1. QXF instrumentation trace development
M. Marchevsky, LBNL
QXF heater trace pattern
Voltage taps layout
Heater delay measurements in LQ
Paschen law and gap between heaters and structure
Bubbles in LQ-style heaters

2. QXF: outer layer, mid-plane MT
HOMMT = mm
350 V, r= W m, d = 25 mm
a = mm (=> mm along the cable)
r1 = 3 mm
L = 15 mm
a = 60 deg
m = 3 mm
b = 203 mm
P/A (straight) = 69 W/cm2
P/A (curved) = 58 W/cm2
Rheater = 5.68 W
29 segments
(Per 6.70 m)
Heating station density is 4x less compared to the SQXF.
n = 2*109 mm / = 18 => hence all strands will be driven normal at once along every 18*Lseg= 4140 mm, or ~0.6 of the full coil length. Hence each strand will be driven normal at least at one spot per full coil length.
Lseg = 230 mm
Hseg = 31.7 mm

3. QXF: outer layer, pole block MT
350 V, r=5*10-7 W m, d = 25 mm
HOPMT = mm
a = mm (=> mm along the cable)
r1 = 3 mm
L = 6 mm
a = 60 deg
m = 3 mm
b = 207 mm
P/A (straight) = 53 W/cm2
P/A (curved) = 45 W/cm2
Rheater = 6.49 W
29 segments
(Per 6.70 m)
Lseg = mm
Hseg = 23.9 mm

4. QXF: inner layer, pole MT
LIMMT =30.75 mm and LIPMT = 9.19 mm
Entire inner layer: mm
350 V, r=5*10-7 W m, d = 25 mm
Proposal: combine mid-plane and pole block heaters in one, spanning the entire width of the inner layer winding of 45.5 mm
a = mm (=> mm along the cable)
r1 = 3 mm
L = 30 mm
a = 60 deg
m = 3 mm
b = 195 mm
29 segments
(Per 6.70 m)
P/A (straight) = 79 W/cm2
P/A (curved) = 66 W/cm2
Rheater = 5.33 W
Lseg = mm
Hseg = 45.3 mm

5. Adiabatic temperature of the heating station
For the highest heating power density, as proposed for the QXF inner layer MT heater (79 W/cm2, 65.7 A of heater current) we obtain temperature rise up to ~340 K!
SS304, d = 25 mm, a = mm, T0 = 5.0 K
Exponential current decay with t = 50 ms is assumed

6. QXF voltage tap layout Compared to the HQ/LQ Vtap layout,
no Vtap were placed in the middle of the straight section. Also, Vtap monitoring first mid-plane turn was eliminated. The Vtaps are routed to both ends of the coil, to keep consistent “twisted pair” style connections for every consecutive segment, without making a large loop.
The first CAD version of the trace design is to follow in Dan’s presentation

7. LQ delay time vs heater power
OL heaters fired
40 W/cm2
25 W/cm2
57 W/cm2
Data by G. Chlachidze
Data by H. Felice
For the outer layer pole block MT the heater power is ~50 W/cm2 at 350 V or ~80 W/cm2 at 450 V.
Hence, we are looking to the heater delays of 13 ms (350 V) to 8 ms (450 V) – at 60% SSL

8. Paschen law and temperature correction
3 mm gap – 1 atm (RT)
~1600 V
1000 V
G. Dakin, "Paschen Curve for Helium,” Electra, vol. 52, pp , 1977.
3 mm gap at 100 kPa (1 atm) corresponds to 1000 V breakout voltage (RT)
However, 6 mm gap would yield ~ 1600 V breakout (less than 2x factor)
Temperature-dependent correction: P(T) = nkT, or at constant pressure n(T)=P/kT.
Thus, 10x temperature reduction would shift the Paschen curve one decade to the left

9. Bubbles in LQ heaters No bubbles under the heating stations !
Can we introduce narrow linear “slits” in the design of the wide portions of the heater traces?
They will not affect much the trace resistance, but will allow for better impregnation of the heater traces to the coil along the areas that are most prone to bubble formation.