig. 2. The quadrupole magnet package cold mass.



II. Magnet Package Tests The magnet SPQA103 was cold tested in January 2016. Fig. 3 shows an overview of the similar SPQA03 magnet and top plate assembly ready to install in the helium dewar, with a 30 mm warm bore tube mounted through and centered in the magnet aperture for magnetic measurements, the right of Fig. 3 is a close-up of SPQA103, note the missing aluminum shield. Warm electrical checks of the assembly and instrumentation were performed prior to cool down, and repeated when cold. The quench performance was tested individually for the quadrupole, vertical dipole and then the horizontal dipole. Each magnet was ramped at 0.5 A/s to 20 A, with no quenches. All three circuits were then powered simultaneously at 20 A for several minutes with no quench, before ramping down to 0 A. High current magnetic measurements were then completed, again with no quenches.

Several Trips occurred due to bad matching of the load with the Ethernet power supply controller (EPSC) daughterboard. The power supply controller's R2 and C2 form a tuning network and dictates the response of the system. When these components match the load, it forms a critically damped and stable system (ideal response with no overshoot or ringing). If there is a mismatch, it can either form an over-damped system (very slow response) or an under-damped system (overshoot and ringing response). By changing the resistor R2 one can move the system response closer to a critically damped system.

Fig. 3. Overview (left) of SPQA03 attached to the header and close-up (right) of the SPQA101 magnet assembly for installation in the stand 3 dewar for cold testing in 4.5 K liquid helium bath.

III. Magnet Package Magnetic Measurement Results The magnet package magnetic measurements were performed by rotational coils at FNAL Stand 3. The rotational coil system utilizes a PC Board design [11] and provides a measurement accuracy of ~1 unit (10 -4). The probe rotates in an anti-cryostat (warm bore tube) placed within the magnet aperture as the assembly is suspended in the LHe vessel. The probe radius is limited by the ~30mm inner diameter of the warm bore. The PCB is 1m long and extends out both ends of the magnet. However, owing to the magnet and warm bore position in the cryostat, the probe is not centered in the magnet, and only extends out the far end by about 100mm; ~200 mm short of capturing the full end field. The board is a spare from a previous project [12]. All harmonics are reported here at a reference radius of 10mm. Compared to previous tests, the rotational coil was fully centered and the previously existing current overshot during the ramping was addressed by tuning a resistor within the power supply controller. The magnet SPQA103 was fabricated by Milhous, this test is the first result of the production unit design and has to be compared with the measurements obtained for the SPQA03 and SPQA04, as well as the first production



unit SPQA101 measurement. Due to low helium inventory only the minimum required measurements were taken to confirm the critical subset of the cold studies needed to establish the magnet operational scenarios for the accelerator and verify reproducibility of magnetic conditions. For reducing the remnant and hysteresis field effects, degaussing and standardization procedures were developed. For degaussing the following current drive formula was used (see Fig. 4):

I ¿k ⋅e−tτ ⋅sin (t 2/m ) ,

Where k, τ, m are coefficients that define the peak current, the current amplitude decay, and the cycle time period.

Fig. 4. Current variation during degaussing.

The TF hysteresis loops were measured once (see Fig. 5, Fig. 6 for TF and Fig. 7 for current profiles). The reproducibility is better than 0.5 %, and meets specification. In comparison with SPQA04 [10] one can clearly see a very similar behavior of the transfer function.

Fig. 5. Quadrupole TF variations for different current ramps shown in Fig. 7, zoom in the region from 0-7A.



Fig. 6. Quadrupole TF variations for different current ramps shown in Fig. 7.

Fig. 7. Current variations for the full hysteresis cycles, the variations for the unipolar ramps and for the partial

standardization cycles in Fig. 5 and Fig. 6.



The integrated magnetic field quality was also investigated. Fig. 8 shows the quadrupole field harmonics at different currents in the range of 0.2 A – 20 A.

Fig. 8. Quadrupole field harmonics at different currents.



One could see that for the whole range of currents all field harmonics are less than 5 units (1 unit=10 -4) at 10 mm reference radius. All harmonics are less than 25 units at 10mm, which is the design specification according to V. Kashikhin.

Fig. 9 and Fig. 13 show the variation of the quadrupole magnetic center displacement for different combinations of the horizontal and vertical dipole corrector currents. The plots have the slope removed after a linear fit, the fit parameter is given in the legend. It should be noted that dx and dy displacements are fully decoupled, they are shown with removed slope in Fig. 10 and Fig 12, respectively; the slope is nearly identical to zero.

In a direct comparison to the SPQA04 and SPQA101 measurements one can note that the slopes of the dx and dy displacement in Fig. 9 and Fig. 13 are within 3% or better.

The shift in the Fig. 11 and Fig 14 of the transfer function can be explained as follows. We observe a change of 50 units in quadrupole strength when the Dipole current Id ramps from I=0A to the Quadrupole current Iq. From the measurements of dipole with the quad at zero current, we measured that the dipole has about 5% (500 units) of Sextupole content. At the reference radius of 10mm, the quad field is about 5e-4 T at 0.4A.

When the dipole is powered from 0A to 0.4A, the change in dipole field (from the corrector) is ~1e-4T (~2.5e-4 T/A). At R=10mm the change in Sextupole is about 5%, or 5e-6T (about 100 units compared to main quad). The feed-down from Sextupole to Quadrupole is 2*dz/R*C3 = 2*0.0022/0.01*100units = 44 units (where the 0.0022 is the 2.2mm change in centering we see when dipole goes from 0A to Id=Iq).

The quad content of the dipole corrector is small, but since we are applying no centering correction to the these Quadrupole and Dipole data sets, we see about 15 units Quadrupole from the Dipole - this is actually feed-down from the Sextupole because the probe is not centered in the aperture; it is measured to be off by ~1mm, this causes about 20units Quadrupole, as one can calculate By=G*(x-a)+Bd[(1+b3*(x-a)^2] and dBy/dx=G+2*Bd*b3*x-2*Bd*b3*a, which is confirmed by simulation from V. Kashikhin.

Fig. 9. Quadrupole magnetic center displacement in the vertical plane at different Horizontal Dipole Corrector

currents.



. Fig. 10. Quadrupole magnetic center displacement in the horizontal plane at different Horizontal Dipole Corrector

currents.

Fig. 11. Quadrupole TF function at different Horizontal Dipole Corrector currents.



Fig. 12. Quadrupole magnetic center displacement in the vertical plane at different Vertical Dipole Corrector currents.



Fig. 13. Quadrupole magnetic center displacement in the horizontal plane at different Vertical Dipole Corrector currents.

Fig. 14. Quadrupole TF function at different Vertical Dipole Corrector currents.



Fig. 15. Quadrupole and dipole currents variations for Fig. 9 to Fig. 14 with a triple repetition. For this magnet only

2 dipole current repetitions were done. Plot is taken from SPQA04 current measurements.

At zero dipole current the field harmonics are less than 5 units (1 unit=10 -4) at 10 mm reference radius, once the dipole correctors are ramped, once can see an increase in the harmonics up to a factor one hundred in the a3 in case of the horizontal dipole corrector and b3 in case of the vertical dipole corrector, as shown in Fig. 16 and Fig. 17. A direct comparison with the SPQA04 and SPQA101 measurement shows nearly identical harmonic values for the a3 or b3 components between the two magnets during the horizontal and vertical dipole variations, a very comparable result. It should be noted that the maximum needed dipole corrector strength is reached at 20 % of the quadruple current, in order to compensate possible 0.5 mm quadrupole magnetic center shift caused by magnet installation and cooling. In this case the Sextupole field component will be much lower than at full current.



Fig. 16. Quadrupole field harmonics at 0.4A quadrupole current for different horizontal dipole currents.



Fig. 17. Quadrupole field harmonics at 0.4A quadrupole current for different vertical dipole currents.



Additional measurements which were requested by Chris Adolphsen.. For simplicity the measurements are labeled CA1- CA4.CA1: Compare unipolar TF results to the results from a random sequence of currents. As expected the TF varies between the minimal and maximum transfer function values of the full hysteresis curve, depending on the step profile.

Fig. 18. Current of Fig. 23.

Fig. 19. TF for a random current walk between 0 and 10 A.

As expected the random current falls in between the up and down hysteresis curves as shown in Fig. 19. There is a consistency of the results between the SPQA04, SPQA101 and SPQA103 measurement.



A second measurement, CA 2, asked for a degauss cycle followed by setting a current and varying the current is within a 15% range. We skipped this measurement as it was previously performed and is very similar to the third request.

Additional measurement CA3 was requested with a similar profile as the measurement CA2, however between each current variation the Quadrupole current was set to zero. Shown in Fig. 20 and Fig. 21 are the results, the shift in the transfer function between stays better than 0.2%. The current of a sub-sample is shown in Fig. 22.

Fig 20. Variation of the transfer function for 15% changes in current around a given set point, data set 1.



Fig 21. Variation of the transfer function for 15% changes in current around a given set point, data set 2.

Fig 22. Current measurement of the 6A main current for the Fig. 20 and Fig. 21.

A fourth CA4 measurement involved powering the Quadrupole and both Dipole correctors simultaneously was requested. The goal was to vary the magnetic center in the range of ±300 µm for three quadrupole currents: 0.4 A, 1 A, and 4 A. Ideally they should result in a straight line with the uniform slope. Shown in Fig 23 is the horizontal Dipole TF and expected dy displacement, in Fig. 24 the vertical Dipole and dx displacement. There is no correlation between horizontal Dipole and dx and vertical Dipole and dy. As one can see, the linear dependency is observed for each Dipole, with small variations on the Quadrupole transfer function.



Fig 23. Variation of the transfer function and expected and measured dy displacement for the horizontal Dipole in measurement CA4.



Fig 24. Variation of the transfer function and expected and measured dx displacement for the vertical Dipole in measurement CA4.



IV. ConclusionThe splittable conduction cooled magnet package SPQA103 was thoroughly tested and showed a good

performance. The magnet package combines a quadrupole with orthogonal dipole correctors. During cold tests the following features were observed and verified:- The field quality and reproducibility are acceptable. - Field geometric harmonics are low and meet the specification.- The magnet was successfully excited to 20 A without quench (20 A is the peak power supply, and operating

current).- This is the second production magnet by the vendor Milhous, the results were compared with previous

obtained measurements of SPQA004 and SPQA101 and found in consistency.

The successfully completed tests validated the magnet design and fabrication of SPQA103.

Acknowledgment The authors would like to thank Prof. Akira Yamamoto (KEK), Chris Adolphsen, Paul Emma (SLAC) for very useful discussions. We are very grateful to the SLAC team for providing and commissioning regulated power supply, and to all FNAL Technical Division personnel involved in the design, fabrication and tests of these magnets.

REFERENCES

[1] “Linac Coherent Light Source,” LCLS-II, 2015:https://portal.slac.stanford.edu/sites/lcls_public/Pages/Default.aspx

[2] V.S. Kashikhin, et al., “Test results of a superconducting quadrupole model designed for linear accelerator applications,” IEEE Transactions on Applied Superconductivity, vol. 19, Issue 3, Part 2, June 2009, pp. 1176-1182.

[3] V. S. Kashikhin, N. Andreev, J. Kerby, Y. Orlov, N. Solyak, M. Tartaglia,and G. Velev, “Superconducting splittable quadrupole magnet for linear accelerators,” IEEE Trans. Appl. Supercond., vol. 22, no. 3, p. 4002904, June 2012.

[4] N. Andreev, V. S. Kashikhin, J. Kerby, N. Kimura, M. Takahashi, M. A. Tartaglia, T. Tosaka, and A. Yamamoto, “Conduction cooling testof a splittable quadrupole for ILC cryomodules,” IEEE Trans. Appl. Supercond., vol. 23, no. 3, p. 3500305, June, 2013.

[5] N. Kimura, N. Andreev, V. S. Kashikhin, J. Kerby, M. A. Tartaglia, and A. Yamamoto, “Cryogenic performance of a conduction cooling splittable quadrupole magnet for ILC cryomodules,” Adv. Cryogenics Engineering, 59A, 2014, pp.407-415.

[6] R. Carcagno, et al, “Magnetic and Thermal Performance of a Conduction-Cooled Splittable Quadrupole,” IEEE Trans. Appl. Supercond., vol. 24, no. 3, p. 4001604, June, 2014.

[7] V.S. Kashikhin, et al., “Compact Superconducting Magnet for Linear Accelerators,” IEEE Trans. Appl. Supercond., vol. 25, Issue: 3, p. 4001705, 2016.

[8] V.S. Kashikhin, et al., “Performance of Conduction Cooled Splittable Superconducting Magnet Package for Linear Accelerators,” IEEE Trans. Appl. Supercond., vol. 26, Issue: 4, p. 4103405, 2016.

[9] J. DiMarco, V. Kashikhin and M. Tartaglia, “TestResults of LCLS-II Cryomodule Magnet SPQA03”, LCLS-II-4.5-EN-0826-R0

[10] J. DiMarco, V. Kashikhin, T. Strauss and M. Tartaglia, “TestResults of LCLS-II Cryomodule Magnet SPQA04”, LCLS-II-4.5-EN-0930-R0

[11] J. DiMarco, et al.,”Application of PCB and FDM Technologies to Magnetic Measurement Probe System Development”, IEEE Trans. on Appl. Supercond., vol. 23, no. 3, 9000505, June 2013.

[12] J. DiMarco et al., “A Fast-Sampling, Fixed Coil Array for Measuring the AC Field of Fermilab Booster Corrector Magnets”, IEEE Trans. on Applied Superconductivity, Vol. 18, No. 2, June 2008.


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cryomodule magnet - fermilab · web viewat zero dipole current the field harmonics are less than 5...

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