1. 1 QXF heater design: current status and the path forward M. Marchevsky (LBNL) 03/06/2014 D.W. Cheng, H. Felice, G. Sabbi (LBNL), G. Ambrosio (FNAL)

2. 2 Outline Current state of the SQXF / QXF heater design Pattern period options for the long QXF Inner layer heater design options Copper plating

3. 3 Heater design goals Our goal is to learn the most about long QXF protection from the SQXF heater performance. We will use SQXF to validate and optimize the final QXF heater geometry. We agreed that SQXF and long QXF should share same design criteria to ensure the above statement is valid and the SQXF heater performance is relevant to the long QXF. We then developed SQXF and QXF heater patterns that include the following key features:  Targeted heat deposition using heating stations  Periodicity derived from the twist pitch of the cable  Optimization of the heating station geometry (width, tilt angle) to improve efficiency

4. 4 SQXF vs QXF trace material and Kapton thickness end-to-end heater configuration heating station geometry (width, rounding, straight ends, tilt angle) concept behind periodicity of the heating stations - it is derived from the twist pitch of the cable power per heating station (in SQXF, we will set it to match the long QXF/450 V equivalent by choosing an appropriate HFU voltage) 1/2 twist pitch base was used for the SQXF and 2x twist pitch base for the long QXF. Patterns were developed individually for the short ( 1 m) and long (~6.7 m) QXF model. They share the SAME: but the difference is:

5. 5 Long QXF 18 segments L seg = 60.7 mm (Per 1.075 m) 29 segments L seg = 230 mm (Per 6.70 m) R heater = 6.49  H OPMT = H IPMT = 23.7 mm R heater = 1.48  H OPMT = H IPMT = 23.7 mm p = 109 mm Current SQXF and QXF patterns (OL) At 100 V => 67 A and 82 W/cm 2 per straight portion of the heating station SQXF At 450 V => 69 A and 87 W/cm 2 per straight portion of the heating station  ss = 5 10 -7  m ; d ss = 25  m l = nw p = (2n-1) w p = (n div 2-1)w l=nw ½ twist pitch base 2x twist pitch base

6. 6 Why not just use the long QXF pattern for SQXF? 1. We will then only have  heating  stations per SQXF length, resulting in the net heater resistance of just  1.1 . Any local non-uniformity in the trace or solder joint resistance will create a “heating station” and may render such heater inconsistent or unreliable. 2. Voltage across such heater should be kept quite low to match the long QXF operation - we will not have a chance to verify if trace insulation can reliably hold 450 V at cold during operation. 3. Large portion of the HFU energy will be dissipated in the heater wiring / solder joints 4. Should we want a quicker protection, we are "hard-limited" by the quench propagation time between the neigboring heating stations (which are 23 cm apart) Can we still learn from SQXF heater test about efficiency of the long QXF heater? Yes, once we measure the SQXF heater delay time and quench propagation velocity. The heater delay (time to quench the entire coil) for the long QXF will be longer than in SQXF by an interval approx. given by the ratio of the half-distance between the heating stations (~ one twist pitch) to the quench propagation velocity.

7. 7 Can we use the SQXF design for the long QXF? YES – by applying copper plating But, if we plate the “pads” with 10 micron of Cu, the net resistance will drop to 5.6  => 80 A (at 450 V) and 116 W/cm 2 Assuming  Cu = 3.6 10 -9  m (at 100 K) The SQXF original design extended to 6.7 m length yield  110 heating stations and the net resistance of 9.1 Ohm => 49 A (at 450 V) and 45 W/cm 2 per heating station – too low power... This is option ONE for the long QXF 6.7 m

8. 8 One twist pitch base pattern L seg = 122 mm (Per 6.70 m) H OPMT = H IPMT = 23.7 mm R heater = 7.35  At 450 V => 61 A and 68 W/cm 2 per straight portion of the heating station 55 segments One twist pitch base trace for SQXF

9. 9 One twist pitch base pattern with Cu plating Plating of the “pads” with 10 micron of Cu will reduce the net resistance to 2.8  => 157 A (at 450 V) and 447 W/cm 2 … or 87 A and 138 W/cm 2 at 250 V 6.7 m This is option TWO for the long QXF

10. 10 Two twist pitch (current) pattern for the long QXF Long QXF 29 segments L seg = 230 mm (Per 6.70 m) R heater = 6.49  H OPMT = H IPMT = 23.7 mm At 450 V => 69 A and 87 W/cm 2 per straight portion of the heating station p = (n div 2-1)w l=nw 2x twist pitch base Plating of the “pads” with 10 micron of Cu will reduce the net resistance to 1.6  => 288 A (at 450 V) and 1510 W/cm 2 … or 160 A and 467 W/cm 2 at 250 V This is option THREE for the long QXF

11. 11 Summary of the options 1. ½ twist pitch base (60.7 mm period) : 5.6  => 80 A (at 450 V) and 116 W/cm 2 2. 1x twist pitch base (122 mm period) : 2.8  => 157 A (at 450 V) and 447 W/cm 2 3. 2x twist pitch base (230 mm period): 1.6  => 288 A (at 450 V) and 1510 W/cm 2 Smallest delay to quench Least overall heater surface is beneficial for electrical strength More available locations to add holes for better impregnation If used for the IL: Smaller length of the “pad” along the cable could help preventing “bubble” formation Smaller overage by the stainless layer improves heat dissipation from the coils HFU voltages near upper limit (~400 V) will be likely required for reliable operation Largest number of “pads” is to be copper plated - this could mean extra work for masking and post-process cleaning and QA. Mid-range HFU voltages (200-300 V) will be sufficient for operation ; there is still a good power margin Still very small (<0.5 ms) additional due to quench propagation An overall good compromise between performance and heater coverage area HFU voltages near upper limit (~400 V) will be likely be required for reliable operation Largest number of “pads” is to be copper plated - this could mean extra work for masking and post-process cleaning and QA. This is the only usable design in case copper deposition cannot be done or problematic for some reason (backup?) largest additional delay due to quench propagation.

12. 12 Inner layer heater L IPMT 9.19 L IMMT 30.75 5.6 If we were to place two separate heaters for the inner layer like we did for the outer layer, the only feasible heater structure for the pole multi-turn L IPMT seems to be a straight strip. Even then, at 6.7 m length and 9.2 mm width its resistance will be  14.6  – too high. Therefore, in the present design the heater that is spanning across the spacer and portions of both (pole and mid-plane) multi-turns. It occupies ~65% of the trace width along the winding. 30.75 SQXF (1.0 m) 16 segments L seg = 61.3 mm R heater = 1.42  H = 30.75 mm QXF (6.7 m) 29 segments H = 30.75 mm L seg =231 mm R heater = 5.76  78 A at 450 V => 111 W/cm 2

13. 13 Alternative options for the IL heater 1. Straight heater strip with periodic heating stations covering only the pole turn. 8 mm 7600 mm 60.7 mm 12.1 mm 110 segments R heater = 3.57  126 A at 450 V => 496 W/cm 2 70 A at 250 V => 153 W/cm 2 2. Two-zone heater strip with periodic heating stations covering both the pole turn and the (portion of) the mid-plain turn. ½ twist pitch base pattern 110 segments 12.1 mm 60.7 mm 22 mm 8 mm R heater = 6.71  67 A at 450 V => 140 W/cm 2

14. 14 Where are we with the Cu plating?  LBNL plating shop can readily plate copper on stainless steel using two bath (activation + plating) electroplating process.  The turn-around time can be in a matter of 1-5 days, depending on the shop schedule  The shop plating bath is  1 m 3 in volume, an so a trace will need to be rolled in some way to be plated at once. Some fixture needs to be developed for the rolled trace plating  For initial prototyping, an adhesive tape can be used as mask. Later on, a way to laminate a removable mask to the trace will need to be developed. Lamination using soluble lacquer or with a photoresist film with subsequent UV exposure could be the options.

15. 15 Coupon plating We have selectively deposited ~ 7 micron thick Cu layer to the coupon of the old HQ trace ( 1 mil Kapton +1 mil SS). Adhesive tape was used for masking

16. 16 Heating station masking Tape masking showed a good result, with some occasional “flaking” of the copper deposit and some dark residue near the edge of the mask The edges can be readily cleaned with soft abrasive paper or powder

17. 17 Resistance test ~ 7 micron of Cu 0.8 Ohm 1.8 Ohm

18. 18 Next plating steps 1. We propose to use HQ traces for further developing and qualifying the plating process (in the next 2-3 weeks)  Step 1: Plate the “old design” HQ trace (continuous strip) – form and deposit periodic heating station pattern using tape masking. Perform electrical qualification (resistance, hipot), check Cu layer adhesion and its thickness variations across the pattern.  Step 2: Plate the “new design” HQ trace (heating stations with 2x twist pitch base periodicity) – deposit on the wide portions, mask the heating stations. Preform electrical QA. If successful, we would propose to validate the Cu-plated trace by installing and testing it in the HQ03 coil 2. Plating and qualification of the SQXF traces will be done next. We will produce several additional SQXF traces for use in plating experiments; those can be later used in the coils upon validating consistency of the process is validated and passing the electrical QA.